JP2018054935A - Optical waveguide element and wavelength filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide element capable of utilizing a photonic crystal to convert inputted light into a different mode and reflect it.SOLUTION: An optical waveguide element comprises an optical waveguide core 30 including a mode conversion part, and a clad 20 enveloping the optical waveguide core. The mode conversion part comprises a photonic crystal formed therein, which includes: a first hole group 61 including a plurality of holes 51 cyclically formed to be arrayed in a position overlapping with a first virtual line segment; and a second hole group 62 including a plurality of holes 52 formed in the same cycle as the first hole group to be arrayed in a position overlapping with the second virtual line segment. The photonic crystal satisfies 2π/Λ=2π(n+n)/λ, where the cycle of the first hole group and the second hole group with respect to wavelength λ is Λ, an equivalent refractive index with respect to p(p is an integer of p≥0)-th mode is n, and an equivalent refractive index with respect to q(q is an integer of q≥0 and q≠p)-th mode is n.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical waveguide element that reflects light of a specific wavelength by a photonic crystal and a wavelength filter including the same.

  In recent years, Si waveguides using Si (silicon) as a waveguide material have attracted attention in developing optical devices advantageous for miniaturization and mass productivity.

  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, realization of photoelectric fusion (silicon photonics) in which electronic functional circuits and optical functional circuits are collectively formed on a chip is expected.

  By the way, in a passive optical network (PON: Passive Optical Network) using a wavelength division multiplexing (WDM) system, a different reception wavelength is assigned to each subscriber side device (ONU: Optical Network Unit). . A station side device (OLT: Optical Line Terminal) generates a downstream optical signal to each ONU at a transmission wavelength corresponding to a reception wavelength of a destination, and multiplexes and transmits them. Each ONU selectively receives an optical signal having a reception wavelength allocated 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. Further, as wavelength filters using Si waveguides, ring resonators (for example, Patent Documents 1 to 3), grating type (for example, Patent Document 4), or directional coupler type (for example, Patent Document 5) wavelength filters. There is. These wavelength filters have the advantage that the output wavelength can be made variable by providing electrodes and applying a voltage. Further, like a grating, there is a structure called a photonic crystal as an element that reflects a specific wavelength in the reverse direction by diffracting light.

JP 2003-215515 A JP 2013-093627 A JP 2006-278770 A JP 2006-330104 A JP 2002-353556 A

  Since the photonic crystal has a high diffraction efficiency, when used as a wavelength filter, it is expected that wavelength separation can be performed with high efficiency. However, the conventional photonic crystal has a structure that performs diffraction in the reverse direction between the fundamental modes and has a limited function. A photonic crystal that converts input light into a different mode and reflects it has not been known.

  Accordingly, an object of the present invention is to provide an optical waveguide element using a photonic crystal, which can convert input light into a different mode and reflect it, and a wavelength filter using the optical waveguide element. is there.

In order to achieve the above-described object, an optical waveguide element according to the present invention includes a first imaginary line segment, a second imaginary line segment parallel to the first imaginary line segment, and the first imaginary line segment and the second imaginary line segment. An optical waveguide core provided at a position overlapping the imaginary line segment and a clad including the optical waveguide core are provided. The optical waveguide core includes a mode conversion unit. In the mode conversion unit, the first hole group including a plurality of holes periodically formed in a position overlapping with the first imaginary line segment, and the position overlapping with the second imaginary line segment, A photonic crystal including a second hole group including a plurality of holes formed at the same period as the first hole group is formed. For a specific wavelength λ, the photonic crystal has a period of the first hole group and the second hole group as Λ, and an equivalent refractive index with respect to the p (p is an integer of p ≧ 0) order mode as n _p , q ( q is an integer of q ≧ 0 and q ≠ p) where n _q is an equivalent refractive index for the next mode, and 2π / Λ = 2π (n _p + n _q ) / λ is satisfied.

