JPH10227930A - Temperature-independent optical waveguide and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a temperature-independent optical waveguide which requires no temperature control and is reliable. SOLUTION: A lower clad 2 is provided on a silicon substrate 1, cores 3 and 3 are provided in an arm shape on the lower clad 2 and covered with an upper clad 4, and the core 3 of one arm waveguide has a groove formed at some lengthwise part of it by etching the upper clad 4; and a filler 5 is provided on the top surface of the exposed core 3 until it reaches the top surface of the upper clad, and an aluminum vapor-deposited film 11 is provided on the top surface of the filler 5. Both end parts of the cores 3 and 3 are connected to an incidence port 9 and a projection port 10 provided on the substrate as well through 3dB couples respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide having a temperature compensation effect in a planar lightwave circuit such as an optical waveguide filter used in the fields of optoelectronics and optical communication, and a method of manufacturing the same. It is.

[0002]

2. Description of the Related Art An optical waveguide (PL) having a core / clad structure provided on a substrate represented by silicon (Si) is known.
C: Planer lightwave Circuit
t) is one of the basic technologies that support the next generation of optical communication and optical computing.

In this PLC, a plurality of optical waveguides are combined to form an optical waveguide on a plane. These circuits include various types such as a 3 dB coupler, an MZ type optical switch, an array waveguide grating type wavelength multiplexer / demultiplexer, an MZ type wavelength filter, a grating type wavelength filter, and a ring resonator. A complex and large-scale PLC capable of handling a large number of wavelengths, such as a programmable wavelength filter, a loop-back type arrayed waveguide grating circuit, and an optical dispersion equalizer, which incorporates a large number of these optical elements, is being developed.

[0004] Even these complex large-scale PLCs are basically optical waveguides, and the structure is such that a core of several μm and a clad structure having a low refractive index exist around the core. The refractive index difference is often about 0.3 to 1%. When light propagates in this optical waveguide in a single mode, there is an effective refractive index such that the core and the clad are viewed as one body. Since the PLC is usually made of quartz glass, the effective refractive index of the optical waveguide formed of quartz glass together with the core and the clad changes due to the temperature dependence of the actual refractive index of quartz glass. It is already known. Generally, glass and semiconductors have a temperature dependence of a positive refractive index, that is, △ n / △ T> 0 (where n is a refractive index,
T is the temperature. )have.

Therefore, the effective refractive index of an optical waveguide having a core and a clad formed of quartz glass also has a positive temperature dependency. For example, when a wavelength filter using an asymmetric Mach-Zehnder circuit is manufactured using this glass waveguide, the filtering wavelength shifts due to the temperature difference of the effective refractive index of the waveguide of ΔL and the difference in the length of the two asymmetric arm waveguides. Will do. This wavelength is 1.55 μm
The value is as large as 0.01 nm / ° C. for the bandpass filter in the wavelength range. Therefore, an operation by strict temperature control by the Peltier element was required.

In order to avoid this, Yonekawa et al. (IEICE Electronics Society Conference C-166,
(1996) is a strip-loaded optical waveguide in which the loading layer is made of polymethyl methacrylate (P
Using MMA), a temperature-independent optical waveguide in which the optical path length temperature coefficient of the waveguide is effectively reduced to zero by a negative effective refractive index and a positive thermal expansion of the substrate is reported. As a result, the temperature range 6
An open ring resonator having a temperature fluctuation of 0.0007 nm / ° C. with a very small temperature range of 0.007 ° C. has been obtained.

Tanobe et al. (C-251 1996, Spring Meeting of the Institute of Electronics, Information and Communication Engineers) reported that a wavelength filter using an asymmetric Mach-Hender circuit made of a semiconductor has an effective refractive index of only the shorter one of two asymmetric arm waveguides. By using a semiconductor material having a larger temperature coefficient, the optical path length temperature coefficients of both arm waveguides are made the same, and the temperature dependence of the wavelength is made zero. Based on this principle, InGaAsP
A 1.55 μm wavelength filter using an asymmetric Mach-Zehnder interferometer made of a / InP-based semiconductor was fabricated, and a value of 0.01 nm / ° C. was obtained as the temperature dependence of the wavelength. Since the temperature dependence of the wavelength is 0.1 nm / ° C. in the semiconductor wavelength filter manufactured by the usual method, the temperature characteristic is improved about 10 times.

[0008]

In a conventional optical waveguide that does not attempt to make the waveguide independent of the temperature, the effective refractive index changes depending on the environmental temperature. We had to rely on a method incorporating a temperature control device such as a Peltier element.
This method increases the size of the device and the continuous consumption of power,
Further, there are many disadvantages such as a decrease in reliability.

