JP4934614B2 - Thermo-optic phase shifter - Google Patents

Description

  The present invention relates to a thermo-optic phase shifter that controls the refractive index of a core by a temperature change caused by heating and changes the phase of guided light.

  In the optical communication field, in order to cope with an increase in communication capacity, multi-channeling has been proposed, and among these, a wavelength division multiplexing (WDM) communication method is considered promising. In addition, for example, in order to realize functional control for each channel, such as switching the power of each channel to be constant or switching, without photoelectric conversion, the number of optical elements corresponding to the number of channels is required. Has been. Therefore, in recent years, there is an increasing need for small optical circuit components that can be applied to optical switches and the like and can be integrated at high density.

  As one of the small optical circuit components, there is a planar light wave circuit (PLC) type device made of silica-based material. Since a PLC type device can use a manufacturing technique of a semiconductor integrated circuit in a manufacturing process, it is easy to manufacture and has an advantage of high functionality and large scale. Furthermore, by adding a thermo-optic phase shifter to the PLC type device, functions such as an optical switch and an optical variable attenuator can be easily expressed, and in recent years, it has been widely used in optical communication devices.

  Here, an example of an optical switch using silica-based PLC will be described. This uses an optical waveguide consisting of a core and a clad of a silica-based material. One optical waveguide is branched into two at the input end, and at least one of them is an optical waveguide having a thermo-optic phase shifter function. The optical waveguide branched in this way is recombined at the output end. The thermo-optic phase shifter used here is composed of, for example, an optical waveguide and a heater disposed on the optical waveguide, and controls the refractive index of the core by changing the temperature of the heater to change the phase of the guided light. .

  By operating the heater and shifting the phase of the light guided to one of the two branched optical waveguides by half the wavelength with respect to the other optical waveguide, the optical output combined at the output end is zero. It can be. Further, if the refractive index of the core is controlled by the temperature change caused by the heater so that the phases of the two branched optical waveguides are matched, the input light can be output as it is. By these things, the optical switch which enables on / off control of the light output from an output terminal is realizable. This optical switch is called a Mach-Zehnder interferometer (MZI) type optical switch.

  FIG. 12 is a cross-sectional view showing the configuration of the thermo-optic phase shifter used in the optical switch as described above. For example, an optical waveguide including a core 1203 made of a silica-based material and a lower clad 1202 made of a silica-based material and an upper clad 1204 is formed on a substrate 1201 made of silicon, and is formed on the upper clad 1204 above the core 1203. A thin film heater 1205 is provided. FIG. 1 shows a cross section perpendicular to the waveguide direction of the optical waveguide. Generally, the cross section of the core 1203 is a square of 4 μm × 4 μm, and the lower clad layer 1202 and the upper clad layer 1203 are about 60 μm in total, and the relative refractive index difference between them is about 1.5%. It is said that. The thin film heater 1205 is made of, for example, chromium (Cr). The response speed of the optical switch configured in this way is several ms.

  Along with the widespread use of optical information communication networks, silica-based PLC optical switch modules using the thermo-optic phase shifter as described above have been commercialized. There is an increasing demand for cost reduction and scale-up of this optical switch module. However, in the silica-based PLC optical switch module using the thermo-optic phase shifter as described above, the heat generated by the heater is large, so the size of the module is large. Scaling is limited to a scale that allows cooling. For this reason, the silica-based PLC optical switch described above is required to reduce the power consumption of the thermo-optic phase shifter.

  As a method of reducing the power consumption of the thermo-optic phase shifter, by forming a heat insulation groove around the thermo-optic phase shifter, the volume that needs to be heated is reduced, and at the same time, the heat generated by the heater is not discharged to the outside. A method for improving thermal efficiency by being confined in a waveguide has been proposed. For example, in order to reduce the diffusion of heat in the direction parallel to the substrate, heat insulation grooves are formed on both sides of the optical waveguide, and the cladding layer on the lower part (substrate side) of the optical waveguide is made thicker. There is a technique for reducing electric power (see Non-Patent Document 1). In this case, power consumption is 45 mW.

