JP2002341162A - Optical waveguide substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide substrate having an optical waveguide consisting of a siloxane polymer formed on a substrate with sufficient adhesion strength. SOLUTION: The optical waveguide substrate is produced by forming an optical waveguide having a lower clad layer 3 consisting of a second siloxane polymer and a core part 4 on a substrate 1 with a buffer layer 2 consisting of a first siloxane polymer interposed. The amount of the organic component content of the first siloxane polymer is larger than that of the second siloxane polymer. By forming the lower clad layer 3 on the buffer layer 2 having low film stress, high film strength and excellent adhesion property with the substrate 1, the buffer layer 2 and the lower clad layer 3 are made to adhere in a good state to each other by the siloxane bonds, hydrogen bonds or the like. Moreover, since the stress due to the optical waveguide formed on the buffer layer 2 can be decreased by the buffer layer 2, the optical waveguide consisting of the siloxane polymer can be formed with sufficient adhesion strength on the substrate 1 in the optical waveguide substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide substrate used for an optical communication module and the like, and more particularly to an optical waveguide substrate having an optical waveguide made of an organic optical material having an increased adhesion strength to a substrate. is there.

[0002]

2. Description of the Related Art Conventionally, an optical communication module or the like has various optical devices mounted on an optical waveguide substrate in which, for example, an electric circuit using a wiring conductor and an optical circuit using an optical waveguide are formed on a silicon substrate. Is used. Further, there has been proposed an optical waveguide substrate in which an optical waveguide is formed on a ceramic circuit substrate which has better electrical high-frequency characteristics and mechanical strength than a silicon substrate, and which can realize a high electrical wiring density by multilayering.

On the other hand, as an optical waveguide, for example, a silica-based optical waveguide in which a three-dimensional clad portion and a core portion are formed using a silica film formed by a flame deposition method on a quartz glass substrate or a silicon substrate, There is an optical waveguide or the like in which a lithium niobate single crystal substrate is used as a clad portion and titanium is thermally diffused on the substrate to form a core portion in a three-dimensional waveguide shape.

However, when these silica-based optical waveguides and the like are used for an optical waveguide substrate, a heat treatment at a high temperature of about 1000 ° C. or more is required to form these optical waveguides. When an optical circuit is formed, an electric circuit substrate serving as a base is damaged.

Therefore, instead of these silica-based optical waveguides or the like which require high-temperature treatment at the time of fabrication, optical waveguides made of organic optical materials which can be formed at a low temperature are being studied. As the organic optical material used for this optical waveguide, PMMA (polymethyl methacrylate), polycarbonate, polyimide, siloxane polymer, BCB (benzocyclobutene), fluorine resin, and the like have been studied. Among them, siloxane polymer is particularly promising as a material for forming an optical waveguide having excellent propagation characteristics and reliability.

As a method of manufacturing an optical waveguide made of these organic optical materials, a lower cladding layer is formed on a silicon substrate or a glass substrate, and then a core layer having a higher refractive index than the lower cladding layer is formed. Then, the core layer is formed by processing the core layer by RIE (reactive ion etching) or the like using a thin film microfabrication technique, and is then covered with an upper cladding layer having a lower refractive index than that of the core. A method of forming an optical waveguide having a shape has been performed.

Here, as a method of forming a layer made of a siloxane polymer, a well-known coating method such as a spin coating method or a bar coating method is used by applying a solution of a siloxane monomer, oligomer or polymer in an organic solvent to be a siloxane polymer. After coating on a substrate, a heat treatment is performed to thermally polymerize to form a siloxane polymer layer.
In addition, a method of forming a siloxane polymer layer by applying ultraviolet light or the like to a substrate and then performing photopolymerization on the substrate is also employed. Among these siloxane polymers, the photopolymerization type siloxane polymer can be polymerized more efficiently than the heat polymerization type siloxane polymer, and it is easy to form an optical waveguide with the siloxane polymer having a small organic component content. .

[0008]

However, when an optical waveguide made of a siloxane polymer is to be formed on a substrate such as a silicon substrate or a ceramic circuit substrate, the adhesion strength between the siloxane polymer and the substrate may be insufficient. There has been a problem that the lower cladding layer made of a siloxane polymer is peeled off from the substrate or cracks are generated in a post-process such as a manufacturing process of the optical waveguide, dicing, or subsequent device mounting.

