JP7023317B2 - Optical wavelength filter and wavelength separation optical circuit - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention includes, for example, an optical wavelength filter that performs combined and demultiplexing of light that can be used to transmit light of a plurality of different wavelengths with a single optical fiber, and a wavelength separation optical circuit having the optical wavelength filter. Regarding.

In recent years, a passive optical network (PON: Passive Optical Network) has become the mainstream as a subscriber optical access system. In a PON, one station-side device (OLT: Optical Line Thermal) 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 units. 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 the downlink communication from OLT to ONU and the uplink communication from ONU to OLT do not interfere with each other. I'm wrong.

Therefore, a combined demultiplexing element is required to demultiplex and combine optical signals having different wavelengths used for downlink communication and uplink communication. In general, OLTs and ONUs space an optical wavelength filter, a photodiode (PD: Photodiode), and a laser diode (LD: Laser Diode) as a junction / demultiplexing element in order to realize a function of transmitting and receiving optical signals having different wavelengths. It is composed by combining.

In order to make spatial coupling, alignment work for aligning the optical axis between the optical wavelength filter, PD, and LD is required. On the other hand, in order to eliminate the work for aligning the optical axes, an optical wavelength filter configured by using a waveguide has been developed. Further, in forming this optical wavelength filter, a silicon (Si) waveguide using a silicon-based material as a waveguide material has attracted attention because of its excellent miniaturization and mass productivity (see, for example, Patent Document 1).

In the Si waveguide, the optical waveguide core, which is substantially a light transmission path, is formed of Si as a material. Then, a clad made of, for example, silica, which has a lower refractive index than Si, covers the periphery of the optical waveguide core. With such a configuration, the difference in refractive index 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, it is possible to realize a small curved waveguide in which the bending radius is reduced to, for example, about 1 μm. Therefore, it is possible to create an optical circuit having the same size as an electronic circuit, which is advantageous for miniaturization of the entire optical device.

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

By the way, in a PON using a wavelength division multiplexing (WDM) technology, a different reception wavelength is assigned to each ONU. The OLT generates a downlink signal to each ONU at a transmission wavelength corresponding to the reception wavelength of the destination ONU, and multiplexes and transmits these. Each ONU selectively receives an optical signal having a reception wavelength assigned to itself from the downlink light signals multiplexed at a plurality of wavelengths. In the ONU, an optical wavelength filter is used to selectively receive the downlink light signal of each reception wavelength. Then, a technique of constructing the optical wavelength filter by the above-mentioned Si waveguide has been realized.

Examples of the optical wavelength filter using a Si waveguide include those using a Mach-Zehnder interferometer and those using an arrayed waveguide grating (AWG). Further, as an optical wavelength filter using a Si waveguide, a ring resonator type, a grating type or a directional coupler type, a variable wavelength filter having an advantage that the output wavelength can be changed and the element structure is simple and easy to use. (See, for example, Patent Document 2). However, all of these optical wavelength filters operate only with a specific polarization.

Further, there is a structure in which a polarization separation element and a polarization rotation element are provided in front of the optical wavelength filter in order to support both TE (Transverse Electric) polarization and TM (Transverse Magnetic) polarization (for example, Non-Patent Document 1). Or see 2).

U.S. Pat. No. 4,860,294 Japanese Patent Application Laid-Open No. 2003-215515

Optics Express vol. 20, No. 26, p. B493-B500, December 10, 2012 Optics Express vol. 23, No. 10, p. 12840-12894, May 18, 2015

Since the above-mentioned AWG and variable wavelength filter have a characteristic of repeatedly outputting light in a plurality of different wavelength bands, they have a plurality of free spectral ranges (FSR). Therefore, in order to extract light of a specific wavelength using these, it is necessary to separately prepare a wavelength filter that cuts out the FSR of a single wavelength band.

In addition, these AWGs and tunable wavelength filters have polarization dependence. Therefore, in order to use it independently of polarization, it is necessary to align the polarizations by using, for example, the above-mentioned polarization separation element and polarization rotation element.

