JP2008139578A - Waveguide type optical isolator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a constitution of a waveguide type optical isolator which has high optical isolation and a small loss and is inexpensive and suitable for mass production. <P>SOLUTION: The waveguide type optical isolator has a first clad layer, a core part and a second clad layer on a substrate, wherein the core part is used as a Faraday rotor, and first and second polarization elements are arranged in the middle of the core part so that the polarization axes of them cross each other at 45°. A groove in which the first and second polarization elements are fit and fixed is formed on the substrate at the least. The bottom of the groove is used as a positioning face when each of the first and second polarization elements is positioned along its reference plane so that an angle formed by the polarization axes of the first and second polarization elements can be adjusted with high precision. The cross-sectional area of a part of the core part is made smaller than those of other portions to enlarge a mode field diameter and reduce the loss of the waveguide type optical isolator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a waveguide type used to prevent light waves emitted from a laser serving as a light source from returning to the light source due to various causes in optical communication, broadcast wave transmission using light, measurement using light, and the like. The present invention relates to an optical isolator.

  FIG. 11 shows a schematic configuration of an optical isolator using a Faraday rotator that is well known in the art. In the figure, 111 is a Faraday rotator, 112 is a polarizer, 113 is an analyzer, 114 is a magnetic field applying means such as a permanent magnet, 115 is a light source composed of a semiconductor laser or the like, and 116 is a propagation direction of light emitted from the light source 115. Indicates.

  Conventionally, as a material of the Faraday rotator 111, for example, a bismuth-substituted rare earth iron garnet single crystal formed on a nonmagnetic garnet substrate by a liquid phase epitaxial method has been used as described in JP-A-7-206593. It was done. In general, an angle formed between the polarization direction of light incident on the Faraday rotator 111 and the polarization direction of light after passing through the Faraday rotator, that is, the Faraday rotation angle is the thickness of the light propagation direction of the Faraday rotator. Is proportional to

  For example, in the case of an optical isolator, the Faraday rotation angle needs to be 45 degrees, and the thickness of the bismuth-substituted rare earth iron garnet is 400 to 500 μm (hereinafter, for obtaining a Faraday rotation angle of 45 degrees). The thickness is referred to as “propagation length”). Usually, in order to obtain such propagation length, after forming the bismuth-substituted rare earth iron garnet thicker than the above-mentioned propagation length by liquid phase epitaxy, the substrate is removed by polishing, and further, the desired Faraday rotation angle is obtained by precision polishing. A processing method has been adopted in which the film thickness required for obtaining is obtained.

On the other hand, as a small-sized and simple structure optical isolator, for example, Japanese Patent Application Laid-Open No. 7-3600 discloses a so-called waveguide type optical isolator. The waveguide type optical isolator disclosed in this publication forms a waveguide made of a YIG single crystal film having a predetermined shape, and then the length in the light propagation direction is changed to a chip shape so that the polarization plane rotates 45 degrees. It was manufactured by a method of cutting and polishing into two, and attaching a polarizer to the polished surfaces at both ends. In the waveguide type optical isolator having such a configuration, a waveguide made of a YIG single crystal film functions as a Faraday rotator.
Japanese Patent Laid-Open No. 7-206593 Japanese Patent Laid-Open No. 7-36000

  The ability of the optical isolator to block the return light to the light source such as a semiconductor laser (hereinafter referred to as “isolation”) adjusts the angle of the extinction axes of the polarizer 112 and the analyzer 113 as well as the characteristics of the Faraday rotator. Depends heavily on the accuracy of Here, the extinction axis refers to the direction of linearly polarized light that has a minimum transmittance when a linearly polarized wave is incident on the polarizer and analyzer. That is, in the optical isolator, when the Faraday rotation angle of the Faraday rotator is set to 45 degrees, and the extinction axes of the polarizer 112 and the analyzer 113 are set to form an angle of 45 degrees, the maximum is obtained. Isolation is obtained. For example, when the Faraday rotation angle of the Faraday rotator is 45 degrees, the alignment angle of the extinction axes of the polarizer and the analyzer is deviated by 1 degree in absolute value, depending on the performance of the polarizer and the analyzer. It is estimated that the amount of degradation of the isolator is about 10 to 15 dB.