Further, since the organic components contained in the siloxane polymer cause absorption loss with respect to light in a wavelength band used in optical communications, the siloxane polymer forming the optical waveguide has a low organic component content. Is desired.

However, a siloxane polymer having a small content of an organic component has a large film stress when a layer is formed on a substrate and has low adhesion to a substrate, as compared with a siloxane polymer having a high content of an organic component. As a result, the lower cladding layer made of the siloxane polymer has a problem that it is easily peeled off from the substrate or cracks are easily generated.

Further, the photopolymerizable siloxane polymer can be polymerized more efficiently than the heat polymerizable siloxane polymer, and it is easy to form an optical waveguide with a siloxane polymer having a small organic component content. Therefore, although it is useful as an optical waveguide material, there is a problem that the adhesion when this layer is formed on an inorganic material such as metal or silicon is poor.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to form an optical waveguide having at least a lower cladding layer made of a siloxane polymer on a substrate with a sufficient adhesion strength. An optical waveguide substrate is provided.

[0013]

SUMMARY OF THE INVENTION An optical waveguide substrate according to the present invention comprises an optical waveguide having a lower cladding layer made of a second siloxane polymer and a core portion on a substrate via a buffer layer made of a first siloxane polymer. A wave path is formed,
An organic component content of the first siloxane polymer is larger than that of the second siloxane polymer.

Further, in the optical waveguide substrate of the present invention, in the above structure, the buffer layer has a refractive index equal to or smaller than that of the lower cladding layer.

Further, in the optical waveguide substrate according to the present invention, in the above structure, the core portion is made of a siloxane polymer having a higher refractive index than the second siloxane polymer.

In the optical waveguide substrate according to the present invention, in the above structure, the first siloxane polymer is of a thermopolymerization type, and the second siloxane polymer is of a photopolymerization type. .

According to the optical waveguide substrate of the present invention, by forming the buffer layer made of the first siloxane polymer having a high organic component content on the substrate, the film stress is small, the film strength is high, and the A buffer layer having excellent adhesion can be obtained, and a lower clad layer made of the second siloxane polymer having a smaller organic component content than the first siloxane polymer is formed through the buffer layer.
The first siloxane polymer of the buffer layer and the second siloxane polymer of the lower cladding layer can be satisfactorily adhered to each other by a siloxane bond, a hydrogen bond, or the like to form an optical waveguide having a sufficient adhesion strength. The layer can alleviate the stress caused by the optical waveguide formed thereon. As a result, it is possible to obtain an optical waveguide substrate in which an optical waveguide having a lower cladding layer made of a siloxane polymer and a core portion with sufficient adhesion strength is formed on the substrate.

When the refractive index of the buffer layer is equal to or smaller than the refractive index of the lower cladding layer, the field distribution of light propagating through the optical waveguide normally exceeds the lower cladding layer. Because the component content is large, the light is absorbed by the buffer layer that absorbs a large amount of light or interferes with the substrate to increase the loss.Thus, the thickness of the lower cladding layer is limited by the area of the light propagating through the optical waveguide. It is necessary to make the thickness such that the distribution does not exceed the lower cladding layer, but even if the thickness of the lower cladding layer is not sufficient, light propagating through the optical waveguide radiates to the buffer layer side. An increase in loss can be suppressed.

When the core is formed of a siloxane polymer having a higher refractive index than the second siloxane polymer,
An optical waveguide substrate on which an optical waveguide made of a siloxane polymer having excellent propagation characteristics and reliability is formed can be obtained.

In the case where the first siloxane polymer is of a thermal polymerization type and the second siloxane polymer is of a photopolymerization type, the content of the organic component of the siloxane polymer in the buffer layer is increased to improve the compatibility with the substrate. It is easy to form a low loss optical waveguide by forming a buffer layer with adhesion strength and capable of effectively relieving stress, and efficiently polymerizing while reducing the organic component content of the siloxane polymer in the lower cladding layer. Becomes

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical waveguide substrate according to the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing an example of an embodiment of the optical waveguide of the present invention. In FIG. 1, 1 is a substrate, 2 is a buffer layer made of a first siloxane polymer formed on a substrate 1, and 3 is a lower cladding layer of an optical waveguide made of a second siloxane polymer formed on a buffer layer 2. , 4
Denotes a core portion of the optical waveguide formed on the lower cladding layer 3,
Reference numeral 5 denotes an upper clad layer of the optical waveguide formed so as to cover the core portion 4.