The present invention has been made in view of the problems of the above-mentioned prior art. An object of the present invention is an optical wavelength filter that realizes polarization-independent wavelength selection with as few elements as possible without separately preparing an element for separating polarization, and a wavelength separation optical circuit having this optical wavelength filter. Is to provide.

In order to achieve the above-mentioned object, the optical wavelength filter of the present invention is an optical waveguide core which is embedded in a support substrate, a clad formed on the support substrate, and provided in parallel with the upper surface of the support substrate. It is configured with and. The optical waveguide core includes a first waveguide core, a central waveguide core, and a second waveguide core arranged in parallel in this order at predetermined intervals.

The central waveguide core and the first waveguide core are the first waveguide core by converting TM-polarized light in a specific wavelength band included in the input light input to the central waveguide core into TE-polarized light. It constitutes a polarization conversion unit that outputs from the output end of. The central waveguide core and the second waveguide core separate the TE-polarized light of a specific wavelength band contained in the input light input to the central waveguide core from the output end of the second waveguide core. It constitutes the polarization separation part to be output.

According to a preferred embodiment of the optical wavelength filter of the present invention, in the polarization conversion unit, the width of the first waveguide core is smaller than the width of the central waveguide core, and is opposite to the first waveguide core on the left and right. An optical waveguide composed of a first waveguide core and a cladding around the first waveguide core is provided so as to be vertically asymmetrical.

Further, according to a further preferred embodiment of the optical wavelength filter of the present invention, an electrode for a heater is provided on a cladding in a region where a first waveguide core and a second waveguide core are provided.

Further, the wavelength separation optical circuit of the present invention is configured to include a wavelength filter unit composed of the above-mentioned optical wavelength filter and a wavelength selection unit. The wavelength selection unit extracts and outputs a plurality of specific wavelengths different from each other from the TE polarization light transmitted from the wavelength filter unit.

Further, according to a preferred embodiment of the wavelength separation optical circuit of the present invention, a light receiving unit including a plurality of light receiving elements is further provided. The wavelength selection unit sends the extracted TE-polarized light of a plurality of specific wavelengths different from each other to different light-receiving elements for each wavelength, and each light-receiving element receives the TE-polarized light transmitted from the wavelength selection unit.

According to the optical wavelength filter and the wavelength separation optical circuit of the present invention, it is possible to realize polarization-independent wavelength selection with as few elements as possible without separately preparing an element for separating polarization.

It is a schematic diagram for demonstrating an optical wavelength filter. It is a figure which shows the simulation result which evaluates the characteristic of an optical wavelength filter. It is a schematic diagram for demonstrating the wavelength separation optical circuit.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the shape, size, and arrangement of each component are only schematically shown to the extent that the present invention can be understood. Further, although a suitable configuration example of the present invention will be described below, the material and numerical conditions of each component are merely suitable examples. Therefore, the present invention is not limited to the following embodiments, and many modifications or modifications can be made to achieve the effects of the present invention without departing from the scope of the configuration of the present invention.

Further, in the following description and each figure, an example in which the width and period of the grating are constant is shown, which is a schematic representation of the structure of the grating. When actually designing and manufacturing an optical wavelength filter, the width and period of the grating do not necessarily have to be constant.

(Light wavelength filter)
A light wavelength filter according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram for explaining an optical wavelength filter. FIG. 1A is a schematic plan view showing an optical wavelength filter. Further, FIG. 1 (B) is a schematic end view of the optical wavelength filter shown in FIG. 1 (A) cut out by an I-I line. 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 defined as the length direction. Further, the direction orthogonal to the upper surface of the support substrate is defined as the thickness direction. Further, the direction orthogonal to the length direction and the thickness direction is defined as the width direction.

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

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

The clad 20 is formed by covering the support substrate 10 with the upper surface 10a of the support substrate 10. The clad 20 is formed of, for example, silicon oxide (SiO ₂ ) as a material.