  Therefore, in order to realize high isolation, it is important to adjust the angle formed by the polarizer 112 and the analyzer 113 to 45 degrees as accurately as possible. Such a situation also applies to the waveguide type optical isolator. It is the same.

  For this reason, in order to obtain high isolation in the above-described conventional optical isolator, this angle alignment adjustment is performed so that the test light is incident from the analyzer side and the intensity of the light passing through the polarizer is minimized. An extremely complicated adjustment such as adjusting the installation angle of the child was necessary. Therefore, this point has become one of the technical obstacles, and it has been difficult to manufacture a large amount of optical isolators having high isolation with high yield.

  As a result of a systematic study on the development of the waveguide type optical isolator by the inventors, it is possible to align the extinction axes of the polarizer and the analyzer with high accuracy by adopting the configuration shown in FIG. 3, for example. Something was found. FIG. 3 is a schematic diagram of the configuration of a waveguide type optical isolator newly invented by the inventors, in which 31 is a substrate, 32 is a lower cladding layer, 33 is a core portion made of a magnetic garnet having a Faraday effect, 34 Is an upper cladding layer, 35 is a polarizer, 36 is an analyzer, 37 is an arrow indicating the propagation direction of light emitted from a light source (not shown), and 38 is a propagation direction of light emitted from the waveguide type optical isolator. It is an arrow which shows.

  In the waveguide type optical isolator in this configuration, both the polarizer 35 and the analyzer 36 are inserted into the groove formed in the core portion, and the bottom surface of the groove portion serves as a reference surface. Axis alignment is possible.

  However, it was newly found that the waveguide type optical isolator having the same configuration has a problem that the loss of the isolator is large although a good extinction ratio is realized.

  An object of the present invention is to provide a configuration of a waveguide type optical isolator that has high isolation and small loss, is inexpensive, and is suitable for mass production.

  The light propagation direction means the direction in which the light emitted from the light source propagates through the waveguide provided with the waveguide type optical isolator. The emission end of the waveguide type optical isolator is emitted from the light source. Means the end where the propagated light propagates through the waveguide provided in the waveguide type optical isolator, and the propagated light is emitted from the waveguide, for example, the end located on the arrow 38 side in FIG. .

In response to the problem to be solved, the first means provided by the present invention is as follows:
A waveguide type optical isolator having a first clad layer on a substrate, a core portion made of a garnet magnetic material having a Faraday effect provided on the first clad layer, and a second clad layer covering the core portion. The first polarizing element from the light source side and the second polarizing element spaced apart from the first polarizing element at the core part other than the end part positioned in the light propagation direction of the core part. Is provided, and at least the second polarizing element is a polarizing plate inserted into the core portion so as to be substantially orthogonal to the light propagation direction of the core portion, and is positioned on the light output end side of the second polarizing element. The waveguide type optical isolator is characterized in that the core section includes a portion in which a cross-sectional area in a direction orthogonal to the light propagation direction of the core section increases toward the light emitting end side.

The second means provided by the present invention includes
In a waveguide type optical isolator having a first clad layer on a substrate, a core portion made of a garnet magnetic material having a Faraday effect provided on the first clad layer, and a second clad layer covering the core portion The first polarizing plate from the light source side and the second polarizing plate are inserted at a desired distance from the first polarizing plate so as to be substantially orthogonal to the light propagation direction of the core portion, and the first 1 and the core part located in the light emission end side of a 2nd polarizing plate has a part where the cross-sectional area of the direction orthogonal to the light propagation direction of this core part increases toward the light emission end side This is a waveguide type optical isolator.

