JP6554571B1 - Optical wavelength filter - Google Patents

Abstract

A narrow transmission peak is realized by operating as a ring resonator using a grating type element having a simple structure. In the first wavelength filter unit 101 and the second wavelength filter unit 201, in the resonant waveguides 171 and 271 between the TE polarization of the first mode and the TM polarization of the first mode for a specific wavelength. Resonate while repeating the conversion. In the first wavelength filter unit, the first mode TE polarized wave propagating through the resonant waveguide is combined with the fundamental mode TE polarized wave propagating through the first access waveguide and the second access waveguide, and the second wavelength filter. The first mode TM polarized wave propagating through the resonant waveguide is coupled to the fundamental mode TM polarized wave propagating through the first access waveguide and the second access waveguide. [Selection] Figure 3

Description

  The present invention relates to an optical wavelength filter suitable for use in performing optical multiplexing / demultiplexing, for example, in order to transmit using a plurality of different wavelengths in one optical fiber.

  In recent years, passive optical networks (PONs) have become mainstream as subscriber optical access systems. In the PON, one station side device (OLT: Optical Line Terminal) and a plurality of subscriber side devices (ONU: Optical Network Unit) are connected via an optical fiber and a star coupler, and one OLT is connected to a plurality of OLTs. Shared by ONU. In PON, the optical signal wavelength used for downlink communication and the optical signal wavelength used for uplink communication are set so that downlink communication from OLT to ONU and uplink communication from ONU to OLT do not interfere with each other. It is wrong.

  Therefore, a multiplexing / demultiplexing element is required to demultiplex and multiplex optical signals having different wavelengths used for downlink communication and uplink communication. Generally, in order to realize the function of transmitting and receiving optical signals of different wavelengths, OLTs and ONUs use an optical wavelength filter as a multiplexing / demultiplexing element, a photodiode (PD: Photodiode), a laser diode (LD: Laser Diode) as a space. Composed and configured.

  In order to perform spatial coupling, an alignment operation for aligning the optical axis between the optical wavelength filter, PD, and LD is required. On the other hand, in order to eliminate the need for the operation for optical axis alignment, an optical wavelength filter configured using a waveguide has been developed. In forming this light wavelength filter, attention is focused on silicon (Si) waveguides that use silicon-based materials as waveguide materials because they are excellent in miniaturization and mass productivity (see, for example, Patent Documents 1 to 5). ).

  In the Si waveguide, an optical waveguide core that substantially becomes a light transmission path is formed using Si as a material. Then, the periphery of the optical waveguide core is covered with a clad made of, for example, silica having a refractive index lower than that of Si. With such a configuration, the refractive index difference between the optical waveguide core and the clad becomes extremely large, so that light can be strongly confined in the optical waveguide core. As a result, a small curved waveguide having a bending radius reduced to, for example, about 1 μm can be realized. Therefore, it is possible to create an optical circuit having a size comparable to that of an electronic circuit, which is advantageous for downsizing the entire optical device.

  Further, in the Si waveguide, it is possible to divert the manufacturing process of a semiconductor device such as a CMOS (Complementary Metal Oxide Semiconductor). Therefore, the realization of photoelectric fusion (silicon photonics) in which an electronic functional circuit and an optical functional circuit are collectively formed on a chip is expected.

  By the way, in a PON using a wavelength division multiplexing (WDM) system, a different reception wavelength is assigned to each ONU. The OLT generates a downstream optical signal to each ONU at a transmission wavelength corresponding to the reception wavelength of the transmission destination, and multiplexes and transmits them. Each ONU selectively receives an optical signal of a reception wavelength assigned to itself from downstream optical signals multiplexed at a plurality of wavelengths. In the ONU, a wavelength filter is used to selectively receive a downstream optical signal of each reception wavelength. And the technique which comprises a wavelength filter with the Si waveguide mentioned above is implement | achieved.

  As a wavelength filter using a Si waveguide, for example, there are a filter using a Mach-Zehnder interferometer and a filter using an arrayed waveguide grating. In addition, as a wavelength filter using a Si waveguide, a ring resonator (see, for example, Patent Documents 6 to 8), a grating type (see, for example, Patent Document 9), or a directional coupler type (see, for example, Patent Document 10) There is. These wavelength filters have the advantage of being able to make the output wavelength variable and easy to use because the element structure is simple.

U.S. Pat. No. 4,860,294 U.S. Patent No. 5,764,826 U.S. Pat. No. 5,960,135 U.S. Patent No. 7,072,541 Japanese Patent Application Publication No. 08-163028 Unexamined-Japanese-Patent No. 2003-215515 JP, 2013-093627, A JP, 2006-278770, A JP 2006-330104 A JP, 2002-353556, A

  In optical communication, since the signal light propagates a long distance in the optical fiber, the polarization state becomes unspecified. For this reason, a wavelength filter that performs wavelength multiplexing or wavelength separation used in optical communication is required to be polarization independent.

  The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to operate as a ring resonator using a grating type element having a simple structure, and thereby to obtain a characteristic having a narrow transmission peak. An object of the present invention is to provide an optical wavelength filter that can be realized.

  In order to achieve the above-mentioned object, an optical wavelength filter according to the present invention comprises: a first access waveguide in which a first input / output unit, a first coupling unit, and a second input / output unit are connected in this order; The second access waveguide in which the third input / output unit, the second coupling unit, and the fourth input / output unit are connected in this order, the first reflection unit, the cavity unit, and the second reflection unit are connected in this order The first coupling unit, the second coupling unit, and the cavity unit are arranged in parallel with each other in the light propagation direction, and the cavity unit is disposed between the first coupling unit and the second coupling unit. The first and second wavelength filter units are configured. The second input / output unit of the first wavelength filter unit and the first input / output unit of the second wavelength filter unit are connected, the fourth input / output unit of the first wavelength filter unit, and the third input of the second wavelength filter unit. The output unit is connected.

  In the first wavelength filter section, for a specific wavelength, TE (Transverse Electoric) polarization (TE0) of the fundamental mode propagating in the first coupling section and TE polarization (TE1) of the first mode propagating in the cavity section In the second reflection unit, TE1 is converted into TM (Transverse Magnetic) polarization (TM1) and reflected, and in the first reflection unit, TM1 is converted into TE1 and reflected. TE1 propagating through the cavity portion and TE0 propagating through the second coupling portion are coupled. Also, in the second wavelength filter unit, TM polarization (TM0) of the fundamental mode propagating in the first coupling unit and TM1 propagating in the cavity unit are coupled to a specific wavelength, and in the second reflection unit, TM1 is converted into TE1 and reflected, and in the first reflecting portion, TE1 is converted into TM1 and reflected, and TM1 propagating through the cavity portion and TM0 propagating through the second coupling portion are coupled.

  According to another preferred embodiment of the optical wavelength filter described above, in the first wavelength filter unit, TE0 propagating in the first coupling unit and TE1 propagating in the cavity unit are coupled to a specific wavelength, In the second reflection part, TE1 is converted into TM1 and reflected, and in the first reflection part, TM1 is converted into TE1 and reflected, and TM1 propagating through the cavity part and TM0 propagating through the second coupling part. And combine. Also, in the second wavelength filter unit, TM0 propagating in the first coupling unit and TM1 propagating in the cavity unit are coupled to a specific wavelength, and in the second reflecting unit, TM1 is converted to TE1 and reflected. In the first reflection portion, TE1 is converted to TM1 and reflected, and TE1 propagating in the cavity portion is coupled to TE0 propagating in the second coupling portion.

