JPH09222525A - Production of optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make productivity high, cost low and loss low and to make it possible to arbitrarily control the refractive index difference between core and clad by forming the cores and upper clad layer by a screen printing method or spin coating method. SOLUTION: This optical waveguide has a lower clad layer 3 on a substrate 2 and the cores 4 having a rectangular section on the lower clad layer 3. Both flanks and front surfaces of the cores 4 are coated with the upper clad layer 5. The formation of the cores 4 and the upper clad layer 5 is executed by applying a coating liquid contg. glass power by screen printing or spin coating, then, baking the coating. The screen printing method or spin coating method is used for forming the lower clad layer 3 in the case the optical waveguide having the structure having the lower clad layer 3 on the substrate 2 is manufactured. A method for applying the coating liquid contg. the glass powder by the screen printing or spin coating, then baking the coating is used for the formation of the cores 4 and the clad layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical waveguide used for optical passive components such as demultiplexers, multiplexers, and optical switching elements in the field of optical communication.

[0002]

2. Description of the Related Art With the practical use of optical communication, optical waveguides are receiving attention. The optical waveguide comprises a core made of a high refractive index material and a clad made of a low refractive index material surrounding the core.

As a method of manufacturing an optical waveguide, a sputtering method, a chemical vapor deposition (CVD) method, a vacuum deposition method, an ion exchange method, etc. have been proposed (for example, optical integrated circuit; co-authored by Nishihara et al .; Ohmsha). P145-p158 (1985)).

Among these manufacturing methods, the sputtering method and C
The method using the VD method or the vacuum deposition method in combination with the fine processing technique can provide a core having a rectangular cross section with a clear boundary. In particular, when the flame deposition (FHD) method, which is an application technology of the optical fiber manufacturing method, and the reactive ion etching technology, which is a glass microfabrication technology, are used together, a waveguide with low loss is obtained (for example, Suzuki et al. , IEICE Transactions CI, Vol.J77-CI, No.5 P184-193 (199
Four) ).

As a waveguide manufactured by the sputtering method,
For example, it is known that a Corning 7059 glass target is used to form a film on a quartz glass substrate, a Pyrex glass substrate, or a soda glass substrate. However, with the sputtering method, it is difficult to form a thin film with high uniformity of thickness over a wide range on the substrate, so it is difficult to fabricate a large number of optical waveguides at the same time using a large-area substrate, and mass production is difficult. Inferior in sex. In addition, since it is difficult to form a dense thin film by the sputtering method, the propagation loss is usually
It will be as large as 3-4 dB / cm. Further, in the sputtering method, if the raw material glass contains many additional elements, the film composition is likely to change depending on the sputtering conditions. Therefore, silica glass is generally used for both the core and the clad. For this reason,
It is difficult to arbitrarily control the refractive index difference between the core and the clad.

As an optical waveguide manufactured by the CVD method,
It is known that a SiO ₂ —GeO ₂ glass film is formed on a quartz glass substrate. In this CVD method, oxygen is used as a carrier gas, and a raw material gas such as SiCl ₄ , GeCl ₄ or the like is introduced into a vacuum chamber to cause an oxidation reaction to form a thin film. The propagation loss of the optical waveguide thus obtained is reported to be 0.1 dB / cm or less. However, this method requires complicated steps, a manufacturing apparatus is expensive, and a source gas having a high risk is used. Therefore, a simpler and safer method is required.

The vacuum vapor deposition method is known as a method for producing a chalcogenide amorphous thin film optical waveguide. According to this method, Mo and T can be used in an environment where the degree of vacuum is 10 ^-3 Pa or less.
The evaporation source is heated by a boat such as a or W to deposit a thin film on the substrate. However, this method is difficult to form a thin film having a high thickness uniformity over a wide range on the substrate, as in the above-described sputtering method.

