JPS5897006A - Production of optical waveguide - Google Patents

Abstract

PURPOSE:To obtain an optical waveguide in a glass substrate by providing the high refractive index layers patterned with the 1st metallic film on the substrate, heating the surface of the substrate via an ion flow limiting layer and the 2nd thin film having a refractive index lower than that of the 1st film and applying voltage thereto. CONSTITUTION:A diffusion blocking film 2 of Al is provided on a glass substrate 1 and the 1st thin film 3 contg. a kind of metal Ag is formed thereon. Electrodes 4, 4' are provided thereon via the film 3, and the substrate is heated to 300 deg.C with a heater 5; at the same time a 300V voltage is applied thereto to form a high refractive index layer 6 on the surface of the substrate 1. Thereafter an ion flow limiting layer 7 which limits the flow of metallic ions, the 1st adhesion intensifying layer 8 consisting of Cr, the 2nd thin film 9 of NaF, and the 2nd adhesion intensifying layer 11 of Cr are formed on the substrate 1. Electrodes 11, 11' are disposed thereon, and the substrate is heated to 300 deg.C, then a 300V voltage is applied, whereby the optical waveguide embedded with the layer 6 in the middle part of the substrate 1 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an optical waveguide in which the optical waveguide is formed inside a substrate.

The optical waveguide used in the so-called flat VJJ type optical circuit, originally used for integrated circuits, basically has a core portion with a relatively high refractive index covered by a core portion with a relatively low refractive index. The structure is becoming a trap.

Conventionally, as a method for manufacturing such an optical waveguide, there is an invention filed on the same day, in which the inventor of the present application is one of the inventors. This is a dry electric field diffusion method in which metal ions such as silver ions that increase the refractive index of the substrate are diffused into a substrate such as glass under the application of an electric field to form a high refractive index layer, and then sodium ions and other metal ions that increase the refractive index of the substrate are diffused. The high refractive index layer is embedded inside the substrate to form an optical waveguide by diffusing metal ions that make the refractive index of the high refractive index layer smaller than that of the high refractive index layer under the application of an electric field. This method has the advantage that all optical waveguides can be formed by a dry process, one optical waveguide can be deeply buried, and the time required for embedding Kl[' is short.

However, since the metal ions used for salt infusion can generally easily move through the substrate to be diffused, more metal ions than are necessary to move the metal ions forming the high refractive index layer can be absorbed into the substrate at once. It has penetrated inside. Therefore, in order to maintain the penetration of the metal ions used for embedding into the substrate until the high refractive index layer is embedded to the desired depth, the thickness of the thin film that serves as a diffusion source for the metal ions used for embedding must be increased. However, as the film thickness increases, the difference in expansion coefficient between the substrate and other thin films such as electrodes formed on the substrate and the weak mutual adhesion force may occur. This has the disadvantage that it tends to peel off from the substrate, causing problems in the embedding process.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, to form the optical waveguide by a dry process, and to maintain the features that the optical waveguide can be deeply embedded and the time required for embedding is short. This eliminates the need to increase the thickness of the thin film that serves as a diffusion source for metal ions used for embedding, and also prevents the thin film from peeling off from the substrate.
<An object of the present invention is to provide a method for manufacturing an optical waveguide that allows a stable embedding process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing an optical waveguide according to the present invention will be described below using examples with reference to the drawings.

1 to 7 show a most preferred embodiment of the method for manufacturing an optical waveguide according to the present invention.

