JP2574606B2 - Dielectric optical waveguide device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the performance of various optical waveguide devices for performing light intensity modulation, optical switching, and the like using a dielectric optical waveguide.

[0002]

2. Description of the Related Art Conventionally, an optical waveguide device, for example, light (intensity)
Modulators, optical switches, optical polarization plane control elements, light propagation mode control elements, etc. form a single mode propagation optical waveguide in a single crystal dielectric having an electro-optic effect such as lithium niobate or lithium tantalate. The shape is devised, the electrodes are provided in an appropriate shape, and the light passing through the optical waveguide is controlled by the electro-optic effect. In the case of a single-crystal dielectric, a metal waveguide, for example, titanium is vapor-deposited and thermally diffused at a high temperature. An optical waveguide is formed by performing a proton ion exchange in phosphoric acid at 200 to 300 ° C., or changing a part of the refractive index by using a metal mask on a predetermined portion. However, since the optical waveguide is formed by the diffusion treatment from the surface in any of the methods, the cross-sectional shape of the optical waveguide is in accordance with the diffusion, so that there are various inconveniences.

One of the major problems is a coupling loss between an optical waveguide and an optical fiber. The cross-sectional shape of the optical fiber is circular or concentric, whereas the shape of the optical waveguide is similar to an inverted triangle due to diffusion from the surface, and the portion where the intensity of the guided light is strongest near the surface. Therefore, the optical coupling with the optical fiber did not work very well, causing a large loss there. In an optical waveguide device, reduction of light coupling loss is an extremely important issue.

[0004] Further, there is another problem that the light propagation loss is increased by performing the diffusion process as compared with before the diffusion. In the case of a titanium diffused optical waveguide, a propagation loss of about 1 dB / cm usually occurs. Reduction of propagation loss has also been a major issue for optical waveguide devices.

[0005] There is also a problem that light damage is increased by the diffusion process. This means that when light of high intensity or light of a short wavelength is put into the diffusion type optical waveguide, the propagation loss increases with time. This is considered to be due to an increase in trapping of electrons in the optical waveguide due to diffusion ions in the optical waveguide used for forming the optical waveguide.

As a method for forming an optical waveguide that is not of the ion diffusion type, a method using a single crystal epitaxial growth film is known. For example, an optical waveguide in which a mixed crystal film of lithium niobate and lithium tantalate is formed on a lithium tantalate substrate is known. However, this method has some limitations. First, the epitaxially grown film has a thickness of 5 μm due to the problem of the growth rate and the strain in the crystal generated during the growth.
It is difficult to practically obtain the above film thickness, and the coupling characteristic with an optical fiber having a core diameter of about 10 μm is deteriorated.

Further, conditions for epitaxial growth are limited. It is difficult to form pure lithium niobate on a lithium tantalate substrate because the epitaxial growth is difficult if the crystal lattice spacing is not substantially the same, so that only the mixed crystal film is grown. In the case of lithium niobate, pure lithium niobate is superior to the mixed crystal film in overall optical waveguide characteristics.

Although the same kind of epitaxial growth is possible, since the crystal orientation is the same, the substrate has a uniform refractive index, and there is a problem that an optical waveguide cannot be formed.

[0009]

As described above, in an optical waveguide element formed by using only the diffusion method from above on a single substrate or an optical waveguide element using an epitaxially grown film, the coupling loss between the optical waveguide and the optical fiber is large. There were problems such as large propagation loss and large optical damage.

[0010]

In order to solve the above-mentioned problems, a glass substrate is provided in a single crystal dielectric substrate having an electro-optic effect directly bonded to a glass substrate or bonded using glass or silicon or a silicon compound. And an optical waveguide confined by a refractive index difference between the optical waveguide and the optical waveguide, and light passing through the optical waveguide is controlled by an electro-optic effect.

[0011]

With the above configuration, an optical waveguide device having a small coupling loss with an optical fiber, a small propagation loss, and a small optical damage can be obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical waveguide device according to an embodiment of the present invention, in particular, a configuration when applied to an optical modulator and a method of manufacturing the same will be described.
This will be described with reference to the drawings.