  Further, according to another preferred embodiment of the above-described optical wavelength filter, in the first wavelength filter unit, TE0 propagating through the first coupling unit and TE1 propagating through the cavity unit are coupled to a specific wavelength. In the second reflecting part, TE1 is converted to TE0 and reflected, and in the first reflecting part, TE0 is converted to TE1 and reflected, and TE1 that propagates through the cavity part and propagates through the second coupling part. And TE0 combine. Also, in the second wavelength filter unit, TM0 propagating in the first coupling unit and TM1 propagating in the cavity unit are coupled to a specific wavelength, and in the second reflecting unit, TM1 is converted to TM0 and reflected. In the first reflection portion, TM0 is converted to TM1 and reflected, and TM1 propagating in the cavity portion is coupled to TM0 propagating in the second coupling portion.

  Further, according to another preferred embodiment of the optical wavelength filter described above, in the first wavelength filter unit and the second wavelength filter unit, the TE0 propagating in the first coupling unit for a specific wavelength, and the cavity unit TE1 that propagates is coupled, and in the second reflection part, TE1 is converted into TE0 and reflected, and in the first reflection part, TE0 is converted into TE1 and reflected, and TE1 that propagates through the cavity part, and The TE0 propagating through the second coupling unit is coupled. Further, between the second input / output unit of the first wavelength filter unit, the first input / output unit of the second wavelength filter unit, the fourth input / output unit of the first wavelength filter unit, and the second of the second wavelength filter unit. Between the three input / output units, a polarization conversion unit for switching TE polarization and TM polarization is provided.

  Further, according to another preferred embodiment of the optical wavelength filter of the present invention, a first access waveguide in which a first input / output unit, a first coupling unit, and a second input / output unit are connected in this order; The second access waveguide in which the third input / output unit, the second coupling unit, and the fourth input / output unit are connected in this order, the first reflection unit, the cavity unit, and the second reflection unit are connected in this order The first coupling unit, the second coupling unit, and the cavity unit are arranged in parallel with each other in the light propagation direction, and the cavity unit is disposed between the first coupling unit and the second coupling unit. In the wavelength filter unit, one of the TE polarization and TM polarization propagating through the first coupling unit and the primary mode propagating through the cavity for a specific wavelength are provided. One polarization is combined, and the second reflection unit converts one polarization of the primary mode to the base. In the first reflection part, one polarization of the fundamental mode or the other polarization of the first mode is converted to the one polarization of the mode or the other polarization of the first mode, and the other polarization of the first mode is One polarization of the primary mode that is converted to one polarization, reflected, and propagates in the cavity, and one polarization of the fundamental mode that propagates in the second coupling unit are coupled.

  According to the optical wavelength filter of the present invention, the wavelength filter section having the resonant waveguide structure including the first reflection section, the cavity section, and the second reflection section operates like a ring resonator, thereby transmitting light. A narrow peak can be realized. In addition, polarization independence can be achieved by providing wavelength filters in two stages.

It is a schematic diagram for demonstrating a wavelength filter part. It is a figure for demonstrating the simulation which evaluates the characteristic of an optical waveguide element. It is a schematic diagram (1) for demonstrating an optical wavelength filter. It is a schematic diagram (2) for demonstrating an optical wavelength filter.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shapes, sizes, and arrangement relationships of respective components are merely schematically shown to the extent that the present invention can be understood. In the following, a preferred configuration example of the present invention will be described. However, the material and numerical conditions of each component are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many changes or modifications that can achieve the effects of the present invention can be made without departing from the scope of the configuration of the present invention.

(Configuration of wavelength filter section)
With reference to FIG. 1, the wavelength filter part with which the optical wavelength filter of this invention is provided is demonstrated. FIG. 1 is a schematic view for explaining a wavelength filter unit. FIG. 1A is a schematic plan view showing a wavelength filter unit. FIG. 1B is a schematic end view of the structure shown in FIG. Here, in FIG. 1A, the planar shape of the optical waveguide core is shown, and other components are omitted.

  In the following description, for each component, the direction along the light propagation direction is the length direction. Further, the direction along the thickness of the support substrate is taken as the thickness direction. Moreover, let the direction orthogonal to a length direction and a thickness direction be a width direction.

  The wavelength filter unit includes a support substrate 10, a clad 20, and an optical waveguide core 30.

  The support substrate 10 is composed of a flat plate made of, for example, single crystal Si.

The cladding 20 is provided on the support substrate 10. The cladding 20 covers the upper surface of the support substrate 10 and is formed so as to include the optical waveguide core 30. The cladding 20 is formed of, for example, silicon oxide (SiO ₂ ) as a material.

The optical waveguide core 30 is formed of, for example, silicon (Si) having a refractive index (3.5) higher than the refractive index (1.45) of the SiO ₂ cladding 20. As a result, the optical waveguide core 30 functions as a light transmission path, and the light input to the optical waveguide core 30 propagates in the propagation direction according to the planar shape of the optical waveguide core 30.

  The thickness of the optical waveguide core 30 is preferably 200 to 500 nm, which is a value capable of achieving a single mode condition in the depth direction. For example, at a wavelength of 1550 nm, the thickness of the optical waveguide core 30 can be 300 nm.

  Here, in order to prevent the light propagating through the optical waveguide core 30 from escaping to the support substrate 10, the optical waveguide core 30 is preferably formed at a distance of at least 1 μm or more from the support substrate 10.

  The wavelength filter unit is formed according to the planar shape of the optical waveguide core 30 and includes the first access waveguide 50, the second access waveguide 60, and the resonance waveguide 70.

  The first access waveguide 50 is configured by connecting a first input / output unit 52, a first coupling unit 54, and a second input / output unit 56 in this order. The second access waveguide 60 is configured by connecting a third input / output unit 62, a second coupling unit 64, and a fourth input / output unit 66 in this order. The resonant waveguide 70 is configured by connecting a first reflecting portion 72, a cavity portion 74, and a second reflecting portion 76 in this order.

  The first coupling portion 54, the second coupling portion 64, and the cavity portion 74 are disposed such that the light propagation directions are parallel to one another. A region constituted by the first coupling portion 54, the second coupling portion 64, and the cavity portion 74 is referred to as a coupling region 80. In the coupling region 80, the cavity portion 74 is disposed between the first coupling portion 54 and the second coupling portion 64.

  The first input / output unit 52, the first reflection unit 72, and the third input / output unit 62 are disposed on the same side with respect to the coupling region 80, and the first reflection unit 72 includes the first input / output unit 52 and the first input / output unit 52. 3 is disposed between the input and output unit 62. Similarly, the second input / output unit 56, the second reflection unit 76, and the fourth input / output unit 66 are disposed on the same side with respect to the coupling region 80, and the second reflection unit 76 is the second input / output unit. 56 and the fourth input / output unit 66.

  The first access waveguide 50 and the second access waveguide 60 are designed to achieve a single mode condition for propagating light of TE polarization and TM polarization.