In the manufacturing method according to this embodiment, as shown in FIG. 1, a pattern is first formed on a glass substrate l of BK7 glass with a thickness of 1 to 3 mm by a vacuum evaporation method. A diffusion prevention layer 2 is provided, which is made of a thin film of Al<=Ram coated by a method. Next, as shown in FIG. 2, a thin chain film 3 of about 1 to 5 .mu.m thick serving as a diffusion source metal is formed by vacuum evaporation, and both upper and lower IIK electrodes 4, 4' are formed. Thereafter, as shown in FIG.
By heating the glass substrate 1 to below the glass strain temperature of ~550°C using a heater 5 and applying an electric field of 2~300 V/mm, silver ions are injected into the glass substrate 1 as shown in FIG. to form a high refractive index portion 6 having a desired diffusion depth. Here, diffusion prevention layer 2. Remaining silver film3. After removing the electrodes 4 and 4', as shown in FIG. 5, an ion flow restriction layer 7 made of a thin aluminum film is first provided on the glass substrate 1 to restrict the flow of metal ions used for embedding. On top of that, there is a first layer made of chromium to strengthen the adhesion between the upper and lower thin films 7°9.
An adhesive force reinforcing layer 8 is provided. This first adhesive force reinforcing layer 8
also functions to restrict the flow of the metal ions used for embedding. Next, on the first adhesive force strengthening layer 8, a thin film 9 of about 2 to 1 fluoride (IJ) is applied, which will serve as a diffusion source for metal ions for embedding the high refractive index portion 6 inside the substrate.
It is provided with a thickness of 0 μm, and an electrode 11 is provided thereon with a second adhesion reinforcing layer 10 made of 1 chromium interposed therebetween. Further, an electrode 11' is provided on the surface of the substrate opposite to the side on which the thin film layers 7, 8, 9110.11 are provided. Here, each of the thin film layers 7.819, 10, 11.11' is formed by vacuum deposition. As shown in FIG.
Sodium ions are diffused into the glass substrate 1 by heating it with a heater 5 to a temperature below the glass strain temperature of about 0.degree. C. and applying an electric field of 2 to 300 V/mm. Embed to the depth of the period. As a result, as shown in FIG. 7, the glass substrate 1oI! A high refractive index layer 6 is formed at a position having a predetermined distance from the two surfaces. This acts as an optical waveguide.

The optical traveling waveguide made according to this example has a refractive index difference Δn with respect to the substrate of 0. O2N2.07, the cross-sectional diameter of the high refractive index portion is 50 μm or more, and the embedding depth is 30 μm or more. This is extremely suitable as a multimode optical waveguide, and the optical waveguide loss is also extremely small. The shaped optical waveguide pattern can be formed into any shape by forming the pattern of the diffusion blocking layer 2 using the conventionally well-known etching, etching, or lift-off method.

One embodiment of the present invention has been described above. Here, although glass was used as the welfare substrate in this example, LiNbO
A crystal substrate such as No. 5 may also be used. Previously, silver was used as the metal contained in the first thin film, but when lithium, such as lithium contained in lithium fluoride, penetrates as a metal ion,
It is clear that other metals having a refractive index greater than that of the substrate may also be used. Moreover, although the vacuum evaporation method was used to form each of the thin film layers, it is also possible to use a deposition method, a taring method, or a chemical deposition method. Of course, it is possible to obtain an optical waveguide suitable for multi-mode systems, but the diffusion time of metal ions and the pattern width of the diffusion blocking layer can be made smaller than those for optical waveguides intended for multi-mode systems. Needless to say, by doing so, a traveling optical waveguide suitable for a single mode system can be obtained.

At the very least, the characteristics of the method for manufacturing an optical waveguide according to the present invention are that it can be manufactured using a dry processing process, and that the film thickness of the diffusion source for embedding metal ions can be thinner than in the conventional method. A stable embedding process can be performed because the source thin film does not peel off and cracks, and the formed optical traveling waveguide has low optical waveguide loss and is thermally and mechanically stable. It is a cape.

[Brief explanation of the drawing]

1 to 7 show side views of a substrate in each process of manufacturing an optical waveguide. The symbols used in the drawings indicate the following. 1... Glass substrate, 2... Diffusion prevention layer, 3... Old... First thin film, 4... Electrode (anode)
, 41... Electrode (cathode), 5... Heater, 6... High refractive index layer, 7... Ion flow limiting layer, 8, 10 ...Adhesive strength layer, 9...
... second thin film, 11 ... electrode (anode),
11'... Electrode (cathode). Figure 1 Figure 3 Figure 4 Figure 7

Claims (1)

[Claims] A first thin film containing at least one metal that increases the refractive index of the substrate when it permeates into the substrate as metal ions is provided on a highly optically transparent substrate, and the first thin film When the substrate provided with is heated and an electric field is applied, the metal contained in the first thin film is infiltrated into the substrate as metal ions to form a high refractive index layer near the surface. Afterwards, a second thin film containing at least one metal that, when infiltrated into the substrate as metal ions, causes the refractive index of the substrate to be smaller than the refractive index of the high refractive index layer. The substrate provided with the second thin film is heated and an electric field is applied to cause the metal contained in the second thin film to permeate into the substrate as metal ions, from the surface of the substrate. In the method for manufacturing an optical waveguide, in which the high refractive index layer is embedded inside a substrate at a predetermined distance to form an optical waveguide, when an electric field is applied between the second thin film and the substrate, the second thin film 1. A method of manufacturing an optical waveguide, which comprises providing at least one ion flow restriction layer for restricting the amount of metal sulfur contained in the metal sulfur.