In addition to these, the optical waveguide can be manufactured by utilizing the ion exchange method. When using the ion exchange method, for example, after heating the glass substrate to a certain temperature or higher,
Desired ions are diffused from the outside into the glass substrate and replaced with Na ⁺ ions or the like inside the glass substrate to give a refractive index distribution inside the glass substrate to form an optical waveguide.
The cross-sectional shape of the optical waveguide manufactured by this ion exchange method is semicircular or elliptical, and the boundary between the core and the clad becomes unclear, so that it is difficult to obtain a sufficient optical confinement effect.

As described above, in each of the above manufacturing methods, there are problems that the manufacturing apparatus is large and expensive, the mass productivity is poor, and the propagation loss is large. For this reason, conventionally, various optical components using an optical waveguide are expensive, and it is also difficult to easily obtain a low-loss optical waveguide.

Further, in the conventional manufacturing method, the core and the clad are generally made of a silica-based material, and the difference in the refractive index between the core and the clad is realized by doping with an additive element such as Ge. There was a limit to the arbitrary control of. Therefore, it has been difficult to manufacture a high-performance optical waveguide for multimode.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical waveguide which is excellent in productivity, inexpensive, low in loss, and capable of arbitrarily controlling a refractive index difference between a core and a clad. It is to provide a method for manufacturing a waveguide.

[0012]

This object is achieved by any one of the following constitutions (1) to (5). (1) A method of manufacturing an optical waveguide in which a peripheral surface of a core is covered with a lower clad layer and an upper clad layer, wherein a coating solution containing glass powder is screen-printed or formed on the core and the upper clad layer. A method for manufacturing an optical waveguide using a method of applying by spin coating and then baking. (2) The method for producing an optical waveguide according to (1) above, wherein a coating solution containing glass powder is applied by screen printing or spin coating to form the lower clad layer, followed by firing. (3) The method of manufacturing an optical waveguide according to (1) or (2) above, wherein the core forming step includes a step of processing the shape by an etching method. (4) The weight average particle diameter of the glass powder is D _50, and the standard deviation of the particle diameters of the glass particles constituting the glass powder is σ.
_{When d} is set, σ _d / D ₅₀ ≦ 5, The method for producing an optical waveguide according to any one of the above (1) to (3). (5) The weight average particle diameter D _{50 of the} glass powder is 0.2 to 2
The method for producing an optical waveguide according to any one of (1) to (4) above, wherein the optical waveguide has a thickness of μm.

[0013]

[Operation and Effect] The optical waveguide has a structure in which the peripheral surface of the core is covered with the lower clad layer and the upper clad layer.
In the present invention, at the time of manufacturing such an optical waveguide, at least the core and the upper clad layer are formed by screen printing or spin coating.

The screen printing method and the spin coating method can increase the productivity because a film having a uniform thickness can be formed on the surface of a large-area substrate, and the complicated steps required in the prior art are not required, resulting in an expensive apparatus. There is no need to use high-risk raw materials. Moreover, according to the present invention, an optical waveguide having extremely small propagation loss can be obtained. Therefore, according to the present invention, an optical waveguide having excellent productivity, low cost and low loss can be realized.

Further, in the manufacturing method of the present invention, the material of the core and the clad layer is not limited, and the degree of freedom in selecting the material is high, so that the difference in the refractive index between the core and the clad layer can be arbitrarily controlled. .

Further, since the flatness of the surface of the core is extremely improved by shaping the core by etching when forming the core, an optical waveguide having a further lower loss can be obtained.

Further, the flatness of the interface between the core and the clad layer can be improved by controlling the weight average particle diameter and the standard deviation of the particle diameter of the glass powder used in the screen printing method and the spin coating method. Since a uniform core and clad layer with few remaining bubbles can be obtained, the propagation loss can be remarkably reduced.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a specific configuration of the present invention will be described in detail.

