JP2009053425A - Method for forming optical waveguide wavelength filter and optical waveguide wavelength filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain the same center wavelength at the same temperature in two polarized light beams having the oscillation planes orthogonal to each other by adjusting temperature characteristics at the center wavelength. <P>SOLUTION: Temperature independence of the optical waveguide for the resonant wavelength of the optical waveguide is achieved by imparting residual stress in the optical waveguide; and polarization independence of the resonant wavelength is achieved by controlling the resonant wavelength difference in the polarized light beams by controlling temperature by using different temperature characteristics of the resonant wavelengths of the polarized beams propagating through the optical waveguide and having polarization directions orthogonal to each other. Further, in the above process of achieving temperature independence and polarization independence, the resonant wavelength is trimmed by irradiating the core with UV rays and controlled to a desired wavelength. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical waveguide wavelength filter, and more particularly to a method of forming an optical waveguide wavelength filter having a desired center wavelength characteristic of the optical waveguide wavelength filter, and an optical waveguide wavelength filter having a desired center wavelength characteristic.

  Add / Drop filters are indispensable for photonic networks that control optical paths by wavelength. As this Add / Drop filter, a stacked microring resonator formed by stacking a core on a clad has been proposed. In this laminated microring resonator, an input-side optical waveguide and an output-side optical waveguide (both are collectively referred to as a bus line) are embedded in a lower clad so as to cross each other, and a ring resonator is stacked at the intersection. To do.

  In general optical waveguide type wavelength filters such as this optical waveguide wavelength filter, temperature independence (athermal) in which the center wavelength of the wavelength filter does not vary with temperature, and polarization in which the center wavelength of the wavelength filter does not vary with the polarization direction. Independence is required.

  In optical communication, it is known that an optical waveguide device such as a wavelength filter including a microring resonator filter has temperature dependence. For example, a wavelength filter or the like generally has temperature dependence, and the filter characteristics change with changes in temperature. A wavelength filter made of a semiconductor has a temperature dependency of about 0.1 [nm / K], and a quartz system has a temperature dependency of about 0.01 [nm / K].

  Optical signals are multiplexed at 32 to 160 waves with a narrow wavelength interval of 0.8 nm (100 GHz) or 0.4 nm (50 GHz) in the wavelength band of 40 to 100 nm in the 1.55 μm band, which is the low loss wavelength band of single mode fiber. In Dense Wavelength Division Multiplexing (DWDM), optical signals are communicated at the above-mentioned narrow wavelength intervals. In an optical communication system, stable operation in a temperature range of about 80 ° C. to 100 ° C. Therefore, temperature dependence is a very big problem.

In general, Fabry-Perot resonators, distributed feedback resonators, Mach-Zehnder interferometer filters, arrayed waveguide grating (AWG) wavelength filters, etc. are known as wavelength filters using interference or resonance. The center wavelength λ _o of the optical path changes due to temperature dependence of the optical path length S.

The center wavelength λ _o is given by the following equation for any type of filter.

λ _o = n _eq L / N

Where L is the length of the optical waveguide (difference in optical path length in Mach-Zehnder type and AWG type), n _eq (= β / κ _o ) is the equivalent refractive index, and N is the resonance (or interference) order. is there. When the temperature dependence of the center wavelength λ _o is obtained using this equation, the following equation is obtained.

dλ _o / dT = (1 / L) · (dS / dT) · (λ _o / n _eq )

Here, (1 / L) · (dS / dT) in the above equation is a value called “optical path length temperature coefficient”. This expression indicates that the temperature dependence of the center wavelength of the filter is proportional to the optical path length temperature coefficient. For example, when the center wavelength λ _o = 1.55 μm, the optical path length temperature coefficient of the glass optical waveguide or the semiconductor optical waveguide is (1 / L) · (dS / dT) ≈10 ⁻⁴ to 10 ⁻⁵ [1 / K] Therefore, the temperature dependence of the center wavelength is approximately dλ _o /dT≈0.01 to 0.1 [nm / K].

  For this reason, in order to put high-density wavelength division multiplexing optical communication into practical use, the temperature dependence of this optical path length becomes a very big problem. Currently, filter characteristics are made independent of temperature by keeping the temperature constant by element heating, but this is disadvantageous in terms of cost and power saving.

  Therefore, as a method for making the wavelength filter temperature-independent, a method in which a material having a negative refractive index temperature coefficient is inserted into a part of the waveguide (Non-Patent Document 1) or a method using a material having a different dn / dT (Non-Patent Document 1) Patent Documents 2 and 3), a method using a polymer material in which a general dielectric waveguide material has dn / dT <0 with respect to dn / dT> 0 (Non-Patent Document 4) have been proposed. The inventor of the present application has proposed an optical waveguide that makes the central wavelength of the optical waveguide temperature independent by giving the optical waveguide a stress distribution (Patent Document 1, Non-Patent Document 5).

  In addition, since the polarized light becomes elliptically polarized light while propagating through the optical waveguide, there is a problem that when the central wavelength of the wavelength filter has polarization dependence, the central wavelength is shifted by the polarized light and crosstalk occurs. In addition, high-density wavelength division multiplexers / demultiplexers are required to be polarization independent. In the high refractive index optical waveguide, polarization independence is achieved by controlling the aspect ratio of the core cross section. However, the condition for this polarization independence has a problem that an allowable range in manufacturing the optical waveguide is small.

  Also, it has been proposed to make the polarization independent by forming a groove in the core and inserting a λ / 2 plate, but there is a problem that it is difficult to reduce the device size.

  In contrast, when the inventor of the present application applies the temperature independence or the temperature dependence reduction using the stress control described above (Patent Document 1) to the microring resonator, the temperature of the resonance wavelength is applied. It has been proposed to make the microring resonator polarization independent by temperature control using the fact that the dependence varies greatly depending on the incident polarization (Non-Patent Document 6).

