JP2014045039A - Dispersion compensator - Google Patents

Abstract

Dispersion compensator having large angular dispersion, wide FSR, and capable of compensating for a decrease in light intensity.
In a dispersion compensator, a first distributed Bragg reflector <01-05>, a first optical confinement <01-07>, an active region <01>, which are sequentially stacked on a substrate <01-09>. -08>, a second optical confinement layer <01-06>, a second distributed Bragg reflector <01-04> having an optical signal input port <01-03> and an angular dispersion output port <01-02> And an optical amplification angle dispersion element <01-00> having an electrode <01-10> provided on the substrate and the second distributed Bragg reflector layer, and a plurality of phase adjustment elements <04-02> The arranged phase adjusters <04-00> and the wavelength multiplexed optical signals output from the optical amplification angle dispersive elements are focused on the phase adjuster groups <05-0 to 05-16> with different phase adjusters for each wavelength. And at least one lens <03>.
[Selection] Figure 2

Description

  The present invention relates to a dispersion compensator used in optical file communication.

  With the explosive spread of the Internet, development of wavelength division multiplexing (WDM) communication technology has been actively conducted. For example, the wavelength selective switch separates the optical signal of a specific wavelength from the wavelength-multiplexed optical signal and performs processing such as routing while maintaining the optical state to flexibly respond to changes in communication demand between nodes. It is possible to do. Under such circumstances, it is required to adaptively compensate for the dispersion value of the dynamically changing path.

  Conventionally, as a dispersion compensator, a dispersion compensator including a VIPA (Virtually Imaged Phased Array), a grating, and a three-dimensional mirror (for example, see Patent Document 1) is known. Also known is a dispersion compensator (for example, see Patent Document 2) provided with AWG (Arrayed Waveguide Grating) and LCOS (Liquid Crystal on Silicon).

  The dispersion compensator of Patent Document 1 is configured such that light of each wavelength angularly dispersed by VIPA undergoes an optical path shift due to a grating, and then the dispersion amount is adjusted for each wavelength by a three-dimensional mirror.

  The dispersion compensator of Patent Document 2 adjusts the amount of dispersion for each wavelength by applying a desired phase shift amount with LCOS to each of the light that is wavelength-separated by AWG and emitted at different angles for each wavelength. This is a configuration.

  FIG. 1 is a diagram illustrating a schematic configuration of a dispersion compensator disclosed in Patent Document 2. In FIG. The dispersion compensator of Patent Document 2 includes an array grating waveguide, a cylindrical lens, a lens, and an LCOS. The wavelength multiplexed optical signal is input to the array grating waveguide, demultiplexed into optical signals of different wavelengths, and output at different angles. The optical signal of each wavelength passes through the cylindrical lens and is condensed (coupled) at different positions (different x-coordinates) on the LCOS by the lens, and phase-adjusted by the phase compensation element (liquid crystal element) constituting the LCOS. Then, the light is reflected on the bottom surface and propagates along the original path, and is again combined by the array grating waveguide.

JP 2002-258207 A International Publication No. 2009/001847 Pamphlet

  However, in the dispersion compensator of Patent Document 1, since the angular dispersion in VIPA remains at about 0.4 to 0.8 degrees / nm, in order to input to the reflecting surface of a three-dimensional mirror having a predetermined size, It is necessary to construct a relatively large optical system in the traveling direction of light, and there is a limit to miniaturization and economy of the apparatus.

  In addition, in the dispersion compensator of Patent Document 2, due to the limitation of FSR in AWG, optical signals of different wavelengths that are not included in one FSR are placed at positions where the coupling position on the two-dimensional plane of LCOS is an integral multiple of FSR It is necessary to construct an optical system so that the condensed positions of wavelengths shifted by an integer multiple of the Free Spectral Range (FSR) do not overlap, and a precise and complex optical system is also required here.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a dispersion compensator having a large angular dispersion and a wide FSR at the same time. Another object of the present invention is to provide a dispersion compensator having an optical amplification function that compensates for a decrease in light intensity after transmission.