The third means provided by the present invention includes
In the waveguide type optical isolator, the polarizing plate is a polarizing glass formed by preferentially aligning and dispersing the longitudinal direction of the acicular metal fine particles in one direction on the glass body.

The fourth means provided by the present invention includes:
In the waveguide type optical isolator, the core portion is a magnetic garnet having a single crystal magneto-optic effect.

Furthermore, the fifth means provided by the present invention includes
In the waveguide type optical isolator, the core portion is a magnetic garnet having a polycrystalline magneto-optical effect.

  Hereinafter, in the waveguide type optical isolator shown in FIG. 3, the cause of the increase in loss and the means for solving it will be described in detail with reference to FIGS. 4a and 4b.

  FIG. 4A is a diagram schematically illustrating how light emitted from the waveguide spreads, and FIG. 4B is a schematic side cross-sectional view schematically illustrating light propagation in the vicinity of the analyzer 36 in FIG. FIG. In FIG. 4a, 41 is a substrate, 42 is a lower clad layer, 43 is a core part, 44 is an upper clad layer, 44 is a light spread schematically shown, and 45 is a light propagated from the exit end of the waveguide. It is an arrow which shows the direction to do. 4b, reference numeral 331 denotes a core portion located on the light source (not shown) side, 332 denotes a core portion located on the emission end side, and 47 and 48 denote light propagation propagating through the core portions 331 and 332, respectively. A direction arrow 441 is a spread of light propagating inside the analyzer 36 schematically shown.

  In general, light emitted into the space from the output end of the waveguide diffuses as schematically shown in FIG. 4a. The degree of diffusion is represented by the numerical aperture (NA) defined by the following equation (1), where the relative refractive index of the space is 1.

In Equation 1, n _core is the refractive index θc of the core portion, and is a total reflection critical angle determined by the refractive index n _core of the core portion 43 and the refractive indexes n _clad of the cladding layers 42 and 44. It is given by the formula.

That is, the degree of diffusion of the light emitted into the space increases with an increase in NA, and NA is proportional to the refractive index of the core portion from Equation (1). The degree of diffusion of the emitted light increases. In addition, the refractive index of the core portion in a waveguide using a general quartz glass is about 1.5, whereas in the case of a core portion made of magnetic garnet, the refractive index is about 2.2. Therefore, the degree of diffusion of the emitted light increases compared to the case of the waveguide using quartz glass.

  In addition, as shown in FIG. 4b, the propagation of light when the waveguide is cut in the middle and the analyzer 36 made of polarizing glass or the like is inserted is the same state, and the light propagating in the core portion 331 47 propagates in the analyzer 36 as shown schematically in the spread 441. Therefore, when the cross-sectional shapes of the core part 332 and the core part 331 are the same, the energy of light propagating in the core part 332 is orthogonal to the beam spread width in the analyzer 36 and the light propagation direction of the core part 332. As a result, the loss of the optical isolator increases as a result of a decrease in proportion to the ratio of the cross-sectional area of the surface (hereinafter referred to simply as “the cross-sectional area of the core portion”).

  As a method of reducing such loss, a method of increasing the cross-sectional area of the core portion 332 on the receiving side can be considered. However, this method is not suitable because the single mode condition of light propagating in the core portion is not satisfied.

That is, according to the present invention, the mode-filled diameter of light propagating through the waveguide (the diameter of propagating light becomes 1 / e ² with respect to the total propagation energy) is the light propagation direction of the core portion constituting the waveguide. Focusing on the fact that it largely depends on the shape of the surface orthogonal to the shape (hereinafter, the shape of the core portion is simply referred to as “core portion shape”), it was completed by utilizing the effect.

  Hereinafter, the loss reduction means of the optical isolator in the present invention will be described.

  5 and 6 show an example of calculation results of the electric field intensity distribution and power distribution of light propagating in the waveguide. The refractive index of the core used for the calculation is 2.20, and the refractive index of the cladding layer is 2.19. Moreover, the cross-sectional shape of the core part is a square. FIG. 5 is a diagram showing the relationship between the distance from the center and the electric field strength with the center of the core portion as the origin. In the figure, the normalized electric field strength means the electric field strength normalized by the electric field strength at the center of the core portion, and the distance from the center is a distance parallel to one side in the square cross section of the core portion.

