JPH03155505A - Optical waveguide and its manufacture - Google Patents

Abstract

PURPOSE:To reduce radiant loss at a curvature part by preparing an optical waveguide formed with a substrate and a metallic element diffused in the substrate according to a desired pattern, and further diffusing an MgO in the curvature part of an optical waveguide pattern and the area of the substrate in the neighborhood of the curvature part. CONSTITUTION:The optical waveguides are the waveguides 4a, 4b formed with the substrate 1 and the metallic element diffused in the substrate 1 according to the desired pattern, and the MgO is diffused in the curvature part of the optical waveguide pattern and the substrate 1 in the neighborhood of the curvature part. For example, MgO layers 6a, 6b are formed at the curvature parts of the optical waveguides 4a, 4b formed by applying the thermal diffusion of Ti to the substrate, and the thermal diffusion is applied, and the MgO is diffused only in the neighborhood of the curvature parts of the waveguides 4a, 4b. When the MgO is further diffused in the optical waveguide in the substrate 1 and the neighborhood of the waveguide, a refractive index is decreased in an area where the MgO is diffused, and the radiant loss can be reduced compared with an ordinary optical waveguide in which only Ti is diffused. Thereby, it is possible to reduce the radiant loss at the curvature part and to form the optical waveguide with uniform radiant loss in spite of the inclusion of the curvature part.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an optical waveguide and a method for manufacturing the same.

More specifically, the present invention relates to an optical waveguide constructed by diffusing a metal element into a substrate, and in particular to a novel optical waveguide with low radiation loss at bent portions, and a method for manufacturing the same.

Conventional technology L+NbO5 with lithium oxide), LiTa0. T1 according to a desired pattern in a substrate formed by et al.
There is an optical waveguide formed by diffusing metal elements such as.

Such optical waveguides can be used to form fine optical waveguide patterns by applying patterning technology in integrated circuits, and are therefore widely used to fabricate optical devices such as optical branching/combining devices. , is expected to be applied to optical integrated circuits.

FIGS. 1A to 1D are diagrams schematically showing the manufacturing process of a directional coupler using an optical waveguide as described above.

First, as shown in FIG. 1(a), 1
1 film 2 is formed. Subsequently, as shown in FIG. 1(b), resist layers 3a and 3b having a desired pattern are formed on the Tll film. Subsequently, by removing the exposed portion of the 11 layer 2 by etching, a desired pattern of the Ti layer 2 is formed on the substrate 1, as shown in FIG. 1(C).
a and 2b are formed. Furthermore, by heating this, Ti
By diffusing the layers 2a, 2b into the substrate l, optical waveguides 4a and 4b are formed in the substrate l, as shown in FIG. 1(d).

As a typical example of a directional coupler, the directional coupler shown in FIG. 1 (6) has a width of 7 μm and a thickness of 700 μm.
It is formed by treating the Ti layer of A at 1000° C. for 6 hours, and the distance between the optical waveguides 4a and 4b at the input end and the output end is 120 μm1.The distance at the coupling part of the core is 6 μm1 for each waveguide 4a, 4b. The radius of curvature at the bent portion is approximately 40 mm. Further, the insertion loss of this directional coupler was 0.5 dB.

Problems to be Solved by the Invention By the way, when forming a directional coupler using the optical waveguides as described above, as shown in FIG. It is about 8 μm. On the other hand, the distance between the optical waveguides at both ends needs to be larger than the diameter of the optical fiber coupled to this coupler. Therefore, two bent portions are inevitably formed in each optical waveguide.

It is generally known that radiation loss in optical waveguides increases at bent portions. Therefore, when it is necessary to form a bend as described above, always consider the bend with the greatest loss as a reference, and in order to reduce the loss, the bend angle should be made as small as possible, and the bend should be It was designed to make the radius of curvature of the part as large as possible.

However, an optical waveguide designed using such a method has a problem in that its size becomes extremely large in order to reduce radiation loss at the bend.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and reduce the radiation loss in the bent portion by a method other than limiting the shape of the bent portion, thereby reducing the size of the optical waveguide including the bent portion. It is said that

According to the present invention, there is provided an optical waveguide formed by a substrate and a metal element diffused into the substrate according to a desired pattern, the bending portion of the optical waveguide pattern and its An optical waveguide is provided further characterized in that MgO is diffused in a region in the substrate in the vicinity.

Further, as a method for manufacturing the optical waveguide according to the present invention, according to the present invention, a metal layer is formed on a substrate according to a desired pattern, and the metal layer is inserted into the substrate by heating the substrate and the metal layer. In the method of manufacturing an optical waveguide by diffusing, furthermore, on the bent part of the pattern and the area near it! After forming a 1gO layer, it is heated to form an IgO layer in the optical waveguide and in the substrate near the optical waveguide.
Provided is a method for manufacturing an optical waveguide, the method comprising the step of diffusing.

Function The main feature of the optical waveguide according to the present invention is that MgO is diffused in the bent portion and the substrate near the bent portion.