  In order to achieve such an object, the present invention provides a dispersion compensator that amplifies an input wavelength-multiplexed optical signal and provides different angular dispersion for each wavelength. Output optical amplification angle dispersion element, a phase adjuster in which a plurality of phase adjustment elements are arranged, and a wavelength adjustment optical signal output from the optical amplification angle dispersion element for each wavelength. At least one lens that collects light in a group, and the light amplification angle dispersion element includes a first distributed Bragg reflector layer, a first light confinement layer, an active region, and a plurality of layers sequentially stacked on the substrate. A second distributed Bragg reflector layer having a second optical confinement layer, an optical signal input port and an angular dispersion output port, and an electrode provided on the substrate and the second distributed Bragg reflector layer, The input wavelength multiplexing Configured to compensate for attenuation of light intensity applied to the signal, each of the phase adjustment element groups of the phase adjuster adds an arbitrary phase to the collected optical signal to compensate for chromatic dispersion, The optical path is configured to invert the optical path, and the optical amplification angle dispersion element is further configured to combine and output optical signals of all wavelengths after phase adjustment. This makes it possible to provide a dispersion compensator having both large angular dispersion and wide FSR characteristics. According to the present invention, the lens can be disposed in the vicinity of the optical amplification angle dispersion element, and the size of the dispersion compensator can be reduced. In addition to the above, it is possible to provide a dispersion compensator capable of compensating for a decrease in light intensity.

  The invention according to claim 2 is the dispersion compensator according to claim 1, wherein a distance between the first distributed Bragg reflector layer and the second distributed black reflector layer is the wavelength multiplexing. The reflectance of the second distributed black reflector layer is lower than the reflectance of the first distributed Bragg reflector layer, and the optical amplification angle dispersive element has the wavelength Multiple optical signals are incident on one of the first distributed black reflector layer or the second distributed black reflector layer at an incident angle θi, reflected at a reflection angle θi, and opposed to the first distributed black reflector. To the other of the first distributed black reflector layer and the second distributed black reflector layer, and performs light propagation by multiple reflection between the first distributed black reflector layer and the second distributed black reflector layer, and Of the incident light on the distributed black reflector layer The wavelength-multiplexed optical signal is output to the outside at a refraction angle θ. At this time, θi is adjusted so that the relationship between the distance d between each refraction point and the wavelength λ of the wavelength-multiplexed optical signal is d << λ. It is characterized by that. As a result, it is possible to provide a dispersion compensator having a larger angular dispersion and a wide FSR characteristic at the same time.

  The invention according to claim 3 is the dispersion compensator according to claim 1 or 2, wherein the beam diameter D condensed on the phase adjusting element group is D ≧ P with respect to the phase adjusting element interval P. It is characterized by being.

  A fourth aspect of the present invention is the dispersion compensator according to any one of the first to third aspects, further comprising a temperature adjuster in contact with the light amplification angle dispersion element, and the light amplification angle dispersion. The angular dispersion provided by the element is controlled by heating or cooling by the temperature regulator.

  A fifth aspect of the present invention is the dispersion compensator according to any one of the first to fourth aspects, wherein in the second distributed Bragg reflector layer, the reflectance of the optical signal input port is the angular dispersion. It is characterized by being smaller than the reflectance of the output port.

  As described above, according to the present invention, it is possible to provide a dispersion compensator having a large angular dispersion and a wide FSR at the same time. In addition, according to the present invention, it is possible to provide a dispersion compensator having an optical amplification function that compensates for a decrease in light intensity.

It is a schematic block diagram of the dispersion compensator described in patent document 2. It is a schematic block diagram of the dispersion compensator concerning one Embodiment of this invention. It is a figure explaining the structure of the amplification dispersion compensating element concerning one Embodiment of this invention. It is a figure which shows the far-field image of the light output from the amplification dispersion compensation element concerning one Embodiment of this invention. It is a figure which shows the angle dispersion characteristic of the amplification dispersion compensating element concerning one Embodiment of this invention. It is a figure which shows the relationship between the refraction angle and light intensity spectrum in the amplification dispersion compensation element concerning one Embodiment of this invention. It is a figure explaining the structure of the amplification dispersion compensating element concerning one Embodiment of this invention. It is a figure which shows the relationship between the temperature and the refraction angle in the amplification dispersion compensation element concerning one Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or similar reference symbols indicate the same or similar elements, and repeated description is omitted.