  FIG. 6 is a diagram showing the relationship between the distance from the center and the integrated power with the center of the core portion as the origin. In the figure, the normalized integrated value of transmission power means an integrated value of power normalized by the total transmission power. The distance from the center is as described above.

  In the figure, 51 and 61 are calculation results when the core portion is a square shape of 5 μm square, and 52 and 62 are calculation results when the core portion is a square shape of 0.8 μm square.

  As shown in FIG. 5, it is understood that the electric field intensity distribution is broader in the case where the core portion has a square shape of 0.8 μm square than in the case of 5 μm. Correspondingly, as shown in FIG. 6, when the shape of the core part is a square of 5 μm square, ˜90% of the total power is propagated in the core part, whereas 0.8 μm In the case of a square corner, the amount is only ˜20% of the total power, and it can be seen that most of the propagation power is propagated as a clad layer, that is, an evanescent component. In other words, it is understood that the mode filled diameter in the case where the core portion has a square shape of 0.8 μm square is larger than the mode filled diameter in the case of 5 μm.

FIG. 7 shows the calculation result of the relationship between the length of one side of the square core portion and the mode filled diameter. Here, the mode filled diameter is, for example, a value that is twice the distance at which the normalized integrated value of propagation power is ~ 0.86 (strictly, 1-1 / e ² ) in the calculation result shown in FIG. is there. As shown in the figure, it can be seen that when the length of one side of the quadrangular core portion is 1 μm or less, the mode field diameter increases rapidly.

  The present invention is intended to improve the above-described loss of the optical isolator by utilizing the effect of increasing the mode filled diameter.

  According to the present invention, a configuration of a waveguide type optical isolator having high isolation, small loss, low cost, and suitable for mass production is provided.

  FIG. 1 shows a first embodiment of a waveguide type optical isolator according to the present invention.

  In the figure, 1 is a substrate, 2 is a lower clad layer, 3 is a core portion made of a magnetic garnet having a Faraday effect located on the emission end side, 4 is an upper clad layer, and 6 is located on the light source (not shown) side. A core portion made of magnetic garnet having a Faraday effect, 5 is a metal film formed on the core portion 6, 7 is an analyzer made of a polarizing plate, 8 is a portion of the core portion 3 whose cross-sectional area changes, 9 Reference numerals 10 denote block arrows indicating the propagation directions of light propagating through the core part 5 and the core part 3, respectively.

  Hereinafter, the operation principle of the optical isolator of this embodiment will be described.

  The metal film 5 provided on the core part 6 is provided as a so-called metal cladding, and the core part provided with the metal film functions as a TE-TM filter.

  Light emitted from a light source (not shown) and incident on the waveguide type optical isolator is composed of a TE wave component (a component whose polarization plane is parallel to the substrate surface) and a TM wave component (the polarization plane is orthogonal to the substrate surface). Although the light includes both of a certain component), the TM wave component is removed by passing through the TE-TM filter. The polarization plane of the TE wave that has passed through the TE-TM filter is rotated by the Faraday effect when propagating in the core portion 6, and immediately before reaching the analyzer 7, the polarization plane is 45 degrees with respect to the substrate surface. Make an angle. Since the transmission axis of the analyzer (axis orthogonal to the extinction axis) is arranged at an angle of 45 degrees with respect to the substrate surface, the polarized wave passes through the analyzer 7 without loss. When passing through the analyzer 7, the light is diffused as described above, and the beam diameter is expanded. However, since the cross-sectional area of the core part 8 (corresponding to the length of one side of the core part) is smaller than that of the other part, the mode filled diameter of the part is larger than that of the other part as described above. Most of the light thus received can be received by the core portion 8. As a result, the light propagating through the core unit 5 can be guided to the core unit 3 without loss.