In a wavelength filter using a semiconductor optical waveguide, the temperature dependence of the filter wavelength was successfully reduced by using two materials having different refractive index temperature coefficients as an asymmetric arm waveguide. Waveguides have the disadvantage that they are difficult to achieve with existing manufacturing techniques.

On the other hand, there has been an attempt to eliminate the temperature dependence of the glass waveguide by effectively setting the temperature coefficient of the optical path length of the waveguide itself to zero, but the dielectric loading type used in this report has been tried. The optical waveguide has a drawback that it is difficult to increase the refractive index difference between the waveguide portion and the clad portion, and is not suitable for the configuration of a practical two-dimensional optical waveguide in which branching and bending are combined. As a conventional technique closest to the present invention, there is a method of eliminating the temperature dependence of the optical path length of the waveguide itself using a dielectric-loaded optical waveguide. However, the structure of the optical waveguide shown here is a dielectric-loaded type, and is not suitable as a practical waveguide due to its unstable propagation loss and large bending loss because it is an open type. Also,
A thin polymer film with a thickness of about 1 μm (width 3 to 4 μm)
m) is extremely unstable since it is only stuck to the glass flat plate,
When the temperature is set to about (.degree. C.), this film comes off, and there is a disadvantage that the film cannot be used as an optical waveguide before the temperature becomes independent.

Accordingly, it is an object of the present invention to provide a highly reliable temperature-independent optical waveguide which does not require a temperature control device, and a method of manufacturing the same.

[0012]

SUMMARY OF THE INVENTION The present invention relates to a completely embedded optical waveguide having a silica-based core and a cladding structure formed on a substrate, and a portion having a negative refraction near or in contact with one or three faces of the core. Rate temperature coefficient,
The most main feature is to use an organic material having high transparency to propagating light as a clad.

That is, in the temperature-independent optical waveguide according to the first aspect of the present invention, in a completely embedded optical waveguide having a silica-based core and a clad structure formed on a substrate, at least a part of the clad includes the core. Wherein a substance having a negative temperature coefficient of refractive index is provided so as to be in contact with.

According to a second aspect of the present invention, there is provided a temperature-independent optical waveguide.
2. The method according to claim 1, wherein the substance having a negative temperature coefficient of refractive index is in contact with at least a part of one of upper surfaces of the core.

According to a third aspect of the present invention, there is provided a temperature-independent optical waveguide,
2. The method according to claim 1, wherein the substance having a negative temperature coefficient of refractive index is in contact with at least a part of three surfaces of an upper surface and a side surface of the core.

The temperature-independent optical waveguide according to claim 4 is
2. The material according to claim 1, wherein the material having a negative refractive index temperature coefficient is embedded in a groove formed on an upper portion of the core and having a length set according to a temperature coefficient of the material and a waveguide length. It is characterized by having.

The temperature-independent optical waveguide according to claim 5 is
2. The method according to claim 1, wherein the substance having a negative temperature coefficient of refractive index is fluorinated polymethyl methacrylate, fluorinated polycarbonate, polystyrene, rubber-like EVA resin, siloxane gel, polysiloxane, diethylene glycol bis, acrylic carbonate, polyvinyl chloride, Poly (4-methylpentene-1), methyl methacrylate /
It is characterized by being at least one organic compound selected from a styrene copolymer and an acrylonitrile / styrene copolymer.

The temperature-independent optical waveguide according to claim 6 is
In a quartz-based core formed on a substrate, a completely embedded optical waveguide having a clad structure, the clad is:
A quartz glass clad disposed at a portion in contact with the core, and a substance having a negative temperature coefficient of refractive index disposed outside at least a part of the quartz glass clad.

The temperature-independent optical waveguide according to claim 7 is
7. The method according to claim 6, wherein the substance having a negative temperature coefficient of refractive index is close to at least a part of one of upper surfaces of the core.

The temperature-independent optical waveguide according to claim 8 is
7. The method according to claim 6, wherein the substance having a negative temperature coefficient of refractive index is close to at least a part of three surfaces of an upper surface and a side surface of the core.

The temperature-independent optical waveguide according to claim 9 is
7. The material according to claim 6, wherein the substance having a negative refractive index temperature coefficient is embedded in a groove formed on an upper portion of the core and having a length set according to a temperature coefficient of the substance and a waveguide length. It is characterized by having.