  A wavelength filter according to the present invention includes the above-described optical waveguide element and an output waveguide core including a coupling portion. The optical waveguide core further includes a multimode waveguide section that is connected in series with the mode conversion section and propagates light of the p-order mode and the q-order mode. The cladding includes an optical waveguide core and an output waveguide core. A coupling region is set in which the multimode waveguide section and the coupling section are spaced apart from each other and arranged side by side. In the coupling region, the q-order mode light propagating through the multimode waveguide section and the r (r is an integer of r ≧ 0) order mode light propagating through the coupling section are coupled.

  In the optical waveguide device of the present invention, the mode conversion unit forms a photonic crystal including two rows of hole groups (the first hole group and the second hole group), so that the fundamental mode of a specific wavelength can be obtained. Light can be converted to the primary mode and reflected.

  Moreover, in the wavelength filter of this invention, a specific wavelength and another wavelength can be isolate | separated by using the optical waveguide element mentioned above, and it can take out by switching a path | route. And by using a photonic crystal, light of a specific wavelength can be reflected with high diffraction efficiency. Therefore, wavelength separation and path switching can be performed with high efficiency.

(A) is a schematic plan view showing the optical waveguide device of the present invention, and (B) is a schematic end view showing the optical waveguide device of the present invention. It is a schematic plan view which shows the modification of a photonic crystal. It is a figure which shows the result of the simulation regarding the characteristic evaluation of the optical waveguide element of this invention. It is a schematic plan view which shows the wavelength filter of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shape, size, and arrangement relationship of each component 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.

(Optical waveguide element)
With reference to FIG. 1, the optical waveguide device of the present invention will be described. FIG. 1A is a schematic plan view showing an optical waveguide element. FIG. 1B is a schematic end view of the optical waveguide element shown in FIG. In FIG. 1A, only the optical waveguide core described later is shown, and the clad and the support substrate are omitted.

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

  The optical waveguide device 100 includes a support substrate 10, a clad 20, an optical waveguide core 30, and an electrode 40.

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

The clad 20 is formed on the support substrate 10 so as to cover the upper surface 10 a of the support substrate 10 and to include the optical waveguide core 30. The clad 20 is formed using, for example, SiO ₂ as a material.

  The optical waveguide core 30 is made of, for example, Si having a refractive index higher than that of the clad 20. As a result, the optical waveguide core 30 functions as a substantial light transmission path, and the input light propagates in the propagation direction according to the planar shape of the optical waveguide core 30. The optical waveguide core 30 is preferably formed at least 1 μm or more away from the support substrate 10 in order to prevent the propagating light from escaping to the support substrate 10.

  Here, the optical waveguide core 30 preferably has a thickness of, for example, 150 to 500 nm in order to achieve a single mode condition in the thickness direction.

  The optical waveguide core 30 is along the first virtual line segment L1 connecting the first point P1 and the second point P2, and along the second virtual line segment L2 connecting the third point P3 and the fourth point P4, and these It is provided at a position overlapping the first virtual line segment L1 and the second virtual line segment L2. The second virtual line segment L2 is parallel to the first virtual line segment L1.

  Furthermore, the optical waveguide core 30 includes a mode conversion unit 31. A photonic crystal is formed in the mode converter 31. The photonic crystal is configured by forming a first hole group 61 and a second hole group 62 in the mode converter 31.

  The first hole group 61 includes a plurality of holes 51 that are periodically formed so as to be arranged at positions overlapping the first virtual line segment L1. The second hole group 62 includes a plurality of holes 52 that are arranged at positions overlapping the second imaginary line segment L <b> 2 and formed at the same period as the first hole group 61. The holes 51 included in the first hole group 61 and the holes 52 included in the second hole group 62 are formed at positions shifted from each other by a half cycle.

  The holes 51 and 52 are formed so as to penetrate the mode conversion part 31 in the thickness direction. Further, here, the holes 51 and 52 have a circular cross-sectional shape orthogonal to the thickness direction.

  The photonic crystal reflects TE-polarized light having a specific wavelength that is input from the fundamental mode into the primary mode. The photonic crystal transmits light of other wavelengths while remaining in the fundamental mode.

The phase matching condition in the photonic crystal is as follows: the formation period of the holes 51 and 52 is Λ, the equivalent refractive index for the TE polarization of the fundamental mode is n ₀ , and the equivalent refractive index n ₁ for the TE polarization of the first mode is It is represented by Formula (1).