  In order to further reduce power consumption, a structure in which a heat insulating gap is formed between the waveguide and the substrate directly under the waveguide in addition to the heat insulating grooves formed on both sides of the waveguide has been proposed (Non-Patent Document 2). reference). In this technology, first, a mask pattern in which a region for forming a heat insulation groove is opened is formed by a photolithography technique, and silicon support for supporting the waveguide is formed on both sides of the waveguide by selective dry etching using the mask pattern as a mask. Excavate from the substrate side to a depth that leaves a lower cladding with a thickness of about 7 μm. Thereby, it will be in the state in which the heat insulation groove | channel was formed, and the volume to heat was reduced.

  Next, a plurality of holes periodically arranged at predetermined intervals are formed on the bottom surface of the heat insulating groove by the same photolithography technique and dry etching technique as described above. Next, the silicon support substrate in the region under the core is removed so that the hole formed in each of the two heat insulation grooves is connected by a wet etching method, and a space (heat insulation gap) is formed under the waveguide. It is assumed that it is formed. By forming the space in this way, the outflow of heat to the silicon support substrate is suppressed. As described above, in this technology, the volume heated by the heat insulating groove is reduced, and additionally, a space is formed under the waveguide to suppress the outflow of heat, thereby realizing a low power operation of 15 mW with a single switch. Yes.

JP 2004-133446 A S.Sohma, et al., "Low switching power silica-based super high delta thermo-optic switch with heat insulating grooves", Electronics Letters, Vol.32, No.3, pp.127-28,2002. Y. Hashizume, et al., "Silica PLC-VOA using suspended narrow ride structures and its application to V-AWG", Optical Society of America, OWO4, 2007.

  However, the above-described thermo-optic phase shifter has a problem in that it is necessary to form a heat insulating groove having a complicated structure, the manufacturing process is complicated, and productivity is poor. In addition, since the heat insulating groove having a complicated structure is formed, there is a problem that the stability as a practical device is low due to manufacturing variations and the like. In addition, depending on the structure of heat insulation, although low power consumption can be obtained, problems such as a decrease in response speed occur.

  On the other hand, with a structure that is practical in terms of ease of manufacture, stability, and the like, the heater and the heat insulating groove cannot be brought too close to the core, and there is a limit to reducing power consumption. For example, in a practical range, it is about 30 mW.

  As described above, at present, there is a problem that it is not easy to realize a thermo-optic phase shifter with lower power consumption in a state that is easy to manufacture and has stability.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a thermo-optic phase shifter with lower power consumption in a state that is easy to manufacture and stable. There is to do.

  The thermo-optic phase shifter according to the present invention includes a lower clad layer made of silicon oxide formed on a support substrate, a core made of single crystal silicon formed on the lower clad layer, and a lower clad layer And an upper clad layer made of silicon oxide formed on the core, and a heater layer disposed in a partial area on the upper clad layer corresponding to the upper part of the core and for heating a predetermined area of the core It is.

  The thermo-optic phase shifter includes two groove portions formed on both sides of the optical waveguide in a predetermined region constituted by the core, and the width of the optical waveguide between the two grooves is at most 20 μm. Further, the groove is formed to a depth at which the surface of the support substrate is exposed.

The thermo-optic phase shifter includes an opening formed in the support substrate corresponding to the region where the heater layer is formed, and the remaining thickness of the support substrate at the bottom of the opening is 1 μm or less. In addition , the heat storage conductive layer is formed at the bottom of the opening without being in contact with the side wall portion of the opening, and is made of a material having a higher thermal conductivity than the material constituting the lower cladding layer.

  The thermo-optic phase shifter may include a coating layer formed on the upper cladding layer so as to cover the heater layer. The covering layer may be made of the same material as the upper cladding layer.

As described above, the present invention includes a heater layer disposed in a partial region on the upper cladding layer corresponding to the upper portion of the core to heat a predetermined region of the core, and, for example, in addition to the heater layer, Two groove portions formed on both sides of the optical waveguide, an opening formed in the support substrate, a heat storage conductive layer at the bottom of the opening, and a covering layer covering the heater layer I made it. As a result, according to the present invention, in a state in which manufacture with ease stability, excellent effect say will be able to suppress the power consumption of the thermo-optic phase shift data is obtained.

