JPH0593813A - Optical directional coupler - Google Patents

Abstract

PURPOSE:To provide the optical directional coupler which is improved in reproducibility by adjusting the coupling rate of the optical directional coupler which consists of quartz waveguides to a constant rate without depending upon the manufacture conditions. CONSTITUTION:The optical directional coupler consisting of two nearby optical waveguides 1b, 1c which are each manufactured on a plane substrate by using quartz-based glass as a material and consists of a core part where light is propagated and a clad part which has a less refractive index at the periphery of the core part than in the core part has support parts 2 and 2a outside and near the optical waveguides.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical directional coupler used in the field of optical communication components.

[0002]

2. Description of the Related Art A silica-based glass waveguide that can be formed on a silicon substrate has characteristics such as low loss, high stability, good workability, and good compatibility with a silica-based fiber. R & D is underway as a conventional waveguide-type optical component. The optical directional coupler having the structure shown in FIG. 4 is one of the important basic components for forming various optical components by the quartz photoconductive path. In FIG. 4, 1 and 1a are waveguides, P ₀ is input light, and P ₁ and P ₂ are output light. In an optical directional coupler, light is split between two adjacent waveguides, and the splitting ratio depends on the length and distance of the adjacent waveguides.

To manufacture a silica-based optical waveguide, the processes are carried out in the order of lower clad layer and core layer deposition on a silicon substrate → transparency → pattern formation → core etching → upper clad deposition → transparency. In this process, the substrate is reheated to 1000 ° C or above for the final clearing of the upper cladding layer. When the upper cladding layer is melted and solidified in the reheating step, the core is also softened and slightly deformed. At this time, in a structure portion where two waveguide cores are close to each other, such as an optical directional coupler, there is a tendency that the cores fall in a direction toward each other due to a contracting force when the upper cladding layer is solidified. This collapse,
Since it depends on the manufacturing conditions, there is a drawback that the coupling ratio of the optical directional coupler varies depending on the manufacturing conditions.

[0004]

DISCLOSURE OF THE INVENTION The present invention improves the reproducibility by adjusting the coupling ratio of an optical directional coupler composed of a silica-based optical waveguide so as to be constant irrespective of manufacturing conditions. To provide an optical directional coupler.

[0005]

According to the present invention, in an optical directional coupler manufactured on a flat substrate, as shown in FIG. 1, support portions are provided on both sides of the optical directional coupler. In FIG. 1, 1b and 1c are waveguides, 2 and 2a are support parts, and P ₀
Is the input light, and P ₁ and P ₂ are the output lights. As described in the related art, without the support portion, the core softens and falls when the upper clad layer is melted and solidified. The effect of the support part is to alleviate the force applied to the core waveguide main body at the time of embedding by heating to a high temperature, and to suppress deformation and collapse. As a result, the coupling ratio of the optical directional coupler, which depends on the manufacturing conditions in the conventional technique, can be made constant with good reproducibility.

[0006]

Embodiments of the present invention will be described in detail below with reference to the drawings. Example 1 In this example, a silica-based glass waveguide type optical directional coupler having a Si substrate was provided with support portions at both ends in the same manner as shown in FIG. FIG. 2 is a diagram showing a manufacturing procedure of the waveguide (cross section aa ') manufactured in this example,
3 is a core layer, 4 is a lower cladding, 5 is a Si substrate, 6 is a resist pattern, 7 and 7a are cores, 8 and 8a are support parts, and 9 are.
Is the upper cladding. The manufacturing procedure is as follows.

(I) Deposition of lower clad layer and core layer on Si substrate by flame deposition (FHD) method (II) Formation of mask pattern by photolithography (III) Formation of core and support section by reactive ion etching (III) IV) Resist removal (V) Deposition of upper clad layer and core by FHD method,
Embedded support

In this example, the waveguide core was made of GeO ₂ -doped silica glass, the structure was rectangular (7 × 7 μm), and the difference in refractive index between the core and the clad was 0.75%. In addition, the waveguide length of the coupling part of the optical directional coupler is 0.4 mm. Regarding the support part, the width was 15 μm and the length was 0.4 mm, and the effect was examined by changing the distance d (see FIG. 1) from the waveguide. FIG. 3 shows the relationship between the coupling ratio of the manufactured optical directional coupler and d. It can be seen that the coupling rate P ₂ / (P ₁ + P ₂ ) increases as the distance d between the support section and the waveguide core increases. From this, it was shown that the collapse was suppressed by the support part.

From the above results, it was confirmed that the present invention can suppress the collapse of the silica-based glass waveguide type optical directional coupler. It should be noted that the size and position of the support portion are not particularly limited. Further, in this example, the case where the support portion was made of the same glass composition as the core portion was described for the sake of simplicity of production, but even if the material of the support portion is different from the core portion, there is no effect on the present invention. Not something to give.

[0010]

As described above, since the optical directional coupler of the present invention has the support portion near the optical waveguide on the outside of the optical waveguide, the optical directional coupler does not depend on the manufacturing conditions. The binding rate of was able to be made constant with good reproducibility.

[Brief description of drawings]

FIG. 1 is a view showing a structure of an optical directional coupler having a support part of the present invention.

FIG. 2 is a diagram showing a manufacturing procedure of the optical directional coupler according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a structure of an optical directional coupler.

FIG. 4 is a diagram showing a structure of an optical directional coupler.

[Explanation of symbols]

 1, 1a, 1b, 1c Waveguide core 2, 2a Support part 3 Core layer 4 Lower clad layer 5 Si substrate 6 Resist pattern 7, 7a Core 8, 8a Support part cross section 9 Upper clad layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayuki Okuno 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. A two-piece structure comprising a core part for transmitting light, which is made of quartz glass on a flat substrate, and a clad part having a refractive index around the core part smaller than that of the core part. 2. An optical directional coupler formed by adjacent optical waveguides of claim 1, wherein the optical directional coupler has a support portion adjacent to the optical waveguide on the outside of the optical waveguide.