Embodiment 1 FIGS. 1 and 2 show a first example of the structure of this embodiment. FIG. 1 shows a case where the present invention is applied to an optical modulator.
A lithium niobate substrate, specifically, an input / output optical waveguide section formed on a lithium niobate substrate 2, and a single crystal dielectric substrate 4 divided from an input section. 5 is the other branch optical waveguide, and 6 and 7 are electrodes formed on both sides of the branch optical waveguide 5. FIG. 2 is a cross-sectional view of the central portion. In the figure, the names of the components 1, 2, 4, 5, 6, and 7 are the same as those in FIG. The branch optical waveguides 4 and 5 have a trapezoidal section and a head portion, and have a so-called ridge-type optical waveguide structure. The cross-sectional shape of the input / output optical waveguide 3 is also the same. Reference numeral 8 denotes a guided light propagation unit. The configuration of the optical modulator itself is what is called a Mach-Zehnder type. The light incident from the input part is split into two, an electric field is applied to one of the branched optical waveguides, and the electro-optical effect is applied to the optical waveguide. The intensity of the light at the output unit is modulated by changing the refractive index of the light and changing the propagation speed of the guided light so that the phase of the light at the recombination unit is different.

A layer having a difference in refractive index of a certain degree or more
When the layers and the layers are stacked, light can be confined in a direction having a large refractive index, and an optical waveguide can be formed. The refractive index of lithium niobate is 2.29, and the refractive index of glass is
Since the light intensity is normally in the range of 1.4 to 1.6, in the case of the structure of this embodiment, light is confined in the lithium niobate substrate. Furthermore, by forming a so-called ridge structure in which only the optical waveguide portion is slightly thicker by etching or the like on the lithium niobate substrate, the portion under the ridge has a larger effective refractive index than the other portions. Light is confined under the ridge, so that the ridge acts as an optical waveguide.

In this case, the waveguide has a trapezoidal or rectangular head and a uniform refractive index inside, so that the center of the guided light is near the center of the optical waveguide and has a shape close to a circle. . The input / output optical waveguide section also has the same shape, so that the coupling efficiency with the optical fiber circular optical waveguide structure having a diameter of about 10 μm is extremely good.

The typical values of the dimensions in this embodiment are as follows: the thickness of the glass substrate 1 is 1 mm, and the thickness of the lithium niobate substrate 2 is 7 mm.
Micron, the height at the ridge top is 3 microns, the optical waveguide width is 10 microns, and the length of the branch optical waveguide is 2c.
m, the length of the entire optical waveguide section is 4 cm. Aluminum was used for the electrodes. With the above-described configuration, the coupling loss with the optical fiber can be reduced to 0.1 mm on one side by bonding using an adhesive whose refractive index is matched.
It became 3 dB or less. When the conventional titanium diffused optical waveguide was used, the coupling loss was about 0.5 to 1.0 dB with the same method of bonding and fixing, so that it was greatly improved. The performance as an optical modulator was almost the same as that of a conventional titanium diffused optical waveguide.

In addition, since a lithium niobate substrate having optical characteristics as a pure single crystal not subjected to ion diffusion processing is used as the optical waveguide, light propagation loss can be extremely reduced. Specifically, 0.1 dB / c
An optical waveguide propagation loss of m or less was easily obtained. In the case of the titanium diffused optical waveguide, the characteristic was significantly improved since the value was 0.5 to 1.0 dB / cm.

Further, the intensity of the incident light is changed from 0 dBm to 20 dB.
m, the state of light damage was observed, but almost no light damage was observed. This is considered to be the effect of using a pure single crystal lithium niobate substrate having very few electron traps as the optical waveguide. The measurement was performed as follows.
The test was performed at a wavelength of 3 μm.

Embodiment 2 FIG. 3 shows a second example of the structure of the optical waveguide device of this embodiment. FIG. 3 also shows a case where the present invention is applied to an optical modulator.
The names and functions of the components up to this point are the same as in the first embodiment. 9 is a low-melting glass layer for joining the glass substrate 1 and the lithium niobate substrate 2. The refractive index of the low-melting glass is about 1.5, and if the thickness is made sufficiently thin, light can be effectively confined in a lithium niobate substrate having a large refractive index as in Example 1. An optical waveguide can be formed. Thereby, the light incident on the lithium niobate substrate 2 was confined in the substrate. Furthermore, by providing a ridge structure, the effective refractive index at the lower part of the ridge is larger than that at the other parts.
Light is confined under the ridge, so that the ridge acts as an optical waveguide.

