JPH06235837A - Light waveguide element - Google Patents

Abstract

PURPOSE:To decrease scattering of guided light due to a fine rough pattern or the like in the interface between a core layer and a clad layer by using a low-cost and easy means. CONSTITUTION:A substrate 11 as the clad layer has a rough surface 14, on which a smoothening layer 12 having the same refractive index as that of the substrate 11 is formed by spin coating, etc. As for the smoothening layer 12, sol-gel glass material essentially comprising SiO2 is used. The refractive index of the glass can be controlled by controlling the concn. of water in the atmosphere for firing the sol-gel glass material. By forming a core layer 13 on the smooth surface of the smoothening layer 12, the rough pattern in the interface between the core layer 13 and the smoothening layer 12 is removed, which prevents scattering of guided light and improves the transmission efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide device in which guided light such as a laser beam propagates through a core layer, and more particularly to an optical waveguide device capable of reducing the propagation loss of the guided light in the core layer.

[0002]

13 and 14 are sectional views for explaining the structure of a conventional optical waveguide device, and FIG. 15 is an enlarged sectional view for explaining the problems of the conventional example. In the optical waveguide device shown in FIG. 13, reference numeral 1 is a substrate. The substrate 1 is made of, for example, an optical material having a sufficient transparency for the wavelength of light used. A core layer 2 made of an optical material having a refractive index higher than that of the substrate 1 is formed on the substrate 1. In this optical waveguide device, the substrate 1 functions as a so-called clad layer, and guided light such as a laser beam propagates in the core layer 2 due to the difference in refractive index between the substrate 1 and the core layer 2.

The optical waveguide device shown in FIG. 14 is composed of a substrate 3 made of a material having a large absorptance with respect to the wavelength of light used, and a clad layer 4 formed on the surface of the substrate 3.
And a core layer 5 made of an optical material having a refractive index larger than that of the cladding layer 4. Also in this case,
Guided light is propagated in the core layer 5. In this type of optical waveguide device, the amplitude distribution of guided light (energy intensity distribution of guided light) depends on the refractive index and thickness of the material forming the core layer.
7 is determined as shown in FIG. Looking at this amplitude distribution 7, a part of it extends to the cladding layer 1 or 4 side, so the light propagation efficiency is easily affected by the surface roughness of the interface between the core layer and the cladding layer.

[0004]

However, as shown in FIG.
In the process of manufacturing the substrate 1 or 3 and the process of manufacturing the cladding layer 4 when manufacturing the optical waveguide device shown in FIG.
Formation of 6b and 6c is unavoidable.
Therefore, as schematically shown by a chain line arrow in FIGS. 13 and 14, scattering of guided light or the like occurs at the interface between the core layer 2 and the substrate 1 or the interface between the core layer 5 and the cladding layer 4. It is easy to reduce the propagation efficiency of guided light.

For this reason, conventionally, the surface of the substrate 1 or 3 and the surface of the cladding layer 4 are optically polished to a smooth surface, and the core layer 2 or 5 is formed after this polishing step. Therefore, not only is the manufacturing efficiency reduced and mass productivity inferior, but it is difficult to control the surface roughness of the substrate and clad layer to be uniform in all products, so that the propagation efficiency of guided light becomes uniform. Product management becomes difficult.

The present invention is intended to solve the above problems,
An object of the present invention is to provide an optical waveguide device capable of improving the propagation efficiency of guided light without using a difficult manufacturing process.

[0007]

In the optical waveguide device according to the present invention, a smoothing layer having a smooth surface is laminated on the cladding layer, and the smoothing layer and the refractive index are formed on the smooth surface of the smoothing layer. The core layers are different from each other.

The smoothing layer preferably has a refractive index substantially the same as that of the cladding layer.

By forming the above-mentioned smoothing layer from a sol-gel glass material whose refractive index can be adjusted, it becomes easy to make the refractive indexes of the cladding layer and the smoothing layer coincide with each other.