According to a tenth aspect of the present invention, in the temperature independent optical waveguide according to the sixth aspect, the substance having the negative temperature coefficient of refractive index is fluorinated polymethyl methacrylate, fluorinated polycarbonate, polystyrene, rubber-like EVA resin, Siloxane gel, polysiloxane, diethylene glycol bis, acrylic carbonate, polyvinyl chloride,
Poly (4-methylpentene-1), fluorinated polymethylmethacrylate, fluorinated polycarbonate, polystyrene, rubber-like EVA resin, siloxane gel, polysiloxane, diethylene glycol bis, acryl carbonate, polyvinyl chloride, poly (4-methylpentene-
1), at least one organic compound selected from a methyl methacrylate / styrene copolymer and an acrylonitrile / styrene copolymer.

A temperature-independent optical waveguide according to an eleventh aspect is characterized in that, in any one of the first to tenth aspects, a metal film or a glass film is provided above the organic substance embedded in the groove.

According to a twelfth aspect of the present invention, there is provided a method of manufacturing a temperature-independent optical waveguide, wherein a core formed on a substrate and a completely embedded optical waveguide having a clad structure are formed, and a part of the core of the optical waveguide is formed. Then, the upper clad is etched right above the core, and a filler having a negative temperature coefficient of refractive index is buried in the etched portion.

A method of manufacturing a temperature-independent optical waveguide according to a thirteenth aspect is characterized in that, in the twelfth aspect, the quartz glass cladding on the core is left in the etching step.

In the method of manufacturing a temperature-independent optical waveguide according to a fourteenth aspect, in the step of forming the upper clad on the lower clad and the core formed on the substrate, it is desired to make the temperature independent before forming the upper clad. A metal mask is placed on the waveguide part, and the other parts are clad to the thickness of the normal upper cladding, and then the metal mask has a negative refractive index temperature coefficient in the groove part due to the placement of the metal mask. It is characterized in that the clad is formed to a thickness of a normal upper clad with a filler.

According to a fifteenth aspect of the present invention, in the method for manufacturing a temperature-independent optical waveguide according to the fourteenth aspect, the step of forming the upper clad by placing the metal mask is at least more than the final clad film thickness. It is characterized in that an upper clad having a small arbitrary thickness is formed.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The point that the present invention differs from the prior art in that the polymer-loaded optical waveguide is made temperature-independent is that the stability of the waveguide itself is improved by using a completely embedded optical waveguide in the present invention. At the same time, an organic compound is buried in the trench (groove), and furthermore, sealing with glass or a metal film can be performed from above, so that the stability is greatly improved as compared with the conventional technology, and the device can sufficiently withstand practical use. That is.

If the temperature coefficient of the refractive index of the core and cladding materials of the optical waveguide is zero and the expansion coefficient is zero, the bandpass wavelength of the asymmetric Mach-Zehnder type wavelength filter constituted by this optical waveguide changes with temperature. No problem should occur in practice. However, a wavelength filter actually made of glass has a temperature dependency of 0.01 nm / ° C. for a filter wavelength, and a wavelength filter made of semiconductor has a temperature dependency of 0.1 nm / ° C., respectively. The present invention reduces the temperature dependence of the filter wavelength and uses an organic compound having a negative refractive index temperature coefficient for a part of the clad in order to reduce the temperature to a practically negligible level. In this case, the temperature coefficient of the refractive index of the glass having the following is canceled out to approach zero. Although the refractive index of the core and the refractive index of the clad are different from each other, one effective refractive index is given from the viewpoint of propagating light. Since most light propagates through the core, if the temperature coefficient of this effective refractive index is made to approach zero with a cladding having a negative temperature coefficient, the negative temperature coefficient of the cladding will be 10 times the absolute value of the glass temperature coefficient. About twice as much is required. This combination is convenient because the temperature coefficient of the refractive index of quartz glass is + 1 × 10 ⁻⁵ , and that of the organic compound is about 10 ×, which is 1-4 × 10 ⁻⁴ .

Further, in these optical waveguides, there is a case where a material having a problem in the adhesiveness cannot be used because the adhesiveness between the organic compound and the glass becomes a problem. As a result, it may be necessary to use another one having a limited temperature coefficient. In order to solve this problem, a thin glass upper cladding or upper cladding is formed in contact with the core, and the thickness is adjusted so that the normal cladding is formed on the thin glass upper cladding or upper cladding. The organic compound was formed up to the thickness. The temperature dependence of the filter wavelength can be reduced by appropriately controlling the thickness of the upper cladding or upper cladding of this thin glass regardless of the temperature coefficient of the organic compound having a negative refractive index temperature coefficient of the upper cladding or upper cladding. It can be even closer to zero.

[0031]

【Example】

(Embodiment 1) FIG. 1 is a structural diagram showing a wavelength filter by an asymmetric Mach-Zehnder interferometer employing a temperature-independent optical waveguide for a longer arm waveguide for explaining a first embodiment of the present invention. (A) is a top view, and (B) is a cross-sectional view taken along a cross-sectional line II ′ on the arm waveguide. In the figure,
1 is a silicon substrate, 2 is a lower cladding, 3 is a core, 4 is an upper cladding, 5 is a filler (also serving as an upper cladding), 6 is a 3 dB coupler, 7 is a long arm waveguide, 8
Is a short arm waveguide, 9 is an input port, 10 is an output port, and 11 is an aluminum evaporated film.