  In the following description, the direction from the first input / output unit 52 to the second input / output unit 56, the direction from the first reflection unit 72 to the second reflection unit 76, and the third input / output unit 62 to the fourth input / output The direction toward the portion 66, that is, the direction from the left to the right in the drawing is referred to as a first direction. In the direction from the second input / output unit 56 to the first input / output unit 52, in the direction from the second reflection unit 76 to the first reflection unit 72, and from the fourth input / output unit 66 to the third input / output unit 62. The direction toward the head, that is, the direction from right to left in the figure, is referred to as a second direction.

  In the coupling region 80, the equivalent refractive index to the TE polarization (TE0) of the fundamental mode propagating in the first coupling portion 54 and the equivalent refractive index to the TE polarization (TE1) of the first mode propagating in the cavity portion 74 are It is designed to match. As a result, in the coupling region 80, TE0 propagating through the first coupling portion 54 and TE1 propagating through the cavity portion 74 are coupled. Therefore, TE0 propagating through the first access waveguide 50 is converted to TE1 in the coupling region 80 and is transferred to the resonant waveguide 70.

  Further, in the coupling region 80, the equivalent refractive index for TE1 propagating in the cavity 74 and the equivalent refractive index for TE0 propagating in the second coupling portion 64 are designed to coincide with each other. As a result, in the coupling region 80, TE1 propagating in the cavity portion 74 and TE0 propagating in the second coupling portion 64 are coupled. Therefore, TE1 propagating through the resonant waveguide 70 is converted to TE0 in the coupling region 80 and moves to the second access waveguide 60.

  A grating is formed in the first reflecting portion 72 and the second reflecting portion 76. The 1st reflection part 72 and the 2nd reflection part 76 are comprised including the base and the protrusion part integrally. The base is formed with a constant width and extending along the light propagation direction, and the protrusions are periodically formed on both side surfaces of the base with the same period Λ. Configure.

  The protruding portion formed on one side surface of the base portion and the protruding portion formed on the other side surface are arranged so as to be shifted by a half cycle (that is, Λ / 2). That is, for a certain position in the longitudinal direction, when the protrusion is disposed on one side, the protrusion is not disposed on the other side, and the protrusion is not disposed on one side; A protrusion is disposed on the side surface. As a result, the gratings are antisymmetric on the left and right.

  In this wavelength filter part, the base part and the protrusion part of the first reflection part 72 and the second reflection part 76 are formed with the same thickness. Further, Si having a thickness smaller than that of the base and the protrusion is formed at the bottom of the grating groove between the protrusions adjacent to each other in the light propagation direction. As a result, the grating is asymmetric at the top and bottom.

  In this way, by making the gratings asymmetric at the top and bottom, and antisymmetrical at the left and right, polarization conversion between TE polarization and TM polarization is efficiently achieved at the time of reflection, and the difference in mode order is even become.

  The phase matching condition by the grating is as follows, assuming that the Bragg wavelength is λ0, the grating period is Λ, the TE-polarized primary mode equivalent refractive index is NTE1, and the TM-polarized primary mode equivalent refractive index is NTM1. It can be represented by 1).

(NTE1 + NTM1) Λ = λ0 (1)
If the design satisfies the above formula (1), either one of TE1 and TM1 can be converted into the other and subjected to Bragg reflection.

  TE0 propagating in the first direction through the first access waveguide 50 is converted to TE1 in the coupling region 80 and transitions to the resonant waveguide 70. TE1 propagates in the resonant waveguide 70 in a first direction. The TE1 propagating in the first direction is converted to TM1 by the second reflecting unit 76, reflected, propagated in the second direction, and travels toward the first reflecting unit 72. In the first reflector 72, TM1 is converted to TE1, reflected, propagated in the first direction, and travels toward the second reflector 76.

  As described above, the first reflective portion 72 and the second reflective portion 76 of the resonant waveguide 70 are reflected while being polarization-converted. At this time, TE1 propagates in the first direction, and TM1 propagates in the second direction.

  The cavity portion 74 is formed with a fixed width that can propagate TM1 and TE1.

  The cavity 74 matches the phase of light having a specific wavelength among the light propagating through the cavity 74. The length of the cavity portion 74 is designed according to the wavelength to be phase matched.

  As a result, the resonant waveguide 70 functions in the same manner as a so-called resonator.

  Of the light resonated in the resonant waveguide 70, a part of TE 1 propagating in the first direction is converted into TE 0 in the coupling region 80 and transferred to the second access waveguide 60. TE0 that has shifted to the second access waveguide 60 propagates through the second access waveguide 60 in the first direction and is output from the fourth input / output unit 66.

  Light other than TE0 having a specific wavelength that resonates in the resonant waveguide 70 propagates through the first access waveguide 50 in the first direction and is output from the second input / output unit 56.

  As described above, in this wavelength filter unit, of the light input to the first input / output unit 52, TE0 of a specific wavelength is output from the fourth input / output unit 66, and the other light is output to the second input / output unit 56.

  Here, an example in which TE0 having a specific wavelength is separated and output has been described, but the present invention is not limited to this.

  For example, in the coupling region 80, the equivalent refractive index with respect to TM0 propagating through the first coupling portion 54 is designed so that the equivalent refractive index with respect to TM1 propagating through the cavity portion 74 matches, and the TM1 propagating through the cavity portion 74 is designed. The equivalent refractive index may be designed to match the equivalent refractive index for TM 0 propagating through the second coupling portion 64.

  In this case, TM0 propagating through the first access waveguide 50 is converted to TM1 in the coupling region 80 and is transferred to the resonant waveguide 70, and TM1 propagating through the resonant waveguide 70 is TM0 in the coupling region 80. To the second access waveguide 60.

  As a result, among the light input to the first input / output unit 52, the light of TM0 of a specific wavelength is output from the fourth input / output unit 66, and the other light is output from the second input / output unit 56 .

  In addition, although an example of the TE1 / TM1 conversion type in which polarization conversion between TE1 and TM1 is performed in the first reflection unit 72 and the second reflection unit 74 has been described, the configuration in which mode order conversion is performed with the same polarization May be. For example, by making the grating symmetrical in the vertical direction and antisymmetric in the horizontal direction, the polarization mode conversion between the TE polarized waves or the TM polarized waves is not performed at the time of reflection, and the mode order difference becomes an odd number.

  The phase matching condition by the grating is that the Bragg wavelength is λ0, the grating period is Λ, the equivalent refractive index for TE1 is NTE1, the equivalent refractive index for TE0 is NTE0, the equivalent refractive index for TM1 is NTE1, and the equivalent refractive index for TM0 is NTM0. It can be represented by the following formula (2) and formula (3).

(NTE1 + NTE0) Λ = λ0 (2)
(NTM1 + NTM0) Λ = λ0 (3)
If the design satisfies the above formula (2), either one of TE1 and TE0 can be converted into the other and subjected to Bragg reflection. That is, the wavelength filter unit can be of TE1 / TE0 conversion type in which polarization conversion between TE1 and TE0 is performed in the first reflection unit and the second reflection unit.

  Similarly, if the design satisfies the above equation (3), either one of TM1 and TM0 can be converted into the other and subjected to Bragg reflection. That is, the wavelength filter unit can be a TM1 / TM0 conversion type that performs polarization conversion between TM1 and TM0 in the first reflection unit and the second reflection unit.

