JP2000258736A - Quartz-base optical switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quartz-base optical switch capable of well executing the control of heat transfer of the heat generated by thin-film heaters. SOLUTION: The quartz-base optical switch, which is disposed with a plurality of optical waveguides consisting of lower clad layers 4, cores 5a and 5b and upper clad layers 6 on an Si substrate 1 and utilizes a thermo-optical effect, is provided with the thin-film heaters 7a and 7b formed on the upper clad layers equal to or slightly larger than the pattern width of the cores right thereunder so as to exist right above the cores of the at least one optical waveguide, and porous silicon regions 8a and 8b formed in the Si substrate surface portion right below the thin-film heaters slightly larger than the pattern width of the thin-film heaters existing right thereabove.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quartz-based optical switch using a thermo-optic effect used in a quartz-based planar lightwave circuit.

[0002]

2. Description of the Related Art Conventionally, as a quartz-based optical switch utilizing this kind of thermo-optic effect, the one disclosed in the literature: Optics, Vol. 21, No. 8 (August 1992), pp. 516 to 520 is known. In particular, FIG. 2 on page 517 of this document shows that:
A symmetric Mach-Zehnder type 2 × 2 optical switch including two 3 dB directional couplers and an arm optical waveguide having the same length is disclosed. In the conventional quartz optical switch disclosed herein, a thin-film heater is provided immediately above a core embedded in a clad on a silicon substrate (hereinafter, referred to as a Si substrate), and the thin-film heater is turned on or off to turn off the quartz-based film. By using the thermo-optic effect, a phase difference is given to give a bar state or a cross state.

[0003]

However, in the above-mentioned conventional quartz optical switch, the heating of the thin film heater causes
Since the switching operation is obtained, when the thin film heater is heated, heat is easily escaping particularly through the Si substrate located below the core, and there is a problem that the switching power is as large as about 500 mW. Further, when a material having a lower thermal conductivity than the Si substrate, for example, quartz, is used for the substrate, diffusion of heat is prevented when the thin film heater is heated, and an optical circuit ( In this case, in addition to the optical waveguide, the optical circuit adjacent to this optical circuit is also affected by heat via the substrate, resulting in an increase in crosstalk and a hindrance to diffusion of heat when the thin film heater is turned off. This causes a problem that the switching speed is reduced.

An object of the present invention is to solve the above-mentioned problems and to provide a quartz-based optical switch capable of well controlling heat conduction of heat generated by a thin film heater.

[0005]

To achieve the above object, according to the first aspect of the present invention, a plurality of quartz-based optical waveguides comprising a lower cladding layer, a core, and an upper cladding layer are provided on a silicon substrate, In a silica-based optical switch utilizing the thermo-optic effect, the pattern width of the core immediately below or above the upper cladding layer is equal to or slightly higher than a predetermined region of the core of at least one optical waveguide. A thin film heater formed to have a large width and a predetermined length, and a size of the thin film heater immediately above a silicon substrate surface portion directly below a thin film heater formation region in an optical waveguide provided with the thin film heater. A porous silicon region formed so as to be equal to or larger than the silicon substrate and having a thermal conductivity smaller than that of the silicon substrate. The features.

According to a second aspect of the present invention, in the quartz optical switch according to the first aspect, the thin film heater and the porous silicon region are provided corresponding to all the optical waveguides.

According to a third aspect of the present invention, there is provided a quartz optical switch using a thermo-optic effect, wherein a plurality of quartz optical waveguides each including a lower cladding layer, a core, and an upper cladding layer are provided on a silicon substrate. Formed on the upper cladding layer to have a size equal to or slightly larger than the pattern width of the core immediately below the upper cladding layer so as to be located immediately above the predetermined region of the core of at least one optical waveguide to a predetermined length. The surface of the silicon substrate almost directly below the core forming region in the optical waveguide provided with the thin film heater and the thin film heater is a silicon portion of the silicon substrate itself, and substantially the same as the thin film heater forming region in the optical waveguide having the thin film heater. The lower cladding sandwiched between the core region portion immediately below and the core region portion of the adjacent optical waveguide facing the core region portion. A porous silicon region formed on the surface portion of the silicon substrate substantially directly below the surface region of the pad layer and having a thermal conductivity set to be smaller than the thermal conductivity of the silicon substrate. .

According to a fourth aspect of the present invention, there is provided a quartz optical switch using a thermo-optic effect, wherein a plurality of quartz optical waveguides each comprising a lower cladding layer, a core, and an upper cladding layer are provided on a silicon substrate. Each of the optical waveguides is formed on the upper cladding layer to have a predetermined length equal to or slightly larger than the pattern width of the core immediately below the upper cladding layer so as to be located immediately above the predetermined region of the core of each optical waveguide. The surface of the silicon substrate directly below the core forming region in each optical waveguide and the silicon substrate itself is a silicon portion as it is, and the adjacent optical waveguide is located at a position almost immediately below the thin film heater forming region in each optical waveguide. It is formed on the surface portion of the silicon substrate substantially immediately below the surface region of the lower clad layer sandwiched between the core region portions, and has a thermal conductivity of Characterized in that a porous silicon region that is set to be smaller than the thermal conductivity of the silicon substrate.