The substrate 1 is a substrate for forming an optical waveguide and for forming an optical circuit and an electric circuit together with another optical waveguide. The substrate 1 is used as a substrate for handling optical signals such as an optical circuit substrate or a photoelectric mixed substrate. For example, a silicon substrate, an alumina substrate, a glass ceramic substrate, a multilayer ceramic electric circuit substrate, a ceramic electric circuit substrate on which a thin film multilayer electric circuit is formed, a plastic electric wiring substrate, and the like can be used.

The first siloxane polymer used for the buffer layer 2 may be basically a resin containing a siloxane bond in the polymer skeleton, and may be polyphenylsilsesquioxane, polydiphenylsilsesquioxane. In addition to siloxane polymers having an alkyl group or a phenyl group such as polymethylphenylsilsesquioxane, siloxane polymers having a vinyl group, an allyl group, an amino group, an epoxy group, an amino acid group, or the like may be used. The first used for the buffer layer 2
When the content of the organic component contained in the siloxane polymer is preferably 10% by weight or more, a sufficient effect as the buffer layer 2 can be obtained with respect to improvement in adhesion strength and relaxation of stress, but more preferably 20% by weight. It is desirable to use one having the above content. However, when the vinyl component or acrylic acid is contained as an organic component, it becomes a polymer with high elasticity, and even if the content is small, a high stress relaxation effect can be obtained. is there. Further, the effect of improving the adhesion strength and relaxing the stress required for the buffer layer 2 depends on the thickness of the layer of the optical waveguide to be formed and the stress load, and is not limited to the above range.

If the content of the organic component is too large, the hardness is lowered, and the glass transition temperature is lowered, and the glass is easily softened at a low temperature. Becomes In order to increase the adhesion strength between the buffer layer 2 and the lower cladding layer 3, it is desirable to form a siloxane bond at the interface.
If the content of the organic component is too large, the amount of silicon atoms becomes relatively small, so that the siloxane bond that can be formed is also reduced, and the adhesion strength between the buffer layer 2 and the lower cladding layer 3 may be insufficient. For example, when a thermoplastic component such as acrylic acid is included as an organic component,
In order to prevent wrinkles and cracks from occurring in the process of forming the optical waveguide, the content of the organic component is desirably about 50% or less. Further, when a phenyl group, a novolak group, or the like is contained as an organic component, a polymer having a high hardness is obtained, so that the content of the organic component can be increased. However, the content is desirably about 70% or less.

In order to form the buffer layer 2, for example, a known coating method such as a spin coating method or a bar coating method is used to apply a solution of a siloxane-based monomer, oligomer or polymer, which is a precursor of a heat-polymerizable siloxane polymer, to an organic solvent. After that, a siloxane polymer layer may be formed by performing heat treatment and thermal polymerization after coating on the substrate 1. The temperature of this heat treatment is desirably 300 ° C. or lower in order to sufficiently leave the organic components and lower the film stress.

Alternatively, a siloxane polymer layer may be formed by similarly coating the substrate 1 using a precursor of a photopolymerization type siloxane polymer, and irradiating light such as ultraviolet light and photopolymerizing the same.

The thickness of the buffer layer 2 may be about 0.1 μm or more. However, in order to sufficiently reduce the stress caused by the optical waveguide formed on the buffer layer 2, the thickness of the buffer layer 2 must be small. It is desirable that the height be 1 μm or more. If it is thicker than necessary, the buffer layer 2
The thickness of the buffer layer 2 needs to be such that the total film stress does not exceed the film strength of the buffer layer 2 because the film strength of the buffer layer 2 does not withstand the entire film stress including the optical waveguide and causes cracks. Normally, there is no problem if the thickness of the buffer layer 2 is 20 μm or less.

As the second siloxane polymer used for the lower cladding layer 3, a siloxane polymer having an organic component content smaller than that of the first siloxane polymer is used, and the skeleton of the polymer basically contains siloxane bonds. Any resin may be used. For example, polyphenylsilsesquioxane, polydiphenylsilsesquioxane, polymethylphenylsilsesquioxane, and the like can be used. The content of the organic component contained in the second siloxane polymer used for the lower cladding layer 3 is preferably smaller than the content of the organic component of the first siloxane polymer so as to minimize the absorption loss of the propagation light. .

Further, in order to suppress the absorption loss of the propagation light by the lower cladding layer 3, the content is desirably 20 wt% or less. However, when hydrogen atoms in organic components are replaced by deuterium or halogen, 1.3μ
Since the light transmittance for propagating light having a wavelength of m to 1.6 μm increases, there is no problem even if the content is increased by the amount replaced by deuterium or halogen.