  The configuration of the dispersion compensator according to the embodiment of the present invention uses an optical amplification angle dispersion element (also referred to as an amplification dispersion compensation element in this specification) instead of the array grating waveguide in the dispersion compensator shown in FIG. It is a configuration. A dispersion compensator according to an embodiment of the present invention includes an optical amplification angle dispersion element, a lens, and a phase adjuster. The optical amplification angle dispersive element consists of a distributed Bragg reflector layer (lower part), a light confinement layer (lower part), an active region, a light confinement layer (upper part), and a distributed Bragg reflector layer (upper part), which are sequentially stacked on the substrate. Prepare. In addition, the optical amplification angle dispersion element can include an optical amplification electrode on the bottom surface of the substrate and the upper surface of the distributed Bragg reflector layer (upper portion). Furthermore, the optical amplification angle dispersion element can include a temperature adjustment element for controlling the refraction angle.

  In the following description, the substrate material of the amplification dispersion element constituting the dispersion compensator is GaAs, the distributed Bragg reflector (DBR) is a GaAlAs / GaAs semiconductor multilayer reflector, and the active region is a GaInAs / GaAs multiple quantum well. Although illustrated, it is by no means limited to this. For example, it goes without saying that the present invention can be implemented even if the substrate material is InP, DBR is an InGaAsP / InP semiconductor multilayer mirror, and the active region is an InGaAsP / InP multiple quantum well. Although the number of wavelength multiplexing is set to 16, it goes without saying that the present invention is not limited to this. Furthermore, although the number of wavelengths is 16 and the number of phase adjusting elements constituting the phase adjusting element group is 16 waves and 3 respectively, it goes without saying that the number of wavelengths is not limited to this.

(First embodiment)
FIG. 2 is a configuration diagram of the dispersion compensator of the present embodiment. The amplification dispersion compensator of this embodiment includes an optical circulator (05-00), an amplification dispersion compensation element (01-00), a lens (03), and an LCOS (04-00).

  The wavelength multiplexed optical signal input to the optical input port (05-01) of the optical circulator propagates through the optical waveguide such as an optical fiber and reaches the optical circulator, and then propagates to the common port of the optical circulator, and the optical fiber or the like. Are input to the optical signal input / output port (01-01) of the amplifying dispersion compensating element (01-00) through the optical waveguide (05-04). After the input, it is optically amplified in the amplification dispersion compensation element and demultiplexed from the angle dispersion output port (01-02) at different angles for each wavelength (02-01, 02-02,... 02-15, 02). -16). In the present embodiment, the case of 16 waves is described. The amplified optical signal output as a demultiplexed wave is phase compensator (04-00) made of LCOS by a lens (03) having a focal length f (06). ) Condensed on the surface (04-01). A plurality of phase compensation elements (04-02) constituting a phase compensator are arranged at the condensed position, and phase compensation element groups (05-01, 05-02,... 05- for each wavelength. 15, 05-16), the desired phase adjustments Φ 1, Φ 2,... Φ 15, Φ 16 are applied and returned to the original path by reflection on the bottom surface of the LCOS. For example, the optical signal having the wavelength indicated by 03-01 is condensed on the phase compensation element group (05-01), and phase adjustment Φ1 is performed here. Similarly, the optical signal having the wavelength indicated by 03-02 is condensed on the phase compensation element group (05-02), where phase adjustment Φ2 is performed. The reflected light of each wavelength propagates through the original path and is output from the common optical port (05-02) of the optical circulator.

