JPH05257021A - Production of optical waveguide - Google Patents

Abstract

PURPOSE:To obtain the process for production capable of producing the optical waveguides which are small in layer thickness within a core layer and clad layer and are small in the propagation loss of light power. CONSTITUTION:A dopant is doped in first and second clad layers 31, 34 and a core layer 32 so as to minimize the difference between the coefft. of thermal expansion of the first and second clad layers 31, 34 and the coefft. of thermal expansion of the core layer 32 in the process for production of the optical waveguides having a stage for forming the first clad layer 31 and the core layer 32 on a substrate 30, a stage for patterning the core layer 32 to desired patterns 33 and a stage for forming the second clad layer 34 on the core layer 32.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical waveguide used for optical communication, and more particularly to a method for manufacturing an optical waveguide made of a quartz material.

[0002]

2. Description of the Related Art A conventional method of manufacturing an optical waveguide using a quartz-based material is performed as follows. That is, as shown in FIG. 1 (A), glass particles are deposited on a silicon substrate 30 by a flame deposition method, B and P are doped so as to have a composition of Si-B-P, and then, on top of that. Glass fine particles are deposited by the flame deposition method, and Si-B-P-
B, P, and Ti are doped so that the composition of Ti is
These are made into transparent glass to form the lower cladding layer 31 and the core layer 32. Next, the core layer 32 is patterned by a normal photolithography method to form a waveguide pattern 33 as shown in FIG. Finally,
As shown in FIG. 1C, glass particles are deposited on the lower clad layer 31 on which the waveguide pattern 33 is formed by a flame deposition method, and B and P are doped to have a composition of Si-BP. Then, the upper clad layer 34 is formed by making it transparent.

Generally, only the core layer is doped with a dopant such as Ti or Ge so as to raise the refractive index of the core layer so that a difference in refractive index between the core layer and the clad layer is provided. This method is a preferable method in consideration of the refractive index design, since it is sufficient to control the amount of the dopant to be doped only in the core layer. In addition to this, the core layer and the cladding layer are each doped with a dopant such as B or P to lower the transparent vitrification temperature of both layers.

[0004]

However, when the core layer and the clad layer are doped by the above method for the purpose of decreasing the refractive index difference and lowering the transparent vitrification temperature, the coefficient of thermal expansion between the core layer and the clad layer is increased. Difference will occur. This is because when Ti is used as a dopant, the thermal expansion coefficient of the core layer and the clad layer decreases, and when the other dopants (Ge, B, P) are doped, the thermal expansion coefficient of the core layer and the clad layer increases. .. For example, when the core layer is doped with Ti to make the refractive index difference between the core layer and the cladding layer, the coefficient of thermal expansion of the core layer is lower than that of the cladding layer, and when the core layer is doped with Ge, the core layer is doped with Ge. Has a coefficient of thermal expansion higher than the coefficient of thermal expansion of the clad layer, and in any case, there is a difference in coefficient of thermal expansion between the core layer and the clad layer.

This difference in coefficient of thermal expansion causes the following problems. Generally, in the transparent vitrification process, the deposited glass fine particles become a core layer and a clad layer.
During cooling of the transparent vitrification, stress is applied to the core layer and the clad layer due to shrinkage. When the doping is performed by the above method, since the coefficient of thermal expansion of the core layer and the coefficient of thermal expansion of the cladding layer are different, the degree of contraction between the core layer and the cladding layer is different. Therefore, between the core layer and the clad layer, one receives a compressive stress and the other receives a tensile stress. In this case, since the core layer and the clad layer are in a softened state at high temperature, they are deformed with each other, and finally the layer thickness and the refractive index vary within each layer. The variations in the layer thickness and the refractive index in each layer, especially in the core layer, bring about a remarkable change in the propagation mode of the optical waveguide and adversely affect the mode field diameter, the coupling coefficient of the directional coupler, etc.
This is a problem in designing the optical waveguide. Furthermore, if this variation becomes large, the optical waveguide obtained will have a large propagation loss of optical power.

The present invention has been made in view of the above points, and it is possible to obtain an optical waveguide in which variations in the layer thickness and the refractive index in the core layer and the cladding layer are small and the propagation loss of optical power is small. The purpose is to provide a method.

[0007]

The inventors of the present invention focused on Ti, which reduces the coefficient of thermal expansion of the core layer and the cladding layer among the dopants actually used, and adjusted the type and doping amount of the dopant. The inventors have found that by reducing the difference in the coefficient of thermal expansion between the core layer and the clad layer, variations in the layer thickness and the refractive index within the layer can be reduced, and the present invention has been completed.

That is, according to the present invention, the step of forming the first clad layer and the core layer on the substrate, the step of patterning the core layer into a desired pattern, and the step of forming the second clad layer on the core layer. In the method for manufacturing an optical waveguide, the first and second clads are arranged such that the difference between the coefficient of thermal expansion of the first and second clad layers and the coefficient of thermal expansion of the core layer is minimized. Provided is a method of manufacturing an optical waveguide, which comprises doping a layer and a core layer with a dopant. Here, the dopant for doping the first and second cladding layers is B,
At least one element selected from the group consisting of P, Ti, Ge, and F, and the dopant for doping the core layer preferably contains Ti.