  The electrode 40 is formed at a position covering a part or all of the cavity portion 74 via the clad 20. When the electrode 40 is formed on the cavity portion 74, the refractive index of the cavity portion 74 can be changed by the thermo-optic effect due to the heat generated by the electrode 40. As a result, the wavelength to be phase-matched by the cavity portion 74 can be changed. The electrode 40 may be formed on all of the first reflecting portion 72, the cavity portion 74, and the second reflecting portion 76.

(Production method)
This optical waveguide device can be easily manufactured by using, for example, an SOI (Silicon On Insulator) substrate. Hereinafter, an example of a method of manufacturing an optical waveguide device will be described.

First, an SOI substrate is prepared in which a support substrate layer, an SiO ₂ layer, and an Si layer are sequentially stacked. Next, dry etching is performed in two steps, for example, and the Si layer is patterned to form thick base portions and protrusions, and thin grating groove portions. As a result, it is possible to obtain a structure in which the SiO ₂ layer is stacked on the support substrate layer as the support substrate 10 and the optical waveguide core 30 is formed on the SiO ₂ layer. In the case where the wavelength filter section is, for example, TE1 / TE0 conversion type, it is not necessary to make the grating upper and lower symmetrical, so dry etching can be performed in one step.

Next, SiO ₂ is formed on the SiO ₂ layer so as to cover the optical waveguide core 30 by using, for example, a CVD (Chemical Vapor Deposition) method. As a result, the optical waveguide core 30 is included by the cladding 20, and an optical waveguide device is obtained.

  Although an example of the Si waveguide has been described here, the present invention can also be realized using a compound semiconductor.

(Characteristics evaluation)
A simulation for evaluating the characteristics of the wavelength filter unit, which is performed using FDTD (Finite Differential Time Domain), will be described with reference to FIG.

  FIG. 2A is a diagram illustrating output intensities of the second input / output unit, the third input / output unit, and the fourth input / output unit when TE0 is input to the TE1 / TE0 conversion type wavelength filter unit. . In FIG. 2, the horizontal axis indicates the wavelength (μm), and the vertical axis indicates the output intensity (dB).

  In FIG. 2 (A), curve I shows the output from the second input / output unit, curve II shows the output from the third input / output unit, and curve III shows the output from the fourth input / output unit. Show. Here, using two-dimensional FDTD, the width of the cavity portion is 1000 nm, the width of the access waveguide is 300 nm, the distance between the first and second coupling portions in the coupling region and the cavity portion is 600 nm, the grating period Λ is 341 nm, The length of each input / output part was 50 μm, and the length of the cavity part was 16 times the grating period Λ.

  In particular, paying attention to the output (III) from the fourth input / output unit, there is a peak in the vicinity of 1.59 μm, indicating that light having a specific wavelength is output.

  FIG. 2B is a diagram illustrating the output intensity from the fourth input / output unit when TE0 is input to the TE1 / TM1 conversion type wavelength filter unit. In FIG. 2B, the horizontal axis indicates the wavelength (μm), and the vertical axis indicates the light intensity (dB).

  Here, using a three-dimensional FDTD, the width of the cavity portion is 1000 nm, the width of the access waveguide is 455 nm, the distance between the first and second coupling portions in the coupling region and the cavity portion is 300 nm, the grating period Λ is 342 nm, The length of each input / output part was 50 μm, and the length of the cavity part was 16 times the grating period Λ.

  As shown in FIG. 2B, there is a peak between 1.59 and 1.6 μm, indicating that light having a specific wavelength is output.

(Optical wavelength filter)
Light wavelength filters (hereinafter also referred to as first to fourth light wavelength filters) according to the first to fourth embodiments of the present invention will be described with reference to FIGS. 3 and 4. FIG.3 and FIG.4 is a schematic diagram for demonstrating a 1st-4th light wavelength filter. FIG. 3 (A) shows a first optical wavelength filter, FIG. 3 (B) shows a second optical wavelength filter, FIG. 4 (A) shows a third optical wavelength filter, FIG. 4 (B) These show the 4th light wavelength filter.

  The 1st-4th optical wavelength filter is provided with the above-mentioned wavelength filter part as the 1st wavelength filter part and the 2nd wavelength filter part. The second input / output unit of the first wavelength filter unit and the first input / output unit of the second wavelength filter unit are connected, the fourth input / output unit of the first wavelength filter unit, and the third input of the second wavelength filter unit. The output unit is connected.

  The first to fourth optical wavelength filters separate TE polarized light and TM polarized light having specific wavelengths from the light input to the first input / output unit (input unit) of the first wavelength filter unit. Hereinafter, operations of the first to fourth optical wavelength filters for TE polarization and TM polarization of a specific wavelength will be described with reference to FIGS. 3 and 4. The light other than the specific wavelength propagates through the first access waveguide of the first wavelength filter unit and the first access waveguide of the second wavelength filter unit, and functions as a first output unit. 2 Although output from the input / output unit, illustration and detailed description are omitted.

(First optical wavelength filter)
The first light wavelength filter will be described with reference to FIG.

  The first optical wavelength filter includes the above-described TE1 / TM1 conversion type wavelength filter unit as the first wavelength filter unit 101 and the second wavelength filter unit 201.

  In the first optical wavelength filter, the first input / output unit of the first wavelength filter unit 101 is an input unit, the second input / output unit of the second wavelength filter unit 201 is a first output unit, and a second wavelength filter unit The fourth input / output unit 201 is a second output unit.

  In the first wavelength filter unit 101, TE0 propagating through the first access waveguide 151 and the second access waveguide 161 and TE1 propagating through the resonant waveguide 171 are coupled in the coupling region. In the second wavelength filter unit 201, TM0 propagating through the first access waveguide 251 and the second access waveguide 261 and TM1 propagating through the resonant waveguide 271 are coupled in the coupling region.

  The light input to the first input / output unit of the first wavelength filter unit 101 propagates in the first direction in the first access waveguide 151, and TE0 is converted to TE1 and is transferred to the resonant waveguide 171, Propagate in the direction. Other light propagates through the first access waveguide 151 in the first direction as it is.

  The resonant waveguide 171 resonates while repeating polarization conversion between TE1 and TM1. TE1 propagates in the resonant waveguide 171 in a first direction, and TM1 propagates in the resonant waveguide 171 in a second direction. TE1 propagating through the resonant waveguide 171 in the first direction is converted to TE0, transferred to the second access waveguide 161, and propagated in the first direction.

  The TE0 transferred to the second access waveguide 161 is output from the fourth input / output unit of the first wavelength filter unit 101, and then input to the third input / output unit of the second wavelength filter unit 201, and the second wavelength filter It propagates through the second access waveguide 261 of the part 201 in the first direction. Further, the light propagating in the first direction through the first access waveguide 151 other than TE0 having a specific wavelength is output from the second input / output unit of the first wavelength filter unit 101 and is output from the second wavelength filter unit 201. 1 is input to the input / output unit and propagates in the first direction through the first access waveguide 251 of the second wavelength filter unit 201.

  Of the light propagating in the first access waveguide 251 in the first direction, TM0 is converted to TM1 and transferred to the resonant waveguide 271 and propagates in the resonant waveguide 271 in the first direction. The other light propagates through the first access waveguide 251 as it is in the first direction.