In this case, the shape of the waveguide is almost the same as that of the first embodiment, and therefore, the coupling efficiency of the optical fiber with the circular optical waveguide structure becomes extremely good.

As a representative value of each dimension, the low melting glass layer 9
When the film thickness is 0.5 μm and other dimensions are the same as those in Example 1, almost the same characteristics as in Example 1 are obtained, and the coupling loss with the optical fiber is 0.3 dB or less on one side, and is greatly reduced. I could improve it. The propagation loss is 0.1
dB / cm was easily obtained. The same effect as in Example 1 was obtained for optical damage.

Embodiment 3 FIG. 4 shows a third example of the structure of the optical waveguide device of this embodiment. FIG. 4 shows a case where the present invention is applied to an optical modulator. In FIG. 4, the names and functions of the components 1 to 7 are the same as in the first embodiment. Reference numeral 10 denotes a silicon layer (silicon film) interposed between the glass substrate 1 and the lithium niobate substrate 2, and the glass layer 1 and the lithium niobate substrate 2
Are directly bonded by a hydroxyl group or oxygen on the surface of the silicon layer (silicon film). Although the refractive index of silicon is different from that of lithium niobate, if the thickness is about 100 nm to about 1 micron and is sufficiently thinner than that of the lithium niobate substrate 2, the difference in the refractive index between the glass substrate and the lithium niobate substrate 2 also results. In addition, light can be effectively confined toward the lithium niobate substrate having a large refractive index, and an optical waveguide can be formed. Further, by directly bonding the glass substrate and the single crystal dielectric substrate via the silicon layer (silicon film), new effects can be obtained in application and production. Made
In terms of fabrication, even if some irregularities and small dust are present at the bonding interface, the process of forming the silicon layer (silicon film)
Since it is taken into the film to some extent and flattened, there is an effect that the production yield of direct bonding is improved.

By using polycrystalline silicon or amorphous silicon as silicon, almost the same effect was obtained in each case. Thereby, the light incident on the lithium niobate substrate 2 was confined in the thin plate. Further, by providing the ridge structure, the portion under the ridge has a larger effective refractive index than the other portions, so that the light is confined under the ridge, and the lower portion of the ridge acts as an optical waveguide.

In this case, the shape of the waveguide is almost the same as that of the first embodiment, and therefore, the coupling efficiency of the optical fiber with the circular optical waveguide structure becomes extremely good.

As a representative value of each dimension, when the thickness of the silicon layer 10 is 0.5 μm and other dimensions are the same as in the first embodiment,
Almost the same characteristics as in Example 1 were obtained. For example, the coupling loss with the optical fiber is 0.3
dB or less, which is a significant improvement. The propagation loss also
0.1 dB / cm was easily obtained as in Example 1. The same effect as in Example 1 was obtained for optical damage.

(Embodiment 4) FIG. 5 shows a fourth example of the structure of the optical waveguide device of the present embodiment. FIG. 5 shows a case where the present invention is applied to an optical modulator. In FIG. 5, the names and functions of the components 1 to 7 are the same as in the first embodiment. Reference numeral 11 denotes a silicon compound layer (silicon compound film) interposed between the glass substrate 1 and the lithium niobate substrate 2, and the glass substrate 1 and the lithium niobate substrate 2 are connected to the silicon layer compound layer (silicon compound film).
Directly joined by hydroxyl groups or oxygen on the surface. Although the refractive index of the silicon compound is different from that of lithium niobate, if the thickness is set to be about 100 nm to 1 micron and sufficiently thinner than that of the lithium niobate substrate 2, the difference in the refractive index between the glass substrate and the lithium niobate substrate 2 can also be obtained. By
Light could be effectively confined to the lithium niobate substrate having a large refractive index, and an optical waveguide could be formed. Further, by directly bonding the glass substrate and the single crystal dielectric substrate via the silicon compound layer (silicon compound film), new effects can be obtained in application and production. Manufacturing
Therefore, even if some unevenness or small dust is present at the bonding interface, in the process of forming the silicon layer compound layer (silicon compound film), it is taken into the film to some extent and flattened, so that the manufacturing yield of direct bonding is increased. This has the effect of improving