Cross-sectional views of structural examples of the optical waveguide of the present invention are shown in FIGS. 1 and 2, respectively. The optical waveguide shown in FIG.
The lower clad layer 3 is provided on the substrate 2, and the lower clad layer 3
A core 4 having a rectangular cross section is provided above, and both side surfaces and an upper surface of the core 4 are covered with an upper clad layer 5. The optical waveguide shown in FIG. 2 has a core 4 having a rectangular cross section on a lower clad layer 3 which also functions as a substrate, and both side surfaces and an upper surface of the core 4 are covered with an upper clad layer 5.

In the present invention, when the optical waveguide having the structure shown in FIG. 2 is produced, a coating liquid containing glass powder is applied to the formation of the core 4 and the upper clad layer 5 by screen printing or spin coating, followed by firing. Use the method. Further, when an optical waveguide having a structure in which the lower clad layer 3 is provided on the substrate 2 as shown in FIG. 1, a screen printing method or a spin coating method is also used for forming the lower clad layer 3.

The case where the present invention is applied to the manufacture of the optical waveguide having the structure shown in FIG. 1 will be described below with reference to the drawings.

In the first embodiment of the present invention, first, referring to FIG.
As shown in (a), the glass paste layer 31 for the lower clad layer is formed on the substrate 2 and dried, or dried and baked. Next, as shown in FIG. 3B, the glass paste layer 41 for core is formed on the glass paste layer 31 for lower clad layer so as to have a predetermined core pattern, and dried or dried and baked. Next, as shown in FIG. 3C, after forming the glass paste layer 51 for the upper cladding layer, it is dried and baked to obtain an optical waveguide.

In FIG. 3B, if a screen printing method is used to form the glass paste layer 41 for core, a predetermined core pattern can be directly obtained. On the other hand, when the spin coating method is used to form the glass paste layer 41 for core, if a concave pattern having a negative shape of the core is previously formed on the glass paste layer 31 for lower cladding layer with a resist or the like, spin coating is performed. At this time, the coating solution penetrates into the recesses, and a core-shaped glass paste layer is obtained. Then, after that, the resist may be removed.

In the second aspect of the present invention, first, referring to FIG.
As shown in (a), the glass paste layer 31 for the lower clad layer is formed on the substrate 2 and dried, or dried and baked. Next, as shown in FIG. 4B, the glass paste layer 41 for core is formed on the entire surface of the glass paste layer 31 for lower clad layer, and dried or dried and baked.

Next, as shown in FIG. 4C, a mask pattern 42 is formed on the core glass paste layer 41. The mask pattern 42 is the glass paste layer 4 for the core.
1 serves as a mask when forming a core pattern by etching or the like, and is preferably made of various metals such as W. In this case, first, a resist layer is formed on the glass paste layer 41 for cores other than the core forming region, and a mask layer is formed thereon by a sputtering method or the like. Next, by removing the resist layer, the mask layer is left only in the core formation region to form the mask pattern 42.

Next, as shown in FIG. 4D, the core glass paste layer 41 is selectively removed except for the area covered with the mask pattern 42 to form a core pattern. It is preferable to use a wet etching method or a dry etching method for this selective removal. As a dry etching method, a reactive ion etching method (RIE
Method), a plasma etching method, an ion beam etching method, and the like can be used, but the method is not particularly limited.
After forming the core pattern, the mask pattern 42 is removed by etching or the like.

Next, as shown in FIG. 4 (e), after forming the glass paste layer 51 for the upper cladding layer, it is dried and baked to obtain an optical waveguide.

In each of the above-mentioned embodiments, if all the glass paste layers are laminated and then fired only once, the number of steps can be reduced, so that the cost can be reduced, and the shape processing by etching becomes easy. On the other hand, if firing is performed every time each paste layer is formed, the flatness of the interface between the core and the clad layer becomes extremely good, and the propagation loss can be significantly reduced. In order to utilize the advantages of both of these methods, for example, firing is not performed until the etching processing of the glass paste layer for the core is completed, and it is fired once after the etching processing is finished, and then the glass paste layer for the upper cladding layer is laminated. It is also preferable to use a firing method.