As shown in FIG. 1, a lower clad 2 is provided on a silicon substrate 1, cores 3, 3 are provided on the lower clad 2 in an arm shape, and these cores 3, 3 are covered with an upper clad 4. The core 3 of one arm waveguide is formed by etching the upper clad 4 in a part of its length in the longitudinal direction to form a groove, and the filler 5 is provided on the exposed upper surface of the core 3 until it reaches the upper surface of the upper clad. , Filler 5
Is provided with an aluminum vapor-deposited film 11 on the upper surface. Both ends of the cores 3 and 3 are connected to an input port 9 and an output port 10 similarly provided on the substrate via 3 dB couplers.

The prepared wavelength filter has a wavelength of 1.55.
Operating in the band of μm, core diameter 6.5 μm, clad 2,
The optical waveguide has a structure in which two asymmetric arm waveguides are sandwiched between two 3 dB couplers 6 by a waveguide having a refractive index of 1.444 and a refractive index of 1.455 of the core 3. The optical path length difference between the arm waveguides 7 and 8 is 8.3 mm. The groove is made in a long arm waveguide and is 8.3 mm long and 0.2 m wide along the waveguide
m. The aluminum vapor-deposited film 11 was formed with a length of 9 mm and a width of 0.4 mm on the filler. As a filler,
A fluorinated epoxy resin was used. 1 of this resin
The temperature coefficient at 55 μm is −3 × 10 ⁻⁴ . As other fillers, fluorinated polymethyl methacrylate,
Fluorinated polycarbonate, polystyrene, rubbery ethylene / vinyl acetate resin (EVA resin), siloxane gel, polysiloxane, diethylene glycol bisacryl carbonate, polyvinyl chloride, poly (4-methylpentene-1), MS resin (methyl methacrylate / Styrene copolymer (MMA-St resin)) and AS resin (acrylonitrile / styrene copolymer (AN-St copolymer)) (Table 1) can be used as the resin.

[0034]

[Table 1]

The operation of the manufactured wavelength filter is performed by irradiating a laser beam to the entrance port 9 and extracting the filter wavelength from the exit port 10 with an optical fiber. The filter wavelength was 1.552 μm, and the temperature characteristics of the filter wavelength were examined as follows. The entire device was placed in an environment tester capable of accurately controlling the temperature and humidity, and the temperature of the wavelength filter was gradually changed so as to be in a sufficiently thermal equilibrium stepwise, and the shift of the filter wavelength was examined. The result is shown in FIG. For comparison, FIG. 9 also shows the temperature dependence of the shift of the filter wavelength of the wavelength filter in which the temperature-independent waveguide is not used for the arm waveguide. In the wavelength filter manufactured by the conventional technique, the wavelength shift was 0.01 nm / ° C., but in this embodiment, since a part of the arm waveguide is a temperature-independent optical waveguide, this temperature dependence is about 10 minutes. It was found that it was reduced to about one.

As shown in Table 1, when the temperature coefficient of the refractive index of the filler is different, the same characteristics as those in FIG. 2 can be obtained by making the following slight design changes. . For example, if the temperature coefficient of the refractive index of the filler is a siloxane gel larger than that of the fluorinated epoxy resin, provide a thin quartz glass upper cladding with a thickness of 0.5 μm on the top of the core and put the filler on it. As a result, the same characteristics as those in FIG. 5 were obtained. When poly (4-methylpentene-1) having a temperature coefficient of the refractive index of the filler smaller than that of the fluorinated epoxy resin is used, the filler has a structure in which the filler directly contacts the core. By making the length 13 mm longer than that of the epoxy resin, the same characteristics as in FIG. 2 were obtained.

As described above, the wavelength filter of the present invention does not need to perform strict temperature control using a Peltier element or the like which always requires power to keep the filter wavelength constant, unlike the conventional wavelength filter. The function can be sufficiently performed with a simple temperature control device or without a control device.

(Embodiment 2) FIG. 3 is a cross-sectional view showing a method of manufacturing a temperature-independent wavelength filter using a temperature-independent optical waveguide for a longer arm waveguide, wherein 1 is a silicon substrate, and 2 is A lower clad, 3 is a core, 4 is an upper clad, 5 is a filler, 11 is an aluminum deposited film, and 12 is a groove. The manufacturing process is shown in order from (A) to (C).