By using silicon oxide or silicon nitride as the silicon compound, almost the same effect was obtained in each case. Thereby, the lithium niobate substrate 2
The light incident on is trapped in the thin plate. Furthermore, by providing a ridge structure, the part under the ridge is
Since the effective refractive index is higher than the other portions, the light is confined under the ridge, and thus the ridge acts as an optical waveguide. The shape of the waveguide in this case is almost the same as that of the first embodiment, and therefore, the coupling efficiency of the optical fiber with the circular optical waveguide structure is very good.

As a representative value of each dimension, when the thickness of the silicon compound 11 was 0.5 μm and other dimensions were the same as those in the first embodiment, almost the same characteristics as in the first embodiment were obtained. For example, the coupling loss with the optical fiber was 0.3 dB or less on one side, similar to the first embodiment, and was significantly improved. In addition, a transmission loss of 0.1 dB / cm was easily obtained as in Example 1. The same effect as in Example 1 was obtained for optical damage.

(Embodiment 5) An example of a method of manufacturing an optical waveguide device of the present embodiment will be described.

First, the surfaces of the mirror-polished glass substrate and lithium niobate substrate were extremely cleaned by etching. Specifically, each surface layer was removed by etching with a hydrofluoric acid-based etching solution and subjected to a hydrophilic treatment. After that, the surface is sufficiently washed with pure water and immediately superimposed uniformly, and the water adsorbed on each surface, more specifically, a hydroxyl group, a constituent component thereof, is generated by an intermolecular force of hydrogen.
A direct bond was easily obtained. Sufficiently strong bonding was obtained with this condition.
The heat treatment at a temperature of 00 ° C. further strengthened the bond. Next, the lithium niobate substrate was thinned by mechanical polishing and etching. After the thickness was reduced to 10 μm, an etching mask was formed on the pattern of the optical waveguide structure shown in Example 1 by photolithography, and portions other than the optical waveguide were etched away by 3 μm by etching. Cr was used as a mask, and a hydrofluoric acid-based etchant was used as an etchant. Thereafter, the mask was removed, and an aluminum electrode was formed by ordinary photolithography and etching techniques. Thus, the structure of the optical waveguide device shown in Example 1 was obtained. The coupling characteristics of the device to an optical fiber, the propagation loss, and the optical damage characteristics were all the same as in Example 1.

(Embodiment 6) Another example of the method of manufacturing the optical waveguide device of the present embodiment will be described.

In the same manner as in Example 5, the surfaces of the mirror-polished glass substrate and the lithium niobate substrate were extremely cleaned and flattened by etching. Next, by sputtering, a low-melting glass thin film
m. Next, in the same manner as in Example 5, the low-melting glass films were brought into contact with each other and heated to a temperature near the melting point of the low-melting glass. As a result, the low-melting glass was softened or melted, and a strong bond was obtained. Although the thickness of the bonding layer varies somewhat depending on the heat treatment temperature, generally, the higher the temperature,
It became thinner than the film thickness formed by sputtering. Thereafter, the aluminum electrode was formed in the same manner as in Example 5, and the structure of the optical waveguide device shown in Example 2 was obtained. The coupling characteristics of this element to an optical fiber, propagation loss, and optical damage characteristics were all the same as in Example 2.

(Embodiment 7) Another example of the method of manufacturing the optical waveguide device of the present embodiment will be described.

In the same manner as in Example 5, the surfaces of the mirror-polished glass substrate and the lithium niobate substrate were made extremely clean and flat by etching. Next, by sputtering, an amorphous silicon thin film
m. Next, in the same manner as in Example 5, the surface of the amorphous silicon film was cleaned and hydrophilically treated with a hydrofluoric acid-based etchant, and immersed in pure water. The heat treatment was performed at a temperature of 1100 ° C.
As a result, a strong bond was obtained via the amorphous silicon film. The higher the heat treatment temperature, the higher the strength of the joint. Thereafter, in the same manner as in Example 5, aluminum electrodes were formed, and the structure of the optical waveguide device shown in Example 3 was obtained.
The coupling characteristics of this element to an optical fiber, propagation loss, and optical damage characteristics were all the same as in Example 3.