On the other hand, if the content of the organic component is too small, cracks may occur due to increased shrinkage and poor elasticity during layer formation. Although this depends on the thickness of the layer and the heat treatment temperature at the time of forming the layer, an organic component content of 5 wt% or more is necessary to form a practical optical waveguide.

In order to form the lower cladding layer 3, for example, an organic solvent solution of a siloxane-based monomer, oligomer or polymer, which is a precursor of a heat-polymerizable siloxane polymer, is coated by a known method such as spin coating or bar coating. After coating on the substrate 1 on which the buffer layer 2 is formed by using the method,
A siloxane polymer layer may be formed by heat treatment and thermal polymerization.

A solution of a siloxane-based monomer or oligomer, which is a precursor of the photopolymerization-type siloxane polymer, and an organic solvent solution of a polymer and a polymerization initiator is buffered by a known coating method such as a spin coating method or a bar coating method. After coating on the substrate 1 on which the layer 2 is formed, ultraviolet light or the like may be irradiated, if necessary, heat treatment may be performed, and photopolymerization may be performed to form a siloxane polymer layer.

At this time, the photopolymerization type siloxane polymer can be polymerized more efficiently than the heat polymerization type siloxane polymer, and a low-loss optical waveguide can be formed with the siloxane polymer having a small organic component content. Therefore, it is suitable for forming the lower cladding layer 3. The heat treatment temperature at the time of forming the lower clad layer 3 is not more than the heat treatment temperature at the time of forming the buffer layer 2 or the glass transition temperature of the buffer layer 2 in order to suppress the occurrence of wrinkles and cracks in the buffer layer 2. .

Here, when the field distribution of the light mainly propagating through the core portion 4 of the optical waveguide exceeds the lower cladding layer 3, the propagating light is transmitted through the buffer layer 2 which has a large absorption of light due to a large organic component content. Loss increases due to absorption or propagation of light interfering with the substrate 1. Therefore, the thickness of the lower cladding layer 3 is usually set such that the field distribution of light propagating through the optical waveguide does not exceed the lower cladding layer 3.

However, even if the thickness of the lower cladding layer 3 is not sufficient for the field distribution of the propagating light, if the refractive index of the buffer layer 2 is made equal to the refractive index of the lower cladding layer 3, Accordingly, the same effect as substantially increasing the thickness of the lower cladding layer 3 can be obtained, and it is possible to suppress the problem caused by the propagation light passing through the lower cladding layer 3. Further, by making the refractive index of the buffer layer 2 smaller than the refractive index of the lower cladding layer 3, the spread of the field distribution of the propagating light to the buffer layer 2 can be suppressed,
Problems caused by the field distribution of the propagating light exceeding the lower cladding layer 3 can be more effectively suppressed. In addition,
In order to reliably suppress the spread of the field distribution of the propagating light to the buffer layer 2, it is preferable that the refractive index of the buffer layer 2 be smaller than the refractive index of the lower cladding layer 3 by 0.2%, more preferably 1% or more. Strictly speaking, using well-known optical waveguide analysis techniques such as optical waveguide theory, finite element method and beam propagation method,
Substrate 1, buffer layer 2, lower cladding layer 3, core 4,
The field distribution of the propagating light may be determined from the refractive index, the thickness, and the like of the upper cladding layer 5 so as not to reach the substrate 1.

The core portion 4 is formed by applying an organic solvent solution of an organic optical material such as polyimide, fluorinated polyimide, siloxane polymer, PMMA, or olefin resin to the substrate 1 on which the lower cladding layer 3 is formed by, for example, spin coating. After forming a layer by applying to a predetermined thickness and performing heat treatment at a temperature equal to or lower than the heat treatment temperature at the time of forming the lower cladding layer 3,
What is necessary is just to form in a predetermined shape on the lower clad layer 3 using well-known thin film fine processing techniques, such as photolithography and RIE. Here, an optical material having a higher refractive index than the lower cladding layer 3 is used for the core portion 4 based on a well-known optical waveguide theory.

The upper clad layer 5 is formed on the core portion 4 and the lower clad layer 3 around the core portion 4 so as to cover the core portion 4. After the core portion 4 is formed, the polyimide, fluorinated polyimide, siloxane polymer, An organic solvent solution of an organic optical material such as PMMA / olefin resin is applied to the substrate 1 on which the lower cladding layer 3 and the core portion 4 are formed to a predetermined thickness by, for example, a spin coating method or the like, and heat-treated.