The optical waveguide core 30 is embedded in the clad 20 in parallel with the upper surface 10a of the support substrate 10. The optical waveguide core 30 is formed of, for example, silicon (Si), which has a refractive index (3.5) higher than the refractive index (1.45) of the cladding 20 of SiO ₂ . 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 400 nm, which is a value that can achieve the single mode condition in the depth direction. For example, when used in the wavelength band of 1550 nm, the thickness of the optical waveguide core 30 can be set to 300 nm. Here, in order to prevent the light propagating through the optical waveguide core 30 from escaping to the support substrate 10, it is preferable that the optical waveguide core 30 is formed at a distance of at least 1 μm or more from the support substrate 10.

This optical wavelength filter can be easily manufactured by using, for example, an SOI (Silicon On Insulator) substrate. Hereinafter, an example of a method for manufacturing the optical wavelength filter shown in FIG. 1 will be described.

First, an SOI substrate is prepared in which a support substrate layer, a SiO ₂ layer, and a Si layer are sequentially laminated. Next, for example, dry etching is performed to pattern the Si layer. As a result, it is possible to obtain a structure in which the SiO ₂ layer is laminated on the support substrate layer as the support substrate 10 and the optical waveguide core 30 is further formed on the SiO ₂ layer. As will be described later, the optical waveguide core 30 has a thick portion and a small portion. Therefore, dry etching is performed in two steps, for example.

Next, for example, using a CVD (Chemical Vapor Deposition) method, SiO ₂ is formed by coating the optical waveguide core 30 on the SiO ₂ layer. As a result, a clad 20 is formed by the SiO ₂ layer of the SOI substrate and the SiO 2 formed on the layer ₂ , and an optical waveguide element used as an optical wavelength filter is obtained.

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

The optical wavelength filter includes a first waveguide core 50, a central waveguide core 40, and a second waveguide core 60 arranged in parallel in this order at predetermined intervals as a portion of the optical waveguide core 30. In this example, the first waveguide core 50, the central waveguide core 40, and the second waveguide core 60 are arranged in parallel and close to each other.

The central waveguide core 40 and the first waveguide core 50 form a polarization conversion unit 32. In the polarization conversion unit 32, the central waveguide core 40 and the first waveguide core 50 have different widths from each other. Here, the width of the central waveguide core 40 is set wider than the width of the first waveguide core 50. The TM polarized light in symmetric mode is excited by a wide waveguide, here the central waveguide core 40. On the other hand, the TE polarization light in the antisymmetric mode is excited by a narrow waveguide, here, the first waveguide core 50. The larger the difference in width between the central waveguide core 40 and the first waveguide core 50, the greater the degree of concentration of light on the excited waveguide. As a result, the light propagating through the central waveguide core 40 excites an extra eigenmode in the first waveguide core 50, and it is suppressed that unnecessary power transfer occurs due to the directional coupling action.

A grating is formed on the first waveguide core 50. The first waveguide core 50 is configured to integrally include a base 52 and protrusions 54a and 54b. The base 52 is formed to have a constant width and extend along the light propagation direction, and the protrusions 54a and 54b are periodically formed on both side surfaces 52a and 52b of the base 52 with a constant period Λ1. It is formed in plurality and constitutes a so-called grating.

The protrusion 54a formed on one side surface (52a in this example) of the base 52 and the protrusion 54b formed on the other side surface (52b in this example) have a half cycle (that is, Λ1 / 2). They are staggered. That is, when the protrusion 54a is arranged on one side surface 52a at a certain position in the longitudinal direction, the protrusion 54b is not arranged on the other side surface 52b, and the protrusion 54a is arranged on one side surface 52a. When not, the protrusion 54b is arranged on the other side surface 52b. As a result, the grating is antisymmetric on the left and right. Further, the base portion 52 and the projecting portions 54a and 54b are formed to have the same thickness.

At the bottom of the grating groove between the protrusions 54a or 54b adjacent to each other in the light propagation direction, a base 52 and Si having a thickness smaller than those of the protrusions 54a and 54b are formed as the slab waveguide 56. As a result, the optical waveguide having a grating, which is composed of the first waveguide core 50 and the clad 20 around it, is asymmetrical in the vertical direction.