(Embodiment 8) Another example of the method of manufacturing the optical waveguide device of this embodiment will be described.

In the same manner as in Example 7, a polycrystalline silicon thin film was formed on each surface by chemical vapor deposition (CVD) on the surfaces of the mirror-polished, clean and flattened glass substrate and lithium niobate substrate. It was formed with a thickness of 0.25 μm. Next, in the same manner as in Example 7, the surface of the polycrystalline silicon film is cleaned and hydrophilically treated with a hydrofluoric acid-based etchant, and is immersed in pure water.
The heat treatment was performed at a temperature of 1100 ° C. As a result, a strong bond was obtained via the polycrystalline silicon film. The higher the heat treatment temperature, the higher the strength of the joint. Thereafter, an aluminum electrode is formed in the same manner as in the fifth embodiment.
Was obtained. The coupling characteristics of this element to an optical fiber, propagation loss, and optical damage characteristics were all the same as in Example 3.

(Embodiment 9) Another example of the method of manufacturing the optical waveguide device of this embodiment will be described.

In the same manner as in Example 7, a silicon oxide thin film was applied to each surface of each of the mirror-polished, cleaned and flattened glass substrate and lithium niobate substrate by chemical vapor deposition (CVD). It was formed with a thickness of 0.25 μm.
Next, in the same manner as in Example 7, the surface of the silicon oxide film was cleaned and hydrophilically treated with a hydrofluoric acid-based etching solution, and the silicon oxide films were immersed in pure water and immediately contacted with each other.
The heat treatment was performed at a temperature of ° C. As a result, a strong bond was obtained via the silicon oxide film. The higher the heat treatment temperature, the higher the strength of the joint. Thereafter, the aluminum electrode was formed in the same manner as in Example 5, and the structure of the optical waveguide device shown in Example 4 was obtained. The coupling characteristics of the device to an optical fiber, the propagation loss, and the optical damage characteristics were all the same as in Example 4.

(Embodiment 10) Another example of the method of manufacturing the optical waveguide device of this embodiment will be described.

In the same manner as in Example 7, a silicon nitride thin film was coated on each surface by chemical vapor deposition (CVD) on the surfaces of the mirror-polished, clean and flattened glass substrate and the lithium niobate substrate. It was formed with a thickness of 0.25 μm.
Next, in the same manner as in Example 7, the surface of the silicon nitride film is cleaned and hydrophilically treated with a hydrofluoric acid-based etching solution, and after dipping in pure water, the silicon nitride films are brought into contact with each other.
The heat treatment was performed at a temperature of ° C. As a result, a strong bond was obtained via the silicon nitride film. The higher the heat treatment temperature, the higher the strength of the joint. Thereafter, the aluminum electrode was formed in the same manner as in Example 5, and the structure of the optical waveguide device shown in Example 4 was obtained. The coupling characteristics of the device to an optical fiber, the propagation loss, and the optical damage characteristics were all the same as in Example 4.

(Embodiment 11) FIG. 6 shows a fifth example of the structure of the optical waveguide device of this embodiment. FIG. 6 also shows a case where the present invention is applied to an optical modulator.
The names and functions of the respective components from 1 to 7 are the same as those in the first embodiment. 2 'is a lithium tantalate substrate. With this configuration, an optical waveguide device similar to that of the first embodiment can be obtained using lithium tantalate based on the same principle as that of the first embodiment. The refractive index of lithium tantalate is about 2.18, which is larger than the refractive index of glass. The shape of the waveguide in this case is almost the same as that of the first embodiment, and therefore, the coupling efficiency of the optical fiber with the circular optical waveguide structure is very good.