2π / Λ = 2π (n ₀ + n ₁ ) / λ (1)
In the photonic crystal, a TE wave having a wavelength λ that satisfies the above equation (1), that is, a TE polarized wave having a Bragg wavelength is Bragg reflected. Accordingly, the width of the mode conversion unit 31, the period of the holes 51 and 52, and the diameter of the holes 51 and 52 are designed so that the above equation (1) is established for the desired wavelength λ to be reflected. .

  Here, as a modification of the photonic crystal, the diameter of the holes 51 and 52 can be changed every period. A modification of the photonic crystal will be described with reference to FIG. FIG. 2 is a schematic plan view for explaining a modification of the photonic crystal. In FIG. 2, the support substrate and the clad are omitted.

  In the configuration example shown in FIG. 2, the diameter increases for each period with respect to the diameters of the holes 51 and 52 in the first period. The diameters of the holes 51 and 52 are the largest in the holes 51 and 52 near the center in the length direction of the mode conversion unit 31. Then, the diameters of the holes 51 and 52 decrease after the holes 51 and 52 which are the maximum.

  Thus, by changing the diameters of the holes 51 and 52 for each period, light scattering in the photonic crystal can be suppressed. Note that the amount of change in the diameter of the holes 51 and 52 is designed according to the wavelength λ to be reflected and the diffraction efficiency.

  The electrode 40 is formed at a position covering the mode converter 31 via the clad 20. Joule heat is generated by passing an electric current through the electrode 40, and the refractive index of the mode converter 31 is changed by the thermo-optic effect caused by the heat generation. As a result, the wavelength reflected by the mode converter 31 can be changed.

  As described above, in the optical waveguide device 100, the mode converter 31 is formed with a photonic crystal including two rows of hole groups (the first hole group 61 and the second hole group 62). The fundamental mode TE polarized light of a specific wavelength can be converted into a primary mode and reflected.

  Therefore, by using the optical waveguide element 100, it is possible to configure a wavelength filter that extracts light having a specific wavelength that passes through the photonic crystal.

  Further, in the optical waveguide device 100, heat can be applied to the mode conversion unit 31 using the electrode 40. Therefore, the wavelength of light reflected and transmitted by the photonic crystal can be changed. Therefore, by using the optical waveguide element 100, a wavelength filter with a variable output wavelength can be configured.

  In this embodiment, the configuration in which the optical waveguide device 100 outputs light of a specific wavelength with respect to the TE polarized wave has been described. However, the optical waveguide device 100 may be configured to output light having a specific wavelength with respect to the TM polarization. In that case, the photonic crystal of the mode conversion unit 31 is designed so that the above equation (1) is established for the TM polarized wave according to the wavelength λ to be reflected. Thereby, the TM polarization of the fundamental mode having a specific wavelength can be converted into the primary mode and reflected by the photonic crystal.

Further, in this embodiment, the configuration in which the light having a specific wavelength is converted from the fundamental mode to the primary mode and reflected in the photonic crystal of the mode conversion unit 31 has been described. However, the photonic crystal of the mode converter 31 converts light of a specific wavelength in the p-order mode (p is an integer of p ≧ 0) into a q-order mode (q is an integer of q ≧ 0 and q ≠ p). And it can also be set as the structure reflected. In that case, the phase matching condition in the photonic crystal of the mode conversion unit 31 is that the period of formation of the holes 51 and 52 is Λ, the equivalent refractive index for p-order mode light is n _p , and the equivalent for q-order mode light. The refractive index n _q is expressed by the following formula (2).

2π / Λ = 2π (n _p + n _q ) / λ (2)
In the photonic crystal, light having a wavelength λ that satisfies the above equation (2), that is, light having a Bragg wavelength is Bragg reflected. The photonic crystal is designed so that the above equation (2) is established with respect to the wavelength λ to be reflected with respect to the TE polarized wave or the TM polarized wave.

  When one of the p-order mode and the q-order mode is a fundamental mode or an even-order mode in which the amplitude distribution is symmetric, and the other is an odd-order mode in which the amplitude distribution is antisymmetric, 51 and holes 52 are formed at positions that are shifted from each other by a half cycle.