In each of the above embodiments, the glass paste layers may be dried until the solvent contained in the layers evaporates. The firing may be performed until each glass paste layer is densified. The firing conditions may be appropriately determined according to the composition of the glass powder, the average particle size, etc., but normally the firing temperature is 5
The baking time is about 0 to 1400 ° C. and the baking time is about 1 to 5 hours.

After the formation of the upper clad layer, the laminated body consisting of the substrate and each layer is cut into a predetermined size, and the end face is polished to obtain an optical waveguide device.

The relationship between the weight average particle diameter D ₅₀ of the glass powder used in each glass paste and the standard deviation σ _d of the particle diameter of the glass particles constituting the glass powder is preferably σ _d / D ₅₀ ≦ 5. Yes, and more preferably σ _d / D ₅₀ ≦ 2. When σ _d / D ₅₀ is too large, that is, when the particle size distribution is wide, the residual bubbles in the core and the clad layer after firing increase and the propagation loss increases. The smaller the particle size of a glass particle, the shorter the melting time.Therefore, if the particle size distribution is wide, it is thought that the small particle melts first and adheres to the large particle, and at that time there are many residual bubbles to trap the bubbles. To be

The D ₅₀ of the glass powder is preferably 0.2 to
It is 2 μm, more preferably 0.5 to 1.5 μm. D
_{When 50} is too large, the flatness of the interface between the core and the clad layer deteriorates, and the propagation loss increases. On the other hand, D
_{When 50} is too small, the residual bubbles in the core and the clad layer after firing increase, and the propagation loss increases. D ₅₀
It is considered that the reason why the number of residual bubbles increases when is too small is that if the particle size is small, even if the particle size is slightly different, there is a difference in the melting rate, which causes trapping of the bubbles as described above.

The D ₅₀ is the particle size when the weight is added up from particles having a small particle size and the integrated value becomes 50% of the weight of all particles. The particle size used for calculating D ₅₀ and σ _d is preferably measured by a particle size distribution meter (Microtrac or the like) using light scattering.

The composition of the glass powder is not particularly limited, and may be any of oxide glass, fluoride glass, chalcogenide glass, etc., and may be appropriately selected according to various characteristics such as required refractive index and transparency. Good. Specifically, for example, as the oxide glass, soda lime glass, borosilicate glass, lead glass, aluminosilicate glass, borate glass, phosphate glass, aluminate glass, titanate glass. Examples of the fluoride glass include ZrF ₄ type glass and AlF ₃ type glass.

In the present invention, since the degree of freedom in selecting the composition of the glass powder is high, it is possible to arbitrarily control the refractive index difference between the core and the clad layer. The refractive index of both the core and the clad layer can be arbitrarily selected from the range of, for example, about 1.4 to 2.0, and it is easy to obtain a refractive index difference of about 25%. In the present invention, since the glass paste layer is fired to form the core and the clad layer, even if there is a large difference in refractive index between the core and the clad layer, almost no stress is generated in the core and the clad layer. Therefore, unlike the case where the sputtering method or the like is used, the substrate does not warp.

The transparency of the core and clad layers may be ensured for the wavelength of light used. Specifically, it is preferable that the light transmittance is 98% or more when the thickness is 10 μm. The wavelength of light used in the optical waveguide is usually selected from the range of 0.4 to 1.6 μm.

Each glass paste is prepared so as to have physical properties suitable for a screen printing method or a spin coating method. In the screen printing method, 25 of glass paste
The viscosity at ℃ is preferably 2000 to 10000 cP,
More preferably, it is 3000 to 6000 cP. Further, in the spin coating method, the viscosity of the glass paste at 25 ° C. is preferably 500 to 4000 cP, more preferably 800 to 2500 cP. If the viscosity of the glass paste is too low, the coating film tends to have uneven thickness, and
It becomes difficult to thicken the coating film. On the other hand, if the viscosity is too high, the surface of the coating film tends to be roughened or wavy.