Y. Inoue, A. Kaneko, F. Hanawa, H. Takahashi, K. Hattori, and S. Sumida, “Athermal silica-based arrayed-waveguide grating multiplexer,” Electron. Lett., Vol.33, no.23, pp.1945-1947 (1997) H. Tanobe, et al., “A Temperature Insensitive InGaAs InP Optical Filter.” IEEE Phton. Technol. Lett., Vol.8, no.11, pp.1489-1491 (1998) H. Tanobe, et al., “Temperature Insensitive Arrayed Waveguide Grating on InP Substrates,” IEEE Phton. Technol. Lett., Vol.10. No.2, pp.235-237 (1998) Y. Kokubun, N. Funato, and M. Takizawa, “Athermal waveguides for temperature independent lightwave devices,” IEEE Photonics Technol. Lett., Vol.5, no.11, pp.1297-1300 (Nov.1993) N.Zaizen, N.Kobayashi, Y.Kokubun, "Athermal microring resonator filter by stress control", MOC’06, Seoul, G-3 (pp.200-201), Sep. 2006 Naoki Kobayashi, Nobuhiro Zaizen, Yasuo Kokubun, “Making Polarization Independent of Microring Resonator Filter Using Stress and Temperature Control”, 54th Joint Conference on Applied Physics, 27p-SG-8, (2007 March 27) Japanese Patent Application No. 2006-071730 JP 2004-264611 A

  In the optical waveguide wavelength filter, the resonance wavelength temperature control of the microring resonator filter using the stress control described above (Non-Patent Document 5) and the polarization independent of the microring resonator filter using the stress and temperature control are described. (Non-patent Document 6) proposes temperature independence and polarization independence for micro devices using high refractive index difference optical waveguides. However, in the production of an actual microring resonator filter, In some cases, the resonance wavelength may deviate from the design value due to fabrication errors caused by fabrication resolution of the photomask, nonuniformity of the core film thickness, or the like.

In order to adjust the resonance wavelength to a predetermined value, the inventors of the present application proposed a trimming method using a UV photosensitive polymer for the cladding, and Ta ₂ O ₅ as a stable resonance wavelength trimming with little change with time. using a wavelength filter using a -S _i O ₂ to the core, after the hydrogen loading on the core, a method of trimming the resonant wavelength by causing by irradiating ultraviolet rays to the core to change the equivalent refractive index of the guided mode (Patent Document 2).

However, the core of Ta ₂ O ₅ -S _i O ₂ used in resonance wavelength trimming shown in the literature mentioned above, there is a problem that the trimming effect of UV irradiation is small.

  In the optical waveguide wavelength filter, the center wavelength of the optical waveguide wavelength filter is required to be independent of temperature and polarization, and the center wavelength is required to be efficiently trimmed to a predetermined wavelength.

  More specifically, it is required to adjust the temperature characteristics at the center wavelength with the same wavelength for two polarized light beams that pass through the optical waveguide and whose vibration planes are orthogonal to each other. In addition, it is required to efficiently trim the center wavelength to a predetermined wavelength.

  Therefore, the present invention aims to solve the above-mentioned conventional problems and to obtain the same center wavelength at a certain temperature by adjusting the temperature characteristics at the center wavelength for two polarized lights whose vibration planes are orthogonal to each other. .

  Furthermore, with respect to two polarized lights whose vibration planes are orthogonal to each other, the temperature characteristics at the center wavelength are adjusted to make temperature independent or polarization independent for at least one of the polarized lights. An object is to efficiently trim the signal to a predetermined wavelength.

  It is another object of the present invention to provide an optical waveguide wavelength filter that can obtain both temperature independence and polarization independence of the center wavelength of the optical waveguide type wavelength filter and a trimming effect having a large center wavelength.

  The optical waveguide according to the present invention has a residual stress inside the optical waveguide, so that the temperature at the center wavelength of one of the polarizations of the two polarizations that pass through the optical waveguide type wavelength filter and whose vibration planes are orthogonal to each other. The characteristics are adjusted to obtain the same center wavelength at a certain temperature.

  By adjusting the temperature characteristics of the center wavelength, the temperature dependence of the center wavelength of at least one of the polarized light (TE polarized light and TM polarized light) whose vibration planes of the optical waveguide type wavelength filter are orthogonal to each other can be achieved. In addition, by utilizing the fact that the temperature characteristics of the center wavelength of polarized light propagating through the optical waveguide and whose vibration planes are orthogonal to each other are different, the center wavelength difference between the two polarizations is controlled by controlling the temperature so that there is no polarization at the center wavelength. Make dependence.

  Further, in the temperature independence and polarization independence, the center wavelength is trimmed by irradiating the core with ultraviolet rays, and the center wavelength is controlled to a desired wavelength.

  The center wavelength trimming is applied to one optical waveguide wavelength filter applied with both temperature independence and polarization independence of one polarization, temperature independence and polarization independence. Each of them may be applied independently for conversion.

In the temperature independence, the inventor of the present application uses the center wavelength in an optical waveguide having a core and a clad in which the temperature coefficient of the refractive index inherent to the material is positive and the dn / dT of the waveguide material is positive. It has been found that the temperature dependence dλ _o / dT of λ _o becomes positive and normally red shifts, but blue shift occurs in an optical waveguide having internal stress. The blue shift means that the temperature dependence dλ _o / dT of the center wavelength λ _o is negative.

In addition, when the inventor of the present application generates an optical waveguide type wavelength filter having a core of SiON on the clad by PE-CVD method using SiON as a core material, the center wavelength is blue-shifted as the temperature rises. Then, it was found that the temperature dependence dλ _o / dT of the center wavelength λ _o is negative.

  The optical waveguide of the present invention is an optical waveguide having a core and a clad having a positive temperature coefficient of refractive index inherent to the material, and the core is equivalent to the waveguide mode of the optical waveguide straddling the core and the clad in the film thickness direction. It has a stress distribution that makes the temperature coefficient of refractive index negative. The temperature coefficient of the equivalent refractive index of the waveguide mode of the optical waveguide is determined by the negative temperature coefficient due to this stress distribution and the positive refractive index temperature coefficient inherent to the core and cladding materials.

  As an aspect in which the optical waveguide has a stress distribution, the optical waveguide of the present invention is generated by forming a core on a clad. When the SiON core is formed on the cladding by chemical vapor deposition, the difference between the linear expansion coefficient of the substrate and the linear expansion coefficient of the optical waveguide film and the conditions during film formation (deposition temperature, input power, pressure, etc.) ) And a stress distribution in the film thickness direction of the core depending on the film thickness and the like.

  The inventor of the present application indicates that the temperature dependency is affected by internal stress, the internal stress affects the temperature dependency in the negative direction, and the positive temperature coefficient is changed to a negative temperature coefficient by the strong internal stress. It was found that polarized light having different vibration planes has a difference in the magnitude of the influence of the internal stress on the temperature coefficient.

  Based on these findings, the present invention changes the temperature dependence of the polarized light with at least one of the polarized lights having different vibration planes according to the internal stress, thereby varying the temperature coefficient of the two polarized lights and changing the center wavelength. Adjust the temperature dependence of.

  For example, the positive temperature coefficient can be adjusted, the positive temperature coefficient can be changed to a negative temperature coefficient, or the negative temperature coefficient can be adjusted.

  In general, when there is no internal stress, there is a shift in the center wavelength of each polarization, and the temperature dependence of the center wavelength for each polarization has a temperature coefficient of almost the same magnitude. In this case, it is difficult to adjust the center wavelength of each polarized light so as to obtain the same center wavelength at the same temperature.