  Further, when both the p-order mode and the q-order mode are the basic mode or the even-order mode, or both are the odd-order mode, the formation positions of the holes 51 and the holes 52 are shifted. Match without any. That is, the hole 51 and the hole 52 are formed at positions where they are symmetrical with each other.

(Characteristic evaluation)
The inventor performed the simulation which evaluates the characteristic of the optical waveguide element 100 using FDTD (Finite Differential Time Domain).

  In this simulation, with respect to the optical waveguide device 100, the fundamental mode TE polarized light is input to the optical waveguide core 30 and transmitted through the mode conversion unit 31, and the mode conversion unit. The intensity of the output light (reflected light) of the first mode TE polarized wave reflected while being mode-converted at 31 was analyzed.

  In this simulation, the optical waveguide device 100 was designed as follows. That is, the thickness of the optical waveguide core 30 was 0.2 μm. The width of the mode converter 31 is 1 μm. The formation period of the holes 51 and 52 is 0.394 μm, and the length of the mode conversion section 31 (that is, the length of the photonic crystal) is 21 periods for the holes 51 and 52. The corresponding length. Further, the photonic crystal has a configuration in which the diameters of the holes 51 and the holes 52 change every period (see FIG. 2), and the maximum diameter of the holes 51 and the holes 52 is 0.2 μm. And both the 1st hole group 61 and the 2nd hole group 62 were designed so that the diameter of the hole 51 and the hole 52 for 5 periods from both ends might become small for every period toward both ends. The diameters of the holes 51 and 52 at both ends of the first hole group 61 and the second hole group 62 were 0.1 μm.

  The result of the simulation is shown in FIG. In FIG. 3, the vertical axis represents the intensity of the output light in dB scale, and the horizontal axis represents the wavelength in μm units. In FIG. 3, a curve 91 indicates the intensity of the transmitted light from the mode conversion unit, and a curve 92 indicates the intensity of the reflected light from the mode conversion unit.

  As shown in FIG. 3, in the wavelength band near 1.5 to 1.75 μm, it can be confirmed that the fundamental mode is reflected while being converted into the primary mode at an extinction ratio of 30 dB or more. Therefore, it was confirmed that extremely high diffraction efficiency can be obtained with the length of the holes 51 and the holes 52 (about 8 μm in terms of the length of the photonic crystal) for 21 cycles.

(Wavelength filter)
A wavelength filter using the above-described optical waveguide device 100 (see FIG. 1) will be described with reference to FIG. FIG. 4 is a schematic plan view showing the wavelength filter. In FIG. 4, only the optical waveguide core and the output waveguide core described later are shown, and the cladding and the support substrate are omitted. In addition, components common to the optical waveguide device 100 are denoted by the same reference numerals, and description thereof is omitted.

  The wavelength filter 200 is configured by adding an output waveguide core 70 to the optical waveguide element 100 described above. The optical waveguide core 30 includes an input unit 32, an input side taper unit 33, a multimode waveguide unit 34, an output side taper unit 35, and a first output unit 36 in addition to the mode conversion unit 31 described above. Yes. The input part 32, the input side taper part 33, the multimode waveguide part 34, the mode conversion part 31, the output side taper part 35, and the first output part 36 are connected in series in this order.

  The input unit 32 is set to a width that achieves a single mode condition for propagating light of TE polarization.

  The input-side taper portion 33 continuously increases in width from one end 33 a connected to the input portion 32 to the other end 33 b connected to the multimode waveguide portion 34. The width of the one end 33 a of the input side taper portion 33 is set equal to the width of the input portion 32. Therefore, the input side taper portion 33 is set so as to achieve the single mode condition for the propagation light of the TE polarized wave at the one end 33a.

  The multimode waveguide unit 34 propagates TE polarized waves in the fundamental mode and the primary mode.

  In the mode converter 31, a photonic crystal that satisfies the above equation (1) is formed with respect to a TE polarized wave having a specific wavelength. The photonic crystal reflects TE-polarized light having a specific wavelength that is input from the fundamental mode into the primary mode. The photonic crystal transmits light of other wavelengths while remaining in the fundamental mode.