  On the contrary, the light returning to the optical isolator is randomly distributed in the polarization direction, but the return light is strictly analyzed by the analyzer 7 (in this case, the analyzer functions as a polarizer. Should be described as “polarizer”, but may be confused, so it is described as “analyzer”.) By transmitting through, the electric field oscillation direction forms an angle of 45 degrees with respect to the substrate surface. Ingredients are taken into the core section 6. The light taken into the core unit 6 propagates in the inside thereof, and due to the nonreciprocity of the Faraday rotation, the polarization direction is a direction perpendicular to the substrate surface, that is, a TM wave immediately before the TE-TM filter. . The TM wave attenuates when passing through the TE-TM filter, and as a result, the return light is prevented from reaching the light source.

FIG. 2 shows a second embodiment of a waveguide type optical isolator according to the present invention.
In the figure, 21 is a core portion sandwiched between the analyzer 35 and the polarizer 36, and 22 is a core portion located on the exit end side of the analyzer 36. That is, the embodiment shown in the figure is positioned on the output end side of the analyzer 36 and the core portion 21 held between the polarizer 35 and the analyzer 36 in the waveguide type optical isolator shown in FIG. In both the core parts 22, the cross-sectional area of the core part in the vicinity of the end part on the light source (not shown) side is made smaller than that of the other parts.

  In the present embodiment, a polarizing plate made of polarizing glass or the like is used as the polarizer 35 instead of the TE-TM filter used in the first embodiment, and transmission between the polarizer 35 and the analyzer 36 is performed. The axes are arranged to make an angle of 45 degrees with each other. The operation principle of the optical isolator of this embodiment is almost the same as that of the first embodiment.

  FIGS. 8-1 to 8-6 schematically show main modes of the shape of the tip of the core portion according to the present invention (the shape of the core portion 8 in FIG. 1 or FIG. 2). In the figure, (a) is a schematic front view seen from the light propagation direction of the core part 8, (b) is a schematic top view of the core part 8 seen from the upper cladding layer side, and (c) is a schematic side view of the core part 8. It is.

  The mode illustrated in FIG. 8A is a mode in which the tip of the core portion 8 has a quadrangular pyramid shape, and the apex of the quadrangular pyramid substantially matches the center line of the core portion.

  The mode shown in FIG. 8-2 is a mode in which a rectangular convex part having a small cross-sectional area is provided at the tip of the core part 8 as compared to the other, and the center line of the rectangular convex part is This is a mode that almost coincides with the center line.

  The mode illustrated in FIG. 8C is a mode in which only one direction of the core portion, that is, the width in the direction parallel to the substrate surface, decreases toward the tip.

  The mode shown in FIG. 8-4 is a mode in which the width of the core portion in the substrate normal direction (in other words, the film thickness) decreases toward the tip.

  The mode shown in FIG. 8-5 is a case where the apex of the quadrangular pyramid is shifted from the center position of the core portion and is on the bottom surface (surface in contact with the lower cladding layer) in the mode shown in FIG.

  The mode illustrated in FIG. 8-6 is a case where one side surface of the rectangular protrusion is substantially the same as the bottom surface of the core unit in the mode illustrated in FIG.

  Among the modes shown in FIGS. 8-1 to 8-6, the mode shown in FIGS. 8-1 and 8-2 is the best mode in that the center of the mode field coincides with the center of the core part. It can be said. However, even in the case of other embodiments, since the effect of expanding the mode field is expected, it is effective for reducing the loss of the waveguide type optical isolator according to the present invention.

  In addition, the shape of the core portion 8 in the waveguide type optical isolator according to the present invention is not limited to the embodiment shown in FIGS. 8-1 to 8-6, and the cross-sectional area is in comparison with other portions. It goes without saying that other varieties can be used as long as they are smaller.

  Hereinafter, the present invention will be described in more detail using examples.