[0010]

In the above means, the smoothing layer is formed on the surface of the clad layer serving as the substrate or the clad layer formed on the surface of the substrate by a method capable of smoothing the surface. Then, a core layer is formed on the smooth surface of this smoothing layer. As a result, it is possible to prevent the guided light from being scattered at the boundary surface between the core layer and the smoothing layer thereunder, and to improve the propagation efficiency of the guided light. Further, the smoothing layer is made of a sol-gel glass material or the like, and the smoothing layer and the cladding layer have substantially the same refractive index, so that the smoothing layer can be optically integrated with the cladding layer.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is an enlarged external perspective view of an optical waveguide device according to the present invention, and FIGS. 2 and 3 are perspective views showing the optical waveguide device of the present invention for each manufacturing process. FIG. 1 shows a two-dimensional optical waveguide device. Reference numeral 11 is a glass substrate 11 using Pyrex glass (trade name) with no surface polishing. In the two-dimensional optical waveguide device shown in FIG. 1, this glass substrate 11 functions as a clad layer. On the surface of this kind of glass substrate 11,
It is unavoidable that fine irregularities 14 are formed due to shrinkage of the glass material in the cooling and hardening process.

Therefore, as shown in FIG. 3, the glass substrate 1
The smoothing layer 12 is formed on the surface of No. 1. This smoothing layer 1
2 is, for example, an alkoxide of Si [Si (O 2) which has the same refractive index as that of the glass substrate 11 after firing.
R) _n : R is an alkyl group] or a glass material containing silazane (see Chemical Formula 1) as a main component.

[Chemical 1]

As this glass material, it is optimum to use a sol-gel glass material prepared by a so-called sol-gel method. Since this sol-gel glass material is formed by a spin coating method or the like, it can enter into the minute irregularities 14 on the surface of the glass substrate 11 to easily smooth the surface, and the interface with the core layer 13 Can be a smooth surface.

In the sol-gel glass material, the refractive index after firing can be adjusted by controlling the water concentration in the atmosphere for firing it. FIG. 5 is a diagram showing the relationship, in which the horizontal axis represents the water concentration in the atmosphere for firing the sol-gel glass material, and the vertical axis represents the refractive index.
For example, the moisture concentration in the atmosphere for firing the sol-gel glass material used as the material of the smoothing layer 12 is 0 ppm to 200 ppm.
By controlling within the range of 00 ppm, the refractive index after firing can be adjusted within the range of about 1.44 to 1.48. Therefore, it can be set to the same refractive index as that of the material used for the cladding layer. When the glass substrate 11 to be the clad layer is the above-mentioned Pyrex glass, its refractive index is 1.472, so if the moisture concentration in the atmosphere for firing the sol-gel glass material forming the smoothing layer 12 is set to 2000 ppm. , The smoothing layer 12 and the glass substrate 11 can have the same refractive index.
1 and the smoothing layer 12 can be optically integrated.

The core layer 1 is formed on the smooth surface of the smoothing layer 12.
3 is formed. The core layer 13 is formed of a material having a higher refractive index than the smoothing layer 12, and for example, the smoothing layer 1
2 has the same refractive index as the substrate 11 of Pyrex glass, the core layer 13 may be, for example, Corning Glass 705.
9 (trade name).

Next, the method for manufacturing the above optical waveguide device will be described in more detail. Pyrex glass (refractive index 1.4
The surface of the non-polished glass substrate 11 according to 72) is washed. Next, a sol-gel glass material (perhydropolysilazane) containing silazane (see Chemical formula 1) as a main component is applied to the surface of the glass substrate 11. As shown in FIG.
The moisture concentration in the atmosphere for firing this sol-gel glass material is set to about 2000 ppm, and its refractive index is made to substantially match that of the Pyrex glass. As a method for smoothing the surface of this layer, for example, a spin coating method is used. In this spin coating method, a glass substrate 11 is placed on a disk, a sol-gel glass material is applied to a region including the glass substrate 11, and the disk is rotated at high speed to cover the surface of the glass substrate 11. The surface becomes smooth.

Then, after drying the substrate 11, the substrate 11 is put into a firing furnace and the sol-gel glass material is fired and cured at a predetermined temperature, whereby the surface is smooth and the glass substrate 1
A smoothing layer 12 that is optically integrated with 1 is formed.
Next, on the surface of the smoothing layer 12, a Corning glass 7059 (trade name) is formed by a sputtering method to form the core layer 1
3 is formed.

