JPH0677088B2 - Method of manufacturing planar optical waveguide - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical component useful in an optical communication system, an optical information processing system, etc., and more particularly to a manufacturing method of a planar optical waveguide which is simple and advantageous in terms of mass productivity. is there.

2. Description of the Related Art With the sophistication of optical communication systems, diversification and specialization of optical-related parts are being promoted, and mass production is being further required in the manufacturing method thereof.

Among them, an optical waveguide is used for short-distance light guide unlike an optical fiber, and is, for example, an optical waveguide means for various optical circuit elements such as modulation, polarization, switch, phase shift, branching, coupling, multiplexing, and photoelectric conversion. Further, it is widely used as an optical waveguide means of an optical integrated circuit incorporating these optical circuit elements.

The optical waveguide includes a two-dimensional optical waveguide that confines light only in the direction perpendicular to the substrate, that is, a planar waveguide, and a three-dimensional waveguide that guides light in the form of a narrow beam with a constant cross-sectional distribution. A common basic structure is a planar waveguide.
In order to confine it in such an optical waveguide, the light propagation path is made as transparent as possible to the wavelength of the propagating light and is formed of a material having a higher refractive index than the surrounding environment.

A typical example of a conventional method for manufacturing an optical waveguide will be described with reference to the drawings.

First, there is a method of forming a plastic optical waveguide by a selective photopolymerization method whose process charts are shown in FIGS. 3 (a) to 3 (d).
According to this method, for example, a film 10 made of a photosensitive monomer is formed (FIG. 3 (a)), a mask 11 having a pattern of an optical waveguide is provided on the surface of the film 10, and then ultraviolet exposure is performed ( FIG. 3 (b)). At this time, the UV-irradiated monomer is cross-linked and polymerized. Then, the mask 11 is removed, and the unreacted monomer in the portion not irradiated with the ultraviolet rays by the mask 11 is removed (FIG. 3 (c)). Furthermore, the removed part is filled with transparent plastic, and a clad layer is formed on both sides of this film 10.
12 is applied (FIG. 3D), and the filled plastic portion is used as the optical waveguide 13.

In addition, a flame deposition method whose outline is shown in FIG. 4 is known. In this method, for example, as shown in FIG. 4, a plurality of flat substrates 15 are arranged on a rotary table 14, and the vicinity of the substrates 15 is heated from one end of the torch 16 while being heated by a heater such as a burner. Glass forming raw material gas 17 and combustion gas 17
A and A are introduced to cause a flame hydrolysis reaction to form glass particles, and these are deposited on the substrate 15. The exhaust gas is discharged through the exhaust pipe 18. By rotating the turntable 14, glass particles can be continuously deposited on the plurality of substrates 15. Further, the substrate having the glass particulate deposited layer is sintered to make the deposited layer transparent.

However, the method as described above has problems that mass productivity is poor due to many steps and complexity, and that the substrate is deformed by heating and the yield is reduced. Further, the plastic optical waveguide has a problem that the transmission loss is essentially large.

To solve these problems, as a method of manufacturing a high-quality planar optical waveguide with high mass productivity, a waveguide layer having a core and a clad on the outer circumference of a hollow glass pipe containing SiO ₂ as a main component is provided as a method. A manufacturing method of forming a structure, and then inserting a core made of a heat-resistant material into a hollow glass pipe, bringing the cores into close contact with each other and flattening them, and then cutting them out into a planar optical waveguide (Japanese Patent Application No. 61- No. 105185) has been proposed. In this manufacturing method, the core layer and the clad layer can be formed by a continuous operation, and the sintering can be performed at the same time as the deposition, so that the number of steps is small and the mass productivity is excellent. Further, since the thickness of the waveguide layer portion can be finely adjusted by stretching in a pipe state, it is possible to easily obtain an extremely high quality planar optical waveguide.

According to this method, even if the area of the portion forming the waveguide layer structure cannot be sufficiently obtained due to the dimensional constraint of the starting material, for example, the waveguide layer is formed to be thick while maintaining the designed ratio. A large amount of planar optical waveguides can be manufactured at a time by stretching the film and adjusting it to a predetermined thickness later.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the above-described method for manufacturing a planar optical waveguide, the outermost layer is heated from the outside during planarization or when adjusting the thickness of the waveguide layer by stretching. It was often observed that the clad layer, which was a material, was gradually volatilized. Therefore, there is a problem that a clad layer having a predetermined thickness cannot be obtained at the final stage.