A first embodiment of the present invention will be described with reference to FIG. 9 (FIGS. 9a to 9e). FIG. 9 is a flowchart showing a manufacturing process of a waveguide type optical isolator according to the present invention. In the figure, 91 is a 3-inch φ (111) face (CaGd) ₃ (MgZrGa) ₅ O ₁₂ single crystal substrate, and 92 is a Tb _2.3 Bi _0.7 Fe _4.6 Ga _0.4 O ₁₂ single crystal. A lower clad layer 93, a core layer made of a Tb _2.3 Bi _0.7 Fe _4.7 Ga _0.3 O ₁₂ single crystal film, and 931 a first core portion obtained by patterning the core layer 93. 932 is the second core part, 933 is the third core part, 94 is the upper clad layer made of Tb _2.3 Bi _0.7 Fe _4.6 Ga _0.4 O ₁₂ , and 95 is the polarizing plate insertion The grooves 96 and 97 are polarizing glass, and the extinction axes of the two make an angle of 45 degrees.

First, a lower clad layer 92 made of Tb2.3Bi0.7Fe4.6Ga0.4O12 single crystal and Tb2.3Bi0.7Fe4 are formed on the surface of a (CaGd) 3 (MgZrGa) 5O12 single crystal substrate 91 by a normal liquid phase epitaxial growth method. A core layer 93 made of a .7Ga0.3O12 single crystal film was sequentially laminated. The thicknesses of the lower cladding layer 92 and the core layer were 7 μm and 5 μm, respectively. (Fig. 9a)
Thereafter, the first core portion 931, the second core portion 932, and the third core portion were formed on the upper core layer by a normal photolithography etching process. The width of each core part was 5 μm, the length of the first core part 931 was 600 μm, the length of the second core part 932 was 570 μm, and the length of the third core part 933 was 600 μm. FIG. 10 schematically shows the tip shapes of the second core portion 932 and the third core portion 933. In the figure, d1 and d2 are dimensions of each part, and φ is an opening angle of the core tip. The d1 of the second and third core portions prepared by the method described above were both about 70 μm, d2 was about 1 μm, and φ was about 4 degrees. (Fig. 9b)
After patterning the core part, 7 μm of Tb2.3Bi0.7Fe4.6Ga0.4O12 was formed as the upper clad layer 94 by liquid phase epitaxial growth under the same conditions as the formation of the lower clad layer so as to cover the core part. (Fig. 9c)
After the formation of the upper clad layer 94, a polarizing plate insertion groove 95 having a width of 35 μm and a depth of 40 μm was formed by a high-precision dicer so as to sandwich the second core portion. The interval between the grooves sandwiching the second core part is 570 μm, similar to the length of the second core part. (Fig. 9d)
After that, the polarizing glass cut into a strip shape having a short side of 10 mm is inserted so as to have the configuration of the polarizer 96 and the analyzer 97 with the second core portion interposed therebetween, and fixed with an optical adhesive (FIG. 9e). Then, the strip was cut for each waveguide, and the end face of the waveguide was exposed by optical polishing, so that an optical isolator substantially the same type as the waveguide type optical isolator shown in FIG. 2 was produced.

  As a result of measuring the characteristics of the produced waveguide type optical isolator, the isolation was ˜23 dB and the loss was ˜1 dB. The measurement wavelength was 1.55 μm.

Comparative example

  As a comparative example, a waveguide type optical isolator having the mode shown in FIG. 3 was prepared under the same conditions as in Example 1. However, in the comparative example, the cross-sectional shape of the core portion is uniform, and is a square shape with one side of ˜5 μm. Further, the length of the core portion held between the polarizer 35 and the analyzer 36 was ˜570 μm as in the first embodiment. The waveguide type optical isolator thus prepared had an isolation of ˜23 dB and a loss of ˜4 dB at a wavelength of 1.55 μm.