FIG. 4A is a sectional view of the optical waveguide device shown in FIG. When the refractive index of the glass substrate 11 is n1 and the refractive index of the smoothing layer 12 is n2, it is possible to set n1 = n2 by controlling the water concentration in the atmosphere in which the sol-gel glass material to be the smoothing layer 12 is fired. Therefore, the glass substrate 11 and the smoothing layer 12 are optically integrated, and the unevenness 14 at the boundary between the two layers prevents scattering of guided light.
When the refractive index of the core layer 13 is n3, (n1 = n2 <
n3).

In FIG. 4A, the amplitude distribution of the guided light is shown by reference numeral 7, and the smoothing layer 12 and the core layer 13 which are the boundaries of the refractive index
There is almost no unevenness on the boundary surface, so that the scattering of light does not occur at this boundary surface, and the propagation efficiency of guided light becomes very high. Further, as shown in FIG. 4B, when the smoothing layer 12 can be formed thick and the amplitude distribution of the guided light does not extend to the glass substrate 11, the glass substrate 11
Does not affect the propagation of guided light, even if the refractive index n2 of the smoothing layer 12 and the refractive index n1 of the glass substrate are different, (n
If 2 <n3), an optical waveguide device having a high guided light propagation efficiency can be constructed.

Next, FIG. 6 shows another embodiment of the present invention.
The case where a two-branch optical waveguide device is configured is shown. FIG. 6 is an enlarged perspective view showing a two-branch optical waveguide device, and FIG.
12 to 12 are perspective views showing a two-branch optical waveguide device in each manufacturing process. The two-branch optical waveguide device shown in FIG.
A (silicon) substrate 21, a cladding layer 22 made of, for example, SiO ₂ vapor-deposited on the substrate 21, and a Si having the same refractive index as that of SiO ₂ glass, similarly to the above.
A smoothing layer 23 formed of a sol-gel glass material containing O ₂ as a main component, and a two-branched optical waveguide 24a formed of Ti (or Ge) -doped SiO ₂ formed on the smoothing layer 23. And this two-branch optical waveguide 24
and a cladding layer 25 formed on a.

The manufacturing process of this two-branch optical waveguide device will be described. As shown in FIGS. 7 and 8, SiO ₂ is deposited by a vapor deposition method to form a cladding layer 22 on the surface of an unpolished Si substrate 21 having irregularities 26 left on the surface. The clad layer 22 in the vapor-deposited state is likely to have irregularities 27 on its surface. The irregularities 27 are irregularities 2 on the surface of the Si substrate 21.
This is due to the effect of 6. Next, as shown in FIG. 9, a sol-gel glass material containing SiO ₂ as a main component is applied onto the clad layer 22 by a spin coating method and further baked to form a smoothing layer 23 having a smooth surface. The smoothing layer 23 is adjusted so that the moisture concentration in the atmosphere for firing the sol-gel glass material as the material is about 7000 ppm, and as a result, as shown in FIG. Is the refractive index of the cladding layer 22 (1.46)
Can almost match.

Thereafter, as shown in FIG. 10, the smoothing layer 2
A SiO ₂ glass material doped with Ti (or Ge) is deposited on the surface of 3 by a vapor deposition method to form a core layer 24. Then, as shown in FIG. 11, a resist pattern of the bifurcated optical waveguide 24a is formed on the core layer 24 by photolithography, and the core layer 24 is partially etched by dry etching as shown in FIG. The branched optical waveguide 24a is formed.

Next, a SiO ₂ glass material is formed into a film by a vapor deposition method so as to cover the bifurcated optical waveguide 24a and a clad layer 25 is formed to obtain the optical waveguide device shown in FIG. This two-branch optical waveguide device has a refractive index (n
4) and the refractive index (n5) of the smoothing layer 23 are substantially equal to each other, and the boundary surface between the core layer 24 (two-branched optical waveguide 24a) having the refractive index n6 (n4 = n5 <n6) and the smoothing layer 23 is Since it is smooth, the scattering of the guided light propagating through the two-branching optical waveguide 24a is eliminated, and the propagation efficiency is increased.