The upper cladding layer 5 does not have to be formed, and may be formed as needed according to the specifications of the optical waveguide. The core portion 4 is formed on the flat upper surface of the lower cladding layer 3 as shown in FIG. 1, and a groove corresponding to the shape and size of the core portion 4 is provided on the upper surface of the lower cladding layer 3. May be formed in this groove.

The height, width and refractive index of the core 4, the thickness and refractive index of the lower cladding layer 3, and the thickness and refractive index of the upper cladding layer 5 are set to desired specifications using a known optical waveguide theory. Just design.

As described above, an optical waveguide having an embedded three-dimensional waveguide shape is manufactured.

In the optical waveguide substrate of the present invention, the core 4
When a siloxane polymer is used as the organic optical material for forming the upper cladding layer 5, for example, an organic solvent containing a precursor of a thermopolymerization type siloxane polymer is applied to the substrate 1 by spin coating or the like, and then the lower cladding layer is used. Layer 3
The core portion 4 having excellent adhesion to the lower cladding layer 3 by a low-temperature heat treatment of about 100 ° C. to 300 ° C. lower than the heat treatment of
And the upper cladding layer 5 can be formed. Further, by using a siloxane polymer containing a metal by mixing a metal alkoxide, the core portion 4 and the upper cladding layer 5 whose refractive index is accurately controlled to a desired value can be easily manufactured, so that propagation characteristics and It is easy to manufacture an optical waveguide having excellent reliability. Furthermore, since the shrinkage during the formation of the layer is small, the surface of each layer made of the siloxane polymer formed on the surface of the substrate 1 is excellent in flatness and smoothness, and the substrate 1 having a large surface roughness or wiring Even when an electric circuit board having large undulations due to conductors is used, an optical waveguide including the buffer layer 2, the lower cladding layer 3, and the core portion 4 can be accurately manufactured thereon.

The siloxane polymer used for the core portion 4 and the upper cladding layer 5 of such an optical waveguide may be basically a resin containing a siloxane bond in the polymer skeleton, for example, polyphenylsilsesquioxane. San polydiphenylsilsesquioxane, polymethylphenylsilsesquioxane, and the like can be used.

[0044]

Next, a specific example of the optical waveguide substrate of the present invention will be described.

Example 1 First, 18 wt% of a methyl group and 16 wt% of a phenyl group were used as organic components on a substrate 1 made of silicon by spin coating and heat treatment at 250 ° C.
% Of the first siloxane polymer having a refractive index of 1.44 and a thickness of 3 μm. Next, an organic solvent solution of a siloxane-based oligomer and a polymerization initiator, which is to be a siloxane polymer, is coated on a substrate using a spin coating method, and then irradiated with ultraviolet light, subjected to a heat treatment at 200 ° C., and subjected to photopolymerization. 15 wt% as the refractive index
A lower cladding layer 3 made of a second siloxane polymer of 1.45 and having a thickness of 9 μm was formed.

Next, using the same photopolymerizable siloxane polymer as the second siloxane polymer, the core portion 4 and the upper cladding layer 5 were formed to form a buried optical waveguide. At this time, the refractive indices of the core 4 and the upper cladding layer 5 were 1.457 and 1.45, respectively, and the width of the core was 8 μm.
m, the height was 8 μm, and the thickness of the upper cladding layer 5 above the core portion 4 was 5 μm. Thus, an optical waveguide substrate of the present invention as shown in FIG. 1 was manufactured.

When the thus obtained optical waveguide substrate of the present invention was cut into chips by dicing,
No abnormalities such as peeling occurred in the optical waveguide. further,
No problem occurred even after leaving for 2,000 hours under a constant temperature and humidity of 85 ° C./85% RH.

Example 2 For comparison with the optical waveguide substrate of the present invention, an optical waveguide substrate of a comparative example in which an optical waveguide was formed without using a buffer layer was manufactured.

First, an organic solvent solution of a siloxane-based oligomer, which is a precursor of a siloxane polymer, and a polymerization initiator is coated on a substrate made of silicon by spin coating, and then irradiated with ultraviolet light and heated at 200 ° C. To form a lower cladding layer comprising a siloxane polymer layer having a refractive index of 1.45 and a thickness of 9 μm.