  On the other hand, according to the present invention, the temperature dependence of at least one polarization of polarized light having different vibration planes is changed by internal stress, and thereby polarized light (TE polarized light and TM polarized light) whose vibration surfaces are orthogonal to each other. ) Can be changed from a state where the temperature coefficients are substantially equal to a state where the temperature coefficients are different. At the point where the temperature characteristics intersect, it becomes possible to obtain the same center wavelength at a certain temperature.

  Therefore, in an optical waveguide in which a core is formed on a clad, the temperature coefficient of the equivalent refractive index is adjusted for at least one polarized light in the waveguide mode of the optical waveguide straddling the core and the clad by the stress distribution. The same center wavelength can be obtained at a certain temperature.

  Furthermore, by controlling the magnitude of the internal stress, the inclination of the temperature coefficient of each polarization can be adjusted to make the temperature independent, and the polarization independent. Further, by trimming the center wavelength to a predetermined wavelength, temperature independence and polarization independence can be achieved at a desired center wavelength.

  In the optical waveguide of the present invention, the stress distribution state of the core is adjusted by etching back a part of the core formed on the clad, whereby the temperature coefficient of the equivalent refractive index can be adjusted.

  This invention can be made into the aspect of the formation method of an optical waveguide wavelength filter, and the aspect of the aspect of an optical waveguide wavelength filter.

  An aspect of the method for forming an optical waveguide wavelength filter of the present invention is a method for forming a wavelength filter having an optical waveguide formed by forming a core on a clad, and includes three aspects depending on the combination of each step. SiON can be used for the core formed on the clad.

  In the first aspect of the method for forming an optical waveguide wavelength filter of the present invention, by applying an internal stress to the optical waveguide, the temperature dependence of the central wavelength of at least one of the two polarized lights whose vibration planes are orthogonal to each other is obtained. A temperature dependence control step for controlling, a central wavelength control step for controlling the center wavelength of the wavelength filter by irradiating the optical waveguide with ultraviolet rays, and an orthogonal polarized light propagating through the optical waveguide by controlling the temperature of the optical waveguide. And a center wavelength difference control step for controlling the center wavelength difference.

  According to the first aspect, the temperature dependence of the central wavelength of the wavelength filter is changed with respect to at least one polarized light by the temperature dependence control step so that both polarized lights have the same central wavelength at a certain temperature. Can do. The inclination of the temperature dependence of the center wavelength can be adjusted by internal stress. For example, you can adjust the magnitude of a positive slope in which the center wavelength increases as the temperature rises, or a negative slope in which the center wavelength decreases as the temperature rises, or change from a positive slope to a negative slope. Alternatively, the gradient of temperature dependence can be made zero.

  In this first aspect, the temperature independence can be made by setting the gradient of temperature dependence of the center wavelength of at least one polarized light to zero.

  Further, the wavelength filter can be made polarization independent by the center wavelength difference control step, and the center wavelength of the wavelength filter can be set to a predetermined wavelength by the center wavelength control step.

  According to the first aspect, the temperature filter is made temperature-independent for at least one polarization by the temperature dependence control step, the wavelength filter is made polarization-independent by the center wavelength difference control step, and the wavelength filter is made by the center wavelength control step. Can be set to a predetermined wavelength.

  The second aspect of the optical waveguide wavelength filter forming method according to the present invention controls the central wavelength temperature dependence of at least one of the two polarized light beams whose vibration planes are orthogonal to each other by applying an internal stress to the optical waveguide. And a central wavelength control step of controlling the central wavelength of the wavelength filter by irradiating the optical waveguide with ultraviolet rays.

  In the temperature dependence control step of the second aspect, as in the first aspect, with respect to the temperature dependence slope of the central wavelength of at least one polarized light, the magnitude of the positive slope, the magnitude of the negative slope, Change from a negative slope to a negative slope and zero.

  According to the second aspect, the temperature dependence of the central wavelength of the wavelength filter is changed with respect to at least one polarization by the temperature dependence control step so that both polarizations have the same central wavelength at a certain temperature. be able to. Further, the wavelength filter can be made temperature-independent, and the center wavelength of the wavelength filter can be set to a predetermined wavelength by the center wavelength control step.

  According to a third aspect of the method for forming an optical waveguide wavelength filter of the present invention, the center wavelength control step of controlling the center wavelength of the wavelength filter by irradiating the optical waveguide with ultraviolet light, and the temperature of the optical waveguide is controlled. And a center wavelength difference control step for controlling a center wavelength difference between orthogonally polarized lights passing through the optical waveguide.

  According to the third aspect, the wavelength filter can be made polarization independent by the center wavelength difference control step, and the center wavelength of the wavelength filter can be set to a predetermined wavelength by the center wavelength control step.

  In each embodiment, the temperature dependence control step forms an optical waveguide having an internal stress by generating a SiON core on the SiO cladding by PE-CVD (plasma CVD). The generated internal stress of the core depends on the difference between the coefficient of linear expansion of the clad and the coefficient of linear expansion of the core, the film formation conditions such as the film formation temperature, input power, and pressure during film formation, and the film thickness.

  In the center wavelength control step of the present invention, the center wavelength of the TE polarized light of the wavelength filter is adjusted to a predetermined wavelength by irradiating the core with ultraviolet rays. The shift amount of the center wavelength due to the irradiation of ultraviolet rays depends on the irradiation time.

  In the center wavelength difference control step of the present invention, the temperature is controlled toward the intersection where the center wavelength temperature characteristic of the TE polarized light and the center wavelength temperature characteristic of the TM polarized light of the wavelength filter intersect. Near the intersection where the central wavelength characteristic of TE polarized light and the central wavelength characteristic of TM polarized light intersect, at the same temperature, the wavelength difference between the central wavelength of TE polarized light and the central wavelength of TM polarized light is reduced, and polarization independence is achieved. .

  An aspect of the optical waveguide wavelength filter of the present invention is an optical waveguide wavelength filter formed by the method for forming an optical waveguide wavelength filter of the present invention.

  An aspect of the optical waveguide wavelength filter of the present invention is a wavelength filter having an optical waveguide formed by forming a core on a clad, and this wavelength filter is a polarization of at least one of two polarizations whose vibration planes are orthogonal to each other. The center wavelength of the wavelength filter is controlled to a predetermined wavelength by ultraviolet irradiation, and by controlling the temperature of the optical waveguide, the difference between the central wavelengths of orthogonal polarizations propagating through the optical waveguide is obtained. Temperature control means for controlling is provided. SiON can be used for the core formed on the clad. The wavelength filter is a combination of a positive refractive index temperature coefficient inherent to the core or clad material for the central wavelength of at least one polarized light, a combination of internal stress, photoelastic effect, and difference in linear expansion coefficient between the substrate and the core. Can be made temperature independent.