For example, in the above embodiment, the case where the present invention is simply applied to the waveguide for propagating the guided light is explained. However, the optical path conversion function of the prism, the lens, etc., the light distribution, the coupling, the polarizer, the mode separation, the wavelength demultiplexing. ， Multiplexing, switch, light deflection,
It can be applied to an optical waveguide device having various functions such as optical modulation, wavelength conversion, and optical amplification. Further, the material of the smoothing layer is not necessarily limited to sol-gel glass, and may be, for example, aluminum nitride (AlN) or sialon (Si-Al).
-O-N) or the like can be used. In these materials, it is possible to adjust the refractive index to match that of the cladding layer by changing the molecular weight of N or the ratio of the molecular weights of O and N. Further, by forming a film of these materials by, for example, a CVD method, a smoothing layer having a smooth surface can be formed.

[0025]

As described above, according to the present invention, since the interface between the core layer and the clad layer has no unevenness and can be made a smooth interface, the interface between the core layer and the clad layer can be made smooth. An increase in propagation loss due to scattering of guided light can be prevented, and an optical waveguide device with good propagation efficiency can be configured.

Further, by making the refractive indexes of the smoothing layer and the clad layer coincide with each other, the smoothing layer and the clad layer can be made into an optically integrated medium, and if the surface of the clad layer is uneven. However, this does not cause a propagation loss of guided light. Therefore, the work of polishing the clad layer becomes unnecessary.

If a sol-gel glass material is used as the material for the smoothing layer, it becomes possible to match the refractive index with that of the cladding layer.

[Brief description of drawings]

FIG. 1 is a perspective view of an optical waveguide device according to the present invention.

FIG. 2 is a perspective view illustrating a substrate (clad layer) simple substance for explaining a manufacturing process of the optical waveguide device shown in FIG.

FIG. 3 is a perspective view showing a state in which a smoothing layer is formed on the substrate shown in FIG.

4A is a cross-sectional view for explaining the amplitude distribution of guided light in the optical waveguide device shown in FIG. 1, and FIG. 4B is a cross-sectional view for showing the amplitude distribution when the smoothing layer is thickened.

FIG. 5 is a diagram showing a relationship between a water concentration and a refractive index in an atmosphere for firing a sol-gel glass material, which is an example of a material for a smoothing layer.

FIG. 6 is a perspective view showing an embodiment when a two-branch optical waveguide device is constructed.

7 is a perspective view showing a single substrate, showing a method for manufacturing the two-branched optical waveguide device shown in FIG. 6. FIG.

8 is a perspective view showing a state in which a clad layer is formed on the substrate shown in FIG.

FIG. 9 is a perspective view showing a state in which a smoothing layer is formed on the surface of a clad layer.

FIG. 10 is a perspective view showing a state in which a core layer is formed on the surface of the clad layer.

FIG. 11 is a perspective view showing a state in which a branch path pattern is printed on the core layer.

FIG. 12 is a perspective view showing a state in which a core layer is subjected to an etching treatment to form a branch pattern.

FIG. 13 is a cross-sectional view illustrating the structure of a conventional optical waveguide device.

FIG. 14 is a cross-sectional view illustrating the structure of a conventional optical waveguide device.

15 is a partial enlarged cross-sectional view of FIG. 13 for explaining the problem of the conventional example.

[Explanation of symbols]

 11, 21 Substrate 12, 23 Smoothing layer 13 Core layer 14 Unevenness 21 Cladding layer 24 Core layer 24a 2 Branch optical waveguide 25 Cladding layer

Claims (3)

[Claims] 1. A smoothing layer having a smooth surface is laminated on the clad layer, and a core layer having a refractive index different from that of the smoothing layer is formed on the smooth surface of the smoothing layer. Characteristic optical waveguide device. 2. The optical waveguide device according to claim 1, wherein the smoothing layer has substantially the same refractive index as the cladding layer. 3. The optical waveguide device according to claim 2, wherein the smoothing layer is made of a sol-gel glass material whose refractive index can be adjusted.