JPH06250037A - Production of optical waveguide - Google Patents

Abstract

PURPOSE:To provide a structure of an optical waveguide having optical amplification function or the like which can be easily produced, and to provide the production method. CONSTITUTION:In the first process, a water-repellent protective film 8 is formed for patterning on a substrate 4 and the area to form the core part 9 is etched in the protective film 8. In the second process, the etched area is coated with a hydrolyzed soln. doped with rare earth elements as the functional material by a sol-gel method, and the core part 9 is formed. In the third process, the protective film 8 is removed and a clad part 10 is formed by sputtering or flame deposition method on the substrate 4 where the core part 9 is formed. Especially, the protective film 8 formed on the substrate 4 has a property to prevent the hydrolyzed soln. doped with rare earth elements from remaining on the surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an optical amplification function,
The present invention relates to an optical waveguide having a function as an optical element such as an optical switch function, and particularly to a structure for obtaining these functions and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, silica-based optical waveguides containing silica glass as a main component have low optical transmission loss, and
It has attracted attention because it can be connected to a silica-based optical fiber with low loss.

As a method of manufacturing this quartz optical waveguide,
For example, Masao Kawauchi, "Application to Quartz-Based Optical Waveguides and Integrated Optical Components" Optics Vol. 18, No. 12 (December 1989) P68
1-686, the fire deposition method (FHD: Flame
The most common method is a combination of glass film formation by hydrolytic deposition and glass film formation by reactive ion etching (RIE).

Specifically, as shown in FIG. 2, first, a glass raw material such as SiCl ₄ , TiCl ₃ or the like is supplied to the burner 1, and the glass fine particles 3 are produced by a hydrolysis reaction and an oxidation reaction in the oxyhydrogen flame 2. Then, this is deposited on a substrate 4 such as a Si wafer to obtain glass fine particle films 5a, 5 having different refractive indexes.
b are sequentially formed ((a) in the same figure). Here, it is assumed that the glass fine particle films 5a and 5b have different compositions (different refractive indexes).

Then, the glass fine particle films 5a and 5b sequentially formed in the above-described steps are heated to a high temperature to make the glass fine particle films 5a and 5b transparent and vitrified into a buffer layer 6a and a core layer 6b (see FIG. b)). The above is the flame deposition method.

Next, the core layer 6 is formed by reactive etching.
An unnecessary portion of b is removed to leave a ridge-shaped core portion 6c (FIG. 7C), and a cladding layer 6d is formed again so as to cover the core portion 6c by the flame deposition method. The system optical waveguide 7 is manufactured ((d) in the same figure).

[0007]

As described above, according to the conventional method for manufacturing a silica-based optical waveguide, the core layer and the clad layer are formed by the flame deposition method. This flame deposition method has a small transmission loss and is suitable for manufacturing passive optical devices such as optical multiplexing / demultiplexing and branching, but it is not suitable for optical devices having optical amplification or optical switch functions. .

That is, in order to have the above function,
It is necessary to dope the core portion with a rare earth element or the like, but in the above-mentioned flame deposition method, glass synthesis is performed in an oxyhydrogen flame at 2000 ° C. or higher, so these additives are crystallized and the glass cannot be doped. There were challenges.

On the other hand, since the glass is synthesized near room temperature (the crystallization of the additive does not occur), there is a sol-gel method as a method capable of uniformly doping the additive in a high concentration.

The sol-gel method is characterized in that a silicon alkoxide is used as a glass raw material and glass can be obtained by a relatively low temperature manufacturing process of about 1000.degree. Further, in the conventional vapor phase method, solution impregnation method, etc., only about 1 wt% of impurities can be doped, and even if doped, the impurities are not uniform (it crystallizes at high temperature).
On the other hand, according to this method, since the processing temperature can be lowered, impurities can be doped up to about 3 wt%, and moreover, it is possible to dope uniformly, so that a glass having a much higher concentration of impurities than the conventional method can be doped. Can be synthesized.

However, the thickness of the coating film that can be formed by the sol-gel method is limited to about 1 μm,
If a film having a thickness larger than that is attempted, peeling or cracking of the film occurs, which causes a problem that a thin film having a thickness of several μm necessary for the core cannot be manufactured. .