This phenomenon is particularly noticeable when a large amount of the additive for adjusting the refractive index is added to the clad layer, but even if the amount of the additive is small, it becomes apparent when the heating time becomes long, and the clad layer has a predetermined thickness. It has been confirmed that it will be several tens of μm thinner.

Therefore, the present invention is to provide a method for manufacturing a planar optical waveguide which is simple and excellent in mass productivity, and which does not damage the waveguide layer structure during heating.

Means for Solving the Problems In view of the above-mentioned current state of the method for manufacturing a planar waveguide, the present inventor has developed a manufacturing method that is simple, has excellent mass productivity, and accurately realizes a predetermined waveguide layer structure. As a result of various studies to achieve this, a hollow glass tube was used as the substrate, multiple layers with different refractive indexes were deposited on the outer surface, and a high-purity quartz glass layer was formed as the outermost layer, which was shaped near the softening point. It was found that the above is extremely effective for achieving the above object, and completed the present invention.

That is, the manufacturing method of the planar waveguide of the present invention, a hollow glass tube outer wall containing SiO ₂ as a main component, a core layer made of glass and a clad layer made of at least one glass, the core layer is an intermediate layer and The core layer is formed so that its refractive index is higher than that of a layer in contact with the core layer, and further, an outermost layer made of high-purity silica glass is formed, and then the hollow glass tube is made of a heat-resistant material. The present invention is characterized in that a child is inserted, these are brought into close contact with each other and molded, and this is cut out to obtain a planar optical waveguide.

In the method of the present invention, it is advantageous to use chemical vapor phase reactivity for forming the glass deposition layer which becomes the core layer, the cladding layer or the high-purity silica glass layer. For example, POD (external plasma method) or the like can be used.

Examples of the hollow glass tube as the substrate include a quartz glass tube containing SiO ₂ as a main component, a Pycor glass tube, a Pyrex glass tube, and the like.

Further, the core layer mainly uses a silane-based gas such as SiCl ₄ or SiHCl ₂ as a glass forming raw material gas, or an alcoholate, and in some cases, an additive such as POCl ₂ , CaCl ₄ , or TiCl ₅ for increasing the refractive index. , TaCl ₃ , SbCl ₃ or their hydrides, alcoholates and the like in combination. These additives can be used as a mixture of two or more kinds, and in addition to the alcoholate, LiOC ₂ H ₅ , Nb (OC ₂ H ₅ ) which is meltable in a volatile organic solvent such as methanol, ethanol or acetone. _Five
A high refractive index glass layer to be the core layer by atomizing an organic solvent such as or an aqueous solution of a water-soluble metal halide (such as ZnCl ₂ ) using an atomizer or ultrasonic waves and introducing these into a plasma forming torch. Obtainable. It goes without saying that these additives can be used as the glass forming raw material itself. The core layer may be composed of a single layer of glass having the same refractive index,
As with graded index optical fiber,
It is also possible to form a plurality of layers so that the refractive index sequentially decreases.

Furthermore, in relation to the cladding layer is a core layer, the additive comprising a lower refractive index than the refractive index of the core layer to the glass-forming raw material (in addition to the additive material to, fluoride, such as SF _6, CF ₄ (Including a halide gas such as BCl ₃ , BBr _{3 and the} like, a hydride, an alcoholate, etc.) is appropriately selected and used to form at least one layer.

When the glass tube portion finally functions as a clad layer, the clad layer obtained from the deposited film may have the same composition as the glass tube.

A mixture of these glass forming raw materials or additives is, for example, in the POD method, Ar as a plasma forming gas.
And introduced into the plasma torch together with O ₂ as a reaction gas, excited and decomposed by the high frequency applied by the high frequency coil set on the outer periphery of the plasma torch to react to form glass particles and deposit on the outer wall of the glass tube, at the same time It is sintered by a plasma flame to form a transparent glass layer.

The mixing ratio of these glass forming raw material gases is appropriately selected as necessary and is not particularly limited.

Thus, after forming a core layer having a predetermined refractive index in the hollow glass tube, at least one clad layer and a high-purity quartz glass layer, a core made of a heat-resistant material having a flat portion is placed in the hollow glass tube. By heating the hollow glass tube from the surroundings by an appropriate means, the glass tube shrinks in the central direction and comes into close contact with the core. A planar waveguide having a predetermined size and shape can be obtained by cutting it with an appropriate means such as a lathe or a diamond cutter.