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

[Embodiment 1]
First, the thermo-optic phase shifter according to the first embodiment will be described. FIG. 1 is a cross-sectional view schematically showing a configuration example of a thermo-optic phase shifter according to Embodiment 1 of the present invention. The thermo-optic phase shifter includes, for example, a support substrate 101 made of single crystal silicon, a lower clad layer 102 made of silicon oxide formed on the support substrate 101, and single crystal silicon formed on the lower clad layer 102. Are disposed on a core 103 composed of a thin wire (silicon thin wire), an upper clad layer 104 made of silicon oxide formed on the lower clad layer 102 and the core 103, and an upper clad layer 104 above the core 103. The heater layer 105 is provided.

  The core 103 has a cross-sectional shape with a width of about 0.4 μm and a height (thickness) of about 0.2 μm. The lower clad layer 102 and the upper clad layer 104 are formed with a film thickness of about 3 μm. For example, the lower cladding layer 102 and the core 103 can be formed by using a well-known SOI (Silicon on Insulator) substrate. The core 103 can be formed by using the buried oxide film of the SOI substrate as the lower cladding layer 102 and processing the SOI layer on the buried oxide film by a known photolithography technique and etching technique. Further, the upper clad layer 104 can be formed by depositing silicon oxide by a known CVD (Chemical Vapor Deposition) method.

  The heater layer 105 is for heating a predetermined region (phase shifter region) of the core 103. For example, the heater layer 105 is a metal film such as chromium or gold-palladium alloy, and has a width of about 5 μm and a film thickness of about 0.15 μm. What is necessary is just to be formed. Moreover, it is formed in a length of about 500 μm in the waveguide direction of the waveguide. For example, the heater layer 105 can be formed by forming a metal film of the above-described material by a PVD (Physical Vapor Deposition) method such as sputtering and processing it by known milling or etching. The heater layer 105 is formed by appropriately setting the material, width, thickness, heater length (waveguide direction), etc. so that the resistance is higher than the resistance of the wiring portion for connecting a power source or the like to the heater layer 105. That's fine.

  Next, a configuration example of an MZI type optical switch as an application example of the thermo-optic phase shifter in the first embodiment will be described with reference to a plan view of FIG. This MZI optical switch forms a Mach-Zehnder interferometer with two optical waveguides. First, an input-side waveguide 201 serving as an input port of one optical waveguide and the other input-side paired therewith A waveguide 211 and an input-side waveguide 201 and a 3 dB directional coupler 202 that couples the input-side waveguide 211 are provided. In addition, one intermediate waveguide 203 and the other intermediate waveguide 213 branched from the 3 dB directional coupler 202 and a 3 dB directional coupler 204 that couples the intermediate waveguide 203 and the intermediate waveguide 213 are provided. Further, one output side waveguide 205 and the other output side waveguide 215 branched from the 3 dB directional coupler 204 are provided. Note that multimode interference branching means may be used instead of the 3 dB directional coupler.

  Among these configurations, the intermediate optical waveguide 213 is provided with the thermo-optic phase shifter 100 according to the first embodiment described above. Here, the interval between the intermediate waveguide 203 and the intermediate waveguide 213 is, for example, about 130 μm. In the intermediate waveguide 213, a heater layer 105 is formed over a length of 500 μm in the waveguide direction to form a phase shifter region. A heater layer 105 is disposed on an upper clad layer 104 (not shown in FIG. 2) corresponding to the upper part of the core 103 constituting the intermediate waveguide 213, and a power source is connected to the heater layer 105 via a predetermined wiring. The core 103 in the intermediate waveguide 213 can be heated.

  Here, FIG. 1 shows a cross section taken along line AA 'in FIG. In addition, also in the input side waveguide 201, the input side waveguide 211, the intermediate waveguide 203, the output side waveguide 205, and the output side waveguide 215, the lower cladding layer 102, the core 103 formed thereon, The upper clad layer 104 is formed on these layers.

  According to the thermo-optic phase shifter of the first embodiment described above, since the core is made of single crystal silicon having a thermo-optic coefficient of about 2e-4, the silica system having a thermo-optic coefficient of 1e-5. One order of magnitude larger than the material core. Therefore, according to the first embodiment, the refractive index change Δn necessary for the phase shift can be obtained with a small temperature rise compared to the case where the silica-based core is used, which is necessary for the phase shift. The power consumption of the heater can be reduced. For example, according to the thermo-optic phase shifter in the first embodiment described above, it operates with a low power consumption of 30 mW.

  Further, according to the first embodiment, the optical waveguide using the core 103 made of a thin silicon wire can increase the relative refractive index difference between the core and the clad to about 40%. Compared to the above, a higher light confinement effect can be obtained. For this reason, it becomes possible to make the cross-sectional dimension of the core 103 on the order of submicron, and light and leakage from the core are small (mode field diameter is small). As a result, it is possible to reduce the cross-sectional area of the waveguide, for example, by reducing the thickness of the cladding, and the heat conduction from the heater layer 105 to the core 103 becomes faster, and the switch response speed can be further increased. it can. For example, according to the first embodiment described above, the switch response speed is 100 μs, and the switch operates at an order of magnitude higher than that of a PLC-type optical switch using a silica-based core.

[Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a cross-sectional view schematically showing a configuration example of the thermo-optic phase shifter in the second embodiment. The thermo-optic phase shifter includes, for example, a support substrate 101 made of single crystal silicon, a lower clad layer 102 made of silicon oxide formed on the support substrate 101, and a silicon thin wire formed on the lower clad layer 102. The structured core 103, the lower clad layer 102, the upper clad layer 104 made of silicon oxide formed on the core 103, and the heater layer 105 disposed on the upper clad layer 104 above the core 103. Prepare. These configurations are the same as those of the thermo-optic phase shifter of the first embodiment described above.

  The thermo-optic phase shifter according to the second embodiment is provided with heat insulating grooves 301 on both sides of the optical waveguide formed by the core 103 in addition to the above-described configuration. The heat insulation groove 301 should just be arrange | positioned in the area | region (phase shifter area | region) in which the heater layer 105 is formed. For example, after forming the upper clad layer 104, the heat insulating groove 301 uses a mask pattern formed by a known photolithography technique, and selects the upper clad layer 104 and the lower clad layer 102 to a predetermined depth by a known etching technique. It is possible to form by removing them. The heat insulating groove 301 may be formed to a depth in the middle of the upper clad layer 104, may be formed to a depth equal to the film thickness of the upper clad layer 104, or a depth until the surface of the support substrate 101 is exposed. Alternatively, it may be formed.

  Next, the relationship between the clad width w (the width of the optical waveguide) that is the distance between the two grooves and the operating power of the thermo-optic phase shifter will be described. FIG. 4A is a characteristic diagram showing the relationship between the clad width w and the operating power in each of the thermo-optic phase shifters having three types of groove depths. In FIG. 4A, a triangle indicates a case where the depth of the heat insulating groove 301 is 2 μm, which is smaller than the film thickness of the upper cladding layer 104, as shown in FIG. 4B. The black squares indicate the case where the depth of the heat insulating groove 301 is 3 μm, which is equal to the film thickness of the upper cladding layer 104, as shown in FIG. Further, as shown in FIG. 4D, the black circle shows the case where the depth of the heat insulating groove 301 is 6 μm, which is equal to the total film thickness of the upper cladding layer 104 and the lower cladding layer 102. .

  From these results, it is understood that when the thickness of the core 103 and the clad layer is the above-described dimensions, the power consumption is reduced when the clad width is narrower than 20 μm. Further, it can be seen that the heat insulating groove 301 has a lower power consumption as it is deeper in the above-described three conditions. Among these, the power consumption is lowest when the surface is formed to a depth at which the surface of the support substrate 101 is exposed, which is the condition shown in FIG. Thus, it can be seen that the power consumption can be reduced by reducing the volume of the object to be heated by forming the heat insulating groove 301 by making the clad width narrower than 20 μm (at most 20 μm). In addition, the result of FIG. 4 is based on simulation.

  Next, a configuration example of the MZI type optical switch device to which the thermo-optic phase shifter in the second embodiment is applied will be described. FIG. 5 is a plan view (a) and a sectional view (b) showing the configuration of this MZI type optical switch device. This device includes an input-side waveguide 501 serving as an input port, a multimode interference branching unit 502 that branches the input-side waveguide 501, one intermediate waveguide 503 branched from the multimode interference branching unit 502, and the other intermediate A waveguide 513, a multimode interference branching unit 504 that couples the intermediate waveguide 503 and the intermediate waveguide 513, and an output-side waveguide 505 connected to the multimode interference branching unit 504 are provided.

  Among these configurations, the intermediate optical waveguide 503 and the intermediate waveguide 513 are provided with the above-described thermo-optic phase shifter in the second embodiment. A heater layer 105 is disposed on the upper clad layer 104 corresponding to the upper part of the core 103 constituting each intermediate waveguide, and a power source is connected to the heater layer 105 via a predetermined wiring. Can be heated. Each thermo-optic phase shifter includes heat insulating grooves 301 on both sides of the optical waveguide formed by the core 103. Between the intermediate waveguide 503 and the intermediate waveguide 513, a heat insulating groove 301 common to both is provided.

  In this PLC device, in each thermo-optic phase shifter, the cladding width was 10 μm, the thickness of the lower cladding layer 102 was 3 μm, and the thickness of the upper cladding layer 104 was 7 μm. Accordingly, the heat insulating groove 301 has a depth of 7 μm. This thermo-optic phase shifter operated at about 26 mW. As described with reference to FIG. 4, the power consumption can be further reduced by narrowing the cladding width.

[Embodiment 3]
Next, Embodiment 3 of the present invention will be described with reference to FIG. 6 and FIG. FIG. 6 is a cross-sectional view schematically showing a configuration example of the thermo-optic phase shifter in the third embodiment. The thermo-optic phase shifter includes, for example, a support substrate 101 made of single crystal silicon, a lower clad layer 102 made of silicon oxide formed on the support substrate 101, and a silicon thin wire formed on the lower clad layer 102. The structured core 103, the lower clad layer 102, the upper clad layer 104 made of silicon oxide formed on the core 103, and the heater layer 105 disposed on the upper clad layer 104 above the core 103. Prepare. These configurations are the same as those of the thermo-optic phase shifter of the first embodiment described above.

  In addition to the configuration described above, the thermo-optic phase shifter according to the third embodiment is provided with an opening 601 that opens to the back side of the support substrate 101 corresponding to the region where the heater layer 105 is formed. It is. The opening 601 may be formed in the above-described phase shifter region in the waveguide direction of the optical waveguide. The opening 601 can be formed by selectively removing the support substrate 101 from the back surface by, for example, wet etching, dry etching, or mechanical polishing. Thus, by providing the support substrate 101 with the opening portion 601, heat that is conducted by the heating of the heater layer 105 and flows out to the support substrate 101 side is suppressed, and the heating to the core 103 is more efficient. Will be able to do. As a result, the power consumption of the thermo-optic phase shifter can be reduced.

  Next, the relationship between the opening width w2 (waveguide width direction) of the opening 601 and the remaining substrate thickness t and the power consumption will be described. First, as shown in FIG. 7A, when the substrate remaining thickness t in the support substrate 101 is thicker than 1 μm, there is no difference in power consumption when the opening 601 is not formed. On the other hand, when the substrate remaining thickness t is less than 1 μm and 0.5 μm or less, it can be seen that the power consumption decreases. In particular, it is possible to reduce the power consumption to 10 mW or less by forming the opening 601 so that the remaining substrate thickness t is substantially zero, in other words, the back surface of the lower cladding layer 102 is exposed. . However, if the remaining substrate thickness t is 0, the lower clad layer 102 may be damaged in the formation of the opening 601, and this damage may increase the loss of the optical waveguide. Good. This result is obtained when the opening width w2 is 40 μm.