The present invention has been made to solve the above problems, and an object thereof is to provide a structure of an optical waveguide having an optical amplification function and the like which can be easily manufactured, and a manufacturing method thereof.

[0013]

In the method of manufacturing an optical waveguide according to the present invention, in the first step, a water-repellent protective film for patterning is formed on a substrate, and a core portion of the protective film is formed. The region is etched, and in the second step, the etched region is coated with a hydrolysis solution doped with a rare earth element as a functional substance by the sol-gel method, and then a core portion is formed, and in the third step, After removing the protective film, the clad portion is formed on the substrate on which the core portion is formed by a sputtering method or a flame deposition method.

In particular, the protective film formed on the substrate is
In order to prevent the hydrolysis solution doped with the rare earth element from remaining on the surface, the glass or resin containing fluorine is characterized by having water repellency. As a concrete resin, a fluororesin such as trifluorochloroethylene, tetrafluoroethylene, tetrafluoroethylene / hexafluoropropylene, or vinylidene fluoride is used. Alternatively, paraffin or silicone may be used.

The substrate and the clad region functioning as the clad region in the optical waveguide have a refractive index different from that of the core portion.

Specifically, the substrate and the clad are doped with fluorine or the like so that the refractive index of the substrate and the clad is lower than that of the core, or each layer of the core is doped with GeO _2. Then, the refractive index of the core portion is set higher than the refractive index of the substrate and the cladding portion. The refractive indices of the substrate and the clad portion do not necessarily have to match.

[0017]

In the method of manufacturing an optical waveguide according to the present invention, the protective film formed on the substrate is formed of a film having a property (water repellency) of preventing the hydrolysis solution doped with the rare earth element from remaining on the surface. ing.

This is because, as shown in the column of the problem, when the layer having a film thickness of 1 μm or more is formed on the substrate by the sol-gel method, the cause of peeling or cracking of the film is considered as follows.

That is, the film formed by the sol-gel method shrinks after coating and before it becomes vitrified. Since this shrinkage occurs not only in the vertical direction with respect to the substrate surface but also in the horizontal direction, the substrate surface shrinks. Rate (almost none)
The stress concentration occurs due to the difference between the film shrinkage rate and the film shrinkage rate, and peeling or cracking occurs.

According to the above recognition, the strain due to the contraction of the film increases as the contact area with the substrate increases, so the strain decreases as the contact area between the film and the substrate decreases.

Therefore, in the step of forming the core portion using the sol-gel method, the protective film to be patterned in advance is formed of a film having a property of preventing the hydrolysis solution doped with the rare earth element from remaining on the surface. As a result, it is possible to prevent the solution from remaining on the surface of the protective film and confine the solution only in the patterned core portion forming region, and reduce the contact area between the core portion and the substrate surface. It becomes possible to do.

Further, by configuring the refractive index of the substrate and the clad portion surrounding the core portion to be lower than the refractive index of the core portion, the function as an optical waveguide is guaranteed.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In the figure, the same parts are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 is a view showing manufacturing steps for explaining a method of manufacturing an optical waveguide according to the present invention, and each step will be described below with reference to this drawing.

First, in the first step, a water-repellent protective film 8 is formed on the substrate 4 (FIG. 9A). Here, the substrate 4 is 30 mm square Si doped with fluorine (F).
O ₂ glass having a refractive index difference of −0.7% lower than that of SiO ₂ formed as the first core layer 8a is used.

Further, the water-repellent protective film 8 is a polymer film containing fluorine (F), and the region of the protective film 8 in which the core portion 9 is formed is etched by the lithography technique (see FIG. (B)).

Next, in a second step, erbium (Er) as a rare earth element which is a functional material is formed on the patterned water-repellent protective film 8 by a sol-gel method.
Is coated with a 3 wt% doped hydrolysis solution,
The hydrolysis solution is prevented from remaining on the surface of the protective film 8, and the hydrolysis solution coated in the area forming the core portion 9 is confined (FIG. 7C).