When the same values as those of the first embodiment were taken as representative values of the respective dimensions, almost the same characteristics as those of the first embodiment were obtained.
With the above configuration, the coupling loss with the optical fiber is 0.3 dB on one side, as in the first embodiment.
The result was as follows, which was greatly improved. In addition, a propagation loss of 0.1 dB / cm was easily obtained as in Example 1.
The same effect as in Example 1 was obtained for optical damage.

(Embodiment 12) Another example of the method of manufacturing the optical waveguide device of the present embodiment will be described.

In the same manner as in Example 5, the surfaces of the mirror-polished, clean and flattened glass substrate and the lithium tantalate plate were cleaned and hydrophilized with a hydrofluoric acid-based etchant, and immersed in pure water. By performing the heat treatment immediately after stacking, a strong joint was obtained. Thereafter, an aluminum electrode was formed in the same manner as in Example 5 to form an aluminum electrode.
The structure of the optical waveguide device shown in FIG. The coupling characteristics of the device to an optical fiber, the propagation loss, and the optical damage characteristics were all the same as in Example 11.

Similarly, in the case of lithium tantalate, an optical waveguide element having a junction made of glass or a junction made of silicon or a silicon compound was obtained. The various characteristics were almost the same as those of the eleventh embodiment.

The effect of the heat treatment of the bonding strengthening in Examples 7-10 and the like is as follows. For example, the bonding strength is increased several times even when the temperature is maintained at 100 ° C. for about one hour, and several tens kg / cm 2.
Was obtained. In general, the higher the temperature and the longer the time, the higher the bonding strength. However, when the temperature was increased to 1100 ° C. or higher, the escape of lithium from the surface of lithium niobate or lithium tantalate became severe, so that the surface characteristics deteriorated greatly and the performance as an optical waveguide element deteriorated. Therefore, the bonding heat treatment temperature was preferably 1100 ° C. or less. Further, in any of the examples, when the glass substrate has a thermal expansion coefficient close to that of the single crystal dielectric substrate to be bonded, the heat treatment can be performed at a higher temperature, and the bonding strength can be increased. Could be made stronger. In this case, even if the processing for thinning was performed by strong polishing or the like, effects such as no peeling or stable operation at higher temperatures as an optical waveguide element were obtained.

In direct bonding, it is considered that a hydroxyl group, hydrogen, or the like in water is adsorbed on the surface of the glass or single crystal dielectric substrate, and bonding is performed by the binding force of the ions. When heat treatment is performed in this state, water gradually escapes from the joint interface, hydrogen of hydroxyl groups and hydrogen directly adsorbed escape, and the remaining oxygen and oxygen on the dielectric surface, which is an oxide, react with the dielectric constituent elements. It is considered that the bonding is strengthened.

Silicon or a silicon compound can easily hydrophilize the surface and easily form a covalent bond with silicon and oxygen usually contained in glass. Is considered to be obtained.

In the above embodiments, examples of lithium niobate and lithium tantalate have been described as examples of single crystal dielectrics. However, the same applies to the case of using other single crystal dielectrics having an electro-optical effect. What can be done is clear in principle.

The thickness of the substrate on which the optical waveguide is formed is:
Since optical communication is generally performed in a single mode, it is desirable to set the substrate thickness to propagate in a single mode.

In this embodiment, the configuration example of the optical modulator has been described. However, if the optical modulator is operated on and off under specific conditions, that is, where the intensity of the emitted light is maximum and where it is minimum, Obviously, it will be an optical switch. It is also apparent that the present invention can be similarly applied to an optical waveguide and an element using the electro-optic effect, and a similar effect can be obtained.

In this embodiment, a specific example of dimensions is shown, but the present invention is not limited to this example.

In each of the embodiments, an example in which two substrates are joined is shown, but three or more substrates can be joined. For example, a single-crystal dielectric substrate can be bonded to the upper and lower surfaces of a glass substrate, and an optical waveguide element can be formed in each single-crystal dielectric substrate, and the present invention is not limited to two substrates.

[0054]

Since the present invention has the above-described structure and manufacturing method, it exhibits the following effects.

Since a structure in which the refractive index of the waveguide portion is uniform can be obtained as the optical waveguide, the symmetry of the cross section of the optical waveguide is good, and the center of propagation of light can be almost at the center of the thin plate. The thickness can be made freely, thereby greatly reducing the coupling loss with the optical fiber.