Each glass paste contains glass powder and a vehicle, and various stabilizers and the like are added if necessary. The vehicle is a binder dissolved in a solvent. The content of each of the glass powder, the binder and the solvent in the paste is not particularly limited and may be appropriately determined so as to obtain a desired viscosity, but normally, the binder is 2 to 15 parts by weight with respect to 100 parts by weight of the glass powder, The solvent is preferably 50 to 90 parts by weight.

The binder and solvent used in the glass paste are not particularly limited, and for example, the binder may be selected from at least one selected from polyvinyl alcohol, polyvinyl butyral, nitrocellulose, polyethylene, polymethacrylic acid ester, ethyl cellulose, etc. Solvents include isopropyl alcohol, toluene,
Trichlorethylene, ethyl alcohol, butanol,
At least 1 from methyl ethyl ketone, terpineol, methyl isobutyl ketone, tetrachlorethylene, etc.
The seed may be selected appropriately.

Although the shape and dimensions of the optical waveguide are not particularly limited, the cross-sectional shape of the core is generally substantially rectangular, the height of the core cross section is about 5 to 100 μm, and the width of the core cross section is about 5 to 100 μm.
The thickness of the upper clad layer and the lower clad layer is about 100 μm and about 30 μm or more.

When the lower clad layer is provided on the substrate as shown in FIG. 1, the substrate material is not particularly limited, and may be appropriately selected from various materials such as glass, semiconductor, single crystal and the like. On the other hand, as shown in FIG. 2, when the lower clad layer 3 also has a function as a substrate, the lower clad layer 3 may be appropriately selected from various glasses such as glass having the same composition as the above-mentioned glass powder.

[0042]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention.

Example 1 (First Mode, Screen Printing Method) An optical waveguide having the structure shown in FIG. 1 was manufactured as follows based on the procedure shown in FIG.

Glass powder (for clad layer) Borosilicate glass, refractive index 1.463, thermal expansion coefficient 32.0 × 10 ^-7 deg ^-1 , D ₅₀ = 1.0 μm, σ _d / D ₅₀ = 0.5

Glass powder (for core) aluminosilicate glass, refractive index 1.474, thermal expansion coefficient 32.5 × 10 ^-7 deg ^-1 , D ₅₀ = 1.0 μm, σ _d / D ₅₀ = 0.5

Each of the above glass powders was mixed with a vehicle to prepare a glass paste for a clad layer (viscosity 5000c).
P) and glass paste for core (viscosity 5000 cP) were prepared. The vehicle was prepared by dissolving a binder (methacrylic acid resin) in a solvent (α-terpineol) and further adding a stabilizer (butyl carbitol acetate and butyl phthalyl butyl glycolate). The mixing amount was 100 parts by weight of glass powder, 10 parts by weight of binder, and 70 parts by weight of solvent.

The glass paste for a clad layer is applied onto a substrate (made of borosilicate glass) by a screen printing method to form a glass paste layer for a lower clad layer having a thickness of 50 μm and dried to volatilize an organic solvent. Let Next, the glass paste for cores was applied by a screen printing method to form a glass paste layer for cores having a thickness of 15 μm and a width of 15 μm, which was dried to volatilize the organic solvent. Then, in an air atmosphere using an electric furnace, 12
Firing was performed at 00 ° C. for 1 hour to obtain a laminated body of the lower clad layer and the core.

Next, the above glass paste for a clad layer is applied onto the lower clad layer and the core by a screen printing method to form a glass paste layer for an upper clad layer having a thickness of 50 μm and dried to remove an organic solvent. Volatilized.
Next, using an electric furnace, in an air atmosphere at 1200 ° C.
And baked for 1 hour to obtain an optical waveguide. In this optical waveguide,
No residual air bubbles were found in the core and clad layers.
Also, laser light was made incident on this optical waveguide from an optical fiber, and the intensity of emitted light and the intensity of reflected light were measured to determine the insertion loss. As a result, the insertion loss was 0.1 dB / cm or less.