Specifically, tetraethoxysilane (TE
OS: tetraethylorthosilicate) 10 ml, ethanol 10 ml, 1N-HCl 4 ml solution ErCl
The ₃ · 6H ₂ O a predetermined amount dissolved stirred sol prepared was coated on the protective film 8 by spin coating (Fig. (C)), after drying 10 hours at 100 ° C.,
The polymer film, which is the protective film 8, is thermally decomposed by heating at 500 ° C. in an oxygen atmosphere to form the core portion 9 having a cross-sectional shape of 5 μm × 5 μm (FIG. 3D).

The thickness of the impurity-doped layer 8b is TE
Hoshino, et al., “Preparation of Quartz Film by Sol-Gel Method” by changing the composition ratio of ethanol to OS and viscosity of sol, in the range of 0.4 to 1.2 μm, 1991 Electronic Information IEICE Spring National Convention, C
-215.

Further, in the third step, the clad portion 10 is formed by the flame deposition method on the substrate 4 on which the core portion 9 is formed, and in the third step, the substrate is formed by the flame deposition method. As in the case of 4, the buried optical waveguide is manufactured by forming the clad portion 9 having a lower refractive index than the core portion 8d (FIG. 6 (e)).

According to the above embodiment, the clad portion 1
Although 0 was formed by the flame deposition method, it is not particularly limited to this forming method, and the same can be formed by using the sputtering method.

Further, although the fluorine-doped SiO ₂ plate is used as the substrate 4 in the above-mentioned embodiment, it is not particularly limited, and a pure SiO ₂ plate, a multi-component glass plate, a Si wafer or the like may be used. Produce an effect.

In the case of the fluorine-doped SiO ₂ plate as the substrate 4 as in this embodiment, since the refractive index of the substrate 4 is lowered, the core portion 9 may be pure quartz, which facilitates the fabrication.

On the other hand, when a pure quartz substrate is used as the substrate 4,
Ge is used as a material for increasing the refractive index when forming the core portion 9.
A function as an optical waveguide is guaranteed by simultaneously adding impurities such as O ₂ .

When a Si wafer or the like is used as the substrate 4, a buffer layer (corresponding to the reference numeral 6a in FIG. 2 in the prior art) is formed before the core portion 9 is formed. deep.

[0036]

As described above, according to the present invention, when a core portion is formed after coating with a hydrolysis solution doped with a rare earth element as a functional substance by a sol-gel method, water repellency protection is performed on a substrate in advance. Since the hydrolysis solution is confined in the area where the core portion is formed by the film, there is an effect that the core portion can be formed without peeling or cracking from the substrate.

Further, according to the present invention, since it is possible to manufacture a waveguide type optical amplifier, it is possible to miniaturize the amplifier in the optical communication field.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a method of manufacturing an optical waveguide according to the present invention.

FIG. 2 is a diagram for explaining a conventional method of manufacturing an optical waveguide.

[Explanation of symbols]

4 ... Substrate, 8 ... Polymer film, 9 ... Core part, 10 ... Clad part.

Claims (6)

[Claims] 1. A first step of forming a protective film for patterning on a substrate and etching a region of the protective film in which a core portion is formed, and a functional substance is applied to the etched region by a sol-gel method. A method of manufacturing an optical waveguide comprising: a second step of forming a core portion to be contained; and a third step of forming a clad portion on a substrate on which the core portion is formed after removing the protective film. 2. The optical waveguide according to claim 1, wherein the surface of the etched protective film is coated with a hydrolysis solution doped with a rare earth element as a functional substance by a sol-gel method to form a core portion. Manufacturing method. 3. The protective film is a film having a property of preventing a hydrolysis solution doped with a rare earth element as a functional substance by the sol-gel method from remaining on the surface.
The optical waveguide manufacturing method according to claim 1 or 2, wherein the optical waveguide is formed of glass containing fluorine, resin, paraffin, or silicone. 4. The method of manufacturing an optical waveguide according to claim 1, wherein the substrate and the clad are doped with impurities so that the refractive index of the substrate and the clad is lower than that of the core. Method. 5. The layers constituting the core portion are doped with impurities so that the layers constituting the core portion have a higher refractive index than the substrate and the cladding portion. A method for manufacturing the optical waveguide described. 6. The method of manufacturing an optical waveguide according to claim 1, wherein in the third step, the clad layer is formed by a sputtering method or a flame deposition method.