  FIG. 3 is a diagram showing a cross-sectional structure of the amplification dispersion compensating element (01-00) of this embodiment and how the i-th wavelength is propagated. The i-th wavelength is output from each of the reflection points at the interval d. An optical waveguide (05-04) such as an optical fiber is optically connected to the optical input port (01-03) of the amplification dispersion compensating element. The amplification dispersion compensation element is provided with an active medium (01-08) for amplifying an optical signal, and an optical confinement layer (01-06, 01-07), a distributed Bragg reflector (DBR) (DBR) ( 01-04, 01-05) are opposed to each other and formed on the substrate (01-09). However, since the DBR arranged at the top on the paper also serves as an angle dispersion output port, the reflectance is designed to be lower than the reflectance of the DBR arranged oppositely. Further, the reflectance of the DBR located at the optical signal input port (01-03) is also designed to be lower than the reflectance of these DBRs. This is for facilitating the incidence of light to the amplification dispersion compensation element. Therefore, in this embodiment, the DBR located at the optical input port, the DBR located at the amplified dispersion compensation optical output port, and the DBR located on the substrate side have 7 pairs, 20 pairs, and 40 pairs of multilayer films. Are formed respectively. However, the number of pairs in the multilayer film is never limited by this value, and it goes without saying that the magnitude relationship between them is important.

The optical signal of wavelength λi input from the optical signal input port propagates (01-11) while being repeatedly reflected between DBRs (01-04, 01-09) arranged opposite to each other, and slow light propagation is performed. At this time, since the light is amplified by the active medium (01-08) injected with current from the electrode (01-10), loss compensation during propagation and further light amplification are possible. It can be provided in the DBR (01-04) located at the output port. Note that the free spectral range (FSR) is expanded by designing the distance d between the reflection points to be sufficiently narrower than the optical signal wavelength. This makes it possible to collectively apply angular dispersion to a relatively wide wavelength range included in the wavelength multiplexed optical signal. Therefore, the incident angle from the inside of the amplification dispersion compensation element to the DBR located at the angular dispersion light output port is θ _i , the refraction angle to the air is θ, the equivalent refractive index of the waveguide constituting the dispersion compensator is n _wg , air When the refractive index of n is n _air (= 1), n _air × sin θ = n _wg × sin θ _i is obtained according to Snell's law, and the waveguide cutoff wavelength is λ _c and the wavelength used is λ. The refraction angle is expressed by the following relational expression. sin θ _i is given by the equation shown in FIG. 3, where k is the wave number vector of the wavelength used, and k = c / λ where c is the speed of light. Similarly, k _c is a wave number vector of the cutoff wavelength.

  The smaller the distance d between the reflection points, the higher the resolution, and the clearer the edge of the spot of the light collected on the phase compensator, the better. The vertical spacing in the multiple reflection in the amplification dispersion compensating element of the present embodiment is a lambda cavity designed to be about the working wavelength, and the spacing d of the reflection points is designed to be narrower than the optical signal wavelength. In addition, the spot of light collected on the phase compensator is made clear.

  In the present embodiment, the beam diameter D collected on the phase adjustment element group of the phase compensator is D ≧ P with respect to the phase adjustment element interval P.

  4 is a far-field image output from the amplification dispersion compensation element, and FIG. 5 is an angular dispersion characteristic graph. However, the wavelength is changed from 960.5 nm to 977.5 nm at step 0.5 nm.

  In FIG. 4, a far-field image observed with different angular dispersion when the wavelength is changed is combined into a single photograph. At this time, a total angular dispersion width of 30 degrees is obtained, and experimental results comparable to the calculation results of FIG. 5 are obtained.

  FIG. 6 shows measured values of the light intensity spectrum for each wavelength, that is, for each refraction angle. It can be seen that a relatively good unimodal spectrum is obtained at all refraction angles, that is, wavelengths, and good resolution is obtained. This characteristic is particularly important when focusing on the LCOS that performs phase adjustment, and is a characteristic that can be sufficiently adapted to the reduction in the size of the phase adjustment element of the phase adjustment element group constituting the LCOS.

  In the present embodiment, an example is shown in which a single lens is used to condense the wavelength multiplexed optical signal output from the optical amplification angle dispersion element to different phase adjustment element groups of the phase adjuster for each wavelength. However, a plurality of lenses may be used.