Note that FIG. 1A shows an example in which the slab waveguide 56 is formed only between the protrusions 54a or 54b, but the present invention is not limited to this. The slab waveguide 56 may be configured to exist in a place other than between the protrusions 54a or 54b.

A vertically asymmetric structure of the grating is required for diffraction between TE-polarized light and TM-polarized light. Further, by configuring the grating to be left-right antisymmetric, diffraction of the TE polarized light in the basic mode and the TM polarized light in the basic mode occurs. By selecting the combination of the TE polarized light in the basic mode and the TM polarized light in the basic mode, it is possible to suppress the occurrence of diffraction to other modes.

Here, a configuration in which the grating is made vertically asymmetric by providing the slab waveguide 56 has been described, but the present invention is not limited to this. An oblique side wall structure may be formed in which the side surface of the first waveguide core 50 is formed so as to be inclined with respect to the upper surface 10a of the support substrate 10. Further, the upper portion of the first waveguide core 50 on which the grating is formed may be made air, and the optical waveguide having the grating may be asymmetrical in the vertical direction.

Of the light input to the input end 40a of the central waveguide core 40, the TM-polarized light in a specific wavelength band is converted into TE-polarized light and used as the first TE-polarized light, which is the output end 50a of the first waveguide core 50. Is output from.

The central waveguide core 40 and the second waveguide core 60 form a polarization separation unit 34. In the polarization conversion unit 34, the central waveguide core 40 and the second waveguide core 60 have different widths from each other. Here, the width of the central waveguide core 40 is set wider than the width of the second waveguide core 60. The larger the difference in width between the central waveguide core 40 and the second waveguide core 60, the greater the degree of concentration of light on the excited waveguide. As a result, the light propagating in the central waveguide core 40 excites an extra eigenmode in the second waveguide core 60, and it is suppressed that unnecessary power transfer occurs due to the directional coupling action.

A grating is formed on the second waveguide core 60. The second waveguide core 60 is configured to integrally include a base 62 and protrusions 64a and 64b. The base 62 is formed to extend along the light propagation direction with a constant width, and the protrusions 64a and 64b are periodically formed on both side surfaces 62a and 62b of the base 62 with a constant period Λ2. It is formed in plurality and constitutes a so-called grating.

The protrusion 64a formed on one side surface (62a in this example) of the base 62 and the protrusion 64b formed on the other side surface (62b in this example) are arranged so as to be aligned in the longitudinal direction. Has been done. That is, when the protrusion 64a is arranged on one side surface 62a at a certain position in the longitudinal direction, the protrusion 64b is also arranged on the other side surface 62b, and the protrusion 64a is arranged on one side surface 62a. When not, the protrusion 64b is not arranged on the other side surface 62b. As a result, the grating is symmetrical on the left and right. Further, the base portion 62 and the protruding portions 64a and 64b are formed to have the same thickness.

Further, a slab waveguide is not formed at the bottom of the grating groove between the protrusions 64a or 64b adjacent to each other in the light propagation direction, and the second waveguide core 60 and the clad 20 around the slab waveguide are formed. The optical waveguide having a grating is symmetrical in the vertical direction.

Of the light input to the input end 40a of the central waveguide core 40, the TE polarization light seeps into the second waveguide core 60, and the TE polarization light in a specific wavelength band is diffracted by the grating to obtain the second light. It is output as 2TE polarized light from the output end 60a of the second waveguide core 60.

According to the optical wavelength filter of the present invention, among the light input from the input end of the central waveguide core, the TM polarized light having a specific wavelength is converted into TE polarized light by the polarization conversion unit 32, and the second light is converted into TE polarized light. It is output as 1TE polarization light from the output end of the first waveguide core 50, TE polarization light of a specific wavelength band is separated by the polarization separation unit 34, and is output of the second waveguide core 60 as the second TE polarization light. Output from the edge. As described above, the optical wavelength filter of the present invention has a function of extracting light in a specific wavelength band with uniform polarization.