<Example 2 (first embodiment, spin coating method)> An optical waveguide was produced in substantially the same manner as in Example 1 except that the spin coating method was used instead of the screen printing method. However, the viscosity of the glass paste for the clad layer was 1500 cP, and the viscosity of the glass paste for the core was 2000 cP. Further, in order to form the core glass paste layer into a linear pattern, after forming the negative resist, the core glass paste was spin-coated. No residual bubbles are observed in this optical waveguide either, and
The insertion loss was 0.1 dB / cm or less.

Example 3 (Second Mode, Screen Printing Method) An optical waveguide having the structure shown in FIG. 1 was manufactured as follows based on the procedure shown in FIG.

First, in the same manner as in Example 1, a glass paste layer for lower clad layer and a glass paste layer for core were laminated and then fired. However, the glass paste layer for core was printed on the entire surface of the glass paste layer for lower clad.

Next, a resist layer having a linear hole portion was formed by photolithography, and a mask layer was formed thereon by a vapor deposition method. After removing the resist layer and leaving only the mask pattern, the core glass paste layer is etched by a reactive ion etching method using CF ₄ + O ₂ to form a core pattern having a rectangular cross section with a line width of 10 μm and a height of 10 μm. did.

Next, using the glass paste for the clad layer, a uniform film having a thickness of 30 μm was formed by a screen printing method to form a glass paste layer for the upper clad layer. Then, after drying to volatilize the organic solvent, the organic solvent was fired to obtain an optical waveguide.

No residual bubbles were observed in this optical waveguide, and the insertion loss was 0.05 dB / cm or less, which was extremely small.

Example 4 (Second Embodiment, Spin Coating Method) Example 3 was repeated except that the screen printing method was replaced by the spin coating method, and the glass paste for the cladding layer and the core of Example 2 was used. An optical waveguide was prepared in the same manner as in. No residual bubbles were observed in this optical waveguide, and the insertion loss was 0.05 dB / cm or less, which was extremely small.

The effects of the present invention are clear from the results of the above examples.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration example of an optical waveguide manufactured by the present invention.

FIG. 2 is a cross-sectional view showing a configuration example of an optical waveguide manufactured by the present invention.

3 (a) to 3 (c) are explanatory views of a first embodiment of the production method of the present invention.

4 (a) to (e) are explanatory views of a second embodiment of the production method of the present invention.

[Explanation of symbols]

 2 substrate 3 lower clad layer 31 glass paste layer for lower clad layer 4 core 41 glass paste layer for core 42 mask pattern 5 upper clad layer 51 glass paste layer for upper clad layer

Claims (5)

[Claims] 1. A method for producing an optical waveguide in which a peripheral surface of a core is covered with a lower clad layer and an upper clad layer, wherein a coating solution containing glass powder is screened for forming the core and the upper clad layer. A method for manufacturing an optical waveguide using a method of baking after applying by printing or spin coating. 2. The method for producing an optical waveguide according to claim 1, wherein a method of applying a coating liquid containing glass powder by screen printing or spin coating and then firing is used for forming the lower clad layer. 3. The method of manufacturing an optical waveguide according to claim 1, wherein the core forming step includes a step of processing the shape by an etching method. Wherein the weight average particle size of the glass powder and D _50, when the standard deviation sigma _d of the particle diameter of the glass particles constituting the glass powder, σ _d / _{D 50} ≦ 5 a claim is 1. A method for manufacturing an optical waveguide according to any one of 1 to 3. 5. The method for producing an optical waveguide according to claim 1, wherein the weight average particle diameter D _{50 of the} glass powder is 0.2 to 2 μm.