  Further, as shown in FIG. 7B, the width w2 of the opening 601 formed in the support substrate 101 is, for example, about 40 μm, so that the power consumption is 10 mW or less, compared with the case where the opening 601 is not formed. Can be greatly reduced. Further, by setting the width of the opening 601 to 120 μm, the power consumption can be reduced to about 3 mW.

  Moreover, it becomes possible to further reduce power consumption by using the heat insulation groove | channel and the said opening part mentioned above in combination. For example, by forming a heat insulating groove with a depth of 3 μm on both sides of the waveguide in the phase shifter region so that the cladding width is 10 μm, in addition, an opening with a thickness of 0 μm and a width of 120 μm is formed on the back surface of the substrate. The power consumption can be reduced to about 1 mW. Furthermore, by optimizing the structure (shape) of the heat insulating groove and the opening, it is possible to reduce the power consumption to the order of μW. In addition, the result of the power consumption suppression mentioned above is based on simulation.

[Embodiment 4]
Next, Embodiment 4 of the present invention will be described with reference to FIG. FIG. 8 is a cross-sectional view schematically showing a configuration example of the thermo-optic phase shifter in the fourth embodiment. The thermo-optic phase shifter includes, for example, a support substrate 101 made of single crystal silicon, a lower clad layer 102 made of silicon oxide formed on the support substrate 101, and a silicon thin wire formed on the lower clad layer 102. The structured core 103, the lower clad layer 102, the upper clad layer 104 made of silicon oxide formed on the core 103, and the heater layer 105 disposed on the upper clad layer 104 above the core 103. Prepare. The thermo-optic phase shifter includes an opening 601 that opens to the back surface side of the support substrate 101 corresponding to the region where the heater layer 105 is formed. These configurations are the same as those of the thermo-optic phase shifter of the third embodiment described above.

  In addition to the above-described configuration, the thermo-optic phase shifter according to the fourth embodiment has a heat storage configured by a high thermal conductivity material having a higher thermal conductivity at the bottom of the opening 106 than that of the material forming the lower cladding layer 102. A conductive layer 801 is provided. The heat storage conductive layer 801 may be formed in the above-described phase shifter region in the waveguide direction of the optical waveguide. Therefore, in the phase shifter region, the core 103 is sandwiched between the heater layer 105 and the heat storage conductive layer 801.

  The heat storage conductive layer 801 should just be comprised from metals, such as aluminum and copper, for example. For example, it can be formed by forming a thin film of the above-described high thermal conductivity material by sputtering or the like and processing it by a known photolithography technique and etching technique. Alternatively, it may be formed by sputtering using a stencil mask. Alternatively, the heat storage conductive layer 801 may be formed by leaving a part of the support substrate 101. In this case, the heat storage conductive layer 801 is composed of single crystal silicon. Note that the heat storage conductive layer 801 is formed so as not to contact the side wall portion of the opening 601. When the heat storage conductive layer 801 is formed in contact with the side wall portion, a heat conduction path from the heat storage conductive layer 801 to the support substrate 101 is formed, and an effect in the heat storage conductive layer 801 described later is reduced.

  According to the thermo-optic phase shifter of the fourth embodiment, since the heat storage conductive layer 801 is provided as described above, the upper cladding layer 104, the core 103, and the lower cladding layer 102 are heated by the heater layer 105. It is suppressed that the conducted heat is conducted and diffused to the support substrate 101, and is conducted and accumulated in the heat storage conductive layer 801. For this reason, in the core 103, in addition to the heater layer 105, the heat storage conductive layer 801 also serves as a heat source. As a result, by providing the heat storage conductive layer 801, the temperature gradient formed from the heater layer 105 to the core 103 becomes smaller than when the heat storage conductive layer 801 is not provided, and the heater layer 105 is set to a constant temperature more than necessary. Without this, the core 103 can be heated to a desired temperature, and power consumption can be suppressed.

  Next, a configuration example of the MZI type optical switch device using the thermo-optic phase shifter in the fourth embodiment will be described with reference to FIG. FIGS. 9A and 9B are plan views (a) and (b) showing the configuration of this MZI type optical switch device. FIG. 9A is a plan view seen from the side where the core 103 is formed, and FIG. 9B is a plan view seen from the support substrate 101 side. This device includes an input-side waveguide 901 serving as an input port, an output-side waveguide 902 serving as an output port, and an output-side waveguide 903. Two thermo-optic phase shifters 911 and thermo-optic phase shifters 912 are connected in series. Thus, a higher extinction ratio can be obtained by providing a two-stage thermo-optic phase shifter from the input port to the output port.

  Among these configurations, an opening 602 that is continuously formed over the two thermo-optic phase shifters 911 and 912 is formed in the support substrate 101, and is continuously formed inside the openings 602. The heat storage conductive layer 802 thus formed is formed. The opening 602 is formed in the portion of the thermo-optic phase shifter 911 and the thermo-optic phase shifter 912 so as to face the formation region of the heater layer 105, and between the thermo-optic phase shifter 911 and the thermo-optic phase shifter 912, It is formed so as to avoid the region where the core 103 is formed, and is formed as one groove. Therefore, the heat storage conductive layer 802 is formed in common in the two thermo-optic phase shifters 911 and thermo-optic phase shifters 912.

  In the two thermo-optic phase shifter 911 and the thermo-optic phase shifter 912 configured as described above, for example, it is easy to make the temperature between them more uniform. Moreover, since the heat from one heater layer 105 is conducted to the other core 103 through the heat storage conductive layer 802, the switch operation can be performed more efficiently. In addition, you may make it combine the heat insulation groove | channel mentioned above in these.

[Embodiment 5]
Next, a fifth embodiment of the present invention will be described. FIG. 10 is a cross-sectional view illustrating a configuration example of the thermo-optic phase shifter according to the fifth embodiment. The thermo-optic phase shifter includes, for example, a support substrate 101 made of single crystal silicon, a lower clad layer 102 made of silicon oxide formed on the support substrate 101, and a silicon thin wire formed on the lower clad layer 102. The structured core 103, the lower clad layer 102, the upper clad layer 104 made of silicon oxide formed on the core 103, and the heater layer 105 disposed on the upper clad layer 104 above the core 103. Prepare. These configurations are the same as those of the thermo-optic phase shifter of the first embodiment described above.

  The thermo-optic phase shifter according to the second embodiment includes a coating layer 1001 formed on the upper cladding layer 104 so as to cover the heater layer 105 in addition to the above-described configuration. For example, after forming the upper clad layer 104 and forming the heater layer 105 thereon, silicon oxide is deposited in the same manner as the upper clad layer 104 to form the cover layer 1001. In other words, the heater layer 105 may be formed in an embedded state in the upper clad layer made of silicon oxide.

  By forming the covering layer 1001 in this manner, heat from the heater layer 105 is conducted to the upper cladding layer 104 in a state where heat dissipation to the upper atmosphere side is suppressed. In addition, damage to the heater layer 105 can be suppressed in the formation of the heat insulating grooves and the formation of the openings in the support substrate 101 described above.

By the way, by providing the coating layer 1001 as described above, it becomes possible to more easily form the spot size conversion section as shown in FIG. 11 (see, for example, Patent Document 1 for the spot size conversion section). ). For example, the covering layer 1001 is made of a material having a refractive index smaller than that of the upper cladding layer 104. For example, the upper cladding layer 104 may be composed of a silicon oxide (SiO _x ) film having a refractive index of 1.52, and the covering layer 1001 may be composed of a silicon oxide (SiO ₂ ) film having a refractive index of 1.47. Using such materials, first, the upper clad layer 104 is formed on the core 103. After that, in the place to be the spot size conversion unit 1101 shown in the plan view of FIG. 11A, the upper cladding layer 104 is finely processed into a predetermined shape, and as shown in the sectional view of FIG. It is assumed that the second core 104a covering the core 103 is formed.