  The resonant waveguide 271 resonates while repeating polarization conversion between TE1 and TM1. TM1 propagates through the resonant waveguide 271 in the first direction, and TE1 propagates through the resonant waveguide 271 in the second direction. TM1 propagating through the resonant waveguide 271 in the first direction is converted to TM0 and transferred to the second access waveguide 261, and propagates through the second access waveguide 261 in the first direction.

  TM0 transferred to the second access waveguide 261 is output from the fourth input / output unit (second output unit) of the second wavelength filter unit 201. Further, light that propagates in the first direction through the first access waveguide 251 other than TM0 is output from the second input / output unit (first output unit) of the second wavelength filter unit 201.

  The TE0 output from the fourth input / output unit of the first wavelength filter unit 101 is input to the third input / output unit of the second wavelength filter unit 201, and as it is, propagates through the second access waveguide 261 in the first direction. , And TM0 are output from the fourth input / output unit (second output unit) of the second wavelength filter unit 201.

  As a result, in the first optical wavelength filter, TE0 and TM0 of a specific wavelength are output from the fourth input / output unit (second output unit) of the second wavelength filter unit 201, and the other light is output as the second wavelength filter Output from the second input / output unit (first output unit) of the unit 201. Thus, the first optical wavelength filter functions as a polarization-independent optical wavelength filter.

(Second optical wavelength filter)
The second light wavelength filter will be described with reference to FIG. 3 (B).

  In the second optical wavelength filter, in the coupling region of the first wavelength filter unit 102, TM1 propagating in the resonant waveguide 172 and TM0 propagating in the second access waveguide 162 are coupled, and the second wavelength filter unit 202 The coupling region is different from the first optical wavelength filter in that TE1 propagating through the resonant waveguide 272 and TE0 propagating through the second access waveguide 262 are designed to be coupled. Therefore, in the second optical wavelength filter, the first input / output unit of the first wavelength filter unit 102 is an input unit, the second input / output unit of the second wavelength filter unit 202 is a first output unit, and The third input / output unit of the wavelength filter unit 102 is a second output unit.

  The other configuration is the same as that of the first light wavelength filter, and thus the overlapping description may be omitted.

  The light input to the first input / output unit (input unit) of the first wavelength filter unit 102 propagates in the first direction through the first access waveguide 152 of the first wavelength filter unit 102, and TE0 is converted to TE1. Then, it shifts to the resonant waveguide 172 and propagates in the first direction. Other light propagates in the first access waveguide 152 in the first direction as it is.

  The resonant waveguide 172 resonates while repeating polarization conversion between TE1 and TM1. TE1 propagates through the resonant waveguide 172 in the first direction, and TM1 propagates through the resonant waveguide 172 in the second direction. TM1 propagating through the resonant waveguide 172 in the second direction is converted into TM0, transferred to the second access waveguide 162, and propagated in the second direction.

  TM0 transferred to the second access waveguide 162 is output from the third input / output unit (second output unit) of the first wavelength filter unit 102. Further, light propagating in the first access waveguide 152 in the first direction other than TE 0 is output from the second input / output unit of the first wavelength filter unit 102, and the first input / output unit of the second wavelength filter unit 202 And propagates in the first direction through the first access waveguide 252 of the second wavelength filter unit 202.

  Of the light propagating in the first access waveguide 252 in the first direction, TM0 is converted to TM1 and transferred to the resonant waveguide 272, and propagates in the resonant waveguide 272 in the first direction. The other light propagates through the first access waveguide 252 as it is in the first direction.

  The resonant waveguide 272 resonates while repeating polarization conversion between TE1 and TM1. TM1 propagates through the resonant waveguide 272 in the first direction, and TE1 propagates through the resonant waveguide 272 in the second direction. TE1 propagating through the resonant waveguide 272 in the second direction is converted to TE0 and transferred to the second access waveguide 262, and propagates through the second access waveguide 262 in the second direction, and the second wavelength filter unit 202 is transmitted. Output from the third input / output unit of

  The TE0 output from the third input / output unit of the second wavelength filter unit 202 is input to the fourth input / output unit of the first wavelength filter unit 102, and as it is, propagates in the second access waveguide 162 in the second direction. The TM0 resonated in the first wavelength filter unit 102 is output from the third input / output unit (second output unit) of the first wavelength filter unit 102.

  Light other than TM0 that propagates in the first direction through the first access waveguide 252 of the second wavelength filter unit 202 is output from the second input / output unit (first output unit) of the second wavelength filter unit 202. The

  As a result, in the second optical wavelength filter, TE0 and TM0 of a specific wavelength are output from the third input / output unit (second output unit) of the first wavelength filter unit 102, and the other light is output as the second wavelength filter Output from the second input / output unit (first output unit) of the unit 202.

  Thus, the second optical wavelength filter functions as a polarization-independent optical wavelength filter. In the second optical wavelength filter, although the optical path length differs between the light resonated by the first wavelength filter unit 102 and the light resonated by the second wavelength filter unit 202, light having a specific wavelength is input. In some cases, it is advantageous in terms of design.

(Third optical wavelength filter)
The third light wavelength filter will be described with reference to FIG. 4 (A).

  The third optical wavelength filter is different from the first optical wavelength filter in that the first wavelength filter unit is a TE1 / TE0 conversion type and the second wavelength filter unit is a TM1 / TM0 conversion type. The other configuration is the same as that of the first light wavelength filter, and thus the overlapping description may be omitted.

  The light input to the first input / output unit (input unit) of the first wavelength filter unit 103 propagates in the first direction in the first access waveguide 153, and TE 0 is converted to TE 1 and is converted to the resonant waveguide 173. Migrate and propagate in the first direction. Other light propagates in the first access waveguide 153 in the first direction as it is.

  The resonant waveguide 173 resonates while repeatedly performing mode order conversion between TE1 and TE0. TE1 propagates through the resonant waveguide 173 in the first direction, and TE0 propagates through the resonant waveguide 173 in the second direction. TE1 propagating through the resonant waveguide 173 in the first direction is converted to TE0, transferred to the second access waveguide 163, and propagated in the first direction.

  The TE0 transferred to the second access waveguide 163 is output from the fourth input / output unit, and then input to the third input / output unit of the second wavelength filter unit 203, so that the second access guide of the second wavelength filter unit 203 is input. The waveguide 263 propagates in a first direction. In addition, light that propagates in the first direction through the first access waveguide 153 other than TE0 is output from the second input / output unit of the first wavelength filter unit 103 and then the first input of the second wavelength filter unit 203. The signal is input to the output unit and propagates in the first direction through the first access waveguide 253 of the second wavelength filter unit 203.

  Of the light propagating in the first access waveguide 253 in the first direction, TM0 is converted to TM1 and transferred to the resonant waveguide 273 and propagates in the resonant waveguide 273 in the first direction. The other light propagates through the first access waveguide 253 in the first direction as it is.

  The resonant waveguide 273 is reflected and resonated while repeating mode order conversion between TM1 and TM0. TM1 propagates through the resonant waveguide 273 in the first direction, and TM0 propagates through the resonant waveguide 273 in the second direction. TM1 propagating through the resonant waveguide 273 in the first direction is converted to TM0 and transferred to the second access waveguide 263, and propagates through the second access waveguide 263 in the first direction.

  TM0 transferred to the second access waveguide 263 is output from the fourth input / output unit (second output unit) of the second wavelength filter unit 203. Light other than TM0 and propagating in the first direction through the first access waveguide 253 is output from the second input / output unit (first output unit) of the second wavelength filter unit 203.