First, in the process (A), quartz glass soot is deposited on a silicon substrate 1 by a flame deposition method, and is further heated and melted to form a lower clad 2 (refractive index 1....).
444, wavelength 1.55 μm) with a thickness of 30 μm. Next, a core layer 3 (refractive index: 1455, wavelength: 1.55 μm) having a slightly increased refractive index was formed to a thickness of 6 μm. Next, the core was processed by photolithography and reactive ion etching to form an asymmetric arm type Mach-Zehnder interference circuit having two 3 dB directional couplers. At this time, the core width was 7 μm. Further, the upper clad 4 was formed to a thickness of 36 μm by a flame deposition method. Up to this point, the method is the same as the conventional method of manufacturing a wavelength filter.

Next, in order to obtain a temperature-independent wavelength filter, in the process (B), the length of the longer arm waveguide is 8.3 mm, which is the difference between the arm waveguide lengths, and the width is 0.1 mm.
Then, a groove was formed by reactive ion etching up to just above the core of the waveguide. By adjusting the length of this groove,
By using fillers having different refractive index temperature coefficients, the filter wavelength can be effectively optimized so as to minimize the temperature dependence of the filter wavelength. With a temperature coefficient of the refractive index of the epoxy resin of −3 × 10 ⁻⁴ , the temperature dependence of the filter wavelength could be minimized by setting the groove length to 8.3 mm. If the temperature coefficient of the filler is small, by increasing this groove length,
Conversely, if the material has a large temperature coefficient, the temperature coefficient of the filter wavelength can be minimized by shortening the material.

Further, in order to perform the process (C), the groove was sufficiently cleaned by ultrasonic cleaning, and then an ultraviolet-curable epoxy resin was applied thereto. Subsequently, irradiation was performed with ultraviolet light (mercury xenon lamp, 200 W) for 5 minutes from immediately above, and heat treatment was performed at 80 ° C. for 3 hours to sufficiently cure the epoxy resin.

It is generally known that when a polymer is used as a filler, its refractive index changes due to moisture absorption. Therefore, in order to avoid a shift in the filter wavelength due to this, aluminum was further evaporated to a thickness of 300 nm from above the epoxy resin using a vacuum evaporation apparatus. This film can also be formed by a sputtering method or the like. As a result, it was observed that the filter wavelength did not change at all even when the environmental temperature of the element was changed.

As described above, following the conventional manufacturing method, the groove can be formed, the filler (epoxy resin) layer can be formed, and the moisture-proof metal film can be formed in a short process. A temperature-independent wavelength filter can be manufactured without increasing the price.

(Embodiment 3) FIG. 4 is a structural diagram showing a wavelength filter using an asymmetric Mach-Zehnder interferometer in which a temperature-independent optical waveguide is used for a longer arm waveguide to explain a third embodiment of the present invention. (A) is a top view,
(B) is a sectional view taken along a sectional line II-II 'on the arm waveguide. In the figure, 1 is a silicon substrate, 2 is a lower cladding, 3 is a core, 4 is an upper cladding, 5 is a filler, 6 is a 3 dB coupler, 7 is a long arm waveguide, 8 is a short arm waveguide, and 9 is incident. Port 10 is an emission port, 11 is an aluminum vapor-deposited film, and 13 is an upper clad of quartz glass formed thinly around the core. The cross-sectional structure of the temperature-independent optical waveguide according to this embodiment is different from that of the first embodiment. In the present embodiment, a quartz glass clad having a thickness of 1 μm is left around the upper part of the core, and the upper part is a groove.

The manufactured wavelength filter has a wavelength of 1.55.
It operates in the band of μm, and has a core diameter of 6.5 μm × 6.5 μm,
Two asymmetric arm waveguides 7 and 8 are formed by a waveguide having a refractive index of 1.444 of the claddings 2 and 4 and a refractive index of 1.455 of the core 3.
Is sandwiched between two 3 dB couplers 6.
The optical path length difference between the arm waveguides 7 and 8 is 8.3 mm. A thin upper cladding 13 of quartz glass was provided to directly contact the core. Its thickness is 1 μm. The groove is made in a long arm waveguide, and the goodness is 8.3 m along the waveguide.
m and a width of 0.2 mm. The aluminum vapor-deposited film 11 was formed with a length of 9 mm and a width of 0.4 mm on the filler.
A fluorinated epoxy resin was used as a filler.
The temperature coefficient of the refractive index of this resin at 1.55 μm is −3 ×
10 ^-4 . It was confirmed that the fillers shown in Table 1 could be used in addition to this filler.