According to a fifth aspect of the present invention, in the quartz optical switch according to the fourth aspect, of the plurality of optical waveguides disposed on the silicon substrate, the two optical waveguides are disposed on both end surfaces of the substrate. Corresponding to one of the optical waveguides, and the silicon substrate substantially immediately below the surface region of the lower cladding layer sandwiched between the core region substantially immediately below the thin film heater formation region and the surface position of the side end surface of the silicon substrate. Another porous silicon region is further provided on the surface portion.

According to a sixth aspect of the present invention, in the quartz optical switch according to any one of the first to fifth aspects, the quartz optical switch is formed by thermally oxidizing porous silicon instead of the porous silicon. Characterized in that a silicon oxide film is used.

According to a seventh aspect of the present invention, in the quartz optical switch according to any one of the first to sixth aspects, the lower cladding layer and the upper cladding layer are respectively formed in common to the respective optical waveguides. It is characterized by having been done.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a symmetric Mach-Zehnder type quartz optical switch according to a first embodiment of the present invention, FIG. 1 (a) is a plan view thereof, and FIG.
1 shows a cross-sectional view taken along the line AB in FIG.

As shown in FIG. 1A, a symmetric Mach-Zehnder type quartz optical switch according to the first embodiment comprises two 3d-type optical switches formed on a Si (silicon) substrate 1.
B-directional couplers 2a and 2b and two same-length arm optical waveguides 3a and 3b are provided. The 3 dB directional couplers 2a and 2b and the arm optical waveguides 3a and 3b have a structure in which a core is sandwiched between a lower clad and an upper clad. In particular, the structure of the arm optical waveguides 3a and 3b is shown in FIG.
As shown in the sectional view along the line B, a lower cladding layer 4 is provided on the Si substrate 1, and cores 5a and 5b are provided on the lower cladding layer 4 corresponding to the arm optical waveguides 3a and 3b.

The upper cladding layer 6 is formed on the upper and side portions of the cores 5a and 5b so as to embed the cores 5a and 5b.
Is provided. The cores 5a and 5b, the lower cladding layer 4 and the upper cladding layer 6 are formed of a quartz-based film, and the refractive indices of the cores 5a and 5b are different from those of the lower cladding layer 4 and the upper cladding layer 6. It is set to be slightly higher than the rate.

Further, thin film heaters 7a and 7b are provided on the upper clad layer 6 so as to be located immediately above predetermined regions of the cores 5a and 5b, respectively. That is,
The patterns of the thin film heaters 7a and 7b are formed such that the patterns of the cores 5a and 5b exist directly below the upper cladding layer 6 in the arm optical waveguide portions 3a and 3b. The formation area of the thin film heaters 7a and 7b is
The width (planar size) is equal to or slightly larger than the pattern width of the cores 5a and 5b immediately below the core 5a and 5b and has a predetermined length.

Further, as shown in FIG. 1B, porous silicon regions 8a and 8b having a thickness of about 10 μm are formed on the surface of the Si substrate 1 almost immediately below the regions where the thin film heaters 7a and 7b are formed. The formation regions of these porous silicon regions 8a and 8b are formed to have a size (planar size) that is equal to or larger than the size of the thin film heaters 7a and 7b immediately above them. Moreover, the thermal conductivity of the porous silicon regions 8a and 8b
Is set so as to be smaller than the thermal conductivity. The provision of the porous silicon regions 8a and 8b is a feature of the symmetric Mach-Zehnder type quartz optical switch according to the first embodiment. In the present embodiment, by providing the porous silicon regions 8a and 8b, the heat conduction of the heat generated by the thin film heater is controlled well.

In the symmetric Mach-Zehnder type quartz optical switch configured as described above, by turning on or off the thin film heater 7a or 7b, the light passing through the arm optical waveguide is utilized by utilizing the thermo-optic effect of the quartz film. To provide a bar state or a cross state, thereby performing a switching operation.

According to the symmetric Mach-Zehnder type quartz optical switch of the first embodiment, the thin film heaters 7a, 7
The surface portion of the Si substrate 1 immediately below the formation region b has a predetermined thickness equal to or larger than the thin film heater (planar size) and has a smaller thermal conductivity than the thermal conductivity of the Si substrate 1 Porous silicon regions 8a, 8b having
Is formed, the rate at which heat is diffused into the Si substrate 1 when the thin film heater 7a or 7b is heated is about 50%.
%, That is, the heat conduction is suppressed, and as a result, the power consumption at the time of switching is reduced from the conventional about 500 mW to about 25%.
It is reduced to 0 mW.

