JP3093362B2 - Optical directional coupler - Google Patents

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 Quartz glass waveguides that can be formed on a silicon substrate have features such as low loss, high stability, good workability, and good matching with quartz fibers, and are practical. Research and development are progressing as typical waveguide type optical components. The optical directional coupler having the structure shown in FIG. 4 is one of important basic components when various optical components are formed by the quartz-based photoconductive path. 1,1a In Figure 4 waveguide, P ₀ is the input light, P _1, P ₂ is the output light. In an optical directional coupler, light is branched between two adjacent waveguides, and the branching ratio depends on the length, distance, and the like of the adjacent waveguides.

In order to manufacture a quartz optical waveguide, a process is performed in the order of lower clad layer and core layer deposition → transparency → pattern formation → core etching → upper clad deposition → transparency on a silicon substrate. In this process, the substrate is reheated above 1000 ° C. for the final upper cladding layer clearing. When the upper cladding layer is melted and solidified in the reheating stage, the core is also softened and slightly deformed. At this time, in the structure portion where the two waveguide cores are close to each other, such as the optical directional coupler, there is a tendency that the core collapses in the direction in which the cores approach due to the contraction force when the upper cladding layer is solidified. This fall,
There is a drawback that the coupling ratio of the optical directional coupler fluctuates depending on the manufacturing conditions because it depends on the manufacturing conditions.

[0004]

SUMMARY 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 a light directional coupler.

[0005]

According to the present invention, a core portion formed on a flat substrate and through which light propagates, and a cladding portion having a refractive index around the core portion smaller than that of the core portion. As shown in FIG. 1, in an optical directional coupler composed of two optical waveguides, an intermediate part of the two optical waveguides is a parallel coupling part closer to the other part. Support portions are provided on both sides of the coupling portion of the directional coupler. In FIG. 1, 1b and 1c are waveguides, 2 and 2a are support portions, P0 is input light, and P1 and P2 are output lights. As described in the related art, if there is no support portion, the core softens and falls down when the upper clad layer is melted and solidified. The effect of the support portion is to reduce the force applied to the core waveguide main body at the time of embedding heated to a high temperature, and to suppress deformation and collapse. As a result, the coupling rate of the optical directional coupler, which depends on the manufacturing conditions in the related art, can be made constant with good reproducibility.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings. Example 1 In this example, a silica glass waveguide type optical directional coupler having a tag on 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 procedure for manufacturing the waveguide (cross section aa ′) manufactured in this example.
3 is a core layer, 4 is a lower clad, 5 is a Si substrate, 6 is a resist pattern, 7, 7a is a core, 8, 8a is a support portion, 9
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 by reactive ion etching ( IV) Resist removal (V) Deposition of upper cladding layer and core by FHD method
Embedding support department

In this embodiment, the core of the waveguide is made of quartz glass doped with GeO ₂ , the structure is rectangular (7 × 7 μm), and the refractive index difference between the core and the clad is 0.75%. The waveguide length at the coupling part of the optical directional coupler was set to 0.4 mm. The support portion was 15 μm in width and 0.4 mm in length, and the effect was examined by changing the distance d from the waveguide (see FIG. 1). FIG. 3 shows the relationship between the coupling ratio of the manufactured optical directional coupler and d. It can be seen that the coupling ratio P ₂ / (P ₁ + P ₂ ) increases as the distance d between the support portion and the waveguide core increases. This indicates that the fall is suppressed by the support portion.

As a result, it has been confirmed that the present invention can suppress the collapse in the silica-based glass waveguide type optical directional coupler. The size of the support portion is not particularly limited. Also, in this embodiment,
For simplicity of manufacture, the case where the support portion is made of the same glass composition as the core portion has been described. However, even if the material of the support portion is different from that of the core portion, it does not affect the present invention at all.

[0010]

As described above, since the optical directional coupler of the present invention has the support portion close to the optical waveguide outside the optical waveguide, the optical directional coupler is independent of the manufacturing conditions. Was able to be kept constant with good reproducibility.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a structure of an optical directional coupler having a support unit according to the present invention.

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

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

FIG. 4 is a diagram illustrating 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 Cross section of support part 9 Upper clad layer

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masayuki Okuno 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-63-49708 (JP, A) (58) ) Surveyed field (Int.Cl. ⁷ , DB name) G02B 6/12-6/14

Claims (1)

(57) [Claims] 1. A light-transmitting core portion made of quartz glass on a flat substrate, and a cladding portion having a refractive index around the core portion smaller than that of the core portion. In the optical directional coupler, an intermediate part of the two optical waveguides is parallel and a coupling part closer to the other part is provided. An optical directional coupler having a support portion near the coupling portion outside the optical waveguide of the book.