JPS6160401B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a tapered optical waveguide formed on a substrate.

Optical waveguides formed on substrates play an important role in reducing the size and integration of optical circuits and improving their reliability. In order to reduce the loss of an optical circuit using this optical waveguide, it is necessary to reduce the loss of the optical waveguide and the coupling loss at the input/output section of the optical circuit. Among these, as an effective means to solve the latter problem, it is known that the input and output ends of the optical waveguide formed on the substrate are made into tapered optical waveguides.

Conventionally, the manufacturing method for this tapered optical waveguide has been described in the magazine Applied Optics (Applied Optics).
Optics) published in the March 1979 issue of G.E.
A manufacturing method as described in a paper by JCCampbell is known. As shown in FIG. 1a, this is a substrate 103 provided with a diffusion stripe pattern 102 formed by etching a part of a diffusion prevention layer 101 made of SiN that has the function of inhibiting ion diffusion.
As shown in Figure 1b, the dashed line A--
Gradually over time, starting from the end closest to A′
By immersing it in AgNO ₃ molten salt 104, the diffusion depth is changed to form a tapered optical waveguide. When the cross-sectional shape of the resulting optical waveguide is shown along the two dashed lines A-A' and B-B' shown in Fig. 1a, each section is shown as shown in Fig. 1c and d. Optical waveguide 10 at the location
5 and 105' have a tapered shape with different cross-sectional sizes. However, because this conventional method forms optical waveguides through natural diffusion, it has drawbacks such as a long manufacturing time and the need to gradually immerse the substrate in molten salt. .

The object of the present invention is to eliminate the above-mentioned drawbacks, to provide a taper which can be manufactured in a shorter time than before, and which simplifies the manufacturing process since diffusion can be carried out over the entire length at once. An object of the present invention is to provide a method for manufacturing a shaped optical waveguide.

That is, the present invention provides a method for manufacturing an optical waveguide in which a high refractive index portion is formed by selectively permeating an optically transparent substrate with metal ions that increase the refractive index of the substrate when permeated into the substrate. , the thickness of the substrate changes in a tapered shape, and the height is increased by infiltrating the metal ions into the substrate in a stripe shape extending in the direction of change in the thickness of the substrate using a field diffusion method. This is a method of manufacturing a tapered optical waveguide, characterized in that a refractive index portion is formed.

Hereinafter, the present invention will be explained in detail with reference to the drawings. FIGS. 2a to 2d are process diagrams for explaining one embodiment of the method for manufacturing a tapered optical waveguide according to the present invention. As shown in Figure 2a, the substrate 1 made of BK7 glass has a tapered thickness.
The thickest part is 2mm and the thinnest part is 0.5mm. Further, a silver diffusion prevention layer 2 is provided on one surface of the substrate 1 by vacuum evaporation of aluminum, and a part of the silver diffusion prevention layer 2 is formed using a lift-off method so that the direction of the stripes is almost the same as the direction of change in the thickness. A stripe pattern 3 for diffusion is formed. Then, as shown in FIG. 2b, a silver thin film layer 4 with a thickness of about 5 to 10 μm and a positive electrode 5 made of aluminum are successively formed thereon by vacuum evaporation. A negative electrode 5' made of aluminum is formed on the surface by vacuum evaporation. Therefore, the substrate is heated to about 330° C. using a heater 6, and the space between the positive electrode 5 and the negative electrode 5' is approximately
Silver ions are diffused into the substrate 1 by applying a DC voltage of 100 V and performing electric field diffusion for about 2 hours. At this time, the strength of the applied electric field is weaker as the thickness of the substrate 1 is thicker, and stronger as the thickness is thinner.
Therefore, the thicker the substrate 1, the shallower the diffusion depth, and the thinner the substrate 1, the deeper the diffusion depth. As a result, tapered high refractive index portions 7, 7' are formed on the substrate 1,
At both end surfaces A and B of the substrate 1 shown in FIG. 2a, the diffusion depth is approximately 100 nm, as shown in FIGS. 2c and d, respectively.
It shows cross-sectional shapes of different sizes, 30 μm and about 10 μm. Here, this cross-sectional shape becomes approximately semicircular because the width of the diffusion stripe 3 becomes wider as the thickness of the substrate 1 becomes thinner. These tapered high refractive index portions 7, 7' become tapered optical waveguides.

As mentioned above, according to the method for manufacturing a tapered optical waveguide according to this embodiment, the manufacturing time can be significantly shortened compared to the conventional method, and the manufacturing process can be simplified because diffusion can be performed over the entire length at once. can be simplified.

An embodiment of the present invention has been described above. Here, in this example, silver ions were used as metal ions, but thallium ions, lithium ions, etc. may also be used. In addition, a dry process was used to infiltrate metal ions into the substrate, but
A wet process in which metal ions in the molten salt permeate may be used. Additionally, the diffusion temperature was increased to 330℃.
However, the diffusion temperature only needs to be higher than the temperature at which metal ions can penetrate into the substrate and lower than the strain temperature of the substrate. Also, the thickness of the board is from 0.5mm to 2mm.
Although a tapered shape that varies up to mm was used, other tapered shapes may be used.

[Brief explanation of the drawing]

1A to 1D are process diagrams for explaining a conventional method for manufacturing a tapered optical waveguide, and FIGS. 2A to 2D are process diagrams for explaining an embodiment of a method for manufacturing a tapered optical waveguide according to the present invention. be. 101...Diffusion blocking layer, 102...Diffusion stripe pattern, 103...Substrate, 104...molten salt, 105, 105'...Optical waveguide, 1...Substrate, 2...Diffusion blocking layer, 3... Diffusion stripe pattern, 4... Silver thin film layer, 5... Positive electrode,
5'... cathode, 6... heater, 7,7'... high refractive index section.

Claims (1)

[Claims] 1. A method for manufacturing an optical waveguide in which a high refractive index portion is formed by selectively permeating an optically transparent substrate with metal ions that increase the refractive index of the substrate when permeated into the substrate, wherein the thickness of the substrate is The high refractive index portion is formed by infiltrating the metal ions into the substrate in a stripe shape extending in the direction of change in the thickness of the substrate using an electric field diffusion method. A method for manufacturing a tapered optical waveguide, characterized in that: