JP2016018005A - Optical waveguide device and manufacturing method thereof, optical receiver circuit, and optical modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide device with higher reliability and lower power consumption, easily integrated and suitable for mass production.SOLUTION: An optical waveguide device 1A includes a waveguide D having a core 4 and a clad 5 on a substrate 3, and a phase adjusting unit 2A for adjusting the phase of light propagating in the waveguide D, the electro-optical layer 10 covering a first electrode 8 and a second electrode 9 located at both sides of the core 4, at least a part of both side surfaces and an upper surface of the core 4, at least a part of a side surface opposed to the core 4 and an upper surface of the first electrode 8, and at least a part of a side surface opposed to the core 4 and an upper surface of the second electrode 9. In the electro-optical layer 10, electric polarization is generated by formation of polarization.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical waveguide device and a method for manufacturing the same, and an optical receiver circuit and an optical modulator provided with such an optical waveguide device.

  In optical fiber communication, there is digital coherent communication as a technology that enables high-capacity and high-speed data transmission. Digital coherent communication requires an optical phase modulator for performing polarization multiplexing / quadrature phase modulation (PDM-IQ modulation) and an optical receiving circuit for performing coherent reception.

  In these optical elements, in order to adjust the phase of the light wave (for example, a constant phase is added to the light wave), a phase shifter that enables phase control of the light wave is necessary. As a technique related to the phase shifter, Patent Document 1 has a configuration in which a thermal diffuser made of an electric resistor is provided on a waveguide and the refractive index of the waveguide is controlled by a thermo-optic (TO) effect. It is disclosed. Non-Patent Document 1 discloses an optical phase modulator using a high-speed phase modulation unit in which an electro-optic (EO) material is combined with a silicon waveguide core.

International Publication No. 2003/048845

“Silicon-organic hybrid (SOH) IQ modulator using the lineai- electro-optic effect for transmitting 16QAM at H2 Gbit / s” Optics Express vol.21, no.ll, pp.13219-13227 (2013)

  However, in the technique described in Patent Document 1, in order to maintain the phase difference at π / 2 using the TO phase shifter, it is necessary to constantly apply a current or voltage to the TO phase shifter to generate heat. Therefore, it is difficult to reduce power consumption.

  In the technique described in Non-Patent Document 1, it is necessary to heat the entire substrate to a high temperature in polarization formation by poling for inducing permanent electric polarization in an EO material. For this reason, there is a possibility of causing damage to the wire bonding portion, damage to the adhesive that adheres and fixes external optical components such as input / output optical fibers, and the like. Therefore, permanent electric polarization is required to maintain the phase difference at π / 2 by heating the entire substrate to a high temperature while monitoring the light output by entering the adjustment light into the optical phase modulator. In addition, it is difficult to set a sufficient appropriate value. Further, each optical phase modulator has a problem that the fluctuation of the individual driving voltage is large and the reliability is lowered.

  In the technique described in Non-Patent Document 1, when the entire substrate is heated to a high temperature, for example, the dopant forming the PN junction is rediffused, or the germanium film or the compound semiconductor film having a low film formation temperature is deteriorated. There is a fear. In this case, integration with the optical phase modulation unit or the light receiving unit becomes difficult.

  Furthermore, in the electrode configuration in the high-speed phase modulation unit described in Non-Patent Document 1, the electrode interval at the time of polling becomes large, and the polling voltage becomes high. In this case, there is a problem that the possibility of damage to the optical phase modulator due to discharge increases and the manufacturing yield decreases. In addition, since the slot waveguide is used as the waveguide of the high-speed optical phase modulation unit, there is a problem that the connection loss with the rectangular waveguide and the propagation loss due to the side wall roughness are large, and the optical loss cannot be reduced.

  One aspect of the present invention has been proposed in view of such conventional problems, and is an optical waveguide device that has low power consumption, is easy to integrate, is suitable for mass production, and has high reliability. An object of the present invention is to provide a manufacturing method thereof, and an optical receiver circuit and an optical modulator provided with such an optical waveguide device.

  One aspect of the present invention is an optical waveguide element including a waveguide formed of a core and a clad on a substrate, the optical waveguide element including a phase adjustment unit that adjusts a phase of light propagating through the waveguide, and the phase adjustment The first electrode and the second electrode provided on both sides of the core, at least a part of both side surfaces and the upper surface of the core, and the side of the first electrode facing the core An electro-optic layer provided so as to cover at least a part of the side surface and the upper surface, and at least a part of the side surface and the upper surface of the second electrode facing the core. An optical waveguide element characterized in that electric polarization is generated in the optical layer by polarization formation is provided.

  In the optical waveguide element, the clad includes a lower clad provided between the substrate and the core, and an upper clad provided on the core and the lower clad, The first electrode is electrically connected to the first upper electrode provided on the upper cladding via the first through electrode penetrating the upper cladding, and the second electrode is connected to the upper cladding. It is preferable that the second upper electrode provided on the upper clad is electrically connected to the second upper electrode through a second through electrode penetrating therethrough.

  In the optical waveguide element, the electro-optical layer is electrically connected to a third upper electrode provided on the upper clad through a third through electrode penetrating the upper clad. Is preferred.

  Further, in the optical waveguide element, it is preferable that the phase adjusting unit has a heater for heating the electro-optic layer, and the heater is provided on the upper clad.

  Further, in the optical waveguide element, the first electrode is electrically connected to a fourth upper electrode provided on the upper clad through a fourth through electrode penetrating the upper clad, The second electrode is electrically connected to a fifth upper electrode provided on the upper cladding via a fifth through electrode penetrating the upper cladding, and the first upper electrode and the fourth electrode By applying a current or voltage to the upper electrode of the first electrode, the first electrode generates heat, and by applying a current or voltage between the second upper electrode and the fifth upper electrode It is preferable that the second electrode generates heat.

  The optical waveguide element preferably includes a gap portion that thermally isolates the phase adjustment portion from the surroundings, and the gap portion includes a groove portion that cuts out at least the cladding in the depth direction.

  Further, in the optical waveguide element, the gap portion includes a pair of groove portions formed at a depth reaching the substrate on both sides of the phase adjustment portion, and a gap between the pair of groove portions. It is preferable to have a void part from which a part has been removed.

  In the optical waveguide element, it is preferable that the core is made of a silicon layer, and the first electrode and the second electrode are made of a diffusion layer formed by doping an impurity into the silicon layer.

  One embodiment of the present invention is a method of manufacturing an optical waveguide device including a waveguide formed of a core and a clad on a substrate, and includes a phase adjustment unit that adjusts a phase of light propagating through the waveguide. When forming, a step of forming the first electrode and the second electrode on both sides of the core, at least a part of both side surfaces and the upper surface of the core, and the core of the first electrode facing the core Forming an electro-optic layer that covers at least a part of the side surface and the upper surface of the second electrode, and at least a part of the side surface and the upper surface of the second electrode facing the core, respectively. Provided is a method for manufacturing a featured optical waveguide device.

  Further, in the method of manufacturing the optical waveguide element, when the first electrode and the second electrode are formed, a silicon layer made of the same layer as the silicon layer serving as the core is patterned, and the patterned silicon It is preferable to form a diffusion layer to be the first electrode and the second electrode by doping an impurity into the layer.

  The method for manufacturing an optical waveguide element includes a step of forming a gap portion that thermally isolates the phase adjustment portion from the surroundings, and when forming the gap portion, on both sides of the phase adjustment portion. After a pair of grooves are formed by etching at a depth from the clad to the substrate, a part of the substrate is selectively removed by etching from the pair of grooves, thereby being continuous between the pair of grooves. It is preferable to form a void.

  One embodiment of the present invention provides an optical receiving circuit including any one of the above optical waveguide elements.

  In the optical receiver circuit, the optical waveguide element includes a first optical branching unit that branches the signal light into a first signal light propagation waveguide and a second signal light propagation waveguide, and propagates the signal light, A second optical branching section for branching and propagating the local light into the first local light propagation waveguide and the second local light propagation waveguide, and a signal propagating through the first signal light propagation waveguide A first optical multiplexing unit that combines light and local light propagating through the first local light propagation waveguide and interferes with each other; and signal light that propagates through the second signal light propagation waveguide And the local light propagating through the second local light propagation waveguide, and a second optical multiplexing unit that interferes with each other, and 1 or 2 that receives the output light of the first optical multiplexing unit The first light receiving unit described above, one or more second light receiving units that receive the output light of the second optical multiplexing unit, A phase adjustment unit provided in either one or both of the first local light propagation waveguide and the second local light propagation waveguide. A frequency shift is applied, a heterodyne beat is generated by interference between the two, and either one of the output electrical signal output from the first light receiving unit or the output electrical signal output from the second light receiving unit Means for detecting the phase of the heterodyne beat using the output electrical signal as a reference signal and the output electrical signal different from the reference signal as an input signal, and maintaining the phase at π / 2; It is preferable that the phase difference between the local light incident on the first optical multiplexing unit and the local light incident on the second optical multiplexing unit can be adjusted to π / 2.

  In the optical receiver circuit, the phase difference is adjusted when a phase difference between local light incident on the first optical multiplexing unit and local light incident on the second optical multiplexing unit is adjusted to π / 2. It is preferably connected to a control board on which a memory in which a set value of current or voltage applied to the adjustment unit is recorded.

  Also, one aspect of the present invention is any one of the above optical receiver circuit adjustment methods, in which a frequency shift is applied to continuous local light for continuous incident light, and a heterodyne beat is generated by interference between the two. The output electrical signal output from the first light receiving unit or the output electrical signal output from the second light receiving unit is used as a reference signal, which is different from the reference signal. Means for detecting the phase of the heterodyne beat using the output electric signal of the other as an input signal in the optical receiving circuit, and maintaining the phase at π / 2, so that the local light incident on the first optical multiplexing unit and A method of adjusting an optical receiving circuit is provided, wherein a phase difference between the light and the local light incident on the second optical multiplexing unit is adjusted to π / 2.

  One embodiment of the present invention provides an optical modulator comprising any one of the above optical waveguide elements.

  In the optical modulator, the optical waveguide element includes a first optical branching section for branching and propagating signal light to a first connection waveguide and a second connection waveguide, and the first connection guide. A second optical branching section for propagating the signal light propagating through the waveguide into the third connecting waveguide and the fourth connecting waveguide, and the signal light propagating through the second connecting waveguide as the fifth A third optical branching portion that branches and propagates to the connection waveguide and the sixth connection waveguide; a first high-speed phase modulation portion provided in the third connection waveguide; and the fourth connection guide. A second high-speed phase modulation section provided in the waveguide; a third high-speed phase modulation section provided in the fifth connection waveguide; and a fourth high-speed phase provided in the sixth connection waveguide. A modulator, and the output light from the first high-speed phase modulator and the output light from the second high-speed phase modulator are combined And combining the output light from the third high-speed phase modulation section and the output light from the fourth high-speed phase modulation section to combine the first light output from the seventh connection waveguide, A second optical multiplexing unit that outputs from the eight connection waveguides, an output light that propagates through the seventh connection waveguide, and an output light that propagates through the eighth connection waveguide, A third optical multiplexing unit that outputs from the connection waveguide; a first light-receiving unit that receives part of the output light propagating through the seventh connection waveguide through the first tap waveguide; Any one of the second light receiving unit that receives part of the output light propagating through the eight connection waveguides via the second tap waveguide, the seventh connection waveguide, and the eighth connection waveguide; A phase adjustment unit provided on one or both of them, and a phase of an electric signal output from the first light receiving unit, and the second light receiving unit As the difference between the phase of the electric signal output is [pi / 2 from, are preferably adjusted current or voltage applied to either or both of the phase adjustment unit.

  Further, in the optical modulator, the difference between the phase of the electrical signal output from the first light receiving unit and the phase of the electrical signal output from the second light receiving unit is π / 2. It is preferable to be connected to a control board on which a memory in which a setting value for adjusting a current or voltage applied to one or both of the phase adjusting units is recorded is mounted.

  One aspect of the present invention is a method for adjusting any one of the optical modulators, wherein the phase of the electrical signal output from the first light receiving unit and the second light receiving unit are output. Provided is an optical modulator adjustment method, wherein a current or voltage applied to one or both of the phase adjustment units is adjusted so that a difference from the phase of an electrical signal is π / 2. To do.

  In the optical modulator, the optical waveguide element is provided in the first branching waveguide and an optical branching section for branching and propagating signal light to the first and second connecting waveguides. The first high-speed phase modulation section, the second high-speed phase modulation section provided in the second connection waveguide, the output light propagating through the first connection waveguide, and the second connection guide An optical multiplexing unit that combines the output light propagating through the waveguide and outputs it from the third connection waveguide, and a part of the output light that propagates through the third connection waveguide is received via the tap waveguide. Phases provided in one or both of the light receiving unit, between the first high-speed phase modulation unit and the optical multiplexing unit, and between the second high-speed phase modulation unit and the optical multiplexing unit An adjustment unit, detecting an electrical signal output from the light receiving unit, and detecting the first high-speed phase modulation unit One or both of the phase adjustment units so that the output light output from the third connection waveguide is maximized in a state where no modulated electric signal is applied to the second high-speed phase modulation unit. The current or voltage applied to the is preferably adjusted.

  The optical modulator detects an electrical signal output from the light receiving unit, and applies the modulated electrical signal to the first high-speed phase modulation unit and the second high-speed phase modulation unit without applying the modulation electrical signal to the first high-speed phase modulation unit. A memory storing a setting value for adjusting a current or a voltage applied to one or both of the phase adjustment units so that the output light output from the three connection waveguides is maximized. It is preferable to be connected to a control board.

  One aspect of the present invention is an adjustment method for any one of the optical modulators, wherein an electrical signal output from the light receiving unit is detected, and the first high-speed phase modulation unit and the second high-speed phase modulation unit are detected. Current applied to one or both of the phase adjustment units so that the output light output from the third connection waveguide is maximized in a state where no modulation electrical signal is applied to the high-speed phase modulation unit. Alternatively, the present invention provides a method for adjusting an optical modulator, characterized by adjusting a voltage.

  As described above, according to one aspect of the present invention, an optical waveguide device having low power consumption, easy integration, suitable for mass production, and having high reliability, a manufacturing method thereof, and such an optical waveguide are provided. It is possible to provide an optical receiving circuit and an optical modulator provided with an element.

It is a cross-sectional schematic diagram which shows the structure of the phase adjustment part in the optical waveguide element of 1st Embodiment. It is a cross-sectional schematic diagram which shows the structure of the phase adjustment part in the optical waveguide element of 2nd Embodiment. (A) is a schematic cross-sectional view along the extending direction of the first electrode of the phase adjusting unit shown in FIG. 2, and (b) is a schematic cross-sectional view along the extending direction of the second electrode of the phase adjusting unit shown in FIG. FIG. It is a plane schematic diagram which shows the structure of the optical waveguide element in the optical receiver circuit of 3rd Embodiment. FIG. 5A is a schematic plan view showing an example of the polarization separation circuit of the optical waveguide element shown in FIG. 4, and FIG. 5B is a schematic plan view showing another example of the polarization separation circuit of the optical waveguide element shown in FIG. . FIG. 5 is a schematic plan view showing configurations of high-frequency electrodes and bonding electrodes in the optical receiver circuit shown in FIG. 4. (A) is sectional drawing which follows the PP line shown in FIG. 6, (b) is sectional drawing which follows the QQ 'line shown in FIG. It is sectional drawing which follows the RR 'line | wire shown in FIG. It is a plane schematic diagram which shows the structure used for the adjustment method of the phase difference of 4th Embodiment. It is a plane schematic diagram which shows the structure of the optical waveguide element in the optical modulator of 5th Embodiment. It is a plane schematic diagram which shows the structure of the optical waveguide element in the optical modulator of 7th Embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In all of the following drawings, in order to make each component easy to see, the scale of the size may be changed depending on the component. In addition, the materials, dimensions, and the like exemplified in the following description are merely examples, and the present invention is not necessarily limited thereto, and can be appropriately modified and implemented without departing from the scope of the invention. .

(Optical waveguide device and manufacturing method thereof)
[First Embodiment]
First, for example, an optical waveguide element 1A shown in FIG. 1 will be described as a first embodiment of the present invention. FIG. 1 is a schematic cross-sectional view showing the configuration of the phase adjusting unit 2A in the optical waveguide element 1A.

  As shown in FIG. 1, the optical waveguide element 1 </ b> A includes a waveguide D constituted by a core 4 and a clad 5 on a substrate 3. The clad 5 has a lower clad 6 provided between the substrate 3 and the core 4, and an upper clad 7 provided on the core 4 and the lower clad 403. The core 4 is provided on the lower clad 6.

The core 4 is made of a crystalline silicon (Si) layer. The clad 5 (the lower clad 6 and the upper clad 7) is made of a silica (SiO ₂ ) layer having a refractive index smaller than that of the core 4. For the production of the optical waveguide element 1A, for example, an SOI (Silicon on insulator) wafer made of Si—SiO ₂ —Si can be used. Specifically, the core 4 can be formed by processing a Si layer (SOI layer) in the uppermost layer of the SOI wafer. When an SOI wafer is used, the lowermost Si serves as the substrate 3 and the buried SiO ₂ layer located in the middle serves as the lower cladding 6.

The waveguide D is configured based on a silicon waveguide having a high refractive index difference in which such an SOI layer is used as a core material and SiO ₂ is used as a cladding material. However, the core material and the clad material are not limited to these materials, and the optical waveguide element 1A is configured using a high refractive index difference waveguide composed of the core and the clad using another semiconductor material or an insulator material. Thus, the object of the present invention can be achieved.

  In the present embodiment, the horizontal direction is the direction parallel to the upper plane of the substrate 3, and the vertical direction is the direction orthogonal to the upper plane of the substrate 3. The width of each part is measured in the horizontal direction, and the height of each part is measured in the vertical direction. The TE polarization is a linear polarization state in which the electric field is parallel to the upper plane of the substrate 3. The TM polarization is a linear polarization state in which the magnetic field is parallel to the upper plane of the substrate 3.

  The core 4 has a rectangular cross section. In the present embodiment, for example, the case where the width of the core 4 is 500 nm, the height of the core 4 is 220 nm, and the length along the waveguide direction of the core 4 is 500 μm to 5 mm is exemplified.

  In a silicon waveguide having a core height of about 200 nm, light of a transverse electric field (TE) polarization in which the electric field is in a linearly polarized state parallel to the substrate surface propagates stably. A transverse magnetic field (TM) polarization in which the magnetic field is in a linear polarization state parallel to the substrate surface tends to have a greater loss than the TE polarization.

  The optical waveguide element 1A includes a phase adjusting unit 2A that adjusts the phase of light propagating through the waveguide D. The phase adjustment unit 2 </ b> A includes a first electrode 8 and a second electrode 9, and an electro-optic (EO) layer 10.

  In addition, a connection waveguide (not shown) having a rectangular core or a rib core made of the same material as that of the core 4 is connected to both ends of the phase adjusting unit 2A in the waveguide direction. The width of the connecting waveguide may be changed in a tapered shape along the waveguide direction in order to reduce light loss and light reflection.

  The first electrode 8 and the second electrode 9 are provided on both sides of the core 4 on the lower cladding 6. In the present embodiment, for example, the distance between the core 4 and the first electrode 8 and the distance between the core 4 and the second electrode 9 are about 300 nm, respectively. These intervals are not limited to this value. When it is necessary to reduce the propagation loss of the core 4, these intervals may be further increased. On the other hand, when it is necessary to reduce the voltage required for polling, which will be described later, these intervals may be further reduced. When these intervals are narrowed, the minimum width is determined by the restriction due to processing accuracy. In the heating process based on optical drawing suitable for mass production, the minimum value is about 100 nm at present.

  The first electrode 8 and the second electrode 9 are formed of a diffusion layer formed by doping impurities into the silicon layer. As the impurity doping method, for example, a thermal diffusion method or an ion implantation method can be used. As the impurity, for example, boron (B) can be used for the P type, and phosphorus (P) can be used for the N type. The first electrode 8 and the second electrode 9 have the same conductivity (both P-type or N-type) and different conductivity (one is P-type and the other is N-type). Type).

  Here, in the manufacturing method of the optical waveguide element 1A of the present embodiment, when the first electrode 8 and the second electrode 9 are formed, a silicon layer made of the same layer as the silicon layer that becomes the core 4 is patterned, A diffusion layer having the same height as the core 4 can be formed by doping the patterned silicon layer with impurities.

  In this case, since the first electrode 8 and the second electrode 9 can be formed using a silicon layer made of the same layer as the silicon layer used as the core 4, processing when manufacturing the optical waveguide element 1A is facilitated.

  The EO layer 10 can be formed by, for example, a lithium niobate (LN) thin film applied by a sol-gel method or a spin-coated EO polymer thin film. For EO materials such as lithium niobate and EO polymers, permanent electrical polarization can be controlled by applying a direct current (DC) voltage. In particular, in a material that causes a glass transition, a DC voltage is applied in a state heated to a temperature higher than the glass transition temperature to orient the electric polarization, and it is cooled to a temperature lower than the glass transition temperature to fix the oriented electric polarization. This induces permanent electrical polarization. Further, when the glass transition temperature is low (for example, about 150 degrees Celsius), permanent electrical polarization may disappear due to an increase in environmental temperature, and predetermined performance may not be satisfied. For this reason, the glass transition temperature is preferably about 200 degrees Celsius or higher.

  The EO layer 10 is opposed to at least a part of both side surfaces and the upper surface of the core 4, at least a part of the side surface and the upper surface of the first electrode 8 facing the core 4, and the core 4 of the second electrode 9. It is provided so as to cover at least a part of the side surface and the upper surface on the side to be processed. In the present embodiment, for example, the case where the width of the EO layer 10 is 800 nm to 2000 nm and the height of the EO layer 10 is 400 nm to 1000 nm from the upper surface of the lower cladding 6 is exemplified. The width and height of the EO layer 10 can be arbitrarily set according to the propagation loss and the polling voltage.

  The first electrode 8 is electrically connected to a first upper electrode 12 provided on the upper clad 7 via a first through electrode 11 penetrating the upper clad 7. The second electrode 9 is electrically connected to a second upper electrode 14 provided on the upper clad 7 via a second through electrode 13 penetrating the upper clad 7. The EO layer 10 is electrically connected to a third upper electrode 16 provided on the upper clad 7 via a third through electrode 15 penetrating the upper clad 7.

  The first through electrode 11, the second through electrode 13, and the third through electrode 15 are called vias (VIA). In a hole that penetrates the upper cladding 7, for example, aluminum (Al), copper ( It can be formed by embedding a conductive material such as Cu) or gold (Au).

  For the first upper electrode 12, the second upper electrode 14, and the third upper electrode 16, a metal film such as aluminum (Al), copper (Cu), gold (Au), etc. formed on the upper cladding 7. Can be formed. In addition, the third through electrode 15 is preferably formed with an increased contact area with the EO layer 10 so that the area covering the upper surface of the EO layer 10 is 50% or more, if possible.

  The phase adjustment unit 2 </ b> A has a pair of heater electrodes 17 and 18 that serve as a heater for heating the EO layer 10. The pair of heater electrodes 17 and 18 are provided outside the first upper electrode 12 and the second upper electrode 14 on the upper clad 7. The first upper electrode 12 and the second upper electrode 14 can be formed of a high-resistance thin film made of, for example, a nickel chrome (NiCr) alloy or the like formed on the upper cladding 7.

  In the phase adjustment unit 2A, it is preferable to locally heat only the periphery of the EO layer 10 by applying current or voltage to the pair of heater electrodes 17 and 18 to generate heat when performing polling. When the substrate 3 is heated, the components around the waveguide D, or external components connected to or bonded to other optical circuits integrated on the same substrate as the waveguide D, the light receiving layer, etc. are also heated. These components can be damaged. On the other hand, when there is a possibility that the pair of heater electrodes 17 and 18 may be damaged by heat generation, the substrate 3 may be heated at the same time to reduce the current or voltage applied to the heater electrodes 17 and 18. However, the amount of heat applied to the substrate 3 needs to be controlled so as not to damage the above-described components.

  The optical waveguide element 1A has a gap portion 19 that thermally isolates the phase adjustment portion 2A from the surroundings. The gap portion 19 has a pair of groove portions 20 and 21 that cut out at least the cladding 5 in the depth direction. In the present embodiment, the pair of groove portions 20 and 21 are formed at a depth reaching the substrate 3. Further, the pair of groove portions 20 and 21 are located outside the pair of heater electrodes 17 and 18. Thereby, the pair of groove portions 20 and 21 thermally isolate the phase adjusting portion 2A from the surroundings on the vertical surface and the horizontal surface of the substrate 3.

  Furthermore, the gap portion 19 may have a gap portion 22 in which a part of the substrate 3 (a region indicated by a broken line in FIG. 1) is continuously removed between the pair of groove portions 20 and 21. In this case, the gap portion 19 is further effective in thermally isolating the phase adjustment portion 2A by being a so-called suspended bridge type (suspended) in which the phase adjustment portion 2A straddles the gap portion 22.

  In the manufacturing method of the optical waveguide element 1A of the present embodiment, when such a suspension bridge type gap portion 19 is formed, a pair of groove portions at a depth from the clad 5 to the substrate 3 on both sides of the phase adjustment portion 2A is formed. 20 and 21 are formed by etching. When forming the grooves 20 and 21, for example, anisotropic etching can be used.

Thereafter, a part of the substrate 3 is selectively removed from the pair of groove portions 20 and 21 by etching, thereby forming a continuous gap portion 22 between the pair of groove portions 20 and 21. When forming the gap 22, reactive ion etching using, for example, SF ₆ can be suitably used as the etching gas in order to selectively remove the substrate 3 made of silicon (Si). In the case of reactive ion etching in the present embodiment, not only the region between the pair of groove portions 20 and 21 (the region indicated by the broken line in FIG. 1), but actually isotropic around the pair of groove portions 20 and 21. Thus, the gap portion 22 expands.

  In the optical waveguide element 1A having the above-described configuration, permanent electrical polarization is induced in the EO layer 10 by poling after the EO layer 10 is formed. At the time of poling, the EO layer 10 is locally heated by the pair of heater electrodes 17 and 18. In addition, the heating is stopped after poling to fix the induced permanent electric polarization. The phase adjusting unit 2A adjusts the phase of light propagating through the waveguide D by adjusting the magnitude of permanent electrical polarization induced in the EO layer 10 according to the polling time and the voltage applied to the EO layer 10. Can do.

  Specifically, when the first electrode 8 and the second electrode 9 have the same conductivity, a DC voltage is applied to the EO layer 10 via the third upper electrode 16 and the third through electrode 15. Apply. On the other hand, the first electrode 8 through the first upper electrode 12 and the first through electrode 11 and the second electrode 9 through the second upper electrode 14 and the second through electrode 13 are grounded, for example. By doing so, it is held at zero potential. Polling can be performed in this state. After polling, the application of the DC voltage is canceled.

  When the first electrode 8 and the second electrode 9 have different conductivity, the third upper electrode 16 and the third through electrode 15 can be omitted. In this case, between the first electrode 8 through the first upper electrode 12 and the first through electrode 11 and between the second electrode 9 through the second upper electrode 14 and the second through electrode 13. DC voltage is applied to Polling can be performed in this state. After polling, the application of the DC voltage is canceled.

  Further, even when the first electrode 8 and the second electrode 9 have the same conductivity, the third upper electrode 16 and the third through electrode 15 can be omitted. In this case, between the first electrode 8 through the first upper electrode 12 and the first through electrode 11 and between the second electrode 9 through the second upper electrode 14 and the second through electrode 13. DC voltage is applied to Polling can be performed in this state. After polling, the application of the DC voltage is canceled.

  When permanent electric polarization occurs in the EO layer 10 due to polarization formation, the arrangement of crystal atoms changes due to the generated electric field, so that the refractive index of the medium changes. Thereby, since the light oozing out from the core 4 is affected by the EO layer 10, the phase of the light propagating through the core 4 can be delayed.

  In the optical waveguide element 1A of the present embodiment, the effective refractive index of the core 4 changes according to the wavelength of incident light, and therefore fine adjustment of the phase may be necessary. In this case, a voltage is applied from at least one of the first upper electrode 12, the second upper electrode 14, and the third upper electrode 16 according to the wavelength of incident light, and the voltage is adjusted. . At this time, by applying an electric field to the EO layer 10, the arrangement of polarized crystal atoms is further distorted, so that the refractive index of the medium can be electrically adjusted. (Whether the refractive index is increased or decreased by polarization depends on the structure.) Thereby, fine adjustment of the phase is possible.

  Further, in the optical waveguide element 1A of the present embodiment, fine adjustment of the phase due to temperature fluctuation is possible as well. Since the polymer material has the temperature dependence of the refractive index opposite to that of the semiconductor and the insulator, there is an advantage that the temperature change of the effective refractive index can be reduced and the fine adjustment of the phase due to the temperature variation can be unnecessary or reduced.

  In the optical waveguide device 1A of the present embodiment, the EO layer 10 described above includes at least a part of both side surfaces and the upper surface of the core 4, and at least a part of the side surface and the upper surface of the first electrode 8 facing the core 4. And at least a part of the side surface and the upper surface of the second electrode 9 facing the core 4.

  In the case of this configuration, the electric field concentrates in the periphery of the core 4, that is, in the region where the intensity of the guided light oozing out from the core 4 is strong, thereby concentrating the electric field and changing the arrangement of the crystal atoms themselves. Therefore, the refractive index changes. Further, since the EO layer 10 is expanded to a position covering a part of the upper surfaces of the first electrode 8 and the second electrode 9, it becomes easy to flatten the upper surface of the EO layer 10. Can be improved. Further, since both side surfaces of the EO layer 10 are separated from the side surfaces facing the core 4 of the first electrode 8 and the second electrode 9, there is a possibility that discharge occurs through both side surfaces of the EO layer 10. Is reduced. Thereby, the possibility of destruction by the discharge of the phase adjusting unit 2A can be reduced.

  Further, in the optical waveguide element 1A of the present embodiment, the heater electrodes 17 and 18 for heating the EO layer 10 described above are provided, and the gap for thermally isolating the phase adjusting unit 2A from the surroundings outside the heater electrodes 17 and 18. The configuration is provided with the portion 19. In the case of this configuration, it is possible to adopt a configuration suitable for locally heating the phase adjustment unit 2A.

  Furthermore, in the optical waveguide element 1A of the present embodiment, by providing the suspension bridge type gap portion 19 described above, both side portions of the phase adjustment portion 2A are thermally isolated by the pair of grooves 20 and 21, and the phase adjustment portion 2A. The lower part is thermally isolated by the gap 22. In this configuration, it is further effective to thermally isolate the phase adjusting unit 2A.

[Second Embodiment]
Next, as a second embodiment of the present invention, for example, an optical waveguide element 1B shown in FIG. 2 and FIGS. 3A and 3B will be described. FIG. 2 is a schematic cross-sectional view showing the configuration of the phase adjusting unit 2B in the optical waveguide element 1B. FIG. 3A is a schematic cross-sectional view along the extending direction of the first electrode 8 of the phase adjusting unit 2B shown in FIG. FIG. 3B is a schematic cross-sectional view along the extending direction of the second electrode 9 of the phase adjusting unit 2B shown in FIG. Moreover, in the following description, about the site | part equivalent to the said optical waveguide element 1A, while omitting description, the same code | symbol shall be attached | subjected in drawing.

  As shown in FIG. 2, the optical waveguide element 1B has a function as a heater (electric resistor) in the first electrode 8 and the second electrode 9 instead of omitting the pair of heater electrodes 17 and 18. It is the structure which made it.

  Specifically, as shown in FIG. 2 and FIG. 3A, the first electrode 8 is a first electrode provided on the upper cladding 7 through a first through electrode 23 that penetrates the upper cladding 7. The upper electrode 24 is electrically connected. The first electrode 8 is electrically connected to a fourth upper electrode 26 provided on the upper clad 7 through a fourth through electrode 25 penetrating the upper clad 7. The first upper electrode 24 and the first through electrode 23, the fourth upper electrode 26 and the fourth through electrode 25 are arranged apart from each other in the extending direction of the first electrode 8.

  Similarly, as shown in FIG. 2 and FIG. 3B, the second electrode 9 has a second upper portion provided on the upper cladding 7 through a second through electrode 27 that penetrates the upper cladding 7. It is electrically connected to the electrode 28. The second electrode 9 is electrically connected to a fifth upper electrode 30 provided on the upper clad 7 via a fifth through electrode 29 penetrating the upper clad 7. The second upper electrode 28 and the second through electrode 27, and the fifth upper electrode 30 and the fifth through electrode 29 are spaced apart from each other in the extending direction of the second electrode 9.

  In the optical waveguide element 1B having the above-described configuration, a voltage is applied between the first upper electrode 24 and the fourth upper electrode 26 and a current flows through the first electrode 8, whereby the first The electrode 8 generates heat. Similarly, when a voltage is applied between the second upper electrode 28 and the fifth upper electrode 30 and a current flows through the second electrode 9, the second electrode 9 generates heat. Thereby, the EO layer 10 can be heated.

  Therefore, in the phase adjustment unit 2B, when the polling is performed, only the periphery of the EO layer 10 can be locally heated by causing the first electrode 8 and the second electrode 9 to generate heat. Further, a DC voltage is applied to the EO layer 10 through the third upper electrode 16 and the third through electrode 15. Alternatively, a DC voltage difference is generated between the first electrode 8 and the second electrode 9. Thereby, polling can be performed.

  As described above, since the optical waveguide element 1B of the present embodiment has basically the same configuration as the optical waveguide element 1A except for the above configuration, it is possible to obtain the same effect as the optical waveguide element 1A. is there. On the other hand, in the optical waveguide device 1B of the present embodiment, by omitting the pair of heater electrodes 17 and 18, the EO layer 10 with high efficiency can be locally heated with a simpler configuration.

  As described above, according to the present embodiment, the optical waveguide elements 1A and 1B that are capable of controlling the phase of a light wave with low power consumption and suitable for integration in optical fiber communication that performs large-capacity and high-speed data transfer. It is possible to provide.

  In this embodiment, the EO layer 10 is used to reduce power consumption, enable local heating suitable for wire bonding, adhesion of external optical components, and integration with a light receiving unit, and low voltage polling. By configuring the optical waveguide elements 1A and 1B that enable the above, it is possible to configure an integrated circuit with low power consumption, easy integration, suitable for mass production, and high reliability.

  The optical waveguide elements 1A and 1B of the present embodiment can be connected in series with a phase shifter using a thermo-optic (TO) effect as a phase shifter using an EO effect. In the TO effect, the phase change is larger than that in the EO effect, and the waveguide length may be shortened. Therefore, when it is required to reduce the propagation loss or the footprint, it is also effective to connect both phase shifters in series.

(Optical receiver circuit)
Next, the optical receiver circuit according to the embodiment of the present invention will be described.
In the optical receiving circuit, a waveguide through which signal light propagates and a waveguide through which local light propagates branch from one incident waveguide to a plurality of waveguides. In order to have a configuration in which the waveguide that branches in this way does not have an intersection, the waveguide through which the signal light propagates and the waveguide through which the local light propagates must pass through opposite sides with respect to the light receiving unit. . When taking out an electric signal output from the light receiving unit, in order to suppress loss and waveform deterioration, an electrode (for example, an electrode pad for wire bonding) for taking out the output from on the chip is adjacent to the chip end. It is preferable to provide them. And between a light-receiving part and an electrode pad is connected with the metal electrode. Therefore, the waveguide can pass under the metal electrode.

In the optical receiver circuit of this embodiment, the optical waveguide device 1A of the first embodiment or the optical waveguide device 1B of the second embodiment can be used. The waveguide used for the optical waveguide element is preferably a silicon waveguide in which the core of the waveguide is made of silicon (Si) and the cladding of the waveguide is made of silica (SiO ₂ ). The silicon waveguide is a high refractive index difference waveguide. In the high refractive index difference waveguide, propagating light is strongly confined in the core. Therefore, if the distance (depth) from the metal electrode to the core is 1 μm or more, the influence of the metal electrode can be ignored (suppressed to a practical level), and the absorption of the propagation light by the conduction electrons in the metal electrode is ignored. it can.

  The substrate-type optical waveguide element can be manufactured with high productivity by forming a waveguide on a wafer and then cutting a large number of chips from the wafer. In order to avoid the impact of cutting the chip from the wafer and the effect of distortion from the chip end, the core of the waveguide is preferably separated from the chip end by 50 μm or more. Further, there is a step of melting solder in order to join the wire to the metal pad during wire bonding. At this time, in order to avoid damage to the waveguide due to the impact of ultrasonic waves or heat, it is preferable that the core of the waveguide is disposed so as to avoid being directly below the electrode pad for wire bonding.

  In an optical circuit for polarization separation used in an optical receiver circuit, a TM polarization light propagating among two waveguides behind a polarization separation waveguide branching section (polarization separation section) is transmitted. A polarization rotation waveguide (polarization rotation unit) is connected to the waveguide, and TM polarization is rotated to TE polarization. Such a polarization separation circuit includes a polarization separation unit that separates a TE polarization and a TM polarization and propagates them to two waveguides, and a polarization rotation unit that rotates the separated TM polarization to a TE polarization. Including. Due to the polarization rotation, the two signal lights output from the polarization separation circuit become TE polarized waves. For this reason, both 90 degree hybrid circuits after separation can be designed to function with respect to TE polarization. As a result, a common configuration can be applied to each 90-degree hybrid circuit, so that the design is simple compared with the conventional technique (when processing is performed with TM polarization).

  In order to incorporate an optical receiving circuit in a compact and pluggable optical transceiver, an optical input terminal into which signal light and local light are input to the optical receiving circuit, and an output pad for extracting an electric signal from the optical receiving circuit are each a chip. It is preferable to arrange on the opposite side. In order to reduce the skew of the output electric signal between the different polarizations, it is preferable to arrange the waveguide so as to eliminate the propagation time difference between the optical signal and the electric signal between the different polarizations. When the polarization rotation is performed as described above, the characteristic of only the TE polarization is involved in the optical signal after the different polarizations are separated. For this reason, since the propagation time difference depends only on the waveguide arrangement, the propagation time difference can be easily estimated.

  When light input to the optical receiving circuit is propagated through an optical fiber, the optical transceiver package is required to have a height that accommodates the connection between the optical receiving circuit chip and the optical fiber. In order to reduce the height of the package, it is preferable to install an optical fiber so that light (each of signal light and local light) is input in parallel to the substrate surface from the end face of the optical receiving circuit chip. In order to provide an optical input terminal and an electrical signal output pad on opposite sides of the optical receiver circuit chip, the optical input terminal for inputting signal light and the optical input terminal for inputting local light are arranged on the same end surface of the chip. It is preferable to do.

In the optical receiver circuit of this embodiment, the optical hybrid circuit includes at least the following elements.
(1) A first light branching section that branches signal light to the first signal light propagation waveguide and the second signal light propagation waveguide to propagate.
(2) A second optical branching unit for branching and propagating the local light to the first local light propagation waveguide and the second local light propagation waveguide.
(3) A first optical multiplexing unit that combines the signal light propagating through the first signal light propagation waveguide and the local light propagating through the first local light propagation waveguide to interfere with each other.
(4) A second optical multiplexing unit that multiplexes the signal light propagating through the second signal light propagation waveguide and the local light propagating through the second local light propagation waveguide to interfere with each other.
(5) A phase adjusting unit provided in one or both of the first local light propagation waveguide and the second local light propagation waveguide.

  According to this optical hybrid circuit, a predetermined phase difference (for example, 90 degrees = π / 2 radians) can be given to the local light that is branched and propagated to the two local light propagation waveguides in the phase adjustment unit. Furthermore, interference light can be output by causing signal light and local light to interfere with each other using an optical multiplexer. Each optical multiplexer generally outputs two interference lights as differential signals.

  A light receiving portion is provided to receive the interference light output from the optical multiplexing portion. The light receiving unit is, for example, a light receiver, a photoelectric conversion element, or the like. The light receiving unit converts the optical signal into an electrical signal and outputs the electrical signal. An electrode for propagating an electrical signal output from the light receiving unit can be provided on the optical waveguide element. For this reason, a part of the waveguide and the optical branching portion included in the optical waveguide element may pass below the electrode that propagates the electric signal.

In the optical waveguide device, it is preferable to satisfy the following requirements in order to make the waveguide have no crossing portion.
(A) The first optical branching unit and the second optical branching unit are arranged so that the propagation direction of the local light in the second optical branching unit faces the propagation direction of the signal light in the first optical branching unit. Is done.
(B) The first optical multiplexing unit and the second optical multiplexing unit are arranged so that the propagation direction of the output light in the second optical multiplexing unit is aligned with the propagation direction of the output light in the first optical multiplexing unit. The

  By satisfying the requirement (A), two signal light propagation waveguides are branched from the first optical branching unit, and two local light propagation waveguides are branched from the second optical branching unit. Are opposite to each other. Then, the local light propagation waveguide can be arranged in a region where the distance between the two signal light propagation waveguides is separated. Therefore, the exit end of the local light propagation waveguide can be brought close to the exit end of the signal light propagation waveguide without crossing the waveguides.

  By satisfying the requirement (B), the signal light propagation waveguide and the local light propagation waveguide can be incident on the optical multiplexer from the incident end on the same side. In the optical multiplexer, an exit end can be provided on the side opposite to the entrance end, and a light receiving unit can be connected to the exit end. Therefore, for example, interference light can be generated using a 2 × 2 branch optical interferometer.

  The waveguide having no intersection is at least a first signal light propagation waveguide, a second signal light propagation waveguide, a first local light propagation waveguide, and a second local light propagation waveguide. It is. It is preferable that all the waveguides including either of these waveguides, in which one or both of the signal light and the local light are propagated in the optical waveguide device, are arranged so as not to overlap each other in plan view with respect to the substrate.

  In order to arrange the signal light propagation waveguide and the local light propagation waveguide so as to satisfy the requirements of (A) and (B), the local light propagation waveguide is arranged so that the propagation direction is aligned with the signal light propagation waveguide. A configuration in which the waveguide is bent by about 180 degrees, a configuration in which the signal light propagation waveguide is bent by about 180 degrees so that the propagation direction is aligned with the local light propagation waveguide, and the signal light propagation waveguide and the local light propagation waveguide are each The structure etc. which bend only about 90 degree | times or another angle are mentioned. In order to suppress the loss of signal light, it is preferable to change the propagation direction of the signal light as much as possible while changing the propagation direction of the signal light as small as possible. For example, a structure in which the local light propagation waveguide passes through the side of the optical multiplexing unit and then is connected to the optical multiplexing unit via a 180-degree bent portion.

  It is preferable that the optical branching portion (second optical branching portion) through which local light propagates is provided on the opposite side of each optical multiplexing portion with respect to each light receiving portion. That is, it is preferable that the light receiving unit is disposed between each optical multiplexing unit and the second optical branching unit in the direction along the light propagation direction with respect to the incident end of the optical multiplexing unit. As a result, the distance between the second optical branching unit and the optical multiplexing unit is longer in the second optical branching unit than the length of the connection waveguide connecting the emission end of the optical multiplexing unit and the light receiving unit. So as to be arranged short. Even when one optical multiplexing unit is arranged between two waveguides for local light propagation, the light receiving unit connected to the optical multiplexing unit can be easily arranged inside these. For example, in FIG. 4 (details will be described later), light receiving portions 110 and 111 are arranged between the optical branching portion 121 and the optical multiplexing portion 109. The two connection waveguides 141 and 142 extending from the optical branching unit 121 are arranged so as to avoid the regions of the optical multiplexing unit 109 and the light receiving units 110 and 111.

  When the signal is multiplexed with the two polarization components of the signal light, the processing unit (for example, reference numerals 150 and 151 in FIG. 4) including the optical hybrid circuit and the light receiving unit described above is provided for each polarization component. Prepared for. The processing unit includes a first optical branching unit, a second optical branching unit, a first optical multiplexing unit, a second optical multiplexing unit, a first light receiving unit, a second light receiving unit, And a phase adjustment unit. The two polarization components included in the signal light are separated by the polarization separation circuit before entering the respective optical hybrid circuits.

[Third Embodiment]
Next, as a third embodiment of the present invention, for example, an optical receiver circuit 101 shown in FIGS. 4 to 8 will be described. FIG. 4 shows a schematic configuration on a single horizontal plane of the optical waveguide element constituting the optical receiving circuit 101.

  The signal light is incident as incident light from one end (incident end) of the incident waveguide 126. The other end (outgoing end) of the incident waveguide 126 is connected to the incident end of the polarization separation circuit 102. The polarization separation circuit 102 has two emission ends. One end of each of the connection waveguides 127 and 128 is connected to these emission ends.

  The polarization separation circuit 102 has two configurations as shown in FIGS. 5 (a) and 5 (b). In the configuration of FIG. 5A, the polarization separation circuit 102 includes a polarization separation unit 201 and a polarization rotation unit 202. The incident end of the polarization separation circuit 102 is the incident end of the polarization separation unit 201. One end (incident end) of each of the connection waveguides 127 and 200 is connected to the two emission ends of the polarization separation unit 201. The polarization rotation unit 202 is provided in the subsequent stage of the polarization separation unit 201, and the incident end of the polarization rotation unit 202 is connected to the other end (output end) of the connection waveguide 200. One of the output ends of the polarization separation circuit 102 is an output end connected to the connection waveguide 127 among the two output ends of the polarization separation unit 201. The other exit end of the polarization separation circuit 102 is the exit end of the polarization rotation unit 202. Here, if the connection waveguide 200 connecting the polarization separation unit 201 and the polarization rotation unit 202 is considered as a part of the connection waveguide 128, the polarization rotation unit 202 is inserted into the connection waveguide 128. It can also be understood.

  In the configuration of FIG. 5B, the polarization separation circuit 102 includes a polarization rotation unit 203 and a polarization separation unit 204. The polarization rotation unit 203 is inserted before the polarization separation unit 204. The incident end of the polarization separation circuit 102 is the incident end of the polarization rotation unit 203. The output end of the polarization rotating unit 203 is connected to one end (incident end) of the connection waveguide 205, and the other end (output end) of the connection waveguide 205 is connected to the incident end of the polarization separation unit 204. Here, assuming that the connecting waveguide 205 connecting the polarization rotating unit 203 and the polarization separating unit 204 is a part of the incident waveguide 126, the polarization rotating unit 203 is inserted into the incident waveguide 126. It can also be understood. One end (incident end) of each of the connection waveguides 127 and 128 is connected to the two output ends of the polarization separation unit 204. Two exit ends of the polarization separation circuit 102 are two exit ends of the polarization separation unit 204.

  In each configuration of the polarization separation circuit 102, the TE polarization component of the incident light is emitted from the exit end to which one end (incident end) of the connection waveguide 127 is connected as TE polarized light. The TM polarization component of the incident light is converted into a TE polarization component and emitted from the exit end to which one end of the connection waveguide 128 is connected as TE polarization light. TE polarization refers to a linear polarization state in which the electric field is parallel to the upper plane of the substrate (see reference numeral 401 in FIG. 7B), and TM polarization refers to a magnetic field parallel to the upper plane of the substrate. Refers to the state of linear polarization. In the following description, a direction parallel to the upper plane of the substrate is defined as a horizontal direction, and a direction orthogonal to the upper plane of the substrate is defined as a vertical direction. The width is measured in the horizontal direction and the height is measured in the vertical direction. 4 to 8 are created so that the paper surface is horizontal.

  5A, the polarization separation unit 201 includes, for example, a rib disclosed in Reference Document 1 (IEEE Photonics Technology Letters vol. 17, no. 1, pp. 100-102, 2005). A directional coupler composed of a waveguide can be used. As an example of dimensions, the width of the top of the core of the rib waveguide is 500 nm, the height from the bottom of the core to the top of the core is 220 nm, the gap (gap) between the waveguides is 300 nm, and the coupling length of the directional coupler is 300 μm. An example is given. An asymmetric rib waveguide can be used for the polarization rotation unit 202 (see, for example, unpublished Japanese Patent Application No. 2013-135492). The TM-polarized guided light incident on the incident end of the polarization rotating unit 202 is rotated by 90 degrees, converted into TE-polarized guided light, and emitted from the output end of the polarization rotating unit 202. .

  In the configuration of FIG. 5B, for example, the polarization rotation unit 203 can be configured using a rib waveguide through which higher-order guided light propagates. In a rib waveguide in which higher-order guided light propagates, the TM polarization component of incident light is converted into guided light of a higher-order TE polarization component due to the asymmetry of the waveguide core cross section in the vertical direction. The TE polarized wave component of the incident light becomes the guided light of the basic TE polarized wave component without being converted. When the polarization separation unit 204 using the asymmetric rib waveguide directional coupler is passed, the fundamental TE-polarized light and the higher-order TE-polarized light are separated. Further, in the waveguide after separation, higher-order TE polarized waves can be propagated as basic TE polarized waves (see unpublished Japanese Patent Application No. 2013-135490).

  According to the polarization separation circuit 102 described above, when the incident light propagating through the incident waveguide includes the basic TE polarization component and the basic TM polarization component, the TE polarization component and the TM polarization component are used. And can be separated. Furthermore, each component can be propagated to the different connection waveguides 127 and 128 from the two emission ends of the polarization separation circuit 102 as the fundamental TE polarized light.

  Next, returning to FIG. 4, the description of the optical receiving circuit 101 will be continued. Each of the optical multiplexing units 105, 109, 113, and 117 has two incident ends and two outgoing ends. One incident end is an incident end for signal light, and the other incident end is an incident end for local light emission. On one side (for signal light), connection waveguides 129 to 132 through which signal light propagates are connected. Connection waveguides 141 to 144 through which local light is propagated are connected to the other incident end (for local light). Interference light generated by combining the signal light and the local light in the optical multiplexing units 105, 109, 113, and 117 is output from the two emission ends.

  The other end (outgoing end) of the connection waveguide 127 is connected to the incident end of the optical branching unit 103. The light branching unit 103 has two emission ends. One end of the connection waveguide 129 is connected to one output end of the optical branching unit 103, and one end of the connection waveguide 130 is connected to the other output end. The other end of the connection waveguide 129 is connected to one incident end (for signal light) of the optical multiplexing unit 105. The other end of the connection waveguide 130 is connected to one incident end (for signal light) of the optical multiplexing unit 109.

  The other end (outgoing end) of the connection waveguide 128 is connected to the incident end of the optical branching unit 104. The light branching unit 104 has two exit ends. One end of the connection waveguide 131 is connected to one emission end of the optical branching section 104, and one end of the connection waveguide 132 is connected to the other emission end. The other end of the connection waveguide 131 is connected to one incident end (for signal light) of the optical multiplexing unit 113. The other end of the connection waveguide 132 is connected to one incident end (for signal light) of the optical multiplexing unit 117.

  The TE-polarized local light is incident from one end (incident end) of the incident waveguide 147. A phase adjusting unit 124 is inserted into the incident waveguide 147. For the phase adjustment unit 124, for example, a thermo-optical phase adjuster using a rectangular waveguide disclosed in Reference Document 2 (Journal of Lightwave Technology vol. 26, no 14, pp. 2235-2244, 2008) is used. Can do. The configuration of the phase adjustment unit 124 is not limited to this, and a rib waveguide can also be used.

  The other end (outgoing end) of the incident waveguide 147 is connected to the incident end of the optical branching section 123. One end (incident end) of each of the connection waveguides 145 and 146 is connected to each of the two emission ends of the optical branching section 123.

  The other end (outgoing end) of the connection waveguide 145 is connected to the incident end of the optical branching unit 121. The two outgoing ends of the optical branching section 121 are connected to one ends of the connection waveguides 141 and 142, respectively. The other end of the connection waveguide 141 is connected to the other incident end (for local light emission) of the optical multiplexing unit 105. The phase adjustment unit 108 is inserted into the connection waveguide 141. The other end of the connection waveguide 142 is connected to the other incident end of the optical multiplexing unit 109 (for local light emission). The phase adjustment unit 112 is inserted into the connection waveguide 142.

  The other end (outgoing end) of the connection waveguide 146 is connected to the incident end of the optical branching unit 122. The two exit ends of the optical branching section 122 are connected to one ends of the connection waveguides 143 and 144, respectively. The other end of the connection waveguide 143 is connected to the other incident end (for local light emission) of the optical multiplexing unit 113. The phase adjustment unit 116 is inserted into the connection waveguide 143. The other end of the connection waveguide 144 is connected to the other incident end (for local light emission) of the optical multiplexing unit 117. The phase adjustment unit 120 is inserted into the connection waveguide 144.

  The phase adjustment units 108, 112, 116 and 120 may have the same configuration as the phase adjustment unit 124 or may have different configurations. Further, the phase adjustment units 108, 112, 116 and 120 may have the same configuration or different configurations. For these phase adjustment units 108, 112, 116, 120 and 124, the phase adjustment unit 2A in the optical waveguide device 1A of the first embodiment or the phase adjustment unit 2B in the optical waveguide device 1B of the second embodiment is used. be able to.

  The I component and the Q component of the coherent optical reception signal are generated by the interference between the local phase light emission and the rank phase (I) component and the quadrature phase (Q) component of the TE polarization component of the incident light. By adjusting the current or voltage applied to the phase adjustment unit 108 or 112, the phase difference between the I component and the Q component is maintained at π / 2, and the crosstalk of the TE polarization component signal is removed.

  Since the phase difference can be held only by driving one of the phase adjusters 108 or 112, either of the phase adjusters 108 or 112 may be omitted. Providing both of the phase adjustment units 108 and 112 can invert the correspondence relationship between the I component and the Q component of the coherent optical reception signal, thereby increasing the degree of freedom of the system configuration. Depending on the specifications required for the optical receiving circuit 101, both the phase adjustment units 108 and 112 may be provided, or either one may be omitted or selected. By applying a voltage for fine adjustment to the phase adjustment unit 108 or 112, the accuracy of the phase difference can be further improved.

  Similarly, the I component and the Q component of the coherent light reception signal are generated due to the interference between the local phase light and the rank phase (I) component and the quadrature phase (Q) component of the TM polarization component of the incident light. By adjusting the current or voltage applied to the phase adjustment unit 116 or 120, the phase difference between the I component and the Q component is maintained at π / 2, and the crosstalk of the TM polarization component signal is removed. As with the phase adjustment unit 108 or 112, either the phase adjustment unit 116 or 120 may be omitted.

  The phase adjustment unit 124 is used to control the phase of the local light with respect to the phase of the incident light independently of the control of the phase difference between the I component and the Q component of the coherent light reception signal of each polarization component. Can be made. When the configuration of the optical receiving circuit 101 is simplified, the phase adjustment unit 124 may be omitted.

  One end of the connection waveguide 133 is connected to one emission end of the optical multiplexing unit 105, and the other end of the connection waveguide 133 is connected to the incident end of the light receiving unit 106. One end of the connection waveguide 134 is connected to the other emission end of the optical multiplexing unit 105, and the incident end of the light receiving unit 107 is connected to the other end of the connection waveguide 134. In the light receiving units 106 and 107, positive and negative electric signals TE / I + and TE / I− of the I component of the coherent light reception signal of the TE polarization component are generated, respectively.

  One end of the connection waveguide 135 is connected to one emission end of the optical multiplexing unit 109, and the other end of the connection waveguide 135 is connected to the incident end of the light receiving unit 110. One end of the connection waveguide 136 is connected to the other emission end of the optical multiplexing unit 109, and the incident end of the light receiving unit 111 is connected to the other end of the connection waveguide 136. In the light receiving units 110 and 111, positive and negative electrical signals TE / Q + and TE / Q− of the Q component of the coherent light reception signal of the TE polarization component are generated, respectively.

  One end of the connection waveguide 137 is connected to one emission end of the optical multiplexing unit 113, and the other end of the connection waveguide 137 is connected to the incident end of the light receiving unit 114. One end of the connection waveguide 138 is connected to the other emission end of the optical multiplexing unit 113, and the incident end of the light receiving unit 115 is connected to the other end of the connection waveguide 138. In the light receiving units 114 and 115, positive and negative electrical signals TM / I + and TM / I− of the I component of the coherent light reception signal of the TM polarization component are generated, respectively.

  One end of the connection waveguide 139 is connected to one emission end of the optical multiplexing unit 117, and the other end of the connection waveguide 139 is connected to the incident end of the light receiving unit 118. One end of the connection waveguide 140 is connected to the other emission end of the optical multiplexing unit 117, and the incident end of the light receiving unit 119 is connected to the other end of the connection waveguide 140. In the light receiving units 118 and 119, positive and negative electrical signals TM / Q + and TM / Q− of the Q component of the coherent light reception signal of the TM polarization component are generated, respectively.

  In order to avoid the waveguide crossing, the local light is guided from the opposite direction to the direction in which the incident light propagates. The characteristics of the path shown in FIG. 4 will be described with respect to some elements of the TE polarization component of the incident light. In contrast to the direction in which a part of the TE polarization component of the incident light is incident from the connection waveguide 129 to one incident end of the optical multiplexing unit 105, a part of the local light emission from the connection waveguide 141 is connected to the connection waveguide 141. Guided inside. The connection waveguide 141 has a 180-degree bent portion 141a. Some elements of the local light propagating through the connection waveguide 141 reverse the propagation direction in the same direction as some elements of the incident light propagating through the connection waveguide 129, and then the other incident end of the optical multiplexing unit 105. To the optical multiplexing unit 105.

  Since the connecting waveguide 141 is made of a high refractive index difference waveguide, the radius of curvature of the 180-degree bent portion 141a can be reduced to about 5 μm without increasing the bending loss. For this reason, the footprint of the optical receiving circuit 101 can be reduced. The length of the connection waveguide 141 along the waveguide direction is also shortened, the propagation loss is reduced, and the optical loss of the optical receiving circuit 101 can be reduced. Two 90 degree bends can be connected in series to form a 180 degree bend.

  The connection waveguide 141 is provided between the side walls of the optical multiplexing unit 105 and the optical multiplexing unit 109. In order to reduce the footprint of the optical receiving circuit 101, it is necessary to shorten the distance between the optical multiplexing unit 105 and the optical multiplexing unit 109 as much as possible. However, in order to avoid light leakage from the connection waveguide 141, the distance between one side wall of the connection waveguide 141 and one side wall of the optical multiplexing unit 105, and the other side wall of the connection waveguide 141 and one of the optical multiplexing unit 109. It is desirable to secure an interval of at least about 2 μm from the side wall.

  There are similar features for the other elements of the TE polarization component of the incident light and the paths of the elements of the TM polarization component of the incident light. For example, some elements of local light emission from the opposite direction with respect to the direction in which some elements of incident light are incident on one incident end of the optical multiplexing units 109, 113, and 117 from the connection waveguides 130, 131, and 132 Are routed through the connecting waveguides 142, 143 and 144. The connecting waveguides 142, 143, and 144 each have a 180-degree bent portion 142a, 143a, and 144a. Some elements of the local light propagating through the connecting waveguides 142, 143, and 144 are reversed in the propagation direction in the same direction as that of some elements of incident light propagating through the connecting waveguides 130, 131, and 132, and then optically multiplexed. The light enters the other incident end of the portions 109, 113, and 117.

  In FIG. 4, the incident end 148 of the incident waveguide 147 and the incident end 125 of the incident waveguide 126 are on the same end surface 101 a of the optical receiving circuit 101. In order to avoid waveguide crossing, the incident waveguide 147 has two 90 degree bends 147a and 147b. The incident end of the incident waveguide 147 does not necessarily have to be on the same end surface as the incident end of the incident waveguide 126. If the end face 101a of the optical receiving circuit 101 where the incident end 125 of the incident waveguide 126 is present is the front face in the vertical direction, the incident end of the incident waveguide 147 has two vertical faces that are in contact with the front end face 101a in the vertical direction. It may be located on either of the side end faces 101b and 101c. In this case, the incident waveguide 147 has one 90-degree bent portion. The end face where the incident end of the incident waveguide 147 is provided may be selected according to the configuration of the housing in which the optical receiving circuit 101 is built.

  If the propagation loss of local light varies depending on the path, the intensity of the coherent light reception signal differs between the TE and TM polarization components or between the I and Q components, which causes a reception error. A path consisting of the connection waveguide 145 and the connection waveguide 141, a path consisting of the connection waveguide 145 and the connection waveguide 142, a path consisting of the connection waveguide 146 and the connection waveguide 143, and a path consisting of the connection waveguide 146 and the connection waveguide 144. It is preferable to set the length of each connection waveguide in the waveguide direction so that the propagation loss is the same for all the four paths. For example, the connecting waveguides 145 and 146 are made equal to each other, and the connecting waveguides 141 to 144 are made equal to each other. For this reason, the optical branching units 121 to 123 are connected to the light receiving units 106, 107, 110, 111, 114, 115, 118, and 119 on the same plane as the horizontal plane where the optical multiplexing units 105, 109, 113, and 117 are located. On the other hand, it is provided in a region opposite to the optical multiplexing units 105, 109, 113, 117.

  For the same reason, it is preferable to equalize the propagation loss for the four paths of incident light. For example, the connecting waveguides 127 and 128 are made equal to each other, and the connecting waveguides 129 to 132 are made equal to each other.

  Next, specific examples of the dimensions of each part will be given, but the present invention is not limited to these specific examples. The cores of the connecting waveguides 127 to 146 and the incident waveguides 126 and 147 have a rectangular cross section having a width of 500 nm and a height of 220 nm in a plane orthogonal to the propagation direction of the guided light. The optical branching sections 103, 104 and 123 are 1 × 2 multimode interferometers composed of slab waveguides having a width of 1500 nm, a length of 1800 nm along the waveguide direction, and a height of 220 nm. The distance between the centers of the two emission ends is 800 nm. The optical multiplexing units 105, 109, 113, and 117 are 2 × 2 multimode interferometers composed of slab waveguides having a width of 1500 nm, a length of 3600 nm along the waveguide direction, and a height of 220 nm. The distance between the centers of the two incident ends and the two outgoing ends is 800 nm. The 1 × 2 and 2 × 2 multimode interferometers are not limited to these dimensions, and are designed in accordance with, for example, the description in Reference 3 (Applied Optics vol. 34, no. 30, pp. 6898-6910, 1995). can do.

  With the configuration schematically shown in FIG. 6, the electrical signals TE / I +, TE / I−, TE / Q +, TE / Q− generated in the light receiving units 106, 107, 110, 111, 114, 115, 118 and 119 are displayed. , TM / I +, TM / I−, TM / Q +, TM / Q− are high-frequency signals through high-frequency signal electrodes 310 to 317 connected to the light receiving units 106, 107, 110, 111, 114, 115, 118 and 119. Output from the bonding electrodes 301 to 308 connected to the signal electrodes 310 to 317. The high frequency signal electrodes 310 to 317 and the bonding electrodes 301 to 308 are provided on the upper surface of the optical receiving circuit 101.

  The TE polarization components are individually listed as follows. The high frequency signal electrode 310 and the bonding electrode 301 are used for propagation of TE / I + generated in the light receiving unit 106. The high frequency signal electrode 311 and the bonding electrode 302 are used for propagation of TE / I− generated in the light receiving unit 107. The high frequency signal electrode 312 and the bonding electrode 303 are used for propagation of TE / Q + generated in the light receiving unit 110. The high frequency signal electrode 313 and the bonding electrode 304 are used for propagation of TE / Q− generated in the light receiving unit 111.

  The TM polarization components are individually listed as follows. The high frequency signal electrode 314 and the bonding electrode 305 are used for propagation of TM / I + generated in the light receiving unit 114. The high frequency signal electrode 315 and the bonding electrode 306 are used for propagation of TM / I− generated in the light receiving unit 115. The high frequency signal electrode 316 and the bonding electrode 307 are used for propagation of TM / Q + generated in the light receiving unit 118. The high frequency signal electrode 317 and the bonding electrode 308 are used for propagation of TM / Q− generated in the light receiving unit 119.

  In order to maintain the high frequency characteristics, it is preferable to shorten the length of the lead wire connected to the bonding electrodes 301 to 308. Therefore, the bonding electrodes 301 to 308 are provided adjacent to the rear end face 101 d of the optical receiving circuit 101. Since incident ends 125 and 148 for incident light and local light and output ends (bonding electrodes 301 to 308) for electrical signals are separated into separate end faces 101a and 101d, the front surface of the housing in which the optical receiving circuit 101 is built in. It is easy to provide a signal light incident end and an electric signal exit end on the rear surface, which is suitable for application to a small pluggable optical transceiver.

  The high frequency signal electrodes 310 to 317 are coplanar waveguide signal electrodes sandwiched between ground electrodes on both sides. The width of the signal electrode is 10 μm, the width of the gap with the ground electrode is 6 μm, and the impedance is designed to be 50Ω. As shown in FIG. 6, the high-frequency signal electrodes 312 to 317 pass over the connection waveguides 141 to 146 and the incident waveguide 147 through which local light is propagated.

  FIG. 7A schematically shows a cross section of the optical receiving circuit 101 on the vertical plane including the broken line PP ′ in FIG. 6. On the substrate 401, a lower clad 402, a core portion of an incident waveguide 147, an upper clad 403, and a high-frequency signal electrode 317 are provided. The ground electrodes 404 and 405 are provided on the upper clad 403 in the same manner as the high-frequency signal electrode 317.

  The substrate 401 is made of crystalline silicon. In order to prevent leakage of guided light to the substrate 401, the height of the lower cladding 402 is set to 2 μm or more. In order to avoid leakage of guided light to the upper side of the optical receiving circuit 101, the height of the upper clad 403 is preferably 1 μm or more. In FIG. 7A, in order to avoid light absorption by the high-frequency signal electrode 317 and the ground electrodes 404 and 405, the height of the upper clad 403 is preferably 2 μm or more. The high-frequency signal electrode 317 and the ground electrodes 404 and 405 are made of aluminum, and their height is set to 1 μm or more in order to avoid attenuation of the electric signal.

  FIG. 7B schematically shows a cross section of the optical receiving circuit 101 on the vertical plane including the broken line QQ ′ in FIG. 6. A ground electrode 406 exists on the upper clad 403. In FIG. 6, the ground electrodes 404, 405 and 406 are not shown. The top surface of the upper cladding 403 is not flat, and undulations occur, such as the top of each connection waveguide rising. Each high-frequency signal electrode may break due to undulations. If necessary, the upper surface of the upper clad 403 is flattened by polishing. The optical waveguide element 410 formed on the substrate 401 includes a core 411 and a clad (a lower clad 402 and an upper clad 403). Connection waveguides 127 to 146 and incident waveguides 126 and 147 in FIG. 4 indicate the arrangement of the core 411 formed on the lower cladding 402.

  The light receiving units 106 to 119 can all have the same configuration. FIG. 8 is a schematic cross-sectional view of the optical receiving circuit 101 including the light receiving unit 119 on the vertical plane including the broken line RR ′. Si contact layers 501 and 502 are provided on both sides of the connection waveguide 140, and a light absorption layer 506 made of germanium (Ge) is provided on the connection waveguide 140. The Si contact layer 501 is connected to the ground electrode 404 through a via (VIA) 503. The Si contact layer 502 is connected to the ground electrode 405 through a via (VIA) 505. The light absorption layer 506 is connected to the high frequency signal electrode 317 through a via (VIA) 504. A similar configuration is disclosed in Reference Document 4 (IEEE Journal of Selected Topics in Quantum Electronics vol. 16, no. 1, pp. 307-315, 2010).

  By using the waveguide configuration of this embodiment, it is possible to provide an optical receiver circuit 101 that does not include a crossed waveguide, is small in size, has low optical loss, and is excellent in high-frequency characteristics. The optical receiving circuit 101 is suitable for a small pluggable optical transceiver for digital coherent use.

  When the local light output is low, incident light that is signal light may be incident from the incident end 148 of the incident waveguide 147, and local light may be incident from the incident end 125 of the incident waveguide 126. Also in this case, the effect described in the present embodiment can be obtained.

[Fourth Embodiment]
Next, as a fourth embodiment of the present invention, a method of adjusting the phase difference between the I component and the Q component of each of the TE and TM polarization components in the optical receiver circuit 101 described in the third embodiment. explain. Further, the configuration of the optical receiving circuit 101 in which the phase difference adjustment information is stored in the memory will be described. As an example of the configuration of the phase difference adjustment method, a schematic diagram of the configuration of the phase difference adjustment method for the processing unit 150 is shown in FIG. The configuration of the optical receiving circuit 101 used here is the same as that shown in FIGS. 7 and 6, but a part thereof is omitted in FIG.

  Continuous light from the wavelength tunable laser 601 transmitted in a single mode is branched into two paths 603 and 604 by a beam splitter 602. Continuous light from one path 603 is incident on the optical receiver circuit 101 from the incident end 125 of the incident waveguide 126 as incident light. The continuous light from the other path 604 is frequency-shifted through the frequency shifter 605 and is incident on the optical receiving circuit 101 from the incident end 148 of the incident waveguide 147 as local light. As the frequency shifter 605, for example, an acousto-optic frequency shifter or an EO frequency shifter can be used. The amount of frequency shift is about five times or more larger than the frequency width of the spectral line of the continuous light, and is in the response frequency band of the RF lock-in amplifier 613 used in this embodiment. A specific example of the frequency shift amount is 10 MHz, for example. As a result of the interference between the incident light and the local light, a heterodyne beat having a frequency equal to the frequency shift is generated.

  A procedure for adjusting the phase difference between the I component and the Q component in the TE polarization component of the incident light to π / 2 will be described. The I component electrical signals TE / I + and TE / I− output from the bonding electrodes 301 and 302 are input to the positive and negative input terminals of the first differential amplifier 611, respectively. An electric signal output from the first differential amplifier 611 is input to the RF lock-in amplifier 613 as a reference signal. Q-component electrical signals TE / Q + and TE / Q− output from the bonding electrodes 303 and 304 are input to the positive and negative input terminals of the second differential amplifier 612, respectively, and output from the second differential amplifier 612. The electric signal is input to the RF lock-in amplifier 613 as an input signal.

  The DC current or DC voltage applied to the phase adjustment unit 108 or 112 is adjusted so that the phase of the heterodyne beat detected by the RF lock-in amplifier 613 matches π / 2. It can adjust similarly with respect to TM component. The reference signal may be a Q component electrical signal and the input signal may be an I component electrical signal. In this case, the phase difference between the I component and the Q component is adjusted so as to coincide with -π / 2.

  In order to adjust the current or voltage applied to the phase adjuster by changing the wavelength or temperature of the incident light, the effective refractive index of the waveguide is changed. Apply to each phase adjuster according to each wavelength or temperature used. The current or voltage to be specified must be specified. Therefore, the current value or voltage necessary for changing the wavelength of the wavelength tunable laser 601 or the temperature around the optical receiving circuit 101 and holding the phase difference between the I component and the Q component at π / 2 at each wavelength or temperature. Record the value. The recorded current value or voltage value is stored in the memory as a lookup table. A control board (control board 620) having a memory 621 storing a lookup table is connected to the optical receiving circuit 101, and the IQ component is controlled by controlling the phase adjusting unit 108 or 112 in response to a change in wavelength or temperature. The phase difference between them can be kept at π / 2.

  The control board 620 includes a control unit 622 that controls the current or voltage applied to the phase adjustment unit 108 or 112. A wiring 623 or 624 is provided between the control unit 622 and the optical receiving circuit 101. The optical receiving circuit 101 includes a bonding electrode 321 or 322 to which a current or voltage to be applied to the phase adjustment unit 108 or 112 is input, and an electrode 323 or 324 to which the applied current or voltage is propagated. The bonding electrode 321 or 322 and the wiring 623 or 624 can be connected by wire bonding. The wiring 623, the bonding electrode 321, and the electrode 323 are provided to connect the control unit 622 and the phase adjustment unit 108. The wiring 624, the bonding electrode 322, and the electrode 324 are provided to connect the control unit 622 and the phase adjustment unit 112.

  The means 600 for applying a frequency shift to continuous local light with respect to continuous incident light includes a tunable laser 601, a beam splitter 602, two paths 603 and 604, and a frequency shifter 605. The means 610 for detecting the phase of the heterodyne beat from the reference signal and the input signal includes differential amplifiers 611 and 612, an RF lock-in amplifier 613, and wirings 614 to 619. These means 600 and 610 can be removed from the optical receiving circuit 101 after the phase difference adjustment process is completed.

  The wirings 614 to 619 are individually connected as follows. The wiring 614 connects between the bonding electrode 301 and the positive input terminal of the first differential amplifier 611, and the wiring 615 connects between the bonding electrode 302 and the negative input terminal of the first differential amplifier 611. A wiring 616 connects between the bonding electrode 303 and the positive input terminal of the second differential amplifier 612, and a wiring 617 connects between the bonding electrode 304 and the negative input terminal of the second differential amplifier 612. The wiring 618 inputs the electrical signal output from the first differential amplifier 611 to the RF lock-in amplifier 613. The wiring 619 inputs the electrical signal output from the second differential amplifier 612 to the RF lock-in amplifier 613.

  The control board 620 including the memory 621 and the control unit 622 is connected to the phase adjustment unit 108 or 112 of the optical receiving circuit 101 when the optical receiving circuit 101 receives signal light. The control unit 622 controls the phase adjustment unit 108 or 112 in response to a change in wavelength or temperature. At this time, by referring to the lookup table stored in the memory 621 and specifying the current or voltage to be applied to the phase adjustment unit, the phase difference between the IQ components can be set to π / 2 even if the wavelength or temperature changes. Can be held in. The control board 620 can include one or both of means for inputting a signal related to a change in the wavelength of the signal light to the control unit 622 and means for inputting a signal related to the ambient temperature of the optical receiving circuit 101 to the control unit 622. In order to measure the temperature around the optical receiver circuit 101 in real time, a temperature sensor can be provided on or near the optical receiver circuit 101.

  The procedure for adjusting the phase difference between the I component and the Q component in the TM polarization component of incident light to π / 2 is the same as in the case of the TE polarization component. In this case, instead of the I-component electrical signals TE / I + and TE / I− output from the bonding electrodes 301 and 302, the I-component electrical signals TM / I + and TM / I output from the bonding electrodes 305 and 306, respectively. -Is used. Further, instead of the Q component electrical signals TE / Q + and TE / Q− output from the bonding electrodes 303 and 304, the Q component electrical signals TM / Q + and TM / Q− output from the bonding electrodes 307 and 308, respectively. Is used.

  When adjusting the phase difference between IQ components in the TM polarization component, the memory 621 and the control unit 622 are connected to the phase adjustment units 116 and 120 (see FIG. 4) instead of the phase adjustment units 108 and 112. The memory 621 and the control unit 622 used for controlling the phase adjustment units 116 and 120 are preferably provided on the same control board 620 as the memory 621 and the control unit 622 used for controlling the phase adjustment units 108 and 112. . The TE polarization component and TM polarization component memory 621 and the control unit 622 may be provided separately. The same memory 621 and control unit 622 may be used for the TE polarization component and the TM polarization component. The control board 620 may further include a control unit used for controlling the phase adjustment unit 124.

  As mentioned above, although this invention has been demonstrated based on suitable embodiment, this invention is not limited to the above-mentioned embodiment, A various change is possible in the range which does not deviate from the summary of this invention.

  In the phase difference adjusting method, the wavelength tunable laser is used as the light source in the present embodiment, but the adjusting method is not limited to this. A single wavelength laser may be used if it does not respond to wavelength changes. Even when dealing with a change in wavelength, it is possible to use a combination of two or more light sources having different wavelengths. In this case, the light source connected to the incident end of the light receiving circuit 101 may be switched every time the phase difference is adjusted for different wavelengths.

  In this embodiment, the light emitted from the same light source is branched into two paths, but this adjustment method is not limited to this. It is also possible to separately provide a light source that generates continuous incident light and a light source that generates continuous local light. In this case, the beam splitter can be omitted. Further, if the wavelengths of continuous light output from the two light sources are different, the frequency shifter can be omitted. However, as in this embodiment, by using one wavelength tunable laser as the light source, phase difference adjustment at different wavelengths can be easily performed.

  In the present embodiment, the frequency shifter is provided in the path through which the local light propagates, but instead, the frequency shifter may be provided in the path through which the incident light propagates. Moreover, you may provide a frequency shifter in both paths, respectively. The means for detecting the phase of the heterodyne beat is not limited to the RF lock-in amplifier. For example, a known phase detector such as a normal lock-in amplifier that operates at about 100 KHz or less (frequency lower than RF) may be used. it can. The electrical signal used for optical signal modulation or the like is preferably a high-frequency signal in order to increase the signal speed, but the present invention is not limited to high-frequency (RF).

(Light modulator)
Next, an optical modulator according to an embodiment of the present invention will be described.
For the optical modulator of this embodiment, the optical waveguide device 1A of the first embodiment or the optical waveguide device 1B of the second embodiment can be used. In the optical waveguide element constituting the optical modulator of this embodiment, TE polarized light propagates before the optical circuit for polarization multiplexing. The TE polarization is rotated to TM polarization through the polarization rotation unit included in the polarization multiplexing optical circuit, and the TE polarization waveguide light is converted to TM polarization waveguide light. The TM-polarized guided light is combined with the TE-polarized guided light at the polarization multiplexing unit.

  In an optical modulator using a silicon waveguide, in order to perform optical modulation by changing the effective refractive index of the silicon waveguide, a high-speed phase modulation unit with a PN junction is provided, and a high-speed electrical signal is provided in the high-speed phase modulation unit. To generate an optical signal having a high bit rate.

  Further, in order to control the phase state of the optical phase modulator and the intensity crossing point of the optical intensity modulator, a monitoring light receiving unit is integrated to make the optical modulator smaller and more functional.

  In a light receiving unit for monitoring integrated in an optical modulator or a light receiving unit integrated in an optical receiving circuit, a germanium thin film or a compound semiconductor thin film is used as a light receiving layer. When the above glass transition temperature is high, the entire substrate is heated to a high temperature, whereby the dopant of the PN junction is re-diffusion and the doping profile is lost, or the light receiving layer is shifted or missing. Further, the adhesive and wire bonding for fixing the external optical component are damaged. For this reason, the phase adjusting unit having the EO material is thermally isolated from the surrounding region, and the surrounding temperature rise is at a level that does not damage the PN junction, the light receiving unit, and the bonded portion of the external optical component as described above. It needs to be suppressed.

  Polling is performed by applying a sine wave signal to the phase modulator and measuring the intensity and phase of the sine wave electrical signal output from the light receiver, and the optical modulator measures the intensity and phase of the output light from the output end. The permanent electric polarization induced by can be set to an appropriate value.

[Fifth Embodiment]
Next, as a fifth embodiment of the present invention, for example, an optical modulator 901 shown in FIG. 10 will be described. FIG. 10 shows a schematic configuration on a single horizontal plane of the optical waveguide element constituting the optical modulator 901.

  Single longitudinal mode continuous light from the wavelength tunable laser is incident from one end (incident end) of the incident waveguide 940 as TE polarized incident light. The wavelength of the incident light is set to a predetermined wavelength. The other end (outgoing end) of the incident waveguide 940 is connected to the incident end of the optical branch 902. The incident end of the connection waveguide 941 is connected to one emission end of the optical branching unit 902. The incident end of the connection waveguide 942 is connected to the other exit end of the optical branching section 902.

  The exit end of the connection waveguide 941 is connected to the entrance end of the optical branching unit 903. The incident end of the connection waveguide 943 is connected to one emission end of the optical branching unit 903. The incident end of the connection waveguide 944 is connected to the other emission end of the optical branching unit 903. The exit end of the connection waveguide 943 is connected to the entrance end of the optical branching unit 905. The exit end of the connection waveguide 944 is connected to the entrance end of the optical branching unit 906.

  The incident end of the connection waveguide 947 is connected to one emission end of the optical branching unit 905. The incident end of the connection waveguide 948 is connected to the other emission end of the optical branching unit 905. The incident end of the connection waveguide 949 is connected to one emission end of the optical branching unit 906. The incident end of the connection waveguide 950 is connected to the other emission end of the optical branching unit 906.

  The output end of the connection waveguide 947 is connected to one incident end of the optical multiplexing unit 917. A high-speed phase modulation unit 909 is inserted into the connection waveguide 947. For the high-speed phase modulation unit 909, for example, a configuration based on a rib waveguide described in Optics Express vol. 19, no. 26, B26 / B31 (2011) can be used. The output end of the connection waveguide 948 is connected to the other incident end of the optical multiplexing unit 917. A high-speed phase modulation unit 910 having the same configuration as that of the high-speed phase modulation unit 909 is inserted into the connection waveguide 948. The incident end of the connection waveguide 955 is connected to the emission end of the optical multiplexing unit 917.

  The output end of the connection waveguide 949 is connected to one incident end of the optical multiplexing unit 918. A high-speed phase modulation unit 911 having the same configuration as that of the high-speed phase modulation unit 909 is inserted into the connection waveguide 949. The output end of the connection waveguide 950 is connected to the other incident end of the optical multiplexing unit 918. A high-speed phase modulation unit 912 having the same configuration as that of the high-speed phase modulation unit 909 is inserted into the connection waveguide 950. The incident end of the connection waveguide 956 is connected to the emission end of the optical multiplexing unit 918.

  The exit end of the connection waveguide 942 is connected to the entrance end of the optical branching section 904. The incident end of the connection waveguide 945 is connected to one emission end of the optical branching unit 904. The incident end of the connection waveguide 946 is connected to the other emission end of the optical branching section 904. The exit end of the connection waveguide 945 is connected to the entrance end of the optical branching unit 907. The exit end of the connection waveguide 946 is connected to the entrance end of the optical branching unit 908.

  The incident end of the connection waveguide 951 is connected to one emission end of the optical branching unit 907. The incident end of the connection waveguide 952 is connected to the other exit end of the optical branching unit 907. The incident end of the connection waveguide 953 is connected to one emission end of the optical branching unit 908. The incident end of the connection waveguide 954 is connected to the other emission end of the optical branching unit 908.