A tunable laser is connected to the input port,
The filter wavelength was checked by monitoring the light from the output port. The entire device was placed in an environmental tester that can accurately control the temperature and humidity, and the temperature of the wavelength filter was changed step by step so that it was in a state of sufficient thermal equilibrium, and the temperature dependence of the filter wavelength shift was examined. . The results are shown in FIG. The temperature dependence of the filter wavelength was reduced in substantially the same manner as in Example 1.

As shown in Table 1, when the temperature coefficient of the refractive index of the filler is different, the thickness of the thin quartz glass clad layer 13 around the upper part of the core is changed to obtain the same value as in FIG. Characteristics were obtained. When the temperature coefficient of the refractive index of the filler is larger than that of the fluorinated epoxy resin, the thickness of the upper cladding 13 around the core is made larger than 1 μm (for example, in the case of siloxane gel, the thickness of the upper cladding 13 around the core is increased). On the other hand, when the temperature coefficient of the refractive index of the filler is smaller than that of the fluorinated epoxy resin, the thickness should be smaller than 1 μm (for example, poly (4-methylpentene-1)). In the case of the above, the thickness of the upper cladding 13 around the core was set to 0.5 μm), and the same characteristics as those in FIG. 5 were obtained. In the case of a smaller fluorinated polymethyl methacrylate resin, the thickness of the upper quartz glass clad 13 in contact with the core is set to 0.2 μm, as shown in FIG.
The same properties as were obtained.

(Embodiment 4) FIG. 6 is a cross-sectional view showing a method of manufacturing a temperature-independent wavelength filter using a temperature-independent optical waveguide for a longer arm waveguide. Is a lower clad, 3 is a core, 4 is an upper clad, 5 is a filler, 11 is an aluminum vapor-deposited film, 12 is a groove, and 13 is an upper clad of quartz glass formed thinly around the core. The same result is obtained when a quartz glass substrate having an equivalent thickness is used instead of the silicon substrate 1. The manufacturing processes of the temperature-independent wavelength filter are shown in order from (A) to (C).

First, in the process (A), a quartz glass soot is deposited on a silicon substrate 1 by a flame deposition method, and is further heated and melted to form a lower clad 2 (refractive index 1.4).
44, wavelength 1.55 μm) with a thickness of 30 μm.
Next, the core layer 3 (refractive index 14
55, wavelength 1.55 μm) to a thickness of 6 μm. Next, the core was processed by photolithography and reactive ion etching so as to form an asymmetric arm-type Mach-Zehnder interference circuit having two 3 dB directional couplers. At this time, the core width was 7 μm. An upper glass clad 13 having a thickness of 1 μm was formed thereon by electron beam evaporation.

In the following process (B), the length along the longer arm waveguide core is 8.3 mm, the width is 2 mm,
A metal mask (not shown) having a thickness of 2 mm was placed, and in this state, quartz glass soot was deposited by a flame deposition method.
Remove the metal mask and heat and melt it to make the upper cladding 4
Was formed with a thickness of 30 μm. The portion where the metal mask was placed remained as the groove 12 because there was no glass soot.

In the process (C), an ultraviolet-curing epoxy resin is applied to the groove 12 and irradiated with ultraviolet rays (mercury xenon lamp, 200 W) for 5 minutes from immediately above, followed by heat treatment at 80 ° C. for 3 hours. Then, the epoxy resin was sufficiently cured.

As in Example 2, in order to avoid a change in the refractive index of the epoxy resin due to moisture absorption, aluminum was vapor-deposited from above the resin to a thickness of 300 nm using a vacuum vapor deposition apparatus.

As described above, the steps of forming a thin upper clad, setting a metal mask, placing an epoxy resin and curing, and forming a metal deposition film on the resin are the same as the conventional manufacturing method. A temperature-independent wavelength filter can now be manufactured simply by adding a process.

(Embodiment 5) FIG. 7 shows the structure of a temperature-independent optical wavelength demultiplexer using the temperature-independent optical waveguide of the present invention as an array waveguide of an arrayed waveguide grating type optical wavelength demultiplexer. FIG. 8 is a top view, and FIG. 8 is a cross-sectional view taken along the line III-III ′ on the arm waveguide shown in FIG. In the figure, 1 is a silicon substrate, 2 is a lower clad, 3 is a core, 4 is an upper clad, 5 is a filler, 9 is an input port, 10 is an output port, 11 is an aluminum deposited film, and 14 is a first slab. A waveguide, 15 is an array waveguide, and I6 is a second slab waveguide. In the case of this embodiment, a series of fillers 5 are provided in the same manner as in the first embodiment so as to cover the waveguides other than the waveguide having the shortest optical path length of the arrayed waveguide 15. However,
Here, the filler 5 is arranged in an isosceles triangular shape in the illustrated example so that the length of the portion of the waveguide covered by the filler 5 increases as the optical path length increases.