When the first and second cladding layers and the core layer are doped with a dopant, the relationship between the dopant amount and the refractive index as shown in FIG. 2 and the dopant amount and the thermal expansion coefficient as shown in FIG. In consideration of the above relationship, the doping amount of each dopant is set so as to make a difference in refractive index between the core layer and the clad layer and minimize the difference in thermal expansion coefficient between both layers.

[0010]

According to the method of manufacturing an optical waveguide of the present invention, the core layer and the cladding layer are doped with a dopant so that the difference between the coefficient of thermal expansion of the cladding layer and the coefficient of thermal expansion of the core layer is minimized. In the cooling process of transparent vitrification, the degree of shrinkage of the core layer and the clad layer can be made uniform. For this reason, both layers are prevented from being deformed from each other and variations in layer thickness and refractive index occur in each layer.

[0011]

EXAMPLES Examples of the present invention will be specifically described below.

First, glass particles for a cladding layer were deposited on a silicon substrate by a flame deposition method, and were doped with 10 mol% of B and 0.3 mol% of P as dopants. Then, glass particles for a core layer are deposited thereon by a flame deposition method, and 0.8 mol% of Ti as a dopant and Ge
Was doped with 0.6 mol%. This was heat-treated at 1350 ° C. for about 60 minutes to be transparent vitrified to form a clad layer and a core layer. Thus, the optical waveguide of the example was manufactured.

On the other hand, B is added to the glass particles for the cladding layer in an amount of 1
0 mol% and P are doped with 0.3 mol%, and the glass fine particles for the core layer are doped with only 3.1 mol% of Ge,
It was made transparent and an optical waveguide of a comparative example was produced.

The variations in the film thickness and the refractive index of the core layer and the cladding layer of the optical waveguides of the obtained Examples and Comparative Examples were measured. The results are shown in Table 1 below. The variation was measured by cutting the optical waveguide at several tens and observing the cross section with an interference microscope.

[0015]

[Table 1] As is clear from Table 1, the optical waveguides of Examples had small variations in film thickness and refractive index. this is,
Since Ti and Ge were used as dopants for the core layer,
This is because the effect of increasing or decreasing the thermal expansion coefficient is canceled out, and the thermal expansion coefficient of the core layer and the thermal expansion coefficient of the clad layer substantially match.

On the other hand, the optical waveguide of the comparative example has a large difference in thermal expansion coefficient between the core layer and the cladding layer,
The variations in film thickness and refractive index were large.

In this embodiment, the combination of the dopants of the clad layer and the core layer (clad layer / core layer) is B-.
P / Ti-Ge was used to adjust the amount of each dopant, but other combinations of dopants (cladding layer / core layer) are B / B-Ti-P, B / B-Ti-Ge, B-.
P / BP-Ti, BP / BP-Ti-Ge, B-
P-Ti / B-P-Ti, B-P-Ti / B-P-Ti
It was confirmed that the same effect was exhibited even when -Ge was used and the amount of each dopant was adjusted. Further, in this embodiment,
Although the cladding layer is not doped with Ge, the cladding layer may be doped with Ge as long as the difference in thermal expansion coefficient between the core layer and the cladding layer is minimized.

Further, although the optical waveguide having the two-layer structure of the clad layer-core layer has been described in the present embodiment, the present invention is also applied to the optical waveguide having the three-layer structure of the clad layer-core layer-clad layer. Needless to say.

The heat treatment conditions for the transparent vitrification in the present invention are appropriately set depending on the kind of dopant and the amount of dopant.

[0020]

As described above, according to the method of manufacturing an optical waveguide of the present invention, an optical waveguide having a small variation in the layer thickness and the refractive index in the core layer and the cladding layer and a small optical power propagation loss can be efficiently obtained. Is something that can be done.

[Brief description of drawings]

1A to 1C are cross-sectional views showing a conventional method for manufacturing an optical waveguide.

FIG. 2 is a graph showing a relationship between a dopant amount and a refractive index.

FIG. 3 is a graph showing the relationship between the amount of dopant and the coefficient of thermal expansion.

[Explanation of symbols]

30 ... Silicon substrate, 31 ... Lower clad layer, 32 ... Core layer, 33 ... Waveguide pattern, 34 ... Upper clad layer.

Claims (2)

[Claims] 1. A step of forming a first clad layer and a core layer on a substrate, a step of patterning the core layer into a desired pattern, and a step of forming a second clad layer on the core layer. In the method for manufacturing an optical waveguide, the first and second cladding layers, and the first and second cladding layers, and the thermal expansion coefficient of the core layer are minimized so as to minimize the difference between the thermal expansion coefficients of the first and second cladding layers and the core layer. A method of manufacturing an optical waveguide, which comprises doping a core layer with a dopant. 2. The dopants for doping the first and second cladding layers are B, P, Ti, Ge, and F.
At least one element selected from the group consisting of
The method of manufacturing an optical waveguide according to claim 1, wherein the dopant with which the core layer is doped contains Ti.