  Further, the temperature control means can control the temperature of the wavelength filter to reduce the center wavelength difference between the orthogonally polarized lights propagating through the optical waveguide, thereby making the wavelength filter polarization independent.

  As described above, according to the present invention, it is possible to obtain the same center wavelength at a certain temperature by adjusting the temperature characteristics at the center wavelength for two polarized lights whose vibration planes are orthogonal to each other.

  In addition, according to the present invention, the temperature characteristics at the center wavelength can be adjusted for two polarized lights whose vibration planes are orthogonal to each other to make the temperature independent and polarization independent. Trimming can be efficiently performed to a predetermined wavelength.

  In the optical waveguide wavelength filter, it is possible to obtain temperature independence and polarization independence of the center wavelength of the optical waveguide wavelength filter and an effective trimming effect of the center wavelength.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  Hereinafter, an example in which the optical waveguide of the present invention is applied to a ring resonator will be described. FIG. 1 is a diagram for explaining an optical waveguide filter in which an optical waveguide of the present invention is applied to a ring resonator.

In FIG. 1, an optical waveguide wavelength filter 1 includes a SiO ₂ cladding 2 formed on a Si substrate 5, and a SiON ring core 3 provided on the cladding 2. In addition, a bus line core 4 that exchanges optical signals with the ring core 3 is provided in the clad 2.

  The ring core 3 has a ring core thickness tr, a ring core width wr, and a ring diameter R, and is provided with an overetch toe interposed on the clad 2. The bus line core 4 has a bus line core thickness tb and a bus line core width wb, and is provided with a separation layer film thickness tsep between the ring core 3 and the bus line core 4.

The optical waveguide wavelength filter 1 having the above-described configuration includes a clad 2, a ring core 3 having a stress distribution on the clad 2, and a bus line core 4. For example, the cladding 2 is made of SiO ₂ , and the ring core 3 and the bus line core 4 are made of SiON. In the optical waveguide wavelength filter 1 having this configuration, the ring core 3 has an air layer as an upper clad. However, a protective clad may be provided above the ring core 3.

  By forming a film on the clad 2 by PE-CVD, a stress distribution is generated in the core 3 in the film thickness direction. This internal stress in the film thickness direction makes the temperature coefficient of the equivalent refractive index of the waveguide mode of the optical waveguide straddling the core 3 and the clad 2 negative. The temperature coefficient of this equivalent refractive index depends on the internal stress, and this internal stress depends on the film thickness of the core 3. Therefore, the temperature coefficient of the equivalent refractive index is adjusted by adjusting the film thickness of the core 3.

The film thickness of the core 3 can be adjusted by etching back the core formed on the clad 2. The etch back can be performed by, for example, ion etching. Ion etching is a kind of dry etching method that is a physical etching that accelerates and collides ions in plasma. In addition to a physical reaction, a chemical reaction can be involved in etching by reactive ion etching (RIE) using reactive ions by selecting a gas. As a gas used for reactive ion etching, for example, a C ₂ F ₆ gas can be used for glass-based materials such as SiO ₂ and SiON.

  As another mode for adjusting the temperature coefficient of the equivalent refractive index, there is a method of annealing by heating the core to a predetermined temperature.

  The phenomenon in which the refractive index changes due to stress is known as the photoelastic effect. Usually, the refractive index temperature dependency of a dielectric is a positive characteristic, and the refractive index increases as the temperature rises. As a result, the resonance wavelength of the dielectric waveguide wavelength filter shows positive temperature dependence, and the resonance wavelength becomes longer and increases red as the temperature rises.

  In general, wavelength filters include those that use interference phenomena such as Mach-Zehnder type and AWG type, and those that use resonance phenomena such as Fabry-Perot resonators and ring resonators. Generally, it is called a center wavelength, and those using a resonance phenomenon are called resonance wavelengths.

  Here, in order to describe an example in which an optical waveguide is applied to a ring resonator, description will be made using terms of resonance wavelength instead of the center wavelength.

  As described above, the dielectric waveguide wavelength filter exhibits a positive temperature dependence when there is no stress, whereas the inventor of the present application has a case where an internal stress exists in the dielectric waveguide wavelength filter. It has been found that the resonance wavelength shows negative temperature dependence, and as the temperature rises, the resonance wavelength becomes shorter and shows a blue shift.

  As a model for explaining this phenomenon, a non-linear model represented by the following equation is assumed by the stress in the direction in which the Young's modulus is orthogonal. This phenomenon is known as stress stiffening.

E _x = (1 + k _y σ _y ) E

Here, the y-axis and z-axis coordinate axes in the plane of the optical waveguide film, also when taking x-axis direction perpendicular to the optical waveguide layer, E _x is the x-direction of the Young's modulus, k _y is the nonlinear coefficient, sigma _y is the stress in the y direction, and E is the normal Young's modulus. Here, the Young's modulus E _x increases the stronger the y direction of initial stress, the stress required to compress only the thermal expansion amount of the substrate is assumed to be increased, the relationship shown in FIG. 2 is obtained. This relationship is consistent with the experimental results.

FIG. 2 is a diagram for explaining the relationship between the initial stress and the temperature dependence. In FIG. 2, until the initial stress is about 10 ⁸ Pa, the photoelastic effect due to the thermal stress accompanying the thermal expansion of the substrate is sufficiently smaller than the TO effect (thermo-optical effect) and can be ignored. When it becomes larger than 10 ⁹ Pa, the photoelastic effect becomes larger than the TO effect (thermo-optic effect).

  Therefore, when the optical waveguide wavelength filter has a large initial stress, the negative temperature dependence due to the photoelastic effect is dominant over the positive temperature dependence due to the TO effect (thermo-optic effect), and the dielectric waveguide wavelength filter The resonance wavelength of this shows negative temperature dependence.

  Since the negative temperature dependence of the resonance wavelength of the waveguide wavelength filter depends on the internal stress, the temperature dependence of the resonance wavelength of the waveguide wavelength filter can be controlled by controlling the internal stress. As described above, the internal stress can be controlled by controlling the film thickness formed by PE-CVD by etching back, or by optimizing the core thickness.

  FIG. 3 shows an outline of the relationship between the magnitude of internal stress and temperature dependence. More specifically, the relationship between the magnitude of internal stress and the temperature dependence of two polarized lights (TE polarized light and TM polarized light) whose vibration planes are orthogonal to each other is shown. Here, the temperature dependence is shown by the change of the resonance wavelength λ with respect to the temperature.

  FIG. 3A shows the temperature dependency when there is no internal stress. In this case, there is a difference between the resonance wavelength of the TE polarized light and the resonance wavelength of the TM polarized light, and their temperature dependency coefficients (inclinations in the figure) are substantially the same, and do not intersect within a predetermined temperature range.

