JPH01314207A - Optical circuit and production thereof - Google Patents

Abstract

PURPOSE:To prevent optical characteristics from being affected by environment by forming the optical circuit of the recesses formed on a substrate surface and the light guides formed alongside the recesses. CONSTITUTION:The crystal substrate recesses 3 are formed by etching the crystal substrate 1. Thermal diffusion or ion exchange of a metal is then executed from the surface of the crystal substrate recesses 3 to form regions 10 having the refractive index higher than the refractive index of the crystal substrate 1. The high-refractive index regions 10 under the recesses 3 are etched. The high-refractive index layers 10 are, therefore, enclosed by low-refractive index regions 6 in the cross direction (direction parallel with the substrate 1 surface direction) and the depth direction is the crystal substrate itself; therefore, the optical circuit consisting of the three-dimensional light guides 2 is obtd. The optical circuit which decreases the influence of environmental temp. and environmental atm. pressure on the optical characteristics of the guided light and assures always the stable optical characteristics of the guided light is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical circuit using an optical waveguide and a method for manufacturing the same.

(Prior art) Optical circuits that freely route three-dimensional optical waveguides formed on a crystal substrate by thermal diffusion or ion exchange of metals are used as optical data transmission lines in optical communication networks, optical switching systems, and optical information systems. There is. FIG. 3 is a cross-sectional view of an optical circuit using a conventional three-dimensional optical waveguide. The conventional three-dimensional optical waveguide 2 is manufactured by forming a region on the surface of the crystal substrate 1 with a refractive index higher than that of the crystal substrate 1 by thermal diffusion or ion exchange of a metal.

(Problems to be Solved by the Invention) In this three-dimensional optical waveguide structure, the guided light is concentrated near the substrate surface, so the optical characteristics of the guided light are sensitive to environmental temperature and atmospheric pressure and therefore easily fluctuate. There is. Another disadvantage is that if microcracks occur on the surface of a crystal substrate due to thermal shock, external pressure, etc., the optical circuit immediately ceases to perform its function.

An object of the present invention is to provide an optical circuit that can always provide stable optical characteristics of guided light, regardless of environmental temperature and atmospheric pressure, and even when microcracks occur on the surface of a crystal substrate due to thermal shock or external pressure. Another object of this invention is to provide a method for manufacturing this optical circuit.

(Means for Solving the Problems) The present invention provides: (1) An optical circuit comprising a recess formed on the surface of a substrate and an optical waveguide formed on the side of the recess.

(2) An optical circuit comprising a recess formed on the surface of a substrate, a low refractive index region formed directly below the recess, and an optical waveguide formed on the sides of the low refractive index region.

(3) A low refractive index region is formed by forming a recess on the surface of the substrate, forming an optical waveguide by thermally diffusing metal through the recess or ion exchange, and etching the substrate immediately below the recess. A method for manufacturing an optical circuit.

It is.

(Function) In the optical circuit of the present invention, since the optical waveguide is provided inside the substrate, the optical characteristics are not affected by the environment.

That is, since a recess is provided on the substrate surface and a high refractive index layer is formed on the side of the recess, the high refractive index layer is formed inside the substrate surface by the depth of the recess. In addition, the region directly under the recess is a low refractive index layer, and the optical waveguide is formed laterally shifted from directly under the recess. Furthermore, as a method for forming the low refractive index layer, there is also a method using doping, but forming it by etching as in the third invention of the present application narrows the high refractive index layer region due to lateral expansion, etc. It's advantageous because you don't have to worry about it. In the case of etching, the influence of the environment from the side of the three-dimensional optical waveguide is considered.
Since microcracks caused by thermal shock, external pressure, etc. occur on the substrate surface, at least the influence of microcracks is reduced.

(Example) Next, the present invention will be explained with reference to the drawings.