  The output-side taper portion 35 continuously decreases in width from one end 35 a connected to the mode conversion portion 31 to the other end 35 b connected to the first output portion 36. The width of the other end 35b of the output side taper portion 35 is set so as to achieve a single mode condition for the propagation light of TE polarization.

  The first output unit 36 is set to a width that achieves the single mode condition for the TE-polarized propagation light.

  The output waveguide core 70 is made of, for example, Si having a refractive index higher than that of the clad 20, similarly to the optical waveguide core 30. The output waveguide core 70 is preferably formed at least 1 μm or more away from the support substrate 10 in order to prevent the propagating light from escaping to the support substrate 10.

  Here, the thickness of the output waveguide core 70 is preferably set to, for example, 150 to 500 nm in order to achieve a single mode condition with respect to the TE polarized wave of propagating light.

  The output waveguide core 70 includes a coupling portion 71 and a second output portion 72.

  The coupling portion 71 is disposed apart from and side by side with the multimode waveguide portion 34 of the optical waveguide core 30. The multimode waveguide section 34 of the optical waveguide core 30 and the coupling section 71 of the output waveguide core 70 are set as coupling areas 80 that are spaced apart from each other and arranged side by side. The second output unit 72 is connected to the coupling unit 71 on the opposite side of the mode conversion unit 31 with the coupling region 80 interposed therebetween.

  In the coupling region 80, the multimode waveguide section 34 and the coupling section 71 are arranged so that their central axes are parallel to each other.

  Further, the coupling portion 71 has a tapered shape in which the width continuously increases from the one end 71 a to the other end 71 b connected to the second output portion 72. The widths of the one end 71a and the other end 71b of the coupling portion 71 are set in correspondence with the equivalent refractive index capable of propagating the fundamental mode TE polarized wave. The coupling unit 71 includes an equivalent refractive index for the TE polarized wave of the first mode propagating through the multimode waveguide unit 34 and the TE of the fundamental mode propagating through the coupling unit 71 between the one end 71a and the other end 71b. It includes a width in which the equivalent refractive index to the polarization matches.

  As a result, in the coupling region 80, the primary mode TE polarized wave propagating through the multimode waveguide unit 34 and the fundamental mode TE polarized wave propagating through the coupling unit 71 can be coupled.

  The second output unit 72 is set to a width that achieves a single mode condition for TE-polarized propagation light.

  In the wavelength filter 200, the fundamental mode optical signal is input to the input unit 32 of the optical waveguide core 30, and sent to the mode conversion unit 31 through the input side taper unit 33 and the multimode waveguide unit 34. The TE polarization of the fundamental mode having a specific wavelength propagating through the mode converter 31 is converted to the primary mode by the photonic crystal, reflected, and sent again to the multimode waveguide unit 34. Other light is output from the first output unit 36 through the output side taper portion 35 in the basic mode. The primary mode TE polarized wave reflected by the photonic crystal and propagating through the multimode waveguide section 34 is converted into the fundamental mode in the coupling region 80 and is transferred to the coupling section 71 of the output waveguide core 70. The basic mode TE polarized wave transferred to the coupling unit 71 is output from the second output unit 72.

  As described above, the wavelength filter 200 can be used as a wavelength filter that separates a specific wavelength from other wavelengths by using the optical waveguide element 100 described above, and switches and extracts the path. Then, by using a photonic crystal in the mode conversion unit 31, light having a specific wavelength can be reflected with high diffraction efficiency. Therefore, wavelength separation and path switching can be performed with high efficiency.

  In this embodiment, the configuration in which the wavelength filter 200 switches the path of a specific wavelength with respect to the TE polarized wave has been described. However, the wavelength filter 200 can also be configured to output light of a specific wavelength with respect to the TM polarization. In that case, the photonic crystal of the mode conversion unit 31 is designed so that the above equation (1) is established for the TM polarized wave according to the wavelength λ to be reflected. Thereby, the TM polarization of the fundamental mode having a specific wavelength can be converted into the primary mode and reflected by the photonic crystal. In that case, the wavelength filter 200 can be used as a wavelength filter that performs path switching for the TM polarization.