  The inventor of the present application has a difference between the influence on the TM polarization and the influence on the TE polarization with respect to the magnitude of the influence of the temperature dependence due to the internal stress on the TE polarization and the TM polarization, and the influence on the TM polarization. Was found to be greater than the effect on TE polarization. More specifically, the temperature dependence of the resonance wavelength shows a positive dependence because the refractive index temperature coefficient is a positive value if there is no internal stress, and shows a characteristic that the resonance wavelength becomes longer as the temperature rises. On the other hand, when the internal stress remains, it affects the negative direction of temperature dependence, and the influence of this negative direction is larger in the TM polarization than in the TE polarization.

  FIG. 3B to FIG. 3F schematically show changes in the temperature-dependent characteristics of the resonance wavelength due to the magnitude of the internal stress. FIG. 3 shows a case where the internal stress increases in the order from FIG. 3B to FIG.

  As shown in FIG. 3A, when there is no internal stress, the coefficient of temperature dependence (gradient in the figure) is almost the same and does not intersect in a predetermined temperature range. On the other hand, when there is an internal stress shown in FIGS. 3B to 3F, a predetermined temperature range is determined depending on the difference between the temperature dependence of TE polarization and the temperature dependence of TM polarization. Can cross and have the same resonant wavelength at a certain temperature.

  FIG. 3B shows a case where the internal stress is small. The influence of the internal stress on the temperature dependence of the TM polarized light is larger than the influence on the temperature dependence of the TE polarized light, and the direction is negative. Therefore, when the internal stress is small, the temperature dependence of TM polarized light and TE polarized light is both positive, and the temperature dependence of TE polarized light is larger in the positive direction than the temperature dependence of TM polarized light.

  The temperature dependence of TE polarization intersects the temperature dependence of TM polarization within a predetermined temperature range, and has the same resonance wavelength at the temperature of this intersection.

  FIG.3 (c) has shown the case where internal stress is the next largest. Since the temperature dependence change of the TM polarization is larger than the temperature dependence change of the TE polarization, the temperature dependence of the TM polarization becomes zero while the temperature dependence of the TE polarization remains positive. In a state where the temperature dependence of the TM polarized light is zero, it means the temperature independence that the resonance wavelength of the TM polarized light does not change even if the temperature changes. Since the temperature dependence of TE polarization remains positive, the resonance wavelength of TE polarization changes in a longer direction as the temperature changes.

  The temperature dependence of TE polarization intersects the temperature dependence of TM polarization within a predetermined temperature range, and has the same resonance wavelength at the temperature of this intersection.

  FIG. 3D shows a case where the internal stress is even greater. Since the change in temperature dependence of TM polarization is larger than the change in temperature dependence of TE polarization, the temperature dependence of TM polarization has a negative temperature dependence while the temperature dependence of TE polarization remains positive. In this state, TE-polarized light and TM-polarized light have temperature dependence in the opposite directions of the positive direction and the negative direction. When the temperature rises, the resonance wavelength of TE-polarized light becomes longer and the resonance wavelength of TM-polarized light is changed. Changes in a shorter direction.

  The temperature dependence of the TE polarization and the temperature dependence of the TM polarization intersect within a predetermined temperature range and have the same resonance wavelength at the temperature of this intersection.

  FIG. 3E shows a case where the internal stress is even greater. Since the temperature dependence change of the TM polarization is larger than the temperature dependence change of the TE polarization, the temperature dependence of the TE polarization becomes zero, and the temperature dependence of the TM polarization has a negative temperature dependence. In a state where the temperature dependence of TE-polarized light is zero, it means temperature-independence that the resonance wavelength of TE-polarized light does not change even if the temperature changes. Since the temperature dependence of TM polarized light is in a negative state, the resonance wavelength of TM polarized light changes in a direction that becomes shorter as the temperature changes.

  The temperature dependence of the TE polarization and the temperature dependence of the TM polarization intersect within a predetermined temperature range and have the same resonance wavelength at the temperature of this intersection.

  FIG. 3F shows a case where the internal stress is even greater. The effect of the internal stress on the temperature dependence of the TM polarization is larger than the influence on the temperature dependence of the TE polarization, and the direction is negative. Therefore, the temperature dependence of the TM polarization and the TE polarization is both negative. The temperature dependence is larger in the negative direction than the temperature dependence of TE polarized light.

  The temperature dependence of the TE polarization and the temperature dependence of the TM polarization intersect within a predetermined temperature range and have the same resonance wavelength at the temperature of this intersection.

  As shown in FIG. 3, the temperature dependence changes according to the magnitude of the internal stress, and more specifically, depending on the magnitude of the internal stress, two polarized lights (TE polarized lights) whose vibration planes are orthogonal to each other. And TM polarization) change in temperature dependence. As shown in FIG. 3B to FIG. 3F, the relationship between the TE polarized light and the TM polarized light changes according to the magnitude of the internal stress, and the temperature coefficients of the TE polarized light and the TM polarized light are made different. And have the same resonance wavelength at the temperature of the intersection.

  Next, a method for forming an optical waveguide wavelength filter of the present invention will be described with reference to the flowchart of FIG. The formation of the optical waveguide wavelength filter of the present invention can be applied to each temperature-dependent aspect shown in FIGS. 3 (b) to 3 (f).

  First, the temperature dependency of the optical waveguide wavelength filter is controlled by the temperature dependency control step, and the temperature coefficients of the resonance wavelengths (center wavelengths) of the two polarized light beams whose vibration planes are orthogonal to each other are made different.

  This temperature dependence can be controlled by the magnitude of the internal stress, as shown in FIGS. 3 (b) to 3 (f). For example, when a small internal stress is applied as shown in FIG. 3B, the temperature dependence of TM polarized light and TE polarized light can both be controlled to have a positive slope. Moreover, by controlling the magnitude of the applied internal stress, the TM polarized light is made temperature independent as shown in FIG. 3C, or the TE polarized light is made temperature independent as shown in FIG. can do.

In the temperature dependence control process, when an optical waveguide is formed by generating a SiON core by PE-CVD (plasma CVD) on the SiO ₂ clad, the temperature dependence depends on the magnitude of the internal stress applied to the core. To control. The internal stress of the generated core is adjusted by the difference between the linear expansion coefficient of the clad and the linear expansion coefficient of the core, the film formation conditions such as the film formation temperature, input power, and pressure during film formation, the film thickness, etc. (S1) .

  Next, the resonance wavelength of the optical waveguide wavelength filter is trimmed by the center wavelength control step to match the design value. In this center wavelength control step, the resonance wavelength (center wavelength) is adjusted to a predetermined wavelength by irradiating the core with ultraviolet rays. The shift amount of the center wavelength due to the irradiation of ultraviolet rays is controlled by adjusting the irradiation time (S2).