Electrodes (not shown) may be formed on the upper clad 20 of the first waveguide core 50 and the second waveguide core 60. By passing an electric current through the electrodes, Joule heat is generated, and the refractive index of the grating can be changed by the thermo-optical effect. As a result, it is possible to change the wavelength that satisfies the phase matching condition in the grating of the first waveguide core 50 and the second waveguide core 60. The location of the electrode may be any position as long as the refractive index of the grating is changed by heat generation, and the electrode can be placed at any suitable location depending on the structure of the optical waveguide core or the like.

In this example, the input waveguide 82 is connected to the input end 40a of the central waveguide core 40 via the tapered waveguide 72, and the output end 50a of the first waveguide core 50 is connected to the output end 50a of the first waveguide core 50 via the tapered waveguide 74. The first output waveguide 84 is connected, and the second output waveguide 86 is connected to the output end 60a of the second waveguide core 60 via the tapered waveguide 76. Suppresses loss at the connection between the central waveguide core 40, the first waveguide core 50, and the second waveguide core 60, and the input waveguide 82, the first output waveguide 84, and the second output waveguide 86. Therefore, it is preferable to provide these tapered waveguides 72, 74 and 76. Further, the first output waveguide 84 and the second output waveguide 86 have an output end 50a of the first waveguide core 50 and an output end 6 of the second waveguide core 60, respectively.
As the distance from 0a increases, it is preferable to gradually increase the distance from the input waveguide 82. With this configuration, it is possible to prevent the first output waveguide 84 and the second output waveguide 86 from being excited by an extra eigenmode.

(Characteristic evaluation)
With reference to FIG. 2, a simulation for evaluating the characteristics of the optical wavelength filter performed using a three-dimensional FDTD (Finite Difference Time Domain) will be described.

In FIGS. 2A and 2B, the wavelength (μm) is shown on the horizontal axis, and the output intensity (a.u.) is shown on the vertical axis. Further, FIG. 2A is a result when TE polarized light is input as input light, and FIG. 2B is a result when TM polarized light is input as input light.

In FIGS. 2A and 2B, the transmitted light transmitted through the central waveguide core 40 and output from the end opposite to the input end 40a is the curve I, and the output end of the first waveguide core 50. The TM diffracted light output from 50a is shown by curve II, and the TE diffracted light output from the output end 60a of the second waveguide core 60 is shown by curve III. Here, the TM diffracted light indicates light that is diffracted by polarization-converting the TM-polarized light among the input lights into TE-polarized light. Further, the TE diffracted light indicates the light obtained by separating and diffracting the TE polarized light among the input lights.

Here, the width of the central waveguide core 40 is 540 nm, and the width of the first waveguide core 50 and the second waveguide core 60 is 340 nm. Further, the gap between the central waveguide core 40 and the first waveguide core 50 and the gap between the central waveguide core 40 and the second waveguide core 60 are set to 300 nm. The width of the first waveguide core 50 is given by the distance between the average position of the side surface on the central waveguide core 50 side and the average position of the side surface on the side opposite to the central waveguide core 40. The width of the second waveguide core 60 is the same. The gap with the central waveguide core 40 is also given from these average positions. The thickness of the central waveguide core 40, the base 52 and the convex portions 54a and 54b of the first waveguide core 50, and the second waveguide core 60 is 220 nm, and the thickness of the slab waveguide 56 is 150 nm.

The grating period Λ1 of the first waveguide core 50 is 399.9 nm, the grating period Λ2 of the second waveguide core 60 is 373.7 nm, and the grating digging, that is, the length of the protrusion in the width direction is 150 nm. It is supposed to be. Further, the length of the central waveguide core, the first waveguide core 50, and the second waveguide core 60 was set to 77 μm.

When the TE polarized light is input, as shown in FIG. 2A, a clear wavelength selection peak is observed in the vicinity of the wavelength of 1.6 μm for the TE diffracted light (III). Further, when the TM polarized light is input, as shown in FIG. 2 (B), a clear wavelength selection peak is observed in the vicinity of 1.6 μm for the TM diffracted light (II). Further, the diffraction efficiencies of the TE diffracted light of FIG. 2 (A) and the TM diffracted light of FIG. 2 (B) are almost the same.