  The TE0 output from the fourth input / output unit of the first wavelength filter unit 103 is input to the third input / output unit of the second wavelength filter unit 203, and as it is, propagates in the second access waveguide 263 in the first direction. , And TM0 are output from the fourth input / output unit (second output unit) of the second wavelength filter unit 203.

  As a result, in the third optical wavelength filter, TE0 and TM0 of a specific wavelength are output from the fourth input / output unit (second output unit) of the second wavelength filter unit 203, and the other light is output as the second wavelength filter Output from the second input / output unit (first output unit) of the unit 203. Thus, the third optical wavelength filter functions as a polarization-independent optical wavelength filter.

  In the first optical wavelength filter, in order to perform polarization conversion between TE polarization and TM polarization in the reflection section provided in the resonant waveguides 171 and 271, it is necessary to make the grating vertically asymmetric, The number of processes such as dry etching in stages increases. On the other hand, since the third optical wavelength filter does not perform polarization conversion in the reflection part provided in the resonant waveguides 173 and 273, it is not necessary to make the grating asymmetrical in the vertical direction. Therefore, although it is difficult to design for mode order conversion of TM polarization, a reduction in manufacturing cost is expected, such as eliminating the need for two-stage dry etching.

(4th optical wavelength filter)
The fourth light wavelength filter will be described with reference to FIG. 4 (B).

  The fourth optical wavelength filter includes the above-mentioned TE1 / TE0 conversion type wavelength filter unit as the second wavelength filter unit 204, and the second input / output unit of the first wavelength filter unit 104 and the second wavelength filter unit 204 A polarization that switches TE polarization and TM polarization between the first input / output unit and between the fourth input / output unit of the first wavelength filter unit 104 and the third input / output unit of the second wavelength filter unit 204 The point provided with the wave converter 300 is different from the third optical wavelength filter. The other configuration is the same as that of the third light wavelength filter, and thus the overlapping description may be omitted.

  The light input to the first input / output unit (input unit) of the first wavelength filter unit 104 propagates in the first direction in the first access waveguide 154, and TE 0 is converted to TE 1 to be the resonant waveguide 174. Migrate and propagate in the first direction. The other light propagates through the first access waveguide 154 as it is in the first direction.

  The resonant waveguide 174 resonates between TE1 and TE0 while repeating mode order conversion. TE1 propagates through the resonant waveguide 174 in the first direction, and TE0 propagates through the resonant waveguide 174 in the second direction. TE1 propagating through the resonant waveguide 174 in the first direction is converted to TE0, transferred to the second access waveguide 164, and propagated in the first direction.

  TE0 that has shifted to the second access waveguide 164 is output from the fourth input / output unit, and then converted to TM0 by the polarization conversion unit 300. TM0 is input to the third input / output unit of the second wavelength filter unit 204 and propagates in the first direction through the second access waveguide 264 of the second wavelength filter unit 204. Light other than TE0 and propagating in the first direction through the first access waveguide 164 is output from the second input / output unit of the first wavelength filter unit 104 and then converted by the polarization conversion unit 300. That is, TM0 output from the second input / output unit of the first wavelength filter unit 104 is converted to TE0. The TE0 is input to the first input / output unit of the second wavelength filter unit 204, and propagates in the first direction through the first access waveguide 254 of the second wavelength filter unit 204.

  Of the light propagating in the first access waveguide 254 in the first direction, TE0 is converted to TE1 and transferred to the resonant waveguide 274, and propagates in the resonant waveguide 274 in the first direction. Other light propagates in the first direction as it is through the first access waveguide 254.

  The resonant waveguide 274 resonates while repeating mode order conversion between TE1 and TE0. TE1 propagates through the resonant waveguide 274 in the first direction, and TE0 propagates through the resonant waveguide 274 in the second direction. TE1 propagating through the resonant waveguide 274 in the first direction is converted to TE0 and transferred to the second access waveguide 264, and propagates through the second access waveguide 264 in the first direction.

  The TE0 transferred to the second access waveguide 264 is output from the fourth input / output unit (second output unit) of the second wavelength filter unit 204. Light other than TE0 and propagating in the first direction through the first access waveguide 254 is output from the second input / output unit (first output unit) of the second wavelength filter unit 204.

  The TM0 input to the third input / output unit of the second wavelength filter unit 204 propagates the second access waveguide 264 in the first direction as it is and, together with TE0, the fourth input / output unit of the second wavelength filter unit 204 (Output from the second output unit).

  As a result, in the fourth optical wavelength filter, TE0 and TM0 of the specific wavelength are output from the fourth input / output unit (second output unit) of the second wavelength filter unit 204, and the other light is output as the second wavelength filter Output from the second input / output unit (first output unit) of the unit 204. Thus, the fourth optical wavelength filter functions as a polarization-independent optical wavelength filter.

  Since the fourth optical wavelength filter does not perform polarization conversion, it is not necessary for the grating to be asymmetrical in the vertical direction. However, in the polarization rotation part, two-step etching is required. Since the grating is only TE polarized light with high diffraction efficiency, the element can be miniaturized.

(Other optical wavelength filters)
The first to fourth optical wavelength filters described above are configured to include two wavelength filter sections, and realize an optical wavelength filter having no polarization. However, when polarization dependence is not required, the optical wavelength filter may be configured with a single wavelength filter unit that functions as a resonator.

10 support substrate 20 clad 30 optical waveguide core 40 electrode 50, 151, 152, 153, 154, 251, 252, 253, 254 first access waveguide 60, 161, 162, 163, 164, 261, 262, 263, 264 Second access waveguide 70, 171, 172, 173, 174, 271, 272, 273, 274 Resonant waveguide 80 Coupling region 101, 102, 103, 104 First wavelength filter unit 201, 202, 203, 204 Second wavelength Filter unit 300 Polarization conversion unit

Claims (6)