The fabricated arrayed waveguide grating type wavelength multiplexer operates in a wavelength band of 1.55 μm and has a core diameter of 7 μm ×
It is composed of a waveguide having a refractive index of 6 μm, a refractive index of the cladding of 1.444, and a refractive index of the core of 1.455, and has a structure in which 70 array waveguides having different lengths are sandwiched between two slap waveguides from both sides. I have. The number of channels is 16 channels, the channel interval is 200 GHz, and the FSR (Free Spe
(ctrum Range) is 3200 GHz, the optical path length difference between the waveguides is 63 μm, and the maximum optical path length difference is 4410 μm.

As the filler, a fluorinated epoxy resin was used. The temperature coefficient of the refractive index of this resin at 1.55 μm is −3 × 10 ⁻⁴ . The resins shown in Table 1 can also be used.

A wavelength tunable laser was connected to one input port, and the filter light was monitored from one output port. The entire device was placed in an environmental tester capable of accurately controlling the temperature and humidity. The temperature was increased stepwise, and after a sufficient thermal equilibrium was reached, the wavelength of the filter light was examined. The observation result is shown in FIG. For comparison, FIG. 9 shows data when the temperature-independent waveguide is not used for the arm waveguide. By using a temperature-independent optical waveguide,
It was found that the temperature dependence was improved to about one tenth or less. This eliminates the need for a temperature control device required for the conventional device, or simplifies temperature control, thereby contributing to improved reliability and reduced system cost.

In the first to fifth embodiments, the aluminum vapor-deposited film is used in order to avoid the influence of humidity, oxygen and the like. A sealing material can be used.
In addition, any filler which is hardly affected by the outside air such as humidity and oxygen can be used without sealing.

[0059]

According to the temperature independent optical waveguide of the present invention, the wavelength shift due to the temperature change is very small in the wavelength filter and the arrayed waveguide grating type wavelength multiplexer / demultiplexer. It can be used without the need for temperature control by a temperature control device, and has the advantage that reliability can be improved by eliminating the temperature control device, and components and the system can be reduced in size and cost by eliminating the temperature control device.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a wavelength filter using an asymmetric Mach-Zehnder interferometer in which a skin-independent optical waveguide for a first embodiment of the present invention is used for a longer arm waveguide, and FIG. FIG. 3B is a sectional view.

FIG. 2 is a graph showing data of a wavelength filter according to a conventional technique and temperature dependence of a wavelength shift of the wavelength filter of the first embodiment.

3A and 3B are cross-sectional views illustrating a method of manufacturing a temperature-independent wavelength filter in which a temperature-independent optical waveguide is used for a longer arm waveguide, and FIG. 3A shows a substrate in which a lower clad, a core, and an upper clad are formed; (B) shows a stage in which a groove is formed in the upper cladding, and (C) shows a stage in which a filler is filled in the groove and the upper surface thereof is sealed.

4A and 4B are structural views of a wavelength filter in which a temperature-independent optical waveguide is used for a longer arm waveguide, wherein FIG. 4A is a top view and FIG. 4B is a cross-sectional view.

FIG. 5 is a graph showing the temperature dependence of the wavelength shift of the wavelength filter according to the related art and the temperature dependence of the wavelength shift of the wavelength filter of the third embodiment.

FIG. 6 is a cross-sectional view showing a method of manufacturing a temperature-independent wavelength filter employing a temperature-independent optical waveguide for a longer arm waveguide, wherein (A) shows a lower clad, a core, and a thin quartz glass clad on a substrate; The step of providing a layer, the step of (B) masking the upper part of one core to form a grooved upper clad, and the step of (C) filling the groove with a filler and sealing the upper surface thereof, respectively. Show.

FIG. 7 is a top view of a temperature-independent optical wavelength multiplexer / demultiplexer using the temperature-independent optical waveguide of the present invention as an array waveguide of an arrayed waveguide grating type wavelength multiplexer / demultiplexer.

FIG. 8 is a cross-sectional view of a temperature-independent optical wavelength multiplexer / demultiplexer using the temperature-independent optical waveguide of the present invention as an array waveguide of an arrayed waveguide grating wavelength multiplexer / demultiplexer.