  Under the same conditions as in Example 1, an optical isolator of substantially the same type as the waveguide type optical isolator shown in FIG. However, in this example, prior to the core pattern formation (FIG. 9b), a two-layer film made of Cr / Au (Cr is on the core layer 93 side) is formed on the entire surface by using a normal sputtering method, and metal cladding is performed. 5 was formed. Each film thickness was Cr: ˜0.05 μm, Au: ˜0.3 μm, and the length in the light propagation direction was ˜5 mm.

Moreover, the shape of the core part 8 is the shape shown in FIG.
In this example, the distance between the end of the metal cladding and the analyzer 7 was ˜570 μm.

  The isolation wavelength at the wavelength of 1.55 μm of the produced optical isolator was ˜18 dB, and the loss was ˜2.5 dB.

In this example, a 3 inch φ c-plane sapphire substrate was used instead of the 3 inch φ (111) face (CaGd) ₃ (MgZrGa) ₅ O ₁₂ single crystal substrate. By an aerosol deposition method on a sapphire substrate, polycrystalline Bi _0.6 Gd _2.4 Fe ₅ O ₁₂ is formed as a lower cladding layer to a thickness of ˜7 μm, and Bi _0.7 Tb _2.3 Fe as a core layer thereon. ₅ O ₁₂ was deposited to a thickness of ˜5 μm. The average particle diameter of the raw material fine particles used here was 0.8 μm, the carrier gas was oxygen, and the flow rate was 5 liters / minute. The opening diameter of the injection nozzle was 0.6 mmφ. Then, the core part was formed by the method similar to the method shown in Example 1. The shapes of the first, second, and third core portions are the same as those shown in the first embodiment. Thereafter, Bi _0.6 Gd _2.4 Fe ₅ O ₁₂ having a thickness of ˜7 μm was formed as an upper cladding layer under the same conditions as the lower cladding layer, and then heat treatment was performed at 700 ° C. for 1 hour.

  The subsequent creation conditions are the same as the conditions shown in the first embodiment.

  As a result of measuring the characteristics of the produced waveguide type optical isolator, the isolation was ˜25 dB and the loss was ˜2 dB. The measurement wavelength was 1.55 μm.

  As described above, the waveguide type optical isolator according to the present invention has been described in detail using the embodiments. However, the present invention is not limited to the shape and manufacturing method described in the examples, and the shape and manufacturing method can be appropriately selected according to desired characteristics.

  The present invention is used as an optical isolator for preventing light waves emitted from a laser serving as a light source from returning to the light source due to various causes in optical communication, broadcast wave transmission using light, measurement using light, and the like. it can.