Since the periphery of the porous silicon regions 8a and 8b is surrounded by the silicon portion of the Si substrate 1 itself, when the thin film heater is turned off, the periphery of the corresponding porous silicon region corresponding to the corresponding arm optical waveguide is turned off. Heat is diffused from the silicon portion (the Si substrate 1 portion), and the influence on the switching operation when the thin film heater is turned off can be reduced.

In the above description, the case where there are two arm optical waveguides has been described. However, the present invention can be applied to a case where there are three or more arm optical waveguides.

In the above description, an example in which a thin film heater and a porous silicon region are provided corresponding to each arm optical waveguide has been described. However, an arm optical waveguide without a thin film heater and a porous silicon region may be provided. Good.

Next, the steps of manufacturing the symmetric Mach-Zehnder type quartz optical switch according to the first embodiment will be described with reference to FIGS. 2 (a) to 2 (e), 3 (a) to 3 (e), and 4 (3). a) ~
This will be described with reference to FIG.

First, as shown in FIG. 2A, a p-type Si substrate 1 having a specific resistance of 0.01 to 1.0 Ω · cm is heated at a temperature of 80 ° C.
Wash for 5 minutes using a mixed solution of H ₂ SO ₄ : H ₂ O ₂ = 1: 1 at ° C. Here, p-type, specific resistance 0.01 to 1.0Ω
The reason for using the cm Si substrate 1 is that light irradiation is necessary during anodization for n-type Si, but light irradiation is not necessary for p-type Si. This is because it is difficult to obtain silicon. next,
After washing the Si substrate 1 with water for 5 minutes, 1% HF at a temperature of 20 ° C.
Wash with the solution for 20 seconds. Next, the Si substrate 1 is
Rinse for minutes.

Next, as shown in FIG. 2B, an Al electrode 10 for anodization is formed on the back surface of the Si substrate 1 by a vacuum evaporation method.

Next, as shown in FIG. 2C, a resist 11 is applied on the surface of the Si substrate 1 using a spin coater (not shown) at a rotation speed of 1000 rpm for 20 seconds.

Next, as shown in FIG. 2D, after the resist 11 is exposed using a mask (not shown) for forming a porous silicon region by a normal photolithography technique,
develop. Thus, a resist pattern 11a having an opening at a position corresponding to the position where the porous silicon region is formed is formed.

Next, as shown in FIG.
_{2 H 5 OH: H 2 O} = 1: 1: 1 mixed solution used, the area where the silicon through the opening of the resist pattern 11a is exposed anodizing. At this time, the Al electrode 10 on the back surface of the Si substrate is positive, the Pt electrode is negative, and connected to a constant current source, the current density is 40 mA / cm ² , and the anodizing time is 5 minutes. By this step, a depth of about 1
0 μm porous silicon regions 8a and 8b are formed.

Next, as shown in FIG. 3A, after removing the resist pattern 11a and further removing the Al electrode 10 on the back surface, the Si substrate 1 including the surface on which the porous silicon regions 8a and 8b are formed is formed. A quartz-based lower cladding layer 4 and a core layer 5 are deposited on the surface of the substrate by plasma chemical vapor deposition using tetraethoxysilane and oxygen as raw materials. Here, the thickness of the lower cladding layer 4 is set to about 20
μm, and the thickness of the core layer 5 is 6 μm. Here, the lower clad layer 4 has a relative refractive index difference of 0.25 to
Fluorine (F) is doped to make it 0.7%. The core layer 5 is not doped. Here, the relative refractive index difference is, for example, 0.5%. Thus, the refractive index of the lower cladding layer 4 is smaller than that of the core layer 5.

Next, as shown in FIG.
After depositing the (amorphous Si) layer 12 by plasma enhanced chemical vapor deposition, a resist 13 is applied by a spin coater (not shown).

Next, as shown in FIG. 3 (c), the substrate is exposed to light by a conventional light exposure apparatus using a core patterning mask (not shown), and then developed. As a result, a resist pattern 13a is formed in which the resist existing at the position where the core pattern is formed is removed and the resist located at a position other than the position where the core pattern is formed is removed. The core patterning mask corresponds to the pattern of the core in the two 3 dB directional couplers and the two arm waveguides of the same length shown in FIG.
This corresponds to the pattern of the core in the B-directional coupler and the arm optical waveguide.

Next, as shown in FIG. 3D, using the resist pattern 13a as a mask, a reactive ion etching apparatus (not shown) is used to a-S with CHBr gas.
The i-layer 12 is patterned by etching to obtain a
-A pattern 12a of the Si layer is obtained.

Next, as shown in FIG.
Using the layer pattern 12a as a mask and using a reactive ion etching apparatus, the core is patterned by etching with CHF ₃ gas to form core patterns 5a and 5b.
Get.

Next, as shown in FIG. 4A, after removing the resist pattern 13a, the a-Si layer pattern 12a is further removed.

Next, as shown in FIG. 4B, a quartz-based upper cladding layer 6 is deposited by plasma enhanced chemical vapor deposition using tetraethoxysilane and oxygen as raw materials. The thickness of the upper cladding layer 6 is about 20 μm on the cores 5a and 5b. Here, the upper cladding layer 6 includes:
Fluorine (F) is doped so as to have the same refractive index as that of the lower cladding layer 4, that is, to make the relative refractive index difference with the core 0.5%.

Next, as shown in FIG. 4C, a Cr film 7 for a thin film heater is formed on the upper clad layer by a vacuum evaporation method. Here, the thickness of Cr is about 0.5 μm.
Next, a resist 14 is applied by a spin coater (not shown).

Next, as shown in FIG. 4 (d), using a mask for patterning a thin film heater (not shown), exposure is performed by a usual exposure apparatus, and development is performed. As a result, a resist pattern 14a is formed in which the resist existing at the position where the thin film heater pattern is formed is removed and the resist at a position other than the thin film heater pattern formation position is removed.

Next, as shown in FIG. 4 (e), using the resist pattern 13a as a mask, the reactive ion etching apparatus (not shown) is used to pattern the Cr film 7 by etching to form a thin film heater. Pattern 7a,
7b is obtained. Finally, the resist pattern 14a is removed. In this way, a symmetric Mach-Zehnder type quartz optical switch including two 3 dB directional couplers and two arm optical waveguides of the same length shown in FIG. 1 is completed.

Next, a second embodiment of the present invention will be described.

FIG. 5 is a diagram showing a configuration of a symmetric Mach-Zehnder type quartz optical switch according to a second embodiment of the present invention. FIG. 5 (a) is a plan view thereof, and FIG.
5A is a cross-sectional view taken along the line AB in FIG. These figures 5
In FIG. 5A and FIG. 5B, the same parts as those in the first embodiment are denoted by the same reference numerals.

The second embodiment differs from the first embodiment in the formation position of the porous silicon region provided in the arm optical waveguide.

Hereinafter, a detailed description will be given with reference to FIGS. 5 (a) and 5 (b).

As shown in FIG. 5A, the symmetric Mach-Zehnder type quartz optical switch according to the second embodiment also includes two 3d-type optical switches formed on a Si (silicon) substrate 1.
B-directional couplers 2a and 2b and two same-length arm optical waveguides 3a and 3b are provided. The 3 dB directional couplers 2a and 2b and the arm optical waveguides 3a and 3b have a structure in which a core is sandwiched between a lower clad and an upper clad. In particular, the structure of the arm optical waveguides 3a and 3b is shown in FIG.
As shown in the sectional view along the line B, a lower cladding layer 4 is provided on the Si substrate 1, and cores 5a and 5b are provided on the lower cladding layer 4 corresponding to the arm optical waveguides 3a and 3b.

The upper cladding layer 6 is formed on the upper and side portions of the cores 5a and 5b so as to embed the cores 5a and 5b.
Is provided. The cores 5a and 5b, the lower cladding layer 4 and the upper cladding layer 6 are formed of a quartz-based film, and the refractive indices of the cores 5a and 5b are different from those of the lower cladding layer 4 and the upper cladding layer 6. It is set to be slightly higher than the rate.

Further, thin film heaters 7a and 7b are provided on the above-mentioned upper cladding layer 6 so as to be located immediately above predetermined regions of the cores 5a and 5b, respectively. That is,
The patterns of the thin film heaters 7a and 7b are formed such that the patterns of the cores 5a and 5b exist directly below the upper cladding layer 6 in the arm optical waveguide portions 3a and 3b. The formation area of the thin film heaters 7a and 7b is
It is formed in a size (planar size) that is equal to or slightly larger than the pattern width of the cores 5a and 5b immediately below it and has a predetermined length.

Further, as shown in FIGS. 5 (a) and 5 (b), the Si film almost immediately below the region where the thin film heaters 7a and 7b are formed is formed.
The surface of the substrate 1 is a silicon portion 1 of the Si substrate itself.
a, 1b, the lower cladding layer 4 sandwiched between a region of the core 5a located substantially immediately below the region where the thin film heater 7a is formed and a region of the core 5b located substantially immediately below the region where the thin film heater 7b is formed. Of S just below the surface region 4a
A porous silicon region 8c having a thickness of about 10 μm is formed on the surface of i-substrate 1.

Further, the region of the core 5a located almost immediately below the region where the thin film heater 7a is formed and the side end surface of the Si substrate 1 are opposed to the porous silicon region 8c with the silicon portion 1a interposed therebetween. A porous silicon region 8d having a thickness of about 10 μm is formed on the surface portion of the Si substrate 1 substantially immediately below the surface region 4b of the lower cladding layer 4 sandwiched between the surface positions.

The region of the core 5b, which is located almost immediately below the region where the thin film heater 7b is formed, and the side end surface of the Si substrate 1 are opposed to the porous silicon region 8c with the silicon portion 1b interposed therebetween. A porous silicon region 8e having a thickness of about 10 μm is formed on the surface portion of the Si substrate 1 substantially immediately below the surface region 4c of the lower clad layer 4 sandwiched between the surface positions. These porous silicon regions 8
The thermal conductivity of c, 8d, 8e is set to be smaller than the thermal conductivity of the Si substrate 1. In the present embodiment, these porous silicon regions 8c, 8d, 8e
Is provided, the heat conduction of the heat generated by the thin-film heater is well controlled.

In the symmetric Mach-Zehnder type quartz optical switch configured as described above, by turning on or off the thin film heater 7a or 7b, the phase difference is converted to the light passing through the arm optical waveguide by using the thermo-optic effect of the quartz film. To provide a bar state or a cross state, thereby performing a switching operation.

According to the symmetric Mach-Zehnder type quartz optical switch of the second embodiment, the thin film heaters 7a and 7
Since the porous silicon region 8c having a thermal conductivity smaller than the thermal conductivity of Si is formed between the adjacent arm optical waveguides on the peripheral surface of the Si substrate 1 except immediately below the b, a predetermined arm optical waveguide is formed. When the corresponding thin film heater is turned on and heated, the rate at which the generated heat diffuses to the adjacent other arm optical waveguide side is reduced. Therefore, crosstalk to another adjacent arm optical waveguide is reduced as compared with the related art. Since the silicon portions 1a and 1b are present on the surface of the Si substrate 1 located immediately below the thin film heater, the rate at which heat is diffused to the silicon portions 1a and 1b of the Si substrate when the thin film heater is turned off. Does not decrease so much, and does not significantly impair the switching speed when the thin film heater is turned off.

Although the silicon portions 1a and 1b are located immediately below the cores 5a and 5b located immediately below the thin film heaters 7a and 7b, porous silicon regions 8c, 8d and 8e are formed on both sides of the silicon portions. Has been
Although not as remarkable as in the case of the first embodiment, when the thin film heater 7a or 7b is heated,
Is reduced to some extent, that is, heat conduction is suppressed. As a result, power consumption during switching can be reduced as compared with the conventional case.

In the above description, the porous silicon regions 8c, 8d and 8e having a thickness of about 10 μm are formed on the peripheral surface of the Si substrate 1 except immediately below the thin film heater. 8c, 8d and 8e are Si
The substrate 1 may be formed so as to slightly enter a portion immediately below the thin film heater.

In the above description, an example in which three regions 8c, 8d, and 8e are provided as the porous silicon regions is shown. However, if only the crosstalk to the adjacent arm optical waveguide is reduced, Porous silicon region 8c
Only need to be provided.

In the above description, the case where there are two arm optical waveguides has been described. However, the present invention can be applied to a case where there are three or more arm optical waveguides.

In the above description, an example in which a thin film heater is provided corresponding to each arm optical waveguide and a porous silicon region is provided between each arm optical waveguide has been described. However, an arm optical waveguide having no thin film heater has been described. In this case, between the arm optical waveguide having the thin-film heater and the optical waveguide having no thin-film heater adjacent to the arm optical waveguide having the thin-film heater, a core region almost immediately below the thin-film heater formation region in the optical waveguide having the thin-film heater may be provided. S which is substantially immediately below the surface region of the lower cladding layer sandwiched between the portion and the core region portion of the adjacent optical waveguide opposing the core region portion.
The porous silicon region may be provided on the surface portion of the i-substrate, and the porous silicon region may not be provided on the surface portion of the Si substrate between the arm optical waveguides having no thin film heater.

Next, the manufacturing steps of the symmetric Mach-Zehnder type quartz optical switch according to the second embodiment will be described with reference to FIGS. 6 (a) to (e), FIGS. 7 (a) to (e), and FIG. a) ~
This will be described with reference to FIG.

First, as shown in FIG. 6A, a p-type Si substrate 1 having a specific resistance of 0.01 to 1.0 Ω · cm
Wash for 5 minutes using a mixed solution of H ₂ SO ₄ : H ₂ O ₂ = 1: 1 at ° C. Here, p-type, specific resistance 0.01 to 1.0Ω
The reason for using the cm Si substrate 1 is that light irradiation is necessary during anodization for n-type Si, but light irradiation is not necessary for p-type Si. This is because it is difficult to obtain silicon. next,
After washing the Si substrate 1 with water for 5 minutes, 1% HF at a temperature of 20 ° C.
Wash with the solution for 20 seconds. Next, the Si substrate 1 is
Rinse for minutes.

Next, as shown in FIG. 6B, an Al electrode 10 for anodization is formed on the back surface of the Si substrate 1 by a vacuum evaporation method.

Next, as shown in FIG. 6C, a resist 11 is applied on the surface of the Si substrate 1 at a rotation speed of 1000 rpm for 20 seconds using a spin coater (not shown).

Next, as shown in FIG. 6D, the resist 11 is exposed by a normal photolithography technique using a mask (not shown) for forming a porous silicon region.
develop. Thus, a resist pattern 11a having an opening at a position corresponding to the formation position of the porous silicon region is formed.

Next, as shown in FIG.
_{2 H 5 OH: H 2 O} = 1: 1: 1 mixed solution used, the area where the silicon through the opening of the resist pattern 11a is exposed anodizing. At this time, the Al electrode 10 on the back surface of the Si substrate is positive, the Pt electrode is negative, and connected to a constant current source, the current density is 40 mA / cm ² , and the anodizing time is 5 minutes. By this step, a depth of about 1
The 0 μm porous silicon regions 8c, 8d, 8e are formed. The porous silicon regions 8c, 8d, 8e
Are formed at peripheral positions except immediately below a region for forming a thin film heater described later.

Next, as shown in FIG. 7A, after removing the resist pattern 11a and further removing the Al electrode 10 on the back surface, the Si including the surface on which the porous silicon regions 8c, 8d and 8e are formed is formed. On the surface of the substrate 1, a quartz-based lower cladding layer 4 and a core layer 5 are deposited by plasma enhanced chemical vapor deposition using tetraethoxysilane and oxygen as raw materials. Here, the thickness of the lower cladding layer 4 is about 20 μm, and the thickness of the core layer 5 is 6 μm. here,
The lower cladding layer 4 has a relative refractive index difference from the core layer 5 of 0.1.
Fluorine (F) is doped to make the content 25 to 0.7%. The core layer 5 is not doped. Here, the relative refractive index difference is, for example, 0.5%. Thus, the refractive index of the lower cladding layer 4 is smaller than that of the core layer 5.

Next, as shown in FIG.
After depositing the (amorphous Si) layer 12 by plasma enhanced chemical vapor deposition, a resist 13 is applied by a spin coater (not shown).

Next, as shown in FIG. 7C, exposure is performed by a normal light exposure apparatus using a core patterning mask (not shown), and development is performed. As a result, a resist pattern 13a is formed in which the resist existing at the position where the core pattern is formed is removed and the resist located at a position other than the position where the core pattern is formed is removed. Here, the surface of the Si substrate 1 immediately below the resist pattern 13a is silicon as it is. The core patterning mask corresponds to the pattern of the core in the two 3 dB directional couplers and the two arm optical waveguides of the same length shown in FIG. 5, and therefore, the resist pattern corresponds to the 3 dB directional coupler and the arm. This corresponds to the core pattern in the optical waveguide.

Next, as shown in FIG. 7D, using the resist pattern 13a as a mask, a reactive ion etching apparatus (not shown) is used to form a-S by CHBr gas.
The i-layer 12 is patterned by etching to obtain a
-A pattern 12a of the Si layer is obtained.

Next, as shown in FIG.
Using the layer pattern 12a as a mask and using a reactive ion etching apparatus, the core is patterned by etching with CHF ₃ gas to form core patterns 5a and 5b.
Get.

Next, as shown in FIG. 8A, after removing the resist pattern 13a, the a-Si layer pattern 12a is further removed.

Next, as shown in FIG. 8B, a quartz-based upper cladding layer 6 is deposited by plasma-enhanced chemical vapor deposition using tetraethoxysilane and oxygen as raw materials. The thickness of the upper cladding layer 6 is about 20 μm on the cores 5a and 5b. Here, the upper cladding layer 6 includes:
Fluorine (F) is doped to have the same refractive index as the lower cladding layer 4, that is, to make the relative refractive index difference with the core 0.5%.

Next, as shown in FIG. 8C, a Cr film 7 for a thin film heater is formed on the upper clad layer by a vacuum evaporation method. Here, the thickness of Cr is about 0.5 μm.
Next, a resist 14 is applied by a spin coater (not shown).

Next, as shown in FIG. 8D, using a thin film heater patterning mask (not shown), exposure is performed by a usual exposure apparatus, and development is performed. As a result, a resist pattern 14a is formed in which the resist existing at the position where the pattern of the thin film heater is formed is removed, and the resist at a position other than the position where the pattern of the thin film heater is formed is removed.

Next, as shown in FIG. 8 (e), using the resist pattern 13a as a mask, the reactive ion etching apparatus (not shown) is used to pattern the Cr film 7 by etching to form a thin film heater. Pattern 7a,
7b is obtained. Finally, the resist pattern 14a is removed. In this way, a symmetric Mach-Zehnder type quartz optical switch composed of two 3 dB directional couplers and two arm optical waveguides of the same length shown in FIG. 5 is completed.

In each of the above-described embodiments, the example in which the Cr film is used as the thin film heater has been described. However, a TaN film may be used.

In each of the above embodiments, an example using porous silicon has been described. However, instead of this porous silicon, a silicon oxide formed by thermally oxidizing porous silicon at a temperature of 1100 ° C. for 2 hours is used. A membrane can also be used. By thermally oxidizing porous silicon,
A thick silicon oxide film having a thickness of 1 μm or more can be obtained relatively easily. Since the thermal conductivity of this silicon oxide film is about 1/100 of that of silicon and the thickness can be made as thick as 1 μm or more, this silicon oxide film can effectively reduce heat conduction. In addition, since the silicon oxide film can make the refractive index and the birefringence equal to those of the quartz film as compared with the porous silicon, the silicon oxide film can also serve as the lower cladding layer.

In each of the above embodiments, a symmetric Mach-Zehnder type quartz optical switch has been described as an example. However, the present invention is not limited to this, and it is applicable to other quartz optical switches utilizing the thermo-optic effect. Applicable.

[0075]

As described above in detail, according to the quartz optical switch of the present invention, by providing the porous silicon region, the heat conduction of the heat generated by the thin film heater can be controlled well. It has the effect that can be done.

More specifically, claims 1 and 2
According to the quartz optical switch according to the invention, the size of the thin film heater is equal to or larger than that of the thin film heater on the surface portion of the Si substrate 1 immediately below the thin film heater formation region.
Since the porous silicon region having a thermal conductivity smaller than the thermal conductivity of the i-substrate is formed, the rate at which the heat is diffused into the Si substrate when the thin-film heater 7 is heated is greatly reduced, and the consumption during switching is reduced. This has the effect of significantly reducing power.

Further, the periphery of the porous silicon region is
When the thin-film heater is turned off, heat is diffused from a silicon portion (a portion of the Si substrate 1) around a corresponding porous silicon region corresponding to the corresponding optical waveguide, and the thin-film heater is surrounded by the silicon portion of the substrate 1 itself. There is also an effect that the influence on the switching operation when the switch is turned off can be reduced.

According to the quartz optical switch of the third and fourth aspects of the present invention, the surface of the Si substrate substantially immediately below the region where the thin film heater is formed is a silicon portion of the Si substrate itself. Since a porous silicon region having a thermal conductivity smaller than the thermal conductivity of Si is formed between an adjacent optical waveguide and the porous silicon region, this occurs when a thin film heater corresponding to a predetermined optical waveguide is turned on and heated. The rate at which heat is diffused to another adjacent optical waveguide is reduced. Therefore, there is an effect that crosstalk to another adjacent optical waveguide is reduced as compared with the related art.
In addition, since the silicon portion of the silicon substrate itself exists in the surface portion of the silicon substrate located almost immediately below the formation region of the thin film heater, heat is generated when the thin film heater is turned off.
The rate of diffusion into the silicon portion of the substrate does not decrease so much, and has an effect that the switching speed when the thin film heater is turned off does not deteriorate much.

According to the quartz optical switch of the fifth aspect of the present invention, the surface of the silicon substrate located immediately below the thin film heater is a silicon portion.
Since porous silicon regions are formed on both sides of these silicon portions, the rate of heat diffusion to the Si substrate when the thin film heater is heated is not as remarkable as in the case of the first or second aspect of the present invention. This has the effect of reducing the heat conduction to some extent, that is, suppressing the heat conduction, and consequently reducing the power consumption during switching as compared with the conventional case.

According to the quartz optical switch of the present invention, a silicon oxide film formed by thermally oxidizing porous silicon is used instead of porous silicon. Since the thermal conductivity is about 1/100 of that of silicon and the film thickness can be increased to 1 μm or more, there is an effect that heat conduction can be effectively reduced. In addition, since the silicon oxide film can make the refractive index and the birefringence equal to those of the quartz film as compared with the porous silicon, the silicon oxide film can also serve as the lower cladding layer, and as a result, the manufacturing process is simplified. ,
There is also an effect that the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a symmetric Mach-Zehnder type quartz optical switch according to a first embodiment of the present invention, FIG. 1 (a) is a plan view thereof, and FIG. FIG. 1B is a cross-sectional view taken along the line AB in FIG.

FIGS. 2 (a) to 2 (e) are views showing a part of a manufacturing process of a symmetric Mach-Zehnder type quartz optical switch according to the first embodiment of the present invention.