  Further, in this embodiment, the configuration in which the light having a specific wavelength is converted from the fundamental mode to the primary mode and reflected in the photonic crystal of the mode conversion unit 31 has been described. However, by forming the photonic crystal so as to satisfy the above formula (2), the photonic crystal may be configured to reflect light of a specific wavelength in the p-order mode by converting it to the q-order mode. it can.

  Furthermore, the light coupled between the multimode waveguide section 34 and the coupling section 71 in the coupling region 80 is not limited to the fundamental mode and the primary mode. The widths of the one end 71a and the other end 71b of the coupling portion 71 are set in correspondence with the equivalent refractive index capable of propagating light in the r (r is an integer of r ≧ 0) order mode. The width up to the other end 71b includes a width where the equivalent refractive index for the q-order mode light propagating through the multimode waveguide section 34 and the equivalent refractive index for the r-order mode light propagating through the coupling section 71 coincide. It can also be designed as follows. In that case, in the coupling region 80, the q-order mode light propagating through the multimode waveguide section 34 and the r-order mode light propagating through the coupling section 71 can be coupled.

(Production method)
The wavelength filter 200 according to this embodiment can be easily manufactured by using, for example, an SOI (Silicon On Insulator) substrate. Hereinafter, a method for manufacturing the wavelength filter 200 will be described.

That is, first, an SOI substrate is prepared in which a support substrate layer, a SiO ₂ layer, and a Si layer are sequentially stacked. Next, the optical waveguide core 30 and the output waveguide core 70 are formed by patterning the Si layer using, for example, an etching technique. 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 and the output waveguide core 70 are further formed on the SiO ₂ layer. Then, for example, by CVD on the SiO ₂ layer, the SiO _2, is formed by covering the optical waveguide core 30 and the output waveguide core 70. As a result, the clad 20 includes the optical waveguide core 30 and the output waveguide core 70. Next, the wavelength filter 200 can be manufactured by forming the electrode 40 on the clad 20.

10: support substrate 20: clad 30: optical waveguide core 31: mode conversion unit 32: input unit 33: input side taper unit 34: multimode waveguide unit 35: output side taper unit 36: first output unit 40: electrode 51 52: hole 61: first hole group 62: second hole group 70: output waveguide core 71: coupling part 72: second output part 80: coupling region 100: optical waveguide element 200: wavelength filter

Claims (4)

An optical waveguide core provided along a first imaginary line segment and a second imaginary line segment parallel to the first imaginary line segment and overlapping the first imaginary line segment and the second imaginary line segment;
A clad including the optical waveguide core,
The optical waveguide core includes a mode conversion unit,
In the mode conversion unit, a first hole group including a plurality of holes periodically formed in a position overlapping with the first virtual line segment, and a position overlapping with the second virtual line segment A photonic crystal including a second hole group including a plurality of holes formed at the same period as the first hole group is formed,
The photonic crystal, for a particular wavelength lambda, the first pore group and the period of the second air hole group lambda, p (p is p ≧ 0 integer) the equivalent refractive index for the next mode n _p , Q (q is an integer of q ≧ 0 and q ≠ p) An optical waveguide device characterized by satisfying 2π / Λ = 2π (n _p + n _q ) / λ, where n _q is an equivalent refractive index for the next mode. 2. The optical waveguide device according to claim 1, wherein the diameters of the holes included in the first hole group and the holes included in the second hole group change for each period. 3. The optical waveguide device according to claim 1, wherein an electrode for applying heat to the mode conversion unit is formed at a position covering the mode conversion unit via the clad. The optical waveguide device according to any one of claims 1 to 3, and an output waveguide core including a coupling portion,
The optical waveguide core further includes a multimode waveguide unit connected in series with the mode conversion unit and propagating light of p-order mode and q-order mode,
The cladding includes the optical waveguide core and the output waveguide core;
A coupling region is set in which the multimode waveguide part and the coupling part are spaced apart from each other and arranged side by side.
In the coupling region, q-order mode light propagating through the multimode waveguide section and r (r is an integer of r ≧ 0) order mode light propagating through the coupling section are coupled. Wavelength filter to be used.

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