Next, using the same photopolymerizable siloxane polymer, a core portion and an upper clad layer were formed to form a buried optical waveguide. At this time, the refractive indices of the core and the upper cladding layer are 1.457 and 1.45, respectively, the width of the core is 8 μm, the height is 8 μm, and the core 4
The thickness of the upper cladding layer 5 at the upper part of was set to 5 μm. Thus, an optical waveguide substrate of a comparative example was manufactured.

When the optical waveguide substrate of this comparative example was cut into chips by dicing, slight but partial peeling was observed in the optical waveguide. In addition, 85 ℃ / 85% R
When left under a constant temperature and humidity of H for 2,000 hours, there were some optical waveguides that were peeled and cracked.

As described above, according to the present invention, it was confirmed that an optical waveguide substrate in which an optical waveguide made of a siloxane polymer was formed on a substrate with sufficient adhesion strength could be provided.

It should be noted that the present invention is not limited to the above-described embodiments, and that various changes and improvements can be made without departing from the scope of the present invention.
For example, the optical waveguide may be a rib-type optical waveguide whose core portion that does not cover the upper clad is exposed, or an optical waveguide made of a siloxane polymer in which hydrogen atoms are deuterated or halogenated.

[0054]

As described above, according to the optical waveguide substrate of the present invention, by forming the buffer layer made of the first siloxane polymer having a large organic component content on the substrate, the film stress is reduced, A buffer layer having high strength and excellent adhesion to the substrate can be obtained, and a lower clad layer made of the second siloxane polymer having an organic component content smaller than that of the first siloxane polymer is formed through the buffer layer. Therefore, the first siloxane polymer of the buffer layer and the second siloxane polymer of the lower cladding layer can be satisfactorily adhered to each other by siloxane bond, hydrogen bond, or the like to form an optical waveguide having sufficient adhesion strength. Further, the stress caused by the optical waveguide formed thereon can be reduced by the buffer layer. As a result, it is possible to obtain an optical waveguide substrate in which an optical waveguide having a lower cladding layer made of a siloxane polymer and a core portion with sufficient adhesion strength is formed on the substrate.

When the refractive index of the buffer layer is equal to or smaller than the refractive index of the lower cladding layer, the field distribution of light propagating through the optical waveguide usually exceeds the lower cladding layer. Because the component content is large, the light is absorbed by the buffer layer that absorbs a large amount of light or interferes with the substrate to increase the loss.Thus, the thickness of the lower cladding layer is limited by the area of the light propagating through the optical waveguide. It is necessary to make the thickness such that the distribution does not exceed the lower cladding layer, but even if the thickness of the lower cladding layer is not sufficient, light propagating through the optical waveguide radiates to the buffer layer side. An increase in loss can be suppressed.

When the core portion is formed of a siloxane polymer having a higher refractive index than the second siloxane polymer,
An optical waveguide substrate on which an optical waveguide made of a siloxane polymer having excellent propagation characteristics and reliability is formed can be obtained.

In the case where the first siloxane polymer is of a heat polymerization type and the second siloxane polymer is of a photopolymerization type, the content of the organic component of the siloxane polymer in the buffer layer is increased to improve the compatibility with the substrate. It is easy to form a low loss optical waveguide by forming a buffer layer with adhesion strength and capable of effectively relieving stress, and efficiently polymerizing while reducing the organic component content of the siloxane polymer in the lower cladding layer. Becomes

As described above, according to the present invention, it is possible to provide an optical waveguide substrate in which an optical waveguide having at least a lower cladding layer made of a siloxane polymer is formed on a substrate with a sufficient adhesion strength.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of an embodiment of an optical waveguide substrate according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Buffer layer 3 ... Lower cladding layer of optical waveguide 4 ... Core part of optical waveguide 5 ... Upper cladding layer of optical waveguide

Claims (4)

[Claims] An optical waveguide comprising a lower cladding layer made of a second siloxane polymer and a core portion formed on a substrate with a buffer layer made of a first siloxane polymer interposed therebetween; An optical waveguide substrate, wherein the organic component content of the polymer is higher than that of the second siloxane polymer. 2. The optical waveguide substrate according to claim 1, wherein a refractive index of said buffer layer is equal to or smaller than that of said lower cladding layer. 3. The optical waveguide substrate according to claim 1, wherein said core portion is made of a siloxane polymer having a higher refractive index than said second siloxane polymer. 4. The optical waveguide substrate according to claim 1, wherein said first siloxane polymer is of a thermopolymerization type, and said second siloxane polymer is of a photopolymerization type.