As described above, the simulation results show that the optical wavelength filter of the present invention has a function of extracting light in a specific wavelength band with uniform polarization.

(Wavelength separation optical circuit)
The wavelength separation optical circuit of the present invention will be described with reference to FIG. FIG. 3 is a schematic configuration diagram of a wavelength separation optical circuit.

The wavelength separation optical circuit includes a wavelength filter unit 100, a wavelength selection unit 200, and a light receiving unit 300. The wavelength filter unit 100 includes an optical wavelength filter described with reference to FIG. The wavelength selection unit 200 is composed of, for example, an AWG. The light receiving unit 300 includes N (N is an integer of 2 or more) light receiving elements 310. Here, a case where N = 4, that is, an example in which the light receiving unit 300 includes four light receiving elements 310 will be described.

The first output waveguide 84 and the second output waveguide 86 of the wavelength filter unit 100 are connected to the wavelength selection unit 200.

Further, the wavelength selection unit 200 is connected to each of the light receiving elements 310 by a connection waveguide 332 constituting the first connection waveguide group 330 and a connection waveguide 342 constituting the second connection waveguide group 340. There is. Here, the space between the wavelength selection unit 200 and the first light receiving element 310-1 is included in the first connection waveguide 332-1 included in the first connection waveguide group 330 and the second connection waveguide group 340. It is connected by a connecting waveguide 342-1. Further, the space between the wavelength selection unit 200 and the second light receiving element 310-2 is included in the second connection waveguide 332-2 included in the first connection waveguide group 330 and the second connection waveguide group 340. It is connected by a second connection waveguide 342-2. Further, the space between the wavelength selection unit 200 and the third light receiving element 310-3 is included in the third connection waveguide 332-3 included in the first connection waveguide group 330 and the second connection waveguide group 340. It is connected by a third connection waveguide 342-3. Further, the space between the wavelength selection unit 200 and the fourth light receiving element 310-4 is included in the fourth connection waveguide 332-4 included in the first connection waveguide group 330 and the second connection waveguide group 340. It is connected by a fourth connection waveguide 342-4. As described above, between the wavelength selection unit 200 and the k-th (k is an integer of 1 or more and N or less) light receiving element 310-k, the k-connection waveguide 332-k included in the first connection waveguide group 330 and the k-connection waveguide 332-k and , Is connected by the k-th connection waveguide 342-k included in the second connection waveguide group 340.

The first output waveguide 84 and the connection waveguide 342 constituting the second connection waveguide group 340 are connected to one of the two slab waveguides included in the AWG, and the second output is connected to the other of the two slab waveguides. The waveguide 86 and the connection waveguide 332 constituting the first connection waveguide group 330 are connected.

The wavelength selection unit 200 extracts and outputs a plurality of specific wavelengths different from each other from the TE polarization in the basic mode of the specific wavelength band transmitted through the first output waveguide 84 of the wavelength filter unit 100. The TE polarization in the basic mode of each output wavelength passes through any of the first to fourth connection waveguides 332-1 to 4 included in the first connection waveguide group 330 according to the wavelength, and the corresponding th-order. It is sent to the first to fourth light receiving elements 310-1 to 4.

Further, the wavelength selection unit 200 extracts and outputs a plurality of specific wavelengths different from each other from the TE polarization light in the basic mode of the specific wavelength band transmitted through the second output waveguide 86 of the wavelength filter unit 100. The output TE-polarized light in the basic mode of each wavelength passes through any of the first to fourth connecting waveguides 342-1 to 4 included in the second connecting waveguide group 340 according to the wavelength, and corresponds to the corresponding first. It is sent to the 1st to 4th light receiving elements 310-1 to 4 and receives light.

As described above, in the wavelength separation optical circuit, by inputting the light of a single wavelength band extracted by the wavelength filter unit 100 to the wavelength selection unit 200, a plurality of different types of light included in the FSR of a single wavelength band are included. It is possible to extract light of a wavelength.