That is, it is known that when MgO is further diffused into the optical waveguide in the substrate and its vicinity, the refractive index decreases in the region where MgO is diffused.

FIGS. 2(a) and 2(5) are graphs showing the refractive index distribution of the optical waveguide due to such Ti diffusion and the decrease in the refractive index due to MgO diffusion.

As shown in Fig. 2(a), T is applied to a substrate such as LiNbO3.
When Ti is diffused, the refractive index of the region where Ti is diffused is higher than that of other regions, and therefore a refractive index difference of Δn1 occurs between the substrate and the optical waveguide.

When lAg0 is diffused into this optical waveguide and the substrate in the area adjacent thereto, the refractive index of both decreases, as shown in FIG. 2('b). Here, the refractive index decrease of the substrate is T
Since the decrease in refractive index is greater than that of the region where Mg 1 is diffused,
The refractive index difference Δn2 between the substrate and the optical waveguide after O diffusion is larger than the refractive index difference Δn1 before diffusion. Therefore, the optical waveguide diffused with MgO has a smaller radiation loss than the normal optical waveguide diffused only with T1.

In this way, 1. By diffusing IgO, the radiation loss at the bent portion can be reduced, so in an optical waveguide including the bent portion, the radiation loss of the entire waveguide can also be reduced. That is, the optical waveguide according to the present invention is an optical waveguide with uniform radiation loss even though it includes a bent portion.

Furthermore, if the same radiation loss as a conventional optical waveguide is allowed, the radius of curvature of the bent portion can be made smaller and the bending angle can be made larger, so the optical waveguide can be made smaller.

Hereinafter, the present invention will be described in more detail with reference to the drawings, but the following disclosure is only one embodiment of the present invention, and does not limit the technical scope of the present invention in any way.

Embodiment FIGS. 1(a) to 1(5) are diagrams showing the manufacturing process of an optical waveguide according to the present invention. Incidentally, the steps shown in FIGS. 1(a) to 1(d) are exactly the same as the conventional method of manufacturing an optical waveguide, so the explanation thereof will be omitted.

That is, as shown in FIG. 1(d), by thermally diffusing T1 into the substrate 1, a pair of optical waveguides 4a and 4b constituting a directional coupler is formed.

Here, according to the present invention, furthermore, the optical waveguides 4a, 4b
A mask layer 5 is formed on a substrate 1 provided with a mask layer 5 such that only the bent portions of the optical waveguides 4a and 4b are exposed. Next, the first
As shown in Figure (e), an MgO layer 6 is formed on the substrate 1 on which the mask layer 5 is mounted.

Subsequently, by removing the mask layer 5, the structure shown in FIG.
As shown in g), there are optical waveguides 4a, 4 on the substrate 1.
λIgO layers 6a and 6b are formed only in the vicinity of the bent portion b. By thermally diffusing the MgO layers 6a and 6b, the waveguide 4a,
A directional coupler using an optical waveguide in which λIgo is diffused only in the vicinity of the bent portion of 4b is obtained.

Here, the dimensions of each optical waveguide 4a, 4b are as already described in the prior art section, and the diffusion of MgO is as follows:
This was done by holding the time.

The insertion loss of the directional coupler using the optical waveguide obtained as described above is significantly reduced to 0.1 dB or less.

As described in detail of the invention, the optical waveguide manufactured according to the present invention has a reduced radiation loss particularly at the bent portions, so that it is possible to create an optical waveguide with uniform radiation loss even though it includes the bent portions. can be formed.

In other words, an optical waveguide with the same performance as the conventional one can be realized with a larger bending angle and a smaller radius of curvature. Therefore, the optical circuit including the bending part can be made more compact.

In addition, in a directional coupler using this optical waveguide, the refractive index distribution at the coupling part is located near the surface.
When used as an optical switch, high efficiency can be achieved and low voltage driving can be easily achieved.

[Brief explanation of the drawing]

FIGS. 1(a) to (d) are diagrams showing the manufacturing process of a general optical waveguide, and FIGS. FIGS. 2(a) and 2(b) are graphs showing the refractive index in such an optical waveguide and the decrease in the refractive index due to the diffusion of MgO. [Main reference numbers] 1... Substrate, 2.2a12b... T1 layer, 3... Resist layer, 4a, 4b... Optical waveguide, 5... Mask layer, 6.6a, 6b- - ・MgO layer

Claims (2)

[Claims] (1) An optical waveguide formed by a substrate and a metal element diffused into the substrate according to a desired pattern, further comprising MgO An optical waveguide characterized by being diffused. (2) forming a metal layer according to a desired pattern on the substrate;
In the method of manufacturing an optical waveguide by diffusing the metal layer into the substrate by heating the substrate and the metal layer, the method further comprises the steps of:
A method for manufacturing an optical waveguide, comprising the step of forming a gO layer and then heating it to diffuse MgO into the optical waveguide and into a substrate near the optical waveguide.