  The output end of the connection waveguide 951 is connected to one incident end of the optical multiplexing unit 919. A high-speed phase modulation unit 913 having the same configuration as that of the high-speed phase modulation unit 909 is inserted into the connection waveguide 951. The output end of the connection waveguide 952 is connected to the other incident end of the optical multiplexing unit 919. A high-speed phase modulation unit 914 having the same configuration as that of the high-speed phase modulation unit 909 is inserted into the connection waveguide 952. The incident end of the connection waveguide 957 is connected to the emission end of the optical multiplexing unit 919.

  The output end of the connection waveguide 953 is connected to one incident end of the optical multiplexing unit 920. A high-speed phase modulation unit 915 having the same configuration as that of the high-speed phase modulation unit 909 is inserted into the connection waveguide 953. The output end of the connection waveguide 954 is connected to the other incident end of the optical multiplexing unit 920. A high-speed phase modulation unit 916 having the same configuration as that of the high-speed phase modulation unit 909 is inserted into the connection waveguide 954. The incident end of the connection waveguide 958 is connected to the emission end of the optical multiplexing unit 920.

  The output end of the connection waveguide 955 is connected to one incident end of the optical multiplexing unit 925. The output end of the connection waveguide 956 is connected to the other incident end of the optical multiplexing unit 925. The incident end of the connection waveguide 959 is connected to the emission end of the optical multiplexing unit 925. A phase adjustment unit 921 is inserted into the connection waveguide 955. A phase adjustment unit 922 is inserted into the connection waveguide 956.

  The output end of the connection waveguide 957 is connected to one incident end of the optical multiplexing unit 926. The output end of the connection waveguide 958 is connected to the other incident end of the optical multiplexing unit 926. The incident end of the connection waveguide 960 is connected to the emission end of the optical multiplexing unit 926. A phase adjustment unit 923 is inserted into the connection waveguide 957. A phase adjustment unit 924 is inserted into the connection waveguide 956.

  The optical branching units 902 to 908 are configured using a 1 × 2 multimode interferometer having the same dimensions as the optical branching unit 103 in the optical receiving circuit 101 of the third embodiment. The optical multiplexing units 917 to 926 are configured to reverse the light propagation direction from the optical branching units 902 to 908. That is, the optical multiplexing units 917 to 926 use the 1 × 2 multimode interferometer that constitutes the optical branching unit 103, and uses the incident end of the optical branching unit 103 as the outgoing end and the two outgoing ends of the optical branching unit 103. It is constituted by a 2 × 1 multimode interferometer serving as each incident end.

  The output end of the connection waveguide 959 is connected to one incident end of the polarization multiplexing circuit 927. The output end of the connection waveguide 960 is connected to the other incident end of the polarization multiplexing circuit 927. The incident end of the output waveguide 961 is connected to the output end of the polarization multiplexing circuit 927.

  The polarization multiplexing circuit 927 uses the same structure as the polarization separation circuit 102 in the optical reception circuit 101 of the third embodiment, and has a configuration in which the light propagation direction is reversed with respect to the polarization separation circuit 102. is there. That is, the polarization multiplexing circuit 927 has a configuration in which the incident end of the polarization separation circuit 102 is an output end, and the two output ends of the polarization separation circuit 102 are respective incident ends.

  The I component and Q component optical signals in the TE polarization and the I component and Q component optical signals in the TM polarization are multiplexed and output from the output end of the output waveguide 961.

  All elements in the optical path from the input end of the connection waveguide 943 to the output end of the connection waveguide 955 constitute a Mach-Zehnder (MZ) modulator that generates an I-component optical signal in TE polarization. All elements in the optical path from the input end of the connection waveguide 944 to the output end of the connection waveguide 956 constitute an MZ modulation unit that generates a Q-component optical signal in TE polarization. In contrast, the former MZ modulator generates a Q-component optical signal in TE polarization, and the latter MZ modulator generates an I-component optical signal in TE polarization. The correspondence relationship may be reversed.

  On the other hand, all elements in the optical path from the incident end of the connection waveguide 945 to the output end of the connection waveguide 957 constitute an MZ modulation unit that generates an I-component optical signal in TM polarization. The light propagating through the MZ modulator is TE polarized light, but is converted to TM polarized light after passing through the polarization multiplexing circuit 927.

  All elements in the optical path from the input end of the connection waveguide 946 to the output end of the connection waveguide 958 constitute an MZ modulation unit that generates a Q-component optical signal in TM polarization. Conversely, the former MZ modulator generates a Q-component optical signal in TM polarization, and the latter MZ modulator generates an I-component optical signal in TM polarization. The correspondence relationship may be reversed.

  In the connection waveguides 955 to 958, incident ends of the tap waveguides 962 to 965 are provided laterally behind the phase adjustment units 921 to 924 inserted therein. Light receiving portions 928 to 931 are connected to the emission ends of the tap waveguides 962 to 965, respectively. The light receiving units 928 to 931 can use the same configuration as the light receiving unit 106 in the optical receiving circuit 101 of the third embodiment.

  Each of the tap waveguides 966 and 967 is provided on the side of each of the connection waveguides 959 and 960. Each of the light receiving portions 932 and 933 is connected to the emission end of each of the tap waveguides 966 and 967.

  It is possible to control the intensity of each IQ component using the light receiving units 928 to 931. In addition, the light receiving units 928 to 931 and the light receiving units 932 and 933 can be used to control the phase difference between IQ components to be held at π / 2. Further, the light receiving units 932 and 933 can be used to control the intensity of the TE-polarized optical signal and the intensity of the TM-polarized optical signal. When these controls are not necessary, the tap waveguides 962 to 965 and the light receiving portions 928 to 931 or the tap waveguides 966 and 967 and the light receiving portions 932 and 933 can be omitted.

  In the optical modulator 901 of the present embodiment, the phase adjustment units 921 to 924 include the phase adjustment unit 2A in the optical waveguide element 1A of the first embodiment or the phase adjustment unit 2B in the optical waveguide element 1B of the second embodiment. Can be used.

  By using the waveguide configuration of the present embodiment, it is possible to provide an optical modulator 901 that is small in size, has low optical loss, and has low crosstalk between IQ components. The optical modulator 901 of this embodiment is suitable for a small pluggable optical transceiver for digital coherent, for example.

  In the optical modulator 901 of the present embodiment, the optical branching units 903 and 904 correspond to the first optical branching unit of the present invention. The optical branching portions 905 and 907 correspond to the second optical branching portion of the present invention. The optical branching portions 906 and 908 correspond to the third optical branching portion of the present invention. The connection waveguides 943 and 945 correspond to the first connection waveguide of the present invention. The connection waveguides 944 and 946 correspond to the second connection waveguide of the present invention. The connection waveguides 947 and 951 correspond to the third connection waveguide of the present invention. The connection waveguides 948 and 952 correspond to the fourth connection waveguide of the present invention. The connection waveguides 949 and 953 correspond to the fifth connection waveguide of the present invention. The connection waveguides 950 and 954 correspond to the sixth connection waveguide of the present invention. The connection waveguides 955 and 957 correspond to the seventh connection waveguide of the present invention. The connection waveguides 956 and 958 correspond to the eighth connection waveguide of the present invention. The connection waveguides 959 and 960 correspond to the ninth connection waveguide of the present invention. The high-speed phase modulation units 909 and 913 correspond to the first high-speed phase modulation unit of the present invention. The high-speed phase modulation units 910 and 914 correspond to the second high-speed phase modulation unit of the present invention. The high-speed phase modulation units 911 and 915 correspond to the third high-speed phase modulation unit of the present invention. The high-speed phase modulation units 912 and 916 correspond to the fourth high-speed phase modulation unit of the present invention. The optical multiplexing units 917 and 919 correspond to the first optical multiplexing unit of the present invention. The optical multiplexing units 918 and 920 correspond to the second optical multiplexing unit of the present invention. The optical multiplexing units 925 and 926 correspond to the third optical multiplexing unit of the present invention. The tap waveguides 962 and 964 correspond to the first tap waveguide of the present invention. The tap waveguides 963 and 965 correspond to the second tap waveguide of the present invention. The light receiving units 928 and 930 correspond to the first light receiving unit of the present invention. The light receiving portions 929 and 931 correspond to the second light receiving portion of the present invention. The phase adjustment units 921 to 924 correspond to the phase adjustment unit of the present invention. Further, either the phase adjustment unit 921 or 922 may be omitted, and either the phase adjustment unit 923 or 924 may be omitted.

[Sixth Embodiment]
Next, as a sixth embodiment of the present invention, a method for adjusting the phase difference between the I component and the Q component in the TE polarization in the optical modulator 901 described in the fifth embodiment will be described. Similarly, in TM polarization, the phase difference between the I component and the Q component can be adjusted.

  A sine wave electrical signal is input to the high-speed phase modulators 909 and 910 as an I-component test optical signal in the TE polarization, and an I-component test light in the TE polarization is derived from the phase of the electrical signal output from the light receiving unit 928. Detect the phase of the signal. In order to remove the distortion of the electric signal output from the light receiving unit 928, the DC reverse bias voltage superimposed on the sine wave electric signal is adjusted.

  A sine wave electric signal is input to the high-speed phase modulators 911 and 912 as a Q component test optical signal in the TE polarization, and a Q component test light in the TE polarization is calculated from the phase of the electric signal output from the light receiving unit 929. Detect the phase of the signal. In order to remove distortion of the electrical signal output from the light receiving unit 929, the DC reverse bias voltage superimposed on the sine wave electrical signal is adjusted.

  By adjusting the current or voltage at the time of polling applied to the phase adjustment unit 921 or 922, or the current or voltage after polling, the phase of the electrical signal output from the light receiving unit 928 is set as the phase of the I component from the light receiving unit 932. The phase of the Q component included in the output electrical signal is adjusted so as to have a difference π / 2 with respect to the I component. Similarly, in the TM polarization, the phase difference between the I component and the Q component can be adjusted.

  The effective refractive index of the waveguide changes due to the change in the wavelength or temperature of the incident light, and the voltage applied to the phase adjustment unit is adjusted so that the phase difference matches π / 2. Accordingly, it is necessary to specify the current or voltage to be applied to each phase adjustment unit. Therefore, the wavelength value of the wavelength tunable laser or the temperature of the optical modulator 901 is changed, and a voltage value necessary for maintaining the phase difference between the I component and the Q component at π / 2 at each wavelength or temperature is recorded. The recorded voltage value is stored in the memory as a lookup table. A control board (control board) equipped with a memory storing a lookup table is connected to the optical modulator, and the phase adjustment unit is controlled in response to a change in wavelength or temperature, so that the phase difference between IQ components is π. / 2.

[Seventh Embodiment]
Next, as a seventh embodiment of the present invention, for example, an optical modulator 1001 shown in FIG. 11 will be described. FIG. 11 shows a schematic configuration on a single horizontal plane of the optical waveguide element constituting the optical modulator 1001.

  Incident light is incident from the incident end of the incident waveguide 1009. The exit end of the incident waveguide 1009 is connected to the incident end of the optical branching unit 1002. The incident end of the connection waveguide 1010 is connected to one emission end of the optical branching unit 1002. The incident end of the connection waveguide 1011 is connected to the other exit end of the optical branching unit 1002. The output end of the connection waveguide 1010 is connected to one incident end of the optical multiplexing unit 1007. The output end of the connection waveguide 1011 is connected to the other incident end of the optical multiplexing unit 1007.

  A high-speed phase modulation unit 1003 and a phase adjustment unit 1005 are inserted into the connection waveguide 1011. A high-speed phase modulation unit 1004 and a phase adjustment unit 1006 are inserted into the connection waveguide 1011. The incident end of the output waveguide 1012 is connected to the output end of the optical multiplexing unit 1007. An optical signal is emitted from the emission end of the emission waveguide 1012. An incident end of the tap waveguide 1013 is provided on the side of the output waveguide 1012. A light receiving unit 1008 is connected to the output end of the tap waveguide 1013.

  In the optical modulator 1001 of the present embodiment, the phase adjustment units 1005 and 1006 include the phase adjustment unit 2A in the optical waveguide element 1A of the first embodiment or the phase adjustment unit 2B in the optical waveguide element 1B of the second embodiment. Can be used.

  An electric signal output from the light receiving unit 1008 is detected by adjusting the current or voltage at the time of polling or the current or voltage after polling to the phase adjusting unit 1005 or the phase adjusting unit 1006. As a result, it is possible to eliminate imbalances in optical characteristics caused by errors in the process of forming the waveguide.

  If the light intensity emitted from the output waveguide 1012 is adjusted to the maximum without applying a modulated electric signal to the high-speed phase modulators 1003 and 1004, the imbalance when used as an intensity modulator is eliminated. be able to.

  When the waveguide configuration of the present embodiment is used for the MZ modulation section in the optical modulator of the fifth embodiment, the phase and light intensity imbalance when used as a phase modulator can be eliminated. The procedure follows the same procedure as in the sixth embodiment, and adjusts the current or voltage at the time of polling applied to the phase adjustment unit 1005 or 1006 or the current or voltage after polling.

  In the optical modulator 1001 of this embodiment, the optical branching unit 1002 corresponds to the optical branching unit of the present invention. The connection waveguide 1010 corresponds to the first connection waveguide of the present invention. The connection waveguide 1011 corresponds to the second connection waveguide of the present invention. The connection waveguide 1012 corresponds to the third connection waveguide of the present invention. The optical multiplexing unit 1007 corresponds to the optical multiplexing unit of the present invention. The high-speed phase modulation unit 1003 corresponds to the first high-speed phase modulation unit of the present invention. The high-speed phase modulation unit 1004 corresponds to the second high-speed phase modulation unit of the present invention. The phase adjustment units 1005 and 1006 correspond to the phase adjustment unit of the present invention. The tap waveguide 1013 corresponds to the tap waveguide of the present invention. The light receiving unit 1008 corresponds to the light receiving unit of the present invention.