Here, an electrode may be formed on the cladding 20 on the upper side of the wavelength filter unit 100 and the wavelength selection unit 200. By passing a current through the electrodes, Joule heat is generated, and the selected wavelength can be changed by the thermo-optical effect. The electrode can be arranged at any suitable location depending on the structure of the optical waveguide core and the like.

10 Support substrate 20 Clad 30 Optical waveguide core 32 Polarization conversion part 34 Polarization separation part 40 Central waveguide core 50 First waveguide core 52, 62 Base 54a, 54b, 64a, 64b Protruding part 56 Slab waveguide 60 Second Waveguide core 72, 74, 76 Tapered waveguide 82 Input waveguide 84 First output waveguide 86 Second output waveguide 100 Waveguide filter section 200 Waveguide section 300 Receiver section 310 Light receiving element 330 First connection waveguide group 332, 342 Connection waveguide 340 Second connection waveguide group

Claims (10)

Support board and
The clad formed on the support substrate and
It comprises an optical waveguide core embedded in the cladding and provided parallel to the top surface of the support substrate.
The optical waveguide core includes a first waveguide core, a central waveguide core, and a second waveguide core arranged in parallel in this order at predetermined intervals.
The central waveguide core and the first waveguide core refer to TM (Transverse Magnetic) polarized light in a specific wavelength band contained in the input light input to the central waveguide core by TE (Transverse Electrical). A polarization conversion unit that converts to polarized light and outputs it from the output end of the first waveguide core is configured.
The central waveguide core and the second waveguide core separate the TE-polarized light of a specific wavelength band included in the input light input to the central waveguide core, and the second waveguide core. Consists of a waveguide that outputs from the output end of
In the polarization conversion unit
The width of the first waveguide core is smaller than the width of the central waveguide core.
The first waveguide core is provided with a left-right antisymmetric grating.
The optical waveguide composed of the first waveguide core and the cladding around the first waveguide core is configured to be vertically asymmetrical.
In the polarization separation part
The width of the second waveguide core is smaller than the width of the central waveguide core.
An optical wavelength filter characterized in that the second waveguide core is provided with a left-right symmetrical grating. In the polarization conversion unit
The optical wavelength filter according to claim 1 , further comprising a slab waveguide formed integrally with the first waveguide core, which is smaller in thickness than the first waveguide core. In the polarization conversion unit
The optical wavelength filter according to claim 1 , wherein the side surface of the first waveguide core is formed so as to be inclined with respect to the upper surface of the support substrate. The invention according to any one of claims 1 to 3 , wherein an electrode for a heater is provided on the clad in the region where the first waveguide core and the second waveguide core are provided. The light wavelength filter described. In the polarization conversion unit
The optical wavelength filter according to claim 1 , wherein the upper portion of the clad is air. A wavelength filter unit including the optical wavelength filter according to any one of claims 1 to 4 .
Equipped with a wavelength selection unit
The wavelength selection unit is a wavelength separation optical circuit characterized by extracting and outputting a plurality of specific wavelengths different from each other from the TE polarization light transmitted from the wavelength filter unit. Further equipped with a light receiving unit including a plurality of light receiving elements,
The wavelength selection unit sends the extracted TE polarized light of a plurality of specific wavelengths different from each other to the light receiving element different for each wavelength.
The wavelength separation optical circuit according to claim 6 , wherein each light receiving element receives TE polarized light transmitted from the wavelength selection unit. The wavelength separation optical circuit according to claim 6 or 7 , wherein an electrode for a heater is provided on the clad in the region where the wavelength filter unit and the wavelength selection unit are provided. A wavelength filter unit including the optical wavelength filter according to claim 5 .
Equipped with a wavelength selection unit
The wavelength selection unit is a wavelength separation optical circuit characterized by extracting and outputting a plurality of specific wavelengths different from each other from the TE polarization light transmitted from the wavelength filter unit. Further equipped with a light receiving unit including a plurality of light receiving elements,
The wavelength selection unit sends the extracted TE polarized light of a plurality of specific wavelengths different from each other to the light receiving element different for each wavelength.
The wavelength separation optical circuit according to claim 9 , wherein each light receiving element receives TE polarized light transmitted from the wavelength selection unit.

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