Further, since a material having good crystallinity such as a pure single-crystal dielectric substrate that has not been subjected to diffusion treatment can be used for the optical waveguide, an optical waveguide device with small light propagation loss and small optical damage can be obtained. I was able to.

Further, by adjusting the coefficient of thermal expansion of the glass substrate to the coefficient of thermal expansion of the single crystal dielectric substrate to be joined, heat treatment for directly improving the joining strength can be performed at a higher temperature and more easily. There were effects such as easier characteristics and stable characteristics up to high temperatures.

In this embodiment, an example of the configuration of the optical modulator has been described. However, since the feature of this embodiment lies in the configuration of the optical waveguide itself, it is basically applicable to various optical waveguide devices using the optical waveguide. The present invention can be widely and generally applied, and is not limited to an optical modulator, but can be applied to an optical waveguide device such as an optical switch, a polarization plane control, and a propagation mode control.

When an epitaxially grown layered structure is used, an expensive single crystal substrate must be used as a substrate. In this embodiment, a glass substrate is used. It is about two orders of magnitude cheaper and has a great industrial effect. Also, since the coefficient of thermal expansion of glass is quite wide, even if the material of the single crystal dielectric for forming the optical waveguide is changed, it is easy to select a glass having a coefficient of thermal expansion that matches the material. There is also an effect that the choice of the dielectric material forming the optical waveguide is expanded.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a sectional configuration diagram of a first embodiment of the present invention.

FIG. 3 is a configuration diagram of a second embodiment of the present invention.

FIG. 4 is a configuration diagram of a third embodiment of the present invention.

FIG. 5 is a configuration diagram of a fourth embodiment of the present invention.

FIG. 6 is a configuration diagram of a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass base 2 Lithium niobate substrate 3 Input / output optical waveguide part 4 First branch optical waveguide 5 Second branch optical waveguide 6 Electrode 7 Electrode 8 Guided light propagation part 9 Low melting glass layer 10 Silicon layer 11 Silicon compound layer 2 '' Lithium tantalate substrate

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-44025 (JP, A) JP-A-64-18121 (JP, A) JP-A-52-145240 (JP, A) JP-A-49-440 98258 (JP, A) JP-A-4-162022 (JP, A) JP-A-58-223106 (JP, A) JP-A-60-51700 (JP, A) JP-A-63-49732 (JP, A) JP-A-4-123018 (JP, A) JP-A-4-116816 (JP, A) APPL. PHYS. LETT. VOL. 56 NO. 24P. 2419-P. 2421 (June 1990)

Claims (5)

(57) [Claims] 1. A single crystal dielectric substrate having an electro-optical effect and a glass substrate is directly bonded and laminated by hydroxyl groups or oxygen on the surface of the glass substrate and the surface of the single crystal dielectric substrate, and A dielectric optical waveguide device comprising an optical waveguide confined in a dielectric substrate due to a difference in refractive index from the glass substrate. 2. A method according to claim 1, wherein the glass substrate and the single crystal dielectric substrate having an electro-optical effect are formed by a silicon film or a silicon compound film formed on a predetermined portion of the glass substrate or the single crystal dielectric substrate. It is characterized by having an optical waveguide that is directly bonded and laminated by a hydroxyl group or oxygen on the surface of the film or the silicon compound film, and is confined in the single crystal dielectric substrate by a difference in refractive index from the glass substrate. A dielectric optical waveguide element. 3. The dielectric optical waveguide device according to claim 1, wherein lithium niobate or lithium tantalate is used as the single crystal dielectric having an electro-optic effect. 4. After the surface of the glass substrate and the surface of the single crystal dielectric substrate are subjected to a hydrophilic treatment, the glass substrate and the single crystal dielectric substrate are superimposed and directly bonded, and heat treatment is performed to improve the bonding strength. A method for manufacturing a dielectric optical waveguide device, wherein an optical waveguide is formed in the single crystal dielectric substrate. 5. A heat treatment temperature of 100 ° C. to 110 ° C.
5. The method for manufacturing a dielectric optical waveguide device according to claim 4 , wherein the process is performed at a temperature of 0.degree.