DESCRIPTION OF SYMBOLS 1A, 1B ... Optical waveguide element, 2A, 2B ... Phase adjustment part, 3 ... Board | substrate, 4 ... Core, 5 ... Cladding, 6 ... Lower cladding, 7 ... Upper cladding, 8 ... 1st electrode, 9 ... 2nd Electrode, 10... Electro-optic (EO) layer, 11... First through electrode, 12... First upper electrode, 13... Second through electrode, 14. Electrode, 16 ... third upper electrode, 17, 18 ... heater electrode (heater), 19 ... gap part, 20,21 ... groove part, 22 ... gap part, 23 ... first through electrode, 24 ... first upper part Electrode, 25 ... 4th through electrode, 26 ... 4th upper electrode, 27 ... 2nd through electrode, 28 ... 2nd upper electrode, 29 ... 5th through electrode, 30 ... 5th upper electrode, D: Waveguide,
DESCRIPTION OF SYMBOLS 101 ... Optical receiver circuit, 102 ... Polarization separation circuit, 103, 104 ... Optical branching part (first optical branching part), 105, 113 ... Optical multiplexing part (first optical multiplexing part), 106, 107, 114 115, light receiving unit (first light receiving unit), 108, 112, 116, 120, 124 ... phase adjusting unit, 109, 117 ... optical multiplexing unit (second optical multiplexing unit), 110, 111, 118, 119 ... light receiving part (second light receiving part), 121, 122 ... light branching part (second light branching part), 123 ... light branching part (first light branching part), 126 ... incident waveguide (for signal light incidence) (Waveguide), 127 to 146... Connection waveguide, 141a, 142a, 143a, 144a... 180 degree bent portion, 147. 151... Processing unit, 201, 204. Separator, 202, 203 ... polarization rotation part, 301-308 ... bonding electrode, 310-317 ... high frequency signal electrode, 401 ... substrate, 402 ... lower clad, 403 ... upper clad, 410 ... optical waveguide element, 411 ... core ,
901: Optical modulator, 903, 904: Optical branching unit (first optical branching unit), 905, 907 ... Optical branching unit (second optical branching unit), 906, 908 ... Optical branching unit (third light) Branching part), 943, 945... Connection waveguide (first connection waveguide), 944, 946... Connection waveguide (second connection waveguide), 947, 951... Connection waveguide (third connection waveguide) , 948, 952... Connection waveguide (fourth connection waveguide), 949, 953... Connection waveguide (fifth connection waveguide), 950, 954... Connection waveguide (sixth connection waveguide), 955, 957 ... connection waveguide (seventh connection waveguide), 956, 958 ... connection waveguide (eighth connection waveguide), 959, 960 ... connection waveguide (ninth connection waveguide), 909, 913 ... High-speed phase modulation section (first high-speed phase modulation section), 910, 914 ... High-speed phase modulation (Second high-speed phase modulation unit), 911, 915... High-speed phase modulation unit (third high-speed phase modulation unit), 912, 916... High-speed phase modulation unit (fourth high-speed phase modulation unit), 917, 919. Optical multiplexing unit (first optical multiplexing unit), 918, 920... Optical multiplexing unit (second optical multiplexing unit), 925, 926... Optical multiplexing unit (third optical multiplexing unit), 962, 964. Waveguide (first tap waveguide), 963, 965... Tap waveguide (second tap waveguide), 928, 930... Light receiving portion (first light receiving portion), 929, 931. Light receiving part), 921 to 924... Phase adjustment part,
DESCRIPTION OF SYMBOLS 1001 ... Optical modulator, 1002 ... Optical branch part, 1010 ... Connection waveguide (1st connection waveguide), 1011 ... Connection waveguide (2nd connection waveguide), 1012 ... Connection waveguide (3rd connection) Waveguide), 1007 ... optical multiplexing unit, 1003 ... high-speed phase modulation unit (first high-speed phase modulation unit), 1004 ... high-speed phase modulation unit (second high-speed phase modulation unit), 1005, 1006 ... phase adjustment unit, 1013: Tap waveguide, 1008: Light receiving portion.

Claims (22)

An optical waveguide device comprising a waveguide constituted by a core and a clad on a substrate,
A phase adjustment unit for adjusting the phase of light propagating through the waveguide;
The phase adjusting unit is
A first electrode and a second electrode provided on both sides of the core;
At least a part of both side surfaces and the upper surface of the core, at least a part of the side surface and the upper surface of the first electrode facing the core, and a side surface of the second electrode on the side facing the core; An electro-optic layer provided so as to cover at least a part of the upper surface, and
An optical waveguide element, wherein the electro-optic layer is electrically polarized by polarization formation. The clad includes a lower clad provided between the substrate and the core, and an upper clad provided on the core and the lower clad,
The first electrode is electrically connected to a first upper electrode provided on the upper clad through a first through electrode penetrating the upper clad,
2. The second electrode is electrically connected to a second upper electrode provided on the upper clad through a second through electrode penetrating the upper clad. 2. An optical waveguide device according to 1.   The electro-optical layer is electrically connected to a third upper electrode provided on the upper clad through a third through electrode penetrating the upper clad. The optical waveguide device described. The phase adjustment unit has a heater for heating the electro-optic layer,
4. The optical waveguide device according to claim 2, wherein the heater is provided on the upper clad. The first electrode is electrically connected to a fourth upper electrode provided on the upper clad via a fourth through electrode penetrating the upper clad,
The second electrode is electrically connected to a fifth upper electrode provided on the upper cladding via a fifth through electrode penetrating the upper cladding,
By applying a current or voltage between the first upper electrode and the fourth upper electrode, the first electrode generates heat,
4. The optical waveguide element according to claim 2, wherein the second electrode generates heat by applying a current or voltage between the second upper electrode and the fifth upper electrode. . A gap portion that thermally isolates the phase adjustment portion from the surroundings;
The optical waveguide device according to claim 1, wherein the gap portion includes a groove portion that cuts out at least the clad in a depth direction.   The gap portion includes a pair of groove portions formed at a depth reaching the substrate on both sides of the phase adjustment portion, and a gap portion in which a part of the substrate is continuously removed between the pair of groove portions. The optical waveguide device according to claim 6, further comprising: The core is made of a silicon layer,
The optical waveguide element according to claim 1, wherein the first electrode and the second electrode are formed of a diffusion layer formed by doping an impurity in a silicon layer. . A method of manufacturing an optical waveguide device comprising a waveguide constituted by a core and a clad on a substrate,
When forming a phase adjustment unit that adjusts the phase of light propagating through the waveguide,
Forming a first electrode and a second electrode on both sides of the core;
At least a part of both side surfaces and the upper surface of the core, at least a part of the side surface and the upper surface of the first electrode facing the core, and a side surface of the second electrode on the side facing the core; Forming an electro-optic layer covering each of at least a part of the upper surface.   When forming the first electrode and the second electrode, the silicon layer made of the same layer as the core silicon layer is patterned, and the patterned silicon layer is doped with impurities, thereby forming the first electrode. The method for manufacturing an optical waveguide element according to claim 9, wherein a diffusion layer to be the first electrode and the second electrode is formed. Forming a gap portion that thermally isolates the phase adjustment portion from the surroundings;
When forming the gap portion, a pair of groove portions are formed by etching at a depth from the clad to the substrate on both sides of the phase adjustment portion, and then a part of the substrate is etched from the pair of groove portions. 10. The method of manufacturing an optical waveguide element according to claim 9, wherein a continuous gap is formed between the pair of grooves by selectively removing the gap.   An optical receiver circuit comprising the optical waveguide device according to claim 1. The optical waveguide element is
A first light branching section for branching and propagating the signal light to the first signal light propagation waveguide and the second signal light propagation waveguide;
A second optical branching portion for branching and propagating the local light to the first local light propagation waveguide and the second local light propagation waveguide;
A first optical multiplexing unit that multiplexes signal light propagating through the first signal light propagation waveguide and local light propagating through the first local light propagation waveguide, and causes the light to interfere with each other;
A second optical multiplexing unit that multiplexes the signal light propagating through the second signal light propagation waveguide and the local light propagating through the second local light propagation waveguide, and interferes with each other;
One or more first light receiving parts for receiving the output light of the first optical multiplexing part; and
One or more second light receiving parts for receiving the output light of the second optical multiplexing part; and
A phase adjustment unit provided in one or both of the first local light propagation waveguide and the second local light propagation waveguide;
Have
A frequency shift is applied to continuous local light with respect to continuous incident light, a heterodyne beat is generated by interference between the two, and an output electrical signal output from the first light receiving unit or output from the second light receiving unit Means for detecting the phase of a heterodyne beat using one of the output electrical signals as a reference signal and an output electrical signal different from the reference signal as an input signal, Is maintained at π / 2, the phase difference between the local light incident on the first optical multiplexing unit and the local light incident on the second optical multiplexing unit can be adjusted to π / 2. The optical receiver circuit according to claim 12, which is possible.   A current applied to the phase adjustment unit when the phase difference between the local light incident on the first optical multiplexing unit and the local light incident on the second optical multiplexing unit is adjusted to π / 2, or 14. The optical receiver circuit according to claim 13, wherein the optical receiver circuit is connected to a control board on which a memory in which a set value of voltage is recorded is mounted. The method for adjusting an optical receiver circuit according to claim 13 or 14,
A frequency shift is applied to continuous local light with respect to continuous incident light, a heterodyne beat is generated by interference between the two, and an output electrical signal output from the first light receiving unit or output from the second light receiving unit Means for detecting the phase of the heterodyne beat using one of the output electrical signals as a reference signal and the output electrical signal different from the reference signal as an input signal. By adjusting the phase to π / 2, the phase difference between the local light incident on the first optical multiplexing unit and the local light incident on the second optical multiplexing unit is adjusted to π / 2. A method of adjusting an optical receiving circuit.   An optical modulator comprising the optical waveguide device according to any one of claims 1 to 8. The optical waveguide element is
A first optical branching section for branching and propagating signal light to the first connection waveguide and the second connection waveguide;
A second optical branching portion for branching and propagating signal light propagating through the first connection waveguide to a third connection waveguide and a fourth connection waveguide;
A third optical branching portion for branching and propagating the signal light propagating in the second connection waveguide to the fifth connection waveguide and the sixth connection waveguide;
A first high-speed phase modulator provided in the third connection waveguide;
A second high-speed phase modulator provided in the fourth connection waveguide;
A third high-speed phase modulator provided in the fifth connection waveguide;
A fourth high-speed phase modulator provided in the sixth connection waveguide;
A first optical multiplexing unit that combines the output light from the first high-speed phase modulation unit and the output light from the second high-speed phase modulation unit and outputs the combined light from a seventh connection waveguide;
A second optical multiplexing unit that combines the output light from the third high-speed phase modulation unit and the output light from the fourth high-speed phase modulation unit, and outputs the combined light from the eighth connection waveguide;
A third optical multiplexing unit for combining the output light propagating through the seventh connection waveguide and the output light propagating through the eighth connection waveguide and outputting from the ninth connection waveguide;
A first light receiving unit that receives a part of the output light propagating through the seventh connection waveguide through the first tap waveguide;
A second light receiving unit that receives a part of the output light propagating through the eighth connection waveguide through the second tap waveguide;
A phase adjustment unit provided in one or both of the seventh connection waveguide and the eighth connection waveguide;
Have
Either of the phase adjustment units so that the difference between the phase of the electrical signal output from the first light receiving unit and the phase of the electrical signal output from the second light receiving unit is π / 2. The optical modulator according to claim 16, wherein a current or voltage applied to one or both is adjusted.   Either of the phase adjustment units so that the difference between the phase of the electrical signal output from the first light receiving unit and the phase of the electrical signal output from the second light receiving unit is π / 2. The optical modulator according to claim 17, wherein the optical modulator is connected to a control board on which a memory in which a setting value for adjusting a current or a voltage applied to one or both is recorded is mounted. The method of adjusting an optical modulator according to claim 17 or 18,
Either of the phase adjustment units so that the difference between the phase of the electrical signal output from the first light receiving unit and the phase of the electrical signal output from the second light receiving unit is π / 2. A method of adjusting an optical modulator, characterized by adjusting a current or voltage applied to one or both. The optical waveguide element is
An optical branching section for branching and propagating signal light to the first connection waveguide and the second connection waveguide;
A first high-speed phase modulator provided in the first connection waveguide;
A second high-speed phase modulator provided in the second connection waveguide;
An optical combining unit that combines the output light propagating through the first connection waveguide and the output light propagating through the second connection waveguide, and outputs the combined light from the third connection waveguide;
A light receiving unit that receives a part of the output light propagating through the third connection waveguide through the tap waveguide;
A phase adjustment unit provided between one or both of the first high-speed phase modulation unit and the optical multiplexing unit, and between the second high-speed phase modulation unit and the optical multiplexing unit;
Have
An electrical signal output from the light receiving unit is detected and output from the third connection waveguide in a state where no modulated electrical signal is applied to the first high-speed phase modulation unit and the second high-speed phase modulation unit. The optical modulator according to claim 16, wherein a current or a voltage applied to one or both of the phase adjustment units is adjusted so that output light to be maximized.   An electrical signal output from the light receiving unit is detected and output from the third connection waveguide in a state where no modulated electrical signal is applied to the first high-speed phase modulation unit and the second high-speed phase modulation unit. Connected to a control board on which a memory that records a setting value for adjusting a current or voltage applied to one or both of the phase adjustment units is mounted so that the output light to be maximized. The optical modulator according to claim 20. The method of adjusting an optical modulator according to claim 20 or 21,
An electrical signal output from the light receiving unit is detected and output from the third connection waveguide in a state where no modulated electrical signal is applied to the first high-speed phase modulation unit and the second high-speed phase modulation unit. A method for adjusting an optical modulator, comprising: adjusting a current or a voltage applied to one or both of the phase adjusting units so that output light to be maximized.

Images