(Second Embodiment)
FIG. 7 is a structural diagram of an amplification dispersion compensation element constituting the amplification dispersion compensator of this embodiment. As an alternative to the amplification dispersion compensator of FIG. 3, it can be used in the configuration of the amplification dispersion compensator described with reference to FIG. In the present embodiment, the amplification dispersion compensation element is different from the amplification dispersion compensation element shown in FIG. 3 in that a temperature adjustment element (07) is provided in addition to the electrode (01-10). In the amplification dispersion compensating element of FIG. 7, the equivalent refractive index n _wg of the waveguide can be changed more by heating or cooling by the temperature adjusting element. Here, the temperature adjustment element is described as a heater, but the present invention is not limited to this, and it goes without saying that a Peltier element, for example, can be substituted. Furthermore, although the arrangement of the temperature adjusting element is in contact with the bottom surface of the substrate, it is sufficient to mount it at a location where the effective refractive index of the waveguide can be changed, and it goes without saying that the position is free.

  FIG. 8 shows measured values of refraction angles and calculated values for each wavelength when the amplification dispersion compensator is heated by a heater. When operated by heating at 60 degrees from the room temperature operation, a result that the refraction angle is increased by about 10 degrees is obtained, and the performance improvement of the amplification dispersion compensator can be realized.

01-00 Optical amplification angle dispersion element (amplification dispersion compensation element)
01-04, 01-05 Distributed Bragg reflector layer 01-06, 01-07 Optical confinement layer 01-08 Active region 01-09 Substrate 01-10 Electrode 03 Lens 04-00 Phase compensator (LCOS)
04-02 Phase compensation element 05-00 Circulator 07 Temperature adjustment element

Claims (5)

An optical amplification angle dispersion element that amplifies the input wavelength-multiplexed optical signal and outputs an angular dispersion different for each wavelength; and
A phase adjuster in which a plurality of phase adjusting elements are arranged;
A dispersion compensator comprising: at least one lens that focuses the wavelength multiplexed optical signal output from the optical amplification angle dispersion element on a different phase adjustment element group of the phase adjuster for each wavelength;
The optical amplification angle dispersion element includes a first distributed Bragg reflector layer, a first optical confinement layer, an active region, a second optical confinement layer, and an optical signal input port, which are sequentially stacked on a substrate. And a second distributed Bragg reflector layer having an angle-dispersed output port, and electrodes provided on the substrate and the second distributed Bragg reflector layer, and provided to the input wavelength-multiplexed optical signal Configured to compensate for intensity decay,
Each of the phase adjustment element groups of the phase adjuster is configured to add an arbitrary phase to the collected optical signal to compensate for chromatic dispersion, and to reverse the optical path,
The dispersion compensator according to claim 1, wherein the optical amplification angle dispersion element is further configured to combine and output optical signals of all wavelengths after phase adjustment. A distance between the first distributed Bragg reflector layer and the second distributed black reflector layer is approximately equal to a wavelength of the wavelength-multiplexed optical signal;
The reflectance of the second distributed black reflector layer is lower than the reflectance of the first distributed Bragg reflector layer,
In the optical amplification angle dispersion element, the wavelength-multiplexed optical signal is incident on one of the first distributed black reflector layer or the second distributed black reflector layer at an incident angle θi and reflected at a reflection angle θi. To the other of the first distributed black reflector layer or the second distributed black reflector layer facing each other, between the first distributed black reflector layer and the second distributed black reflector layer A portion of the wavelength-multiplexed optical signal that propagates light by multiple reflection and enters the second distributed black reflector layer is output to the outside at a refraction angle θ, and at this time, the distance d between each refraction point and 2. The dispersion compensator according to claim 1, wherein θi is adjusted such that the relationship of the wavelength λ of the wavelength multiplexed optical signal is d << λ.   3. The dispersion compensator according to claim 1, wherein a beam diameter D focused on the phase adjusting element group satisfies D ≧ P with respect to the phase adjusting element interval P. 4.   A temperature regulator abutted on the light amplification angle dispersion element; and the angle dispersion provided by the light amplification angle dispersion element is controlled by heating or cooling by the temperature regulator. The dispersion compensator according to any one of claims 1 to 3.   5. The dispersion compensator according to claim 1, wherein in the second distributed Bragg reflector layer, the reflectance of the optical signal input port is smaller than the reflectance of the angular dispersion output port. .

Images