1 is a first embodiment of a waveguide type optical isolator according to the present invention; 2 shows a second embodiment of a waveguide type optical isolator according to the present invention. FIG. 3 is a schematic configuration diagram relating to a waveguide type optical isolator. The figure which showed typically a mode that the light radiate | emitted from the waveguide spreads. 4 is a schematic cross-sectional side view schematically showing the state of light propagation in the vicinity of the analyzer 36 in FIG. Calculation result of electric field intensity distribution of light propagating in the waveguide. Calculation result of power distribution of light propagating in the waveguide. The calculation result about the relationship between the length of one side of a square-shaped core part, and a mode filled diameter. The schematic of the front-end | tip shape of the core part which consists of this invention. The schematic of the front-end | tip shape of the core part which consists of this invention. The schematic of the front-end | tip shape of the core part which consists of this invention. The schematic of the front-end | tip shape of the core part which consists of this invention. The schematic of the front-end | tip shape of the core part which consists of this invention. The schematic of the front-end | tip shape of the core part which consists of this invention. The flowchart which shows the manufacturing process of the waveguide type optical isolator which consists of this invention. Schematic of the tip shape of the 2nd core part 932 and the 3rd core part 933. FIG. The structure schematic of the optical isolator using the conventional bulk type Faraday rotator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Lower clad layer 3 Core part which consists of magnetic garnet which has a Faraday effect located in the output end side 4 Upper clad layer 5 Core part which consists of magnetic garnet which has a Faraday effect located in the light source (not shown) side 6 Core Metal film 7 formed on the portion 6 Analyzer 8 comprising a polarizing plate Portions 9 and 10 in which the cross-sectional area of the core portion 3 changes, showing the propagation direction of light propagating in the core portion 5 and the core portion 3 respectively. Block arrow 21 Core portion 22 sandwiched between analyzer 35 and polarizer 36 Core portion 31 positioned on emission end side of analyzer 36 Substrate 32 Lower clad layer 33 Core portion 34 made of magnetic garnet having Faraday effect Cladding layer 35 Polarizer 36 Analyzer 37 Arrow indicating the propagation direction of light emitted from a light source (not shown) 38 From the waveguide type optical isolator Arrow 331 indicating the propagation direction of the emitted light Core portion 332 located on the light source (not shown) side Core portion 41 located on the emission end side Substrate 42 Lower clad layer 43 Core portion 44 Upper clad layer 45 Output end of the waveguide Arrows 47 and 48 indicating directions in which the light emitted from the light propagates Arrows 441 indicating the propagation direction of light propagating through the core portions 331 and 332 respectively Spreading of light propagating through the analyzer 36 schematically illustrated 51, 61 Calculation results when the core portion is a square shape of 5 μm square 52, 62 Calculation results when the core portion is a square shape of 0.8 μm square 913 (111) plane of 3 inches φ (CaGd ) 3 (MgZrGa) 5O12 single crystal substrate 92 Lower clad layer 93 made of Tb2.3Bi0.7Fe4.6Ga0.4O12 single crystal 93 Core layer 931 made of Tb2.3Bi0.7Fe4.7Ga0.3O12 single crystal film Part 932 second core part 933 third core part 94 upper clad layer 95 made of Tb2.3Bi0.7Fe4.6Ga0.4O12 polarizing plate insertion grooves 96 and 97 are polarizing glasses d1 and d2 are dimensions φ of each part Opening angle 111 at the tip of the head Faraday rotator 112 Polarizer 113 Analyzer 114 Magnetic field applying means 115 such as a permanent magnet Light source 116 comprising a semiconductor laser or the like Propagation direction of light emitted from the light source 115

Claims (5)

  A waveguide type optical isolator having a first clad layer on a substrate, a core portion made of a garnet magnetic material having a Faraday effect provided on the first clad layer, and a second clad layer covering the core portion. The first polarizing element from the light source side and the second polarizing element spaced apart from the first polarizing element at the core part other than the end part positioned in the light propagation direction of the core part. Is provided, and at least the second polarizing element is a polarizing plate inserted into the core portion so as to be substantially orthogonal to the light propagation direction of the core portion, and is positioned on the light output end side of the second polarizing element. The waveguide type optical isolator is characterized in that the core portion to be provided has a portion whose cross-sectional area in the direction orthogonal to the light propagation direction of the core portion increases toward the light emitting end side.   In a waveguide type optical isolator having a first clad layer on a substrate, a core portion made of a garnet magnetic material having a Faraday effect provided on the first clad layer, and a second clad layer covering the core portion The first polarizing plate from the light source side and the second polarizing plate are inserted at a desired distance from the first polarizing plate so as to be substantially orthogonal to the light propagation direction of the core portion, and the first 1 and the core part located in the light emission end side of a 2nd polarizing plate has a part where the cross-sectional area of the direction orthogonal to the light propagation direction of this core part increases toward the light emission end side And a waveguide type optical isolator.   3. The waveguide-type light according to claim 1, wherein the polarizing plate is a polarizing glass obtained by preferentially aligning and dispersing the longitudinal direction of the acicular metal fine particles in one direction on a glass body. Isolator.   4. The waveguide type optical isolator according to claim 1, wherein the core portion is a magnetic garnet having a single crystal magneto-optic effect.   4. The waveguide type optical isolator according to claim 1, wherein the core part is a magnetic garnet having a polycrystalline magneto-optical effect.