FIG. 9 is a graph showing the temperature dependence of one wavelength of a temperature-independent optical wavelength multiplexer / demultiplexer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Lower clad 3 Core 4 Upper clad 5 Filler 6 3dB coupler 7 Long arm waveguide 8 Short arm waveguide 9 Incident port 10 Outgoing port 11 Aluminum vapor deposition film 12 Groove 13 Quartz glass formed thin around core Upper cladding 14 first slab waveguide 15 arrayed waveguide 16 second slab waveguide

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsutoshi Hoshino 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Japan Telegraph and Telephone Corporation (72) Inventor Kenji Yokoyama 3-19, Nishishinjuku, Shinjuku-ku, Tokyo No. 2 Nippon Telegraph and Telephone Corporation (72) Inventor Ken Sukekawa 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Katsuharu Okamoto 3-19 Nishishinjuku, Shinjuku-ku, Tokyo No. 2 Nippon Telegraph and Telephone Corporation

Claims (15)

[Claims] 1. A completely embedded optical waveguide having a silica-based core and a cladding structure formed on a substrate, and a negative refractive index temperature coefficient disposed at least in part on the cladding so as to be in contact with the core. A temperature-independent optical waveguide provided with a substance having: 2. The temperature-independent optical waveguide according to claim 1, wherein the substance having a negative temperature coefficient of refractive index is in contact with at least a part of one of upper surfaces of the core. . 3. The temperature according to claim 1, wherein the substance having a negative temperature coefficient of refractive index is in contact with at least a part of three surfaces of an upper surface and a side surface of the core. Independent optical waveguide. 4. A material having a negative refractive index temperature coefficient is embedded in a groove formed on an upper portion of the core and having a length set according to a temperature coefficient of the material and a waveguide length. The temperature-independent optical waveguide according to claim 1, wherein: 5. The substance having a negative temperature coefficient of refractive index includes fluorinated polymethyl methacrylate, fluorinated polycarbonate, polystyrene, rubber-like EVA resin, siloxane gel, polysiloxane, diethylene glycol bis, acryl carbonate, polyvinyl chloride, Poly (4
The temperature-independent optical waveguide according to claim 1, wherein the optical waveguide is at least one organic compound selected from the group consisting of -methylpentene-1), a methyl methacrylate / styrene copolymer, and an acrylonitrile / styrene copolymer. 6. A completely embedded optical waveguide having a quartz core and a clad structure formed on a substrate, wherein the clad is a quartz glass clad provided in a portion in contact with the core, and a quartz glass clad formed of a quartz glass clad. A substance having a negative refractive index temperature coefficient disposed outside at least a part of the temperature-independent optical waveguide. 7. The temperature-independent light guide according to claim 6, wherein the substance having a negative temperature coefficient of refractive index is close to at least a part of one of upper surfaces of the core. Wave path. 8. The core according to claim 6, wherein the material having a negative temperature coefficient of refractive index is close to at least a part of three surfaces of an upper surface and a side surface of the core. Temperature independent optical waveguide. 9. A material having a negative temperature coefficient of refractive index embedded in a groove formed on an upper portion of the core and having a length set according to a temperature coefficient of the material and a waveguide length. The temperature-independent optical waveguide according to claim 6, wherein: 10. The substance having a negative temperature coefficient of refractive index includes fluorinated polymethyl methacrylate, fluorinated polycarbonate, polystyrene, rubber-like EVA resin, siloxane gel, polysiloxane, diethylene glycol bis, acrylic carbonate, polyvinyl chloride, Poly (4
-Methylpentene-1), fluorinated polymethylmethacrylate, fluorinated polycarbonate, polystyrene, rubber-like EVA resin, siloxane gel, polysiloxane, diethylene glycol bis, acrylic carbonate, polyvinyl chloride, poly (4-methylpentene-1), The temperature-independent optical waveguide according to claim 6, wherein the optical waveguide is at least one organic compound selected from a methyl methacrylate / styrene copolymer and an acrylonitrile / styrene copolymer. 11. The temperature-independent optical waveguide according to claim 1, wherein a metal film or a glass film is provided on the organic material embedded in the groove. 12. A completely buried optical waveguide having a core and a cladding structure formed on a substrate, and an upper cladding is etched on a part of the core of the optical waveguide to a position immediately above the core. A method for manufacturing a temperature-independent optical waveguide, characterized by burying a filler having a negative refractive index temperature coefficient in a portion. 13. The method of manufacturing a temperature-independent optical waveguide according to claim 12, wherein in the etching step, a silica glass clad on a core is left. 14. In a step of forming an upper clad on a lower clad and a core formed on a substrate, a metal mask is placed on a waveguide portion to be made temperature-independent before forming the upper clad, and other portions are placed on the waveguide. Form the clad to the thickness of the normal upper clad, and then place a metal mask to form the clad to the normal upper clad thickness with a filler having a negative refractive index temperature coefficient in the grooved area. A method of manufacturing a temperature-independent optical waveguide. 15. An upper cladding having an arbitrary thickness at least smaller than a final cladding thickness as a step prior to the step of forming an upper cladding with the metal mask placed thereon. 15. The method for producing a temperature-independent optical waveguide according to item 14.