1985-03-07
1987-09-15
Sikes, William L.
350 9612, G02B 612
Patent
active
046935436
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an optical integrated circuit and, more particularly, to an optical integrated circuit which is featured in that it provides an outstanding reduction in optical transmission losses by the use of a heat-resistant high-molecular resin as a cladding layer.
BACKGROUND ART
Generally speaking, an optical integrated circuit is constructed of a complicated combination of structures, as shown in FIG. 1. On a substrate (of, for example, gadolinium-gallium-garnet: GGG) 1, more specifically, an optical waveguide layer (of, for example, yttrium-iron-garnet: YIG) 2 which has a higher refractive index than that of the substrate 1 is formed, and optical waveguide strips (called "ridges") 3 are formed thereon. Light is transmitted through the ridges so that, when two ridges are provided adjacent to each other, as shown in FIG. 1, all the optical energy of the light propagating through ridge 3-1 is transferred to ridge 3-2 within a longitudinal range that is determined by the shape, refractive index, etc., of the ridges. In this case, transfer to the ridge 3-2 can be prevented by placing magnets 4-1, 4-2 which apply magnetic fields to the ridges on the tops of the ridges, as shown in FIG. 2(a), and by controlling the intensities of the magnetic fields thereof so that the light propagating through the ridge 3-1 can emanate from an output terminal for the ridge 3-1. It is customary to use serpentine coils (i.e., wound coils) instead of the magnets to control the magnetic fields. In this case, it is difficult to form the coils directly onto the ridges, and a flat medium must be formed on the ridges before the coils can be formed on the flat medium. On the other hand, when the substrate 1 is made of an electro-optical crystal (e.g., gallium arsenide, GaAs) and the optical waveguide layer 2 is made of an electrooptical crystal which has a higher refractive index than that of the first crystal (e.g., GaAs with a higher resistance), electrodes 5-1 and 5-2 are attached to the tops of the ridges, as shown in FIG. 2(b), and an electrode 6 is attached to the bottom of the substrate so that the transfer of light can be prevented by a control of the voltage between the two terminals. This is the principle of an optical switch within an optical integrated circuit. The former type of switch employs a magneto-optical effect whereas the latter employs an electro-optical effect. Generally speaking, an optical integrated circuit makes use of the electromagnetic effect. FIG. 1 shows the simplest case thereof, but an optical integrated circuit usually has a complicated shape. For example, the optical integrated circuit can have a construction such as that shown in FIG. 3.
A problem with a complicated optical integrated circuit which has such curved optical waveguides concerns how much the optical transmission losses can be reduced. A special problem is losses due to optical scattering. These scattering losses are partly caused by irregularities due to thermal fluctuations in the material making up the optical waveguides, and partly by the structure of the optical waveguides themselves. The former type of scattering is determined by the material, and results in a loss of about 0.8 dB/km for an optical wavelength of 1 .mu.m, which is so small that it can be neglected in an optical integrated circuit. However, the latter type of scattering varies so much according to the method by which optical waveguides are manufactured that it raises a very serious problem.
In order to form the ridges, a wet-etching method or a dry-etching method is usually used. In the wet-etching method, the desired portions of the YIG or the like are etched with hot phosphoric acid; and in the dry-etching method, the desired portions of the YIG are mechanically etched by argon ions (Ar.sup.+) striking the YIG. The sides of the ridges prepared by these methods are irregular, as indicated at 7 in FIG. 4. These irregularities 7 are caused by unevenness in the etching and the material used, or by irregularities in the photo-ma
REFERENCES:
patent: 4286838 (1981-09-01), Huignard et al.
patent: 4472020 (1984-09-01), Evanchuk
patent: 4609252 (1986-09-01), Wong et al.
Ishida Koji
Matsumura Hiroyoshi
Gonzalez Frank
Hitachi , Ltd.
Sikes William L.
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