  Next, by the center wavelength difference control step, the wavelength difference between the resonance wavelengths (center wavelengths) of the two polarized light beams whose vibration planes are orthogonal to each other is reduced to match the resonance wavelengths. The two polarizations of the wavelength filter have an intersection where the temperature characteristics intersect due to the temperature coefficient of the resonance wavelength (center wavelength) being different depending on the temperature dependence control process.

  Temperature control is performed toward an intersection where the resonance wavelength (center wavelength) temperature characteristic of the TE polarized light of the wavelength filter and the resonance wavelength (center wavelength) temperature characteristic of the TM polarization intersect. Near the intersection where the central wavelength characteristic of TE polarized light and the central wavelength characteristic of TM polarized light intersect, at the same temperature, the wavelength difference between the central wavelength of TE polarized light and the central wavelength of TM polarized light is reduced, and polarization independence is achieved. . By using the polarization independence by temperature control, it is possible to compensate for the polarization dependence accompanying the manufacturing error of the optical waveguide wavelength filter (S3).

  Hereinafter, an embodiment of a method for forming an optical waveguide wavelength filter will be described with reference to FIGS. Here, an example of the mode shown in FIG. 3E is shown in each mode of change in temperature dependence shown in FIG. In FIG. 3 (e), temperature can be made independent for one polarized light (TE polarized light) by internal stress, and the resonance wavelength can be adjusted to a predetermined wavelength, and polarization independent at that wavelength. It is an aspect.

  FIG. 5 is a flowchart for explaining an embodiment of a method for forming an optical waveguide wavelength filter, and FIG. 6 is a diagram showing temperature characteristics of a resonance wavelength in each step of an embodiment of the method for forming an optical waveguide wavelength filter. FIG. 7 is a diagram showing temperature characteristics of the resonance wavelengths of the TE-polarized light and the TM-polarized light of the optical waveguide wavelength filter of the present invention, and FIG. 8 is a diagram showing a schematic configuration of the trimming process of the optical waveguide wavelength filter of the present invention. FIG. 9 is a diagram showing a shift in resonance wavelength when ultraviolet light is irradiated for 5 minutes in the optical waveguide wavelength filter of the present invention, and FIG. 10 is a case where ultraviolet light is irradiated for 10 minutes in the optical waveguide wavelength filter of the present invention. It is a figure which shows the shift of a resonant wavelength.

  First, temperature independence is achieved by the temperature dependence control process of the optical waveguide wavelength filter.

  In TE-polarized light and TM-polarized light, temperature dependency is controlled by controlling the temperature coefficient of the TO effect (thermo-optic effect), and temperature dependency is reduced or temperature dependency is reduced. This temperature dependence is performed by applying internal stress to the core. This internal stress can be formed by forming a SiON core on the cladding by PE-CVD.

  FIG. 6A is a schematic diagram for explaining temperature independence by the temperature dependence control process. In FIG. 6A, light propagating through the optical waveguide wavelength filter includes TE polarized light and TM polarized light whose vibration planes are orthogonal to each other. This TE / TM polarized light has a temperature-dependent difference that expands due to internal stress. Here, by controlling the internal stress, the fluctuation of the resonance wavelength with respect to the temperature of the TE-polarized light is reduced, and the temperature is made independent or controlled so as to reduce the temperature dependence.

  As a result, the resonance wavelength of TE-polarized light does not change even when the temperature changes, and maintains substantially the same wavelength. On the other hand, the resonance wavelength of TM polarized light has a temperature dependency and has a negative dependency.

  The normal TO effect (thermo-optic effect) shows almost the same temperature dependence in TE / TM polarized light, but the difference in temperature dependence between polarized lights becomes larger due to the photoelastic effect due to internal stress. FIG. 7 shows an actual measurement result of temperature characteristics of resonance wavelengths of TE polarized light and TM polarized light (S11).

  Next, the optical waveguide wavelength filter is trimmed to adjust the resonance wavelength (center wavelength) to a predetermined wavelength.

  In the optical waveguide wavelength filter of the present invention, the resonant wavelength of the optical waveguide wavelength filter formed by film formation does not necessarily match the desired wavelength, and may deviate from the design value. As described above, when the resonance wavelength deviates from the design value, the resonance wavelength of the optical waveguide wavelength filter is adjusted to the design value by the trimming process. This trimming is performed by irradiating the core with ultraviolet rays.

  FIG. 6B is a schematic diagram for explaining a resonance wavelength control process by trimming. In FIG. 6B, the thin solid line and the broken line indicate the resonance wavelength temperature dependence of the TE polarized light and the TM polarization before trimming, and the thick solid line and the broken line indicate the TE polarized light after the trimming. The resonance wavelength temperature dependence of TM and the resonance wavelength temperature dependence of TM polarized light are shown. The resonance wavelength of TE polarized light is adjusted to a desired wavelength λo by UV trimming by ultraviolet irradiation.

  FIG. 8 shows a schematic configuration of the trimming process of the optical waveguide wavelength filter. This step can be performed by irradiating ultraviolet rays from a light source (not shown) toward the upper surface of the optical waveguide wavelength filter.

  The shift amount of the resonance wavelength by trimming can be controlled by the irradiation time of ultraviolet rays. FIG. 9 shows a case where ultraviolet rays are irradiated for 5 minutes, and FIG. 10 shows an actual measurement result when ultraviolet rays are irradiated for 10 minutes. In this example, the resonance wavelength temperature dependency of TE polarized light and the resonance wavelength temperature dependency of TM polarized light shift while maintaining substantially the same relationship, and the longer the irradiation time, the larger the shift to the short wavelength side. .

  FIG. 11 shows another example of trimming by ultraviolet irradiation, and shows a case where ultraviolet rays are irradiated for 5 minutes. Also in this example, the resonance wavelength shifts while maintaining substantially the same relationship between the resonance wavelength temperature dependency of the TE polarized light and the resonance wavelength temperature dependency of the TM polarization.

In the example shown in FIG. 11, the wavelength λ of ultraviolet rays is 254 nm, the irradiation power is 42.6 mW / cm ² , and the irradiation time is 5 minutes.

  Therefore, the resonance wavelength can be controlled by controlling the irradiation time of ultraviolet rays (S12).

  Next, the polarization is made independent by the process of controlling the difference in the resonance wavelength (center wavelength) of the optical waveguide wavelength filter.

  In TE-polarized light and TM-polarized light, the polarization dependence is controlled by controlling the temperature, thereby making the polarization independent or reducing the polarization dependence. This polarization dependence is performed, for example, by controlling the temperature of the optical waveguide wavelength filter by temperature control means such as a Peltier element.

  FIG. 6C is a schematic diagram for explaining the step of making polarization independence. In FIG. 6C, the resonance wavelength is adjusted to the design value. However, the resonance wavelength may be shifted from the design value. Therefore, the polarization independence step is performed after the temperature independence step of either TE polarization or TM polarization, and then the resonance wavelength is controlled by trimming to match the resonance wavelength with the design value. Also good.

  In FIG. 6C, the temperature characteristics of the resonance wavelengths of the TE polarized light and the TM polarized light intersect, and at this intersection, the TE polarized light and the TM polarized light have the same resonant wavelength. When the temperature of the optical waveguide wavelength filter is lower than the temperature To at the intersection, the movement to the intersection can be performed by heating the optical waveguide wavelength filter by the temperature control means. When the temperature is higher than To, it can be performed by cooling the optical waveguide wavelength filter by the temperature control means.

In FIG. 6C, the polarization independence is performed in a state where the resonance wavelength of the TE polarized light is adjusted to the design value λ _o by trimming, so that the resonance wavelengths of the TE polarized light and the TM polarized light are both set to the design value λ _o. Can be adapted to

  FIG. 12 shows a state before and after trimming by ultraviolet irradiation. After adjusting the TE polarization to the design value by trimming, the polarization dependence is made independent or the polarization dependence is reduced by adjusting the resonance wavelength of the TE polarization and the resonance wavelength of the TM polarization by temperature control.

  By using the polarization independence by temperature control, it is possible to compensate for the polarization dependence accompanying the manufacturing error of the optical waveguide wavelength filter (S13).

  Hereinafter, another embodiment of the method for forming the optical waveguide wavelength filter will be described with reference to FIGS. FIGS. 13 to 16 show examples of cases where the temperature dependence differs depending on the difference in internal stress, and correspond to FIGS. 3B, 3C, 3D, and 3F, respectively. To do.

  The form example shown in FIG. 13 is an example in which both TM polarized light and TE polarized light have a positive slope temperature dependency.

  First, in the temperature dependence control step shown in FIG. 13A, by applying an internal stress, the resonance wavelength of TE polarized light and the resonance wavelength of TM polarized light have positive and different temperature dependence.

Next, the optical waveguide wavelength filter is trimmed to adjust the resonance wavelength (center wavelength) to a predetermined wavelength. In the resonance wavelength control step by trimming shown in FIG. 13B, the thin solid line and the broken line indicate the temperature dependence of the resonance wavelength of the polarized light before trimming, and the thick solid line and the broken line indicate the resonance of the polarized light after trimming. The wavelength temperature dependence is shown. By the UV trimming by ultraviolet irradiation, the resonance wavelength at which the TE polarized light and the TM polarized light intersect is adjusted to the desired wavelength λ _o .

  Next, the resonance wavelength (center wavelength) difference of the optical waveguide wavelength filter is controlled. By controlling the temperature in TE polarized light and TM polarized light, the wavelength difference between both resonance wavelengths is reduced, and the polarization dependence is reduced or the polarization is made independent.

  In the polarization independence step shown in FIG. 13C, the temperature characteristics of the TE polarized light and the TM polarized light intersect each other, and the TE polarized light and the TM polarized light have the same resonant wavelength at this intersection. By heating or cooling the optical waveguide wavelength filter by a temperature control means (not shown), the resonance wavelengths of the TE polarized light and the TM polarized light are adjusted to a desired wavelength λo determined at the intersection.

  The form example shown in FIG. 14 is an example in which TM polarized light has zero temperature dependence and TE polarized light has a positive slope temperature dependence.

  First, in the temperature dependency control step shown in FIG. 14A, by applying internal stress, the TM polarization resonance wavelength has zero temperature dependency, and the TE polarization resonance wavelength has a positive temperature dependency. To have.

Next, the optical waveguide wavelength filter is trimmed to adjust the resonance wavelength (center wavelength) to a predetermined wavelength. In the resonance wavelength control step by trimming shown in FIG. 14 (b), the thin solid line and the broken line indicate the resonance wavelength temperature dependence of the polarized light before trimming, and the thick solid line and the broken line indicate the resonance of the polarized light after trimming. The wavelength temperature dependence is shown. The resonance wavelength of TM polarized light is adjusted to a desired wavelength λ _o by UV trimming by ultraviolet irradiation.

  Next, the resonance wavelength (center wavelength) difference of the optical waveguide wavelength filter is controlled to make polarization independent. In TE-polarized light and TM-polarized light, the polarization dependence is controlled by controlling the temperature, thereby making the polarization independent or reducing the polarization dependence.

In the polarization independence step shown in FIG. 14C, the temperature characteristics of the TE polarized light and the TM polarized light intersect each other, and at this intersection, the TE polarized light and the TM polarized light have the same resonant wavelength. By heating or cooling the optical waveguide wavelength filter by a temperature control means (not shown), the resonance wavelengths of the TE polarized light and the TM polarized light are adjusted to a desired wavelength λ _o determined at the intersection.

  The form example shown in FIG. 15 is an example in which TM polarized light has a temperature dependence of a negative slope, and TE polarized light has a temperature dependence of a positive slope.

  First, in the temperature dependency control step shown in FIG. 15A, by applying internal stress, the TE polarization resonance wavelength has a positive temperature dependency, and the TM polarization resonance wavelength has a different negative temperature dependency. Give sex.

Next, the optical waveguide wavelength filter is trimmed to adjust the resonance wavelength (center wavelength) to a predetermined wavelength. In the resonance wavelength control step by trimming shown in FIG. 15B, the thin solid line and the broken line indicate the temperature dependence of the resonance wavelength of the polarized light before trimming, and the thick solid line and the broken line indicate the resonance of the polarized light after trimming. The wavelength temperature dependence is shown. By the UV trimming by ultraviolet irradiation, the resonance wavelength at which the TE polarized light and the TM polarized light intersect is adjusted to the desired wavelength λ _o .

  Next, the resonance wavelength (center wavelength) difference of the optical waveguide wavelength filter is controlled. By controlling the temperature in TE polarized light and TM polarized light, the wavelength difference between both resonance wavelengths is reduced, and the polarization dependence is reduced or the polarization is made independent.

  In the polarization independence step shown in FIG. 15C, the temperature characteristics of the TE polarized light and the TM polarized light intersect, and the TE polarized light and the TM polarized light have the same resonant wavelength at this intersection. By heating or cooling the optical waveguide wavelength filter by a temperature control means (not shown), the resonance wavelengths of the TE polarized light and the TM polarized light are adjusted to a desired wavelength λo determined at the intersection.