FIGS. 1(a) and 1(b) are cross-sectional views of an optical circuit using a three-dimensional optical waveguide according to an embodiment of the present invention. When thermal diffusion or ion exchange of metal is carried out from the two crystal substrate recesses 3 on the crystal substrate 1 into the crystal substrate 1, the construction method for lateral diffusion and ion exchange of the respective metals is such that the region 4 is located in the crystal substrate recess. They intersect in the interspace region 5. Therefore, the refractive index of the region 5 between the crystal substrate recesses is larger than that of the crystal substrate 1. If region b (hereinafter referred to as low refractive index region) directly under the crystal substrate recess 3 sandwiching the crystal substrate inter-recess region 5 is made to have a lower refractive index than the crystal substrate inter-recess region 5, the crystal substrate inter-recess region 5 will be The refractive index is higher than that of the substrate region, and the region 5 between the recesses of the crystal substrate becomes a three-dimensional optical waveguide 2. Since the optical circuit consisting of this three-dimensional optical waveguide 2 is formed at a position buried by a depth W from the surface of the crystal substrate 1, the optical circuit consisting of the three-dimensional optical waveguide formed on the surface of the conventional crystal substrate 1 is It is less affected by the environmental temperature and pressure than the conventional one, and is also unaffected by the occurrence of minute cracks on the surface of the crystal substrate due to thermal shock or external pressure, so it always maintains stable optical characteristics of guided light. A circuit is obtained.

In the present invention, the depth W from the surface of the crystal substrate 1 on which the three-dimensional optical waveguide 2 is formed is allowed to range from several μm to several μm, and the maximum depth W is limited by the thickness t of the crystal substrate 1. Further, the width d of the three-dimensional optical waveguide 2 can be freely set by selecting the length l of the low refractive index region or the length L of the region 5 between the recesses of the crystal substrate. The crystal substrate 1 may be a ferroelectric material such as an LtNb03 substrate, a dielectric material such as a glass substrate, GaAs, I
Compound semiconductors such as nP and semiconductors such as Si are used. In the case of a LiNbo3 substrate, Ti or the like is used for metal thermal diffusion, and H10 exchange or the like is used for ion exchange.

At this time, the lateral diffusion and lateral loading are (0
, 5 to 1) dz or ion exchange depth dz (0
, 5 to 1) dz.

In FIG. 1, FIG. 1(a) shows an optical circuit consisting of one three-dimensional optical waveguide 2, and FIG. 1(b) shows an optical circuit consisting of a plurality of three-dimensional optical waveguides 2. .

Next, a method for manufacturing an optical circuit according to the present invention will be explained using the drawings. FIG. 2 is a process diagram of an embodiment of the optical circuit manufacturing method of the present invention. First, a crystal substrate recess 3 is formed by etching the crystal substrate 1. As shown in FIG. At this time, ion beam etching, reactive ion etching, reactive ion beam etching, wet etching, etc. are used for etching (step A). Next, thermal diffusion or ion exchange of metal is performed from the surface of the crystal substrate recess 3 to form a region 10a (hereinafter referred to as a high refractive index layer) having a higher refractive index than the crystal substrate 1 (step B). Next, the high refractive index layer 10 directly under the crystal substrate recess 3 is etched. At this time, the same method as in step A is used for etching (step C). Through the above steps, the high refractive index layer 10 is surrounded by the low refractive index region 6 in the lateral direction (parallel to the surface direction of the crystal substrate 1), and is composed of the three-dimensional optical waveguide 2 in the depth direction due to the crystal substrate itself. An optical circuit according to the invention is obtained.

(Effects of the Invention) By using the optical circuit and its manufacture according to the present invention, the influence of environmental temperature and atmospheric pressure on the optical characteristics of guided light is small;
Furthermore, an optical circuit can be obtained that is unaffected even when minute cracks occur on the surface of the crystal substrate due to thermal shock or external pressure, and always maintains stable optical characteristics of guided light.

[Brief explanation of the drawing]

FIG. 1 (aXb) is a sectional view of an optical circuit according to an embodiment of the present invention, FIG. 2 is a method for manufacturing an optical circuit according to an embodiment of the present invention, and FIG.
The figure is a sectional view of a conventional optical circuit. 1... Crystal substrate 2... Three-dimensional optical waveguide 3... Crystal substrate recess 4... Lateral diffusion region for metal thermal diffusion or lateral spread region for ion exchange 5... Region between crystal substrate recesses 6...Low refractive index region 10...High refractive index layer

Claims (3)

[Claims] (1) An optical circuit comprising a recess formed on the surface of a substrate and an optical waveguide formed on the side of the recess within the substrate. (2) An optical circuit comprising a recess formed on the surface of a substrate, a low refractive index region formed directly under the recess, and an optical waveguide formed on the side of the low refractive index region. (3) A low refractive index region is formed by forming a recess on the substrate surface, forming an optical waveguide by thermally diffusing metal from the recess or ion exchange, and etching the substrate immediately below the recess. A method for manufacturing an optical circuit.