FIGS. 3 (a) to 3 (e) are views showing a part of a manufacturing process of a symmetric Mach-Zehnder type quartz optical switch according to the first embodiment of the present invention.

FIGS. 4A to 4E are diagrams illustrating a part of a manufacturing process of the symmetric Mach-Zehnder type quartz optical switch according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a symmetric Mach-Zehnder type quartz optical switch according to the first embodiment of the present invention, FIG. 5 (a) is a plan view thereof, and FIG. FIG. 5B is a cross-sectional view taken along the line AB in FIG.

FIGS. 6 (a) to 6 (e) are views showing a part of a manufacturing process of a symmetric Mach-Zehnder type quartz optical switch according to a second embodiment of the present invention.

FIGS. 7A to 7E are diagrams illustrating a part of a manufacturing process of a symmetric Mach-Zehnder type quartz optical switch according to a second embodiment of the present invention.

FIGS. 8 (a) to 8 (e) are views showing a part of a manufacturing process of a symmetric Mach-Zehnder type quartz optical switch according to a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Si (silicon) substrate 2a, 2b 3dB Directional coupler 3a, 3b Arm optical waveguide 4 Lower clad layer 5 Core layer 5a, 5b Core 6 Upper clad layer 7 Cr film for thin film heater 7a, 7b Thin film heater 8a, 8b, 8c, 8d, 8e Porous silicon region 10 Al electrode 11a Resist pattern 12a a-Si layer pattern 13a Resist pattern

Claims (7)

[Claims] 1. A quartz optical switch using a thermo-optic effect, wherein a plurality of quartz optical waveguides each comprising a lower cladding layer, a core, and an upper cladding layer are provided on a silicon substrate. A thin film heater formed on the upper cladding layer to have a predetermined length equal to or slightly larger than the pattern width of the core immediately below the upper cladding layer so as to be located immediately above the predetermined region; In the optical waveguide provided with the thin-film heater, on the surface of the silicon substrate immediately below the region where the thin-film heater is to be formed, the heat conductivity of the silicon substrate is set to be equal to or larger than the size of the thin-film heater immediately above. A quartz-based optical switch having a porous silicon region set to be smaller than the conductivity. 2. The quartz optical switch according to claim 1, wherein said thin film heater and said porous silicon region are provided corresponding to all optical waveguides. 3. A silica-based optical switch using a thermo-optic effect, wherein a plurality of silica-based optical waveguides each including a lower cladding layer, a core, and an upper cladding layer are provided on a silicon substrate. A thin film heater formed on the upper cladding layer to have a predetermined length equal to or slightly larger than the pattern width of the core immediately below the upper cladding layer so as to be located immediately above the predetermined region; The surface of the silicon substrate almost directly below the core forming region in the optical waveguide provided with the thin film heater is a silicon portion of the silicon substrate itself, and the core region in the optical waveguide having the thin film heater is located almost immediately below the thin film heater forming region. The surface region of the lower cladding layer sandwiched between the portion and the core region portion of the adjacent optical waveguide opposing the core region portion. Silica-based optical switch, characterized in that the silicon surface portion of the substrate to be formed and its thermal conductivity immediately below is provided a porous silicon region that is set to be smaller than the thermal conductivity of the silicon substrate. 4. A quartz optical switch comprising a plurality of silica-based optical waveguides comprising a lower cladding layer, a core, and an upper cladding layer disposed on a silicon substrate, wherein a core of each optical waveguide is provided. A thin film heater formed on the upper cladding layer to have a predetermined width equal to or slightly larger than the pattern width of the core immediately below the upper cladding layer so as to be located immediately above the predetermined region; The surface of the silicon substrate directly below the core formation region in the optical waveguide is the silicon portion of the silicon substrate itself, and the core region between the core regions almost immediately below the thin film heater formation region in each optical waveguide in each adjacent optical waveguide. The thermal conductivity of the silicon substrate is formed on the surface portion of the silicon substrate substantially immediately below the surface region of the lower cladding layer interposed therebetween. Silica-based optical switch, characterized in that a porous silicon region is set to be smaller. 5. A core corresponding to two optical waveguides disposed on both side end faces of a substrate among a plurality of optical waveguides disposed on a silicon substrate and located substantially immediately below a thin film heater formation region thereof. Another porous silicon region is further provided on the surface portion of the silicon substrate substantially immediately below the surface region of the lower cladding layer sandwiched between the region portion of the silicon substrate and the surface position of the side end surface of the silicon substrate. 5. The quartz optical switch according to 4. 6. The quartz system according to claim 1, wherein a silicon oxide film formed by thermally oxidizing porous silicon is used in place of said porous silicon. Light switch. 7. The quartz according to claim 1, wherein the lower clad layer and the upper clad layer are formed in common for each optical waveguide. System light switch.