  The form example shown in FIG. 16 is an example in which TM polarized light has a temperature dependency of negative inclination, and TE polarized light has a temperature dependency of inclination smaller than that of negative TM polarization.

  First, in the temperature dependence control step shown in FIG. 16A, by applying an internal stress, the TE polarization resonance wavelength and the TM polarization resonance wavelength have different negative temperature dependence.

Next, the optical waveguide wavelength filter is trimmed to adjust the resonance wavelength (center wavelength) to a predetermined wavelength. In the resonance wavelength control step by trimming shown in FIG. 16B, the thin solid line and the broken line indicate the temperature dependence of the resonance wavelength of the polarized light before trimming, and the thick solid line and the broken line indicate the resonance of the polarized light after trimming. The wavelength temperature dependence is shown. By the UV trimming by ultraviolet irradiation, the resonance wavelength at which the TE polarized light and the TM polarized light intersect is adjusted to the desired wavelength λ _o .

  Next, the resonance wavelength (center wavelength) difference of the optical waveguide wavelength filter is controlled. By controlling the temperature in TE polarized light and TM polarized light, the wavelength difference between both resonance wavelengths is reduced, and the polarization dependence is reduced or the polarization is made independent.

In the polarization independence step shown in FIG. 16C, the temperature characteristics of the TE polarized light and the TM polarized light intersect each other, and at this intersection, the TE polarized light and the TM polarized light have the same resonant wavelength. By heating or cooling the optical waveguide wavelength filter by a temperature control means (not shown), the resonance wavelengths of the TE polarized light and the TM polarized light are adjusted to a desired wavelength λ _o determined at the intersection.

  The present invention can be applied to a waveguide type optical wavelength filter, an optical sensor, and the like.

It is a figure for demonstrating the optical waveguide filter which applied the optical waveguide of this invention to the ring waveguide. It is a figure for demonstrating the relationship between initial stress and temperature dependence. It is a figure which shows the outline of the relationship between the magnitude | size of internal stress, and temperature dependence. It is a flowchart for demonstrating the formation method of the optical waveguide wavelength filter of this invention. It is a flowchart for demonstrating one form of the formation method of the optical waveguide wavelength filter of this invention. It is a figure which shows the temperature characteristic of the resonant wavelength in each process of one form of the formation method of the optical waveguide wavelength filter of this invention. It is a figure which shows the temperature characteristic of the resonant wavelength of TE polarized light and TM polarized light of the optical waveguide wavelength filter of this invention. It is a figure which shows schematic structure of the trimming process of the optical waveguide wavelength filter of this invention. In the optical waveguide wavelength filter of this invention, it is a figure which shows the shift of the resonant wavelength at the time of irradiating an ultraviolet-ray for 5 minutes. In the optical waveguide wavelength filter of this invention, it is a figure which shows the shift of the resonant wavelength at the time of irradiating with an ultraviolet-ray for 10 minutes. It is a figure which shows the other example of the trimming by ultraviolet irradiation in the optical waveguide wavelength filter of this invention. It is a figure which shows the state before and behind trimming by ultraviolet irradiation in the optical waveguide wavelength filter of this invention. It is a figure for demonstrating the other form of the formation method of the optical waveguide wavelength filter of this invention. It is a figure for demonstrating the other form of the formation method of the optical waveguide wavelength filter of this invention. It is a figure for demonstrating the other form of the formation method of the optical waveguide wavelength filter of this invention. It is a figure for demonstrating the other form of the formation method of the optical waveguide wavelength filter of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical waveguide wavelength filter 2 ... Cladding 3 ... Ring core 4 ... Bus line core 5 ... Substrate

Claims (10)

In a method for forming a wavelength filter having an optical waveguide formed by forming a core on a clad,
By applying an internal stress to the optical waveguide, the temperature dependence of controlling the temperature dependence of the central wavelength of at least one of the two polarized lights whose vibration planes are orthogonal to each other, and making the temperature coefficients of the two polarized lights different from each other Control process;
A central wavelength control step of controlling the central wavelength of the wavelength filter by irradiating the optical waveguide with ultraviolet rays;
And a center wavelength difference control step of controlling a center wavelength difference between polarized lights whose vibration planes propagating through the optical waveguide are orthogonal to each other by controlling the temperature of the optical waveguide. Forming method. In a method for forming a wavelength filter having an optical waveguide formed by forming a core on a clad,
By applying an internal stress to the optical waveguide, the temperature dependence of controlling the temperature dependence of the central wavelength of at least one of the two polarized lights whose vibration planes are orthogonal to each other, and making the temperature coefficients of the two polarized lights different from each other Control process;
And a central wavelength control step of controlling a central wavelength of the wavelength filter by irradiating the optical waveguide with ultraviolet rays. In a method for forming a wavelength filter having an optical waveguide formed by forming a core on a clad,
A central wavelength control step of controlling the central wavelength of the wavelength filter by irradiating the optical waveguide with ultraviolet rays;
A center wavelength difference control step for controlling a center wavelength difference between polarized lights whose vibration planes passing through the optical waveguide are orthogonal to each other by controlling the temperature of the optical waveguide, Forming method.   4. The method of forming an optical waveguide wavelength filter according to claim 1, wherein the core is SiON. In the temperature dependence control step, an optical waveguide having internal stress is formed by forming a SiON core on the SiO ₂ cladding by PE-CVD, and the temperature of the center wavelength of at least one of TE polarized light and TM polarized light is formed. 3. The method of forming an optical waveguide wavelength filter according to claim 1, wherein dependency is controlled.   5. The optical waveguide wavelength filter according to claim 1, wherein the center wavelength control step adjusts the center wavelength of at least one of TE polarized light and TM polarized light of the wavelength filter to a predetermined wavelength. 6. Forming method.   The center wavelength difference control step performs temperature control toward the intersection where the center wavelength temperature characteristic of the TE polarized light of the wavelength filter and the temperature characteristic of the center wavelength of the TM polarized light intersect, thereby the center wavelength of the TE polarized light and the center of the TM polarized light. 4. The method for forming an optical waveguide wavelength filter according to claim 1, wherein a wavelength difference with the wavelength is reduced.   An optical waveguide wavelength filter formed by the forming method according to claim 1. In a wavelength filter having an optical waveguide formed by forming a core on a clad,
The wavelength filter has temperature coefficients different from each other in the temperature dependence of the center wavelength of two polarized light beams whose vibration planes are orthogonal to each other.
The center wavelength of the wavelength filter is controlled to a predetermined wavelength by ultraviolet irradiation,
An optical waveguide wavelength filter comprising temperature control means for controlling a center wavelength difference between orthogonally polarized light propagating through the optical waveguide by controlling a temperature of the optical waveguide.   The optical waveguide wavelength filter according to claim 9, wherein the core is SiON.