Each,
A first access waveguide in which a first input / output unit, a first coupling unit, and a second input / output unit are connected in this order;
A second access waveguide in which the third input / output unit, the second coupling unit, and the fourth input / output unit are connected in this order;
The first reflecting portion, the cavity portion, and the second reflecting portion are provided with a resonant waveguide connected in this order,
The first reflecting portion and the second reflecting portion are asymmetrical in the upper and lower directions, and are composed of left and right antisymmetric gratings,
The first coupling unit, the second coupling unit, and the cavity unit are arranged such that light propagation directions are parallel to each other,
The cavity part includes first and second wavelength filter parts disposed between the first coupling part and the second coupling part,
A second input / output unit of the first wavelength filter unit and a first input / output unit of the second wavelength filter unit are connected;
A fourth input / output unit of the first wavelength filter unit and a third input / output unit of the second wavelength filter unit are connected;
In the first wavelength filter unit,
The gratings constituting the first and second reflectors have a grating period of Λ, a Bragg wavelength of λ0, a first-order mode TE (Transverse Electric) polarization equivalent refractive index of NTE1, and a first-order mode TM. It is configured such that the equivalent refractive index of (Transverse Maganetic) polarization is NTM1, and the design satisfies (NTE1 + NTM1) Λ = λ0,
For a specific wavelength
Wherein the T E polarization of the fundamental mode propagating a first coupling portion, said cavity portion and the TE-polarized first-order mode propagating binds to,
In the second reflective portion, it reflects and converts the TE polarized first-order mode to the T M polarization of the first-order mode,
In the first reflection unit, the first mode TM polarized wave is converted to the first mode TE polarized wave and reflected, and
And TE-polarized first-order mode propagating through the cavity, TE polarization and is coupled to the fundamental mode propagating through the second coupling part,
In the second wavelength filter unit,
The gratings constituting the first reflecting portion and the second reflecting portion have a grating period of Λ, a Bragg wavelength of λ0, an equivalent refractive index of TE polarized light in the first mode, NTE1, and an equivalent of TM polarized light in the first mode. It is configured with a design that satisfies (NTE1 + NTM1) Λ = λ0, where NTM1 is the refractive index,
For the particular wavelength
Wherein the TM polarization of the fundamental mode propagating a first coupling portion, said cavity portion and the TM polarized waves of the first-order mode propagating binds to,
In the second reflecting section, the first mode TM polarized wave is converted to the first mode TE polarized wave and reflected,
In the first reflection unit, the first mode TE polarized wave is converted to the first mode TM polarized wave and reflected, and
And TM polarization of the first-order mode propagating through the cavity, TM polarization and is coupled to the fundamental mode propagating through the second coupling part,
The top and bottom asymmetry and the left and right antisymmetric gratings are
A base which is formed to extend along the light propagation direction with a constant width;
Protrusions formed of periodic ridges on both sides of the base and
With
The protrusion formed on one side surface of the base and the protrusion formed on the other side surface are arranged so as to be offset from each other by a period Λ / 2,
The base and the projection are formed with the same thickness,
The optical wavelength filter according to claim 1, wherein a bottom portion between the protrusions adjacent in the propagation direction is made of the same material as the base and the protrusion and has a smaller thickness than the base and the protrusion . Each,
A first access waveguide in which a first input / output unit, a first coupling unit, and a second input / output unit are connected in this order;
A second access waveguide in which the third input / output unit, the second coupling unit, and the fourth input / output unit are connected in this order;
The first reflecting portion, the cavity portion, and the second reflecting portion are provided with a resonant waveguide connected in this order,
The first reflecting portion and the second reflecting portion are asymmetrical in the upper and lower directions, and are composed of left and right antisymmetric gratings,
The first coupling unit, the second coupling unit, and the cavity unit are arranged such that light propagation directions are parallel to each other,
The cavity part includes first and second wavelength filter parts disposed between the first coupling part and the second coupling part,
A second input / output unit of the first wavelength filter unit and a first input / output unit of the second wavelength filter unit are connected;
A fourth input / output unit of the first wavelength filter unit and a third input / output unit of the second wavelength filter unit are connected;
In the first wavelength filter unit,
The gratings constituting the first and second reflectors have a grating period of Λ, a Bragg wavelength of λ0, a first-order mode TE (Transverse Electric) polarization equivalent refractive index of NTE1, and a first-order mode TM. It is configured such that the equivalent refractive index of (Transverse Maganetic) polarization is NTM1, and the design satisfies (NTE1 + NTM1) Λ = λ0,
For a specific wavelength
Wherein the TE polarization of the fundamental mode propagating a first coupling portion, said cavity portion and the TE-polarized first-order mode propagating binds to,
The second reflection unit converts TE polarization of the first mode into TM polarization of the first mode and reflects it.
In the first reflection unit, the first mode TM polarized wave is converted to the first mode TE polarized wave and reflected, and
And TM polarization of the first-order mode propagating through the cavity, TM polarization and is coupled to the fundamental mode propagating through the second coupling part,
In the second wavelength filter unit,
The gratings constituting the first reflecting portion and the second reflecting portion have a grating period of Λ, a Bragg wavelength of λ0, an equivalent refractive index of TE polarized light in the first mode, NTE1, and an equivalent of TM polarized light in the first mode. The refractive index is NTM1, and it is configured with a design that satisfies (NTE1 + NTM1) Λ = λ0,
For the particular wavelength
Wherein the TM polarization of the fundamental mode propagating a first coupling portion, said cavity portion and the TM polarized waves of the first-order mode propagating binds to,
The second reflection unit converts the TM polarization in the first mode into a TE polarization in the first mode and reflects it.
In the first reflection unit, the first mode TE polarized wave is converted to the first mode TM polarized wave and reflected, and
And TE-polarized first-order mode propagating through the cavity, TE polarization and is coupled to the fundamental mode propagating through the second coupling part,
The top and bottom asymmetry and the left and right antisymmetric gratings are
A base which is formed to extend along the light propagation direction with a constant width;
Protrusions formed of periodic ridges on both sides of the base and
With
The protrusion formed on one side surface of the base and the protrusion formed on the other side surface are arranged so as to be offset from each other by a period Λ / 2,
The base and the projection are formed with the same thickness,
The optical wavelength filter according to claim 1, wherein a bottom portion between the protrusions adjacent in the propagation direction is made of the same material as the base and the protrusion and has a smaller thickness than the base and the protrusion . Each,
A first access waveguide in which a first input / output unit, a first coupling unit, and a second input / output unit are connected in this order;
A second access waveguide in which a third input / output unit, a second coupling unit, and a fourth input / output unit are connected in this order;
The first reflecting portion, the cavity portion, and the second reflecting portion are provided with a resonant waveguide connected in this order,
The first reflective portion and the second reflective portion are vertically symmetrical, and are configured of left and right antisymmetric gratings.
The first coupling portion, the second coupling portion, and the cavity portion are disposed such that the light propagation directions are parallel to one another.
The cavity part includes first and second wavelength filter parts disposed between the first coupling part and the second coupling part,
A second input / output unit of the first wavelength filter unit and a first input / output unit of the second wavelength filter unit are connected;
A fourth input / output unit of the first wavelength filter unit and a third input / output unit of the second wavelength filter unit are connected;
In the first wavelength filter unit,
The gratings constituting the first reflection unit and the second reflection unit have a grating period of Λ, a Bragg wavelength of λ0, an equivalent refractive index of TE (Transverse Electric) polarization of the first mode is NTE1, and a TE polarization of the basic mode. With the equivalent refractive index of the wave as NTE0, it is configured with a design that satisfies (NTE1 + NTE0) Λ = λ0,
For a specific wavelength
Wherein the TE polarization of the fundamental mode propagating a first coupling portion, said cavity portion and the TE-polarized first-order mode propagating binds to,
In the second reflection unit, the first mode TE polarized wave is converted to the fundamental mode TE polarized wave and reflected,
The first reflection unit converts TE polarization of the fundamental mode into TE polarization of the first mode and reflects it;