Examples of the core material include carbon, boron nitride, alumina, beryllia, silicon carbide and the like.

Further, the core may have various shapes, and may have any shape such as a triangular prism, a quadrangular prism, or another polygonal prism.

Effect According to the production method of the present invention, fluorine or B ₂ O ₃ which lowers the refractive index is appropriately added to the silica glass so that the refractive index of the cladding layer becomes lower than the refractive index of the core layer. In addition to the refractive index, a small amount of GeO ₂ , TiO ₂ , P ₂ O _5, etc. may be added for the purpose of adjusting the thermal expansion coefficient. These additives are used properly according to the application of the product.

For example, when a relatively high refractive index difference is required, silica glass with GeO ₂ added to the core layer and silica glass with fluorine added to the cladding layer are used. For applications requiring radiation resistance, high-purity silica glass is used as the core layer, and fluorine-doped silica glass is used as the cladding layer. In any case, the thicknesses of the core layer and the cladding layer are set according to the required optical characteristics and mechanical characteristics. Therefore, when forming the core layer and the clad layer on the outer circumference of the hollow glass tube, it is necessary to manufacture each layer thickness in accordance with the ratio of the design layer thickness.

However, as described above, when the film is stretched and flattened, the cladding layer portion may be volatilized by heating from the outer periphery, and a predetermined layer thickness may not be obtained. Generally, such an amount of volatilization varies depending on the heating temperature, the heating time and the composition of the layer. In the case of high-purity quartz glass, for example, hydrogen 80
When directly heated for 1 hour with an oxyhydrogen flame of 1 and 50 l of oxygen, the amount of volatilization is about 10 and several μm, and the amount of volatilization is extremely small and the performance as a protective layer is high.

After planarization, the high-purity silica glass protective layer can be removed by a method such as dry etching, a chemical such as hydrofluoric acid, or a method such as mechanical polishing. Thus, the finally obtained planar optical waveguide can be molded as designed.

As described above, according to the method of the present invention, the outermost high-purity silica glass layer serves as a protective layer, and volatilization of the cladding layer during heat processing can be prevented.

Examples Hereinafter, the method for manufacturing the planar optical waveguide of the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited by the following examples.

1 (a) to 1 (c) are process diagrams of a method of manufacturing a planar optical waveguide according to an embodiment of the present invention.

It was produced using the external POD method described above. SiCl ₄ and CC in high frequency plasma flame (output 3.4MHz, 5.5kV, 4.5A)
l ₂ F ₂ was introduced, and this flame flow was blown onto the outer surface of the quartz glass pipe 1 for a substrate that rotates in the axial direction and reciprocates, and the cladding layer 3, the core layer 2 and the cladding layer are provided on the outer periphery of the glass pipe 1. The waveguide structure was formed in the order of 3, and the high-purity silica glass protective layer 4 was further formed. In producing the clad 3, both SiCl ₄ and CCl ₂ F ₂ were added together at 350 cc / min, and in producing the core layer 2 and the high-purity silica glass protective layer 4, Si was added.
Cl ₄ alone was introduced into the plasma flame at a flow rate of 50 cc / min, and the glass particles deposited on the outer wall of the quartz glass pipe 1 were sintered to form each layer. The relative refractive index difference between the clad layer and the core layer can be calculated by adding F to the clad layer.
It was set to 1.0%. The thickness of the core layer, the clad layer, and the high-purity silica glass protective layer were all about 65 μm. This was stretched while heating with an oxyhydrogen burner so that the thickness of each layer was about 50 μm.

The intermediate product 5 thus obtained has a structure as shown in FIG. The intermediate product 5 has a core 6 made of a heat-resistant material (carbon) having a flat surface that is in close contact with the intermediate product 5.
As shown in FIG. 1 (b), the intermediate product 5 of FIG. 1 (a)
The intermediate product 5 shrinks by being inserted into the inside and heated (1500 ° C.) from the outer periphery of the intermediate product 5 by the heating means 7 (see FIG. 1 (c)), and a molded body corresponding to the shape of the core Is obtained, and a flat optical waveguide having a structure as shown in FIG. 2 (a) can be easily obtained by cutting it out.