  After that, by forming a film of the material to be the coating layer 1001 from the region of the intermediate waveguide 503 and the intermediate waveguide 513 to the spot size conversion unit 1101, in the region of the thermo-optic phase shifter, FIG. As shown in FIG. 11C, a coating layer 1001 is formed on the heater layer 105, and in the spot size conversion unit 1101, an upper cladding layer 1001a in the spot size conversion region is formed as shown in FIG. 11C. State. According to the spot size converter 1101 formed in this way, an optical fiber having a large mode field diameter or a silica-based optical waveguide circuit is connected to the input-side waveguide 501 and the output-side waveguide 505 by converting the mode field diameter. Can be made. Further, as described above, the spot size conversion unit 1101 can be formed almost simultaneously with the formation of the upper clad layer 104 and the covering layer 1001, and thus has an advantage from the viewpoint of productivity.

The covering layer 1001 is not limited to SiO _x and may be any material that has a refractive index lower than that of silicon (refractive index: 3.478) and can form the upper cladding layer, the second core, and the like. For example, nitrogen is added. Further, silicon oxide (silicon oxynitride) or a polymer material (plastic) that can be used as an optical material may be used.

It is sectional drawing which shows typically the structural example of the thermo-optic phase shifter in Embodiment 1 of this invention. 3 is a plan view showing a configuration example of an MZI type optical switch as an application example of a thermo-optic phase shifter in Embodiment 1. FIG. It is sectional drawing which shows typically the structural example of the thermo-optic phase shifter in Embodiment 2 of this invention. A characteristic diagram (a) showing the relationship between the clad width w and the operating power in each of the three types of thermo-optic phase shifters, and explanatory diagrams (b), (c) explaining the state of each groove depth ), (D). FIG. 6 is a plan view (a) and a cross-sectional view (b) showing a configuration of an MZI type optical switch device as an application example of a thermo-optic phase shifter in the second embodiment. It is sectional drawing which shows typically the structural example of the thermo-optic phase shifter in Embodiment 2 of this invention. FIG. 10 is a characteristic diagram showing the relationship between the opening width w2 (waveguide width direction) and the remaining substrate thickness t of the thermooptic phase shifter opening 601 and the power consumption in the second embodiment. It is sectional drawing which shows typically the structural example of the thermo-optic phase shifter in this Embodiment 4. FIG. 10 is a plan view showing a configuration example of an MZI type optical switch device using a thermo-optic phase shifter in a fourth embodiment. It is sectional drawing which shows the structural example of the thermo-optic phase shifter in Embodiment 5 of this invention. It is the top view (a) and sectional drawing (b), (c) which show the structural example of the thermo-optic phase shifter in Embodiment 5 of this invention. It is sectional drawing which shows the structure of the thermo-optic phase shifter used for an optical switch.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Support substrate, 102 ... Lower clad layer, 103 ... Core, 104 ... Upper clad layer, 105 ... Heater layer.

Claims (5)

A lower clad layer made of silicon oxide formed on a support substrate;
A core made of single crystal silicon formed on the lower cladding layer;
An upper cladding layer made of silicon oxide formed on the lower cladding layer and the core;
A heater layer disposed in a partial region on the upper cladding layer corresponding to the upper portion of the core to heat a predetermined region of the core ;
An opening formed in a support substrate corresponding to a region where the heater layer is formed;
A heat storage conductive layer formed at a bottom portion of the opening without being in contact with a side wall portion of the opening and made of a material having a higher thermal conductivity than a material constituting the lower cladding layer ;
Thermo-optic phase shifter the remaining thickness of the supporting substrate at the bottom of the opening is characterized that you have been a 1μm or less. The thermo-optic phase shifter according to claim 1,
Comprising two grooves formed on both sides of the optical waveguide in the predetermined region composed of the core;
A thermo-optic phase shifter characterized in that the width of the optical waveguide between the two grooves is at most 20 μm. The thermo-optic phase shifter according to claim 2,
The groove is formed to a depth at which the surface of the support substrate is exposed. The thermo-optic phase shifter. In the thermo-optic phase shifter according to any one of claims 1 to 3 ,
A thermo-optic phase shifter comprising: a coating layer formed on the upper cladding layer so as to cover the heater layer. The thermo-optic phase shifter according to claim 4 ,
The thermo-optical phase shifter, wherein the coating layer is made of the same material as the upper cladding layer.

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