And TE-polarized first-order mode propagating through the cavity, TE polarization and is coupled to the fundamental mode propagating through the second coupling part,
In the second wavelength filter unit,
The gratings constituting the first reflecting portion and the second reflecting portion have a grating period of Λ, a Bragg wavelength of λ0, a TM (Transverse Magnetic) polarization equivalent refractive index of NTM1, and a fundamental mode of TM polarization. The equivalent refractive index of the wave is NTM0, and it is configured with a design that satisfies (NTM1 + NTM0) Λ = λ0,
For the particular wavelength
Wherein the TM polarization of the fundamental mode propagating a first coupling portion, said cavity portion and the TM polarized waves of the first-order mode propagating binds to,
In the second reflection unit, the first mode TM polarized wave is converted to the fundamental mode TM polarized wave and reflected,
In the first reflection unit, the TM polarization of the fundamental mode is converted to the TM polarization of the first mode and reflected;
And TM polarization of the first-order mode propagating through the cavity, TM polarization and is coupled to the fundamental mode propagating through the second coupling part,
The top and bottom symmetrical and left and right antisymmetric gratings are
A base which is formed to extend along the light propagation direction with a constant width;
Protrusions formed of periodic ridges on both sides of the base and
With
The protrusion formed on one side surface of the base and the protrusion formed on the other side surface are arranged so as to be offset from each other by a period Λ / 2,
The light wavelength filter according to claim 1, wherein the base and the projection are formed to have the same thickness . Each,
A first access waveguide in which a first input / output unit, a first coupling unit, and a second input / output unit are connected in this order;
A second access waveguide in which the third input / output unit, the second coupling unit, and the fourth input / output unit are connected in this order;
The first reflecting portion, the cavity portion, and the second reflecting portion are provided with a resonant waveguide connected in this order,
The first reflecting portion and the second reflecting portion are symmetric in the vertical direction, and are composed of a left-right antisymmetric grating,
The first coupling unit, the second coupling unit, and the cavity unit are arranged such that light propagation directions are parallel to each other,
The cavity part includes first and second wavelength filter parts disposed between the first coupling part and the second coupling part,
A second input / output unit of the first wavelength filter unit and a first input / output unit of the second wavelength filter unit are connected;
A fourth input / output unit of the first wavelength filter unit and a third input / output unit of the second wavelength filter unit are connected;
In the first wavelength filter unit and the second wavelength filter unit,
The gratings constituting the first reflection unit and the second reflection unit have a grating period of Λ, a Bragg wavelength of λ0, an equivalent refractive index of TE (Transverse Electric) polarization of the first mode is NTE1, and a TE polarization of the basic mode. With the equivalent refractive index of the wave as NTE0, it is configured with a design that satisfies (NTE1 + NTE0) Λ = λ0,
For a specific wavelength
Wherein the TE polarization of the fundamental mode propagating a first coupling portion, said cavity portion and the TE-polarized first-order mode propagating binds to,
In the second reflection unit, the first mode TE polarized wave is converted to the fundamental mode TE polarized wave and reflected,
The first reflection unit converts TE polarization of the fundamental mode into TE polarization of the first mode and reflects it;
And TE-polarized first-order mode propagating through the cavity, TE polarization and is coupled to the fundamental mode propagating through the second coupling part,
Between the second input / output unit of the first wavelength filter unit, the first input / output unit of the second wavelength filter unit, the fourth input / output unit of the first wavelength filter unit, and the second wavelength filter unit between the third output portion of, comprising a polarization conversion unit to replace the TE polarization and TM polarization,
The top and bottom symmetrical and left and right antisymmetric gratings are
A base which is formed to extend along the light propagation direction with a constant width;
Protrusions formed of periodic ridges on both sides of the base and
With
The protrusion formed on one side surface of the base and the protrusion formed on the other side surface are arranged so as to be offset from each other by a period Λ / 2,
The light wavelength filter according to claim 1, wherein the base and the projection are formed to have the same thickness . A first access waveguide in which a first input / output unit, a first coupling unit, and a second input / output unit are connected in this order;
A second access waveguide in which the third input / output unit, the second coupling unit, and the fourth input / output unit are connected in this order;
The first reflecting portion, the cavity portion, and the second reflecting portion are provided with a resonant waveguide connected in this order,
The first coupling portion, the second coupling portion, and the cavity portion are disposed such that the light propagation directions are parallel to one another.
The cavity portion includes a wavelength filter portion disposed between the first coupling portion and the second coupling portion;
(A)
The first reflecting portion and the second reflecting portion are asymmetrical in the upper and lower directions, and are composed of left and right antisymmetric gratings,
The gratings constituting the first and second reflectors have a grating period of Λ, a Bragg wavelength of λ0, a first-order mode TE (Transverse Electric) polarization equivalent refractive index of NTE1, and a first-order mode TM. It is configured such that the equivalent refractive index of (Transverse Maganetic) polarization is NTM1, and the design satisfies (NTE1 + NTM1) Λ = λ0,
In the wavelength filter unit,
For a specific wavelength
The fundamental mode propagating a first coupling portion, and one of the polarization of the TE polarization and the TM polarization, whereas the polarization bound of the first-order mode propagating through the cavity,
In the second reflection part, one polarization of the primary mode is converted to the other polarization of the primary mode and reflected,
In the first reflecting part, the other polarized wave of the first mode and reflects converted into one of the polarization of the first-order mode, and,
Wherein the one polarization of the first-order mode propagating through the cavity portion, the one and the polarization bound of the fundamental mode propagating through the second coupling part, or,
(B)
The first reflective portion and the second reflective portion are vertically symmetrical, and are configured of left and right antisymmetric gratings.
The gratings constituting the first reflection unit and the second reflection unit have a grating period of Λ, a Bragg wavelength of λ0, an equivalent refractive index of TE polarization in the first mode, NTE1, and an equivalent refraction of TE polarization in the fundamental mode. Design that satisfies (NTE1 + NTE0) Λ = λ0 or (NTM1 + NTM0) Λ = λ0, where NTE is the index of refraction, NTM1 is the equivalent refractive index of TM polarization in the first mode, and NTM0 is the equivalent refractive index of TM polarization in the fundamental mode. Configured and
In the wavelength filter unit,
For a specific wavelength
One of the TE polarization and the TM polarization of the fundamental mode propagating in the first coupling portion is coupled to one polarization of the first mode propagating in the cavity portion;
In the second reflection unit, one polarization of the primary mode is converted to one polarization of the fundamental mode and reflected,
In the first reflection unit, one polarization of the fundamental mode is converted to one polarization of the primary mode and reflected, and
The one polarization of the first mode propagating in the cavity and the one polarization of the fundamental mode propagating in the second coupling unit are combined,
The top and bottom asymmetry and the left and right antisymmetric gratings are
A base which is formed to extend along the light propagation direction with a constant width;
Protrusions formed of periodic ridges on both sides of the base and
With
The protrusion formed on one side surface of the base and the protrusion formed on the other side surface are arranged so as to be offset from each other by a period Λ / 2,
The base and the projection are formed with the same thickness,
The bottom portion between the protrusions adjacent in the propagation direction is formed of the same material as the base and the protrusion and has a smaller thickness than the base and the protrusion,
The top and bottom symmetrical and left and right antisymmetric gratings are
A base which is formed to extend along the light propagation direction with a constant width;
Protrusions formed of periodic ridges on both sides of the base and
With
The protrusion formed on one side surface of the base and the protrusion formed on the other side surface are arranged so as to be offset from each other by a period Λ / 2,
The light wavelength filter according to claim 1, wherein the base and the projection are formed to have the same thickness . The optical wavelength filter is
An optical waveguide core;
And a clad including the optical waveguide core,
The electrode for changing the equivalent refractive index of the said resonant waveguide is provided on the said clad of the position which coats the said resonant waveguide, The claim as described in any one of the Claims 1-5 characterized by the above-mentioned. Optical wavelength filter.

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