Further, the high-purity silica glass protective layer 4 was removed by polishing to obtain a planar optical waveguide as shown in FIG. 2 (b).

Comparative Example To compare with the above example, by the same operation as the example, the cladding layer on the outer periphery of the quartz glass tube using the POD method,
A waveguide layer structure was formed in the order of the core layer and the clad layer. However, in this comparative example, the high-purity silica glass protective layer was not formed. The thickness of each layer was 80 μm. An intermediate product was obtained by stretching while heating with an oxyhydrogen burner so that each layer had a thickness of about 50 μm. Further, the same operation as in the above example was performed to obtain a planar optical waveguide as a product.

The planar optical waveguide thus obtained was examined by interference microscopy, and it was found that the clad layer on the core layer disappeared. In addition, the thickness of the clad layer between the core layer and the glass tube is about 60 μm, whereas the thickness of the core layer is only about 50 μm, and it was confirmed that part of the core layer disappeared. It was

Effects of the Invention As described above, according to the method for manufacturing a planar optical waveguide of the present invention, by the high-purity silica glass protective layer that is the outermost layer,
It is possible to manufacture a high-quality planar optical waveguide with high accuracy without damaging the waveguide layer structure during heat processing such as stretching and flattening.

Therefore, the method for manufacturing a planar optical waveguide of the present invention can be utilized over a wide range.

[Brief description of drawings]

1 (a) to 1 (c) are process drawings of the method for manufacturing a planar optical waveguide of the present invention, FIG. 2 is a perspective view of the planar optical waveguide manufactured by the present invention, and FIG. (A) thru | or (d) are explanatory drawings which show the manufacturing method by the conventional selective photopolymerization method, and FIG. 4 is explanatory drawing which shows the manufacturing method by the conventional flame deposition method. (Main reference numbers) 1 ... glass tube, 2 ... core layer, 3 ... cladding layer, 4 ... protective layer, 5 ... intermediate product, 6 ... core, 7 ... heating means, 10 ... … Film, 11 …… Mask, 12 …… Clad layer, 13 …… Optical waveguide, 14 …… Rotary table, 15 …… Substrate, 16 …… Torch, 17 …… Glass forming raw material gas, 18 …… Exhaust pipe

Claims (10)

[Claims] 1. A hollow glass tube outer wall containing SiO ₂ as a main component,
A core layer made of glass and at least one clad layer made of glass are formed such that the core layer is an intermediate layer and the refractive index of the core layer is higher than the refractive index of the layer in contact with the core layer, and Forming the outermost layer made of high-purity quartz glass, then inserting a core made of a heat-resistant material into the hollow glass tube, molding these by sticking them to each other, and cutting this out to obtain a planar optical waveguide. A method of manufacturing a featured planar optical waveguide. 2. The outermost layer made of the high-purity quartz glass,
The method according to claim 1, wherein the method is formed with a thickness of at least 20 μm or more. 3. The intimate contact between the hollow glass tube and the core is achieved by externally heating and contracting the hollow glass tube.
Method described in section. 4. The core layer, the clad layer and the outermost layer made of the high-purity silica glass are formed by forming the core layer on the outer wall of the hollow glass tube, and then forming the clad layer on the core layer. 4. The method according to claim 1, further comprising forming a layer and then forming an outermost layer made of the high-purity silica glass on the cladding layer. the method of. 5. The core layer, the clad layer, and the outermost layer made of the high-purity quartz glass are formed by forming the clad layer, the core layer, the clad layer, and the high-purity quartz on the outer wall of the hollow glass tube. A method according to any one of claims 1 to 3, characterized in that it comprises forming the outermost layer of glass in that order. 6. The method according to claim 1, wherein the core layer is composed of a single layer made of glass having the same refractive index. . 7. The core layer is composed of a plurality of glass layers whose refractive index decreases toward the clad layer, as claimed in any one of claims 1 to 5. The method described. 8. The core according to any one of claims 1 to 7, wherein the core is made of carbon, boron nitride, alumina, beryllia or silicon carbide. the method of. 9. The core layer, the clad layer, and the outermost layer made of high-purity silica glass are formed by a chemical vapor deposition method, according to any one of claims 1 to 8. The method according to item 1. 10. The clad layer is formed by a chemical vapor phase reaction of a mixed gas of a glass forming raw material gas and a refractive index adjusting additive.
Method described in section.