JP3006301B2 - Manufacturing method of glass waveguide - Google Patents

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 a glass waveguide, and more particularly, to a method for improving a etching property and a transmission loss characteristic.

[0002]

2. Description of the Related Art In general, a glass waveguide is manufactured by forming a core porous glass layer as a core on a quartz glass substrate or a substrate having quartz glass formed on a silicon surface, and thereby forming a reactive glass layer. After a core is formed by ion etching (RIE) or the like, a porous glass layer for a clad serving as a clad is formed by a fire deposition method and is formed into a transparent glass.

Conventionally, in order to improve the waveguide characteristics, a porous glass layer for a core is heat-treated before forming a core pattern, and sintered so that the bulk density of the glass layer becomes 1.9 g / cm ³ or more. (Japanese Unexamined Patent Publication (Kokai) No. 61-198107), or a method in which a porous glass layer for a core is heat-treated to be transparent to form a transparent glass layer (Japanese Unexamined Patent Publication (Kokai) No. 63-6).
509).

Normally, in such a glass waveguide, the core is formed in a rectangular shape in cross section, and its size is about 8 × 8 μm in a single mode glass waveguide, and the size is about 8 × 8 μm. Is about 50 × 50 μm. In etching a core pattern having such dimensions, if the core glass layer has a bulk density of 1.9 g / cm ³ or more or is made of transparent glass, RIE is performed.
The time required for such etching required about 1 hour at a depth of 8 μm and about 7 hours at a depth of 50 μm. Further, the etched surface at this time was rough, so that the loss of the glass waveguide was relatively large.

[0005]

As described above, the bulk density of the core glass layer to be etched is 1.9 g / cm.
^The conventional method of manufacturing a glass waveguide in which the glass layer is made ³ or more or the core glass layer is made transparent is disadvantageous in that the etching time required for forming the core pattern is long and the workability is poor. There is also a problem that the state of the etched surface is poor and transmission loss is large.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned disadvantages of the prior art, and to provide a method of manufacturing a glass waveguide which has a short etching time, is excellent in mass productivity, and has a low loss independent of the state of an etched surface. is there.

[0007]

According to a method of manufacturing a glass waveguide of the present invention, a porous silica glass core layer is formed on a quartz glass substrate or a substrate having quartz glass formed on a silicon surface. After increasing the bulk density of the porous glass layer for the core in a porous state by heat treatment, a core pattern is formed from the porous glass layer for the core having the increased bulk density. A quartz-based porous glass layer for a clad is formed, and a porous glass layer for a clad and a porous glass layer for a core for forming a core pattern are simultaneously vitrified. In this case, it is preferable that the bulk density of the core porous glass increased by the heat treatment is 0.8 to 1.5 g / cm ³ .

[0008]

When the core pattern is formed in a transparent glass state or a state close thereto, the loss of the waveguide becomes very high. As a cause, in the case of a transparent glass state or a state close to this, it can be determined that the etched surface is rough by scanning electron microscope measurement, and this surface is not uniform even after the formation of the clad glass in the next step. It is thought to be. In the present invention, of course, the etched surface is rough. However, although there is a difference in bulk density, a clad made of porous glass is also formed on a core pattern made of porous glass, so even if the etched surface of the core is in a bad state, it fuses with each other during transparent glass. As a result, the scattering loss is reduced. Further, since the formation of the core pattern is not performed in a transparent glass state or a state close to the transparent glass state but in a porous glass state, the etching time is shortened.

As shown in FIG. 2, the bulk density is 0.6 to
At 0.7 g / cm ³ , the etching time is as fast as about 5 minutes, but the roughness of the etched surface is large, and fine bubbles are generated at the interface during the vitrification, resulting in an increase in loss. Also 1.7
At g / cm ³ , the etching time takes about 35 minutes, and the time is not significantly reduced. Further, at 2.0 g / cm ³ , the loss is 0.09 dB / cm, almost the same as that of the transparent glass.
Met. From the above, when it is found that there is no air bubble at the core interface after the production and that the etching can be performed in less than half of the conventional time, the bulk density of the core porous glass layer is 0.8 to 1.5 g / A range of cm ³ is appropriate.

[0010]

【Example】

FIG. 1 shows a manufacturing process of a glass waveguide according to an embodiment of the present invention. On a quartz glass substrate 2 having a thickness of 1 mm and an outer diameter of 3 inches, a core porous glass layer 1 serving as a core was formed to a thickness of 40 μm by a fire deposition method (A). Glass composition of the porous glass layer 1 is a TiO ₂ -P ₂ O ₅ -SiO ₂ based glass. The bulk density at this time was 0.45 g / cm ³ .

Substrate 2 on which core porous glass layer 1 is deposited
Was heat-treated at 1050 ° C. in He gas to change the porous glass layer 1 to a porous glass layer 3 for a high bulk density core by increasing the bulk density while maintaining the porous glass state (B). The bulk density after the heat treatment was 1.1 g / cm ³ .

A tungsten silicide film (WSi film) is formed on the surface of the porous glass layer 3 for high bulk density by sputtering.
Then, after applying a photoresist and transferring the core pattern with a mask aligner, the WSi film is first etched by RIE, and the porous glass layer 3 for a high bulk density core is etched using the WSi film as a mask. Then, a core pattern 4 was formed (C). At this time, the core pattern was a straight line, and its cross-sectional rectangular shape was about 8 × 8 μm for single mode.

After that, a porous glass layer 5 for cladding was formed to a thickness of 50 μm by a fire deposition method (D).
Glass composition of the porous glass layer 5 is _{P 2 O 5 -B 2 O 3} -
It is a SiO ₂ glass.

Finally, in a He gas atmosphere at 1300 ° C., the core pattern 4 made of a porous glass layer and the porous glass layer for cladding 5 are simultaneously vitrified to form a core 6 and a cladding layer 7 to form a glass conductor. Waveguides were produced (E).

The transmission loss of the single-mode linear waveguide manufactured as described above was as low as 0.02 dB / cm. The etching time in the present example was 15 minutes, which was reduced to 1/4 compared to the conventional one hour.

Comparative Example For comparison, a glass waveguide was manufactured in the same manner as in the example except that the porous glass layer for the core was transparently vitrified and then etched. The loss of the waveguide was as high as 0.1 dB / cm.

[0017]

According to the present invention, a low loss glass waveguide is produced because the core and the clad are fused together to improve the adhesiveness when the transparent glass is used, because the etching time can be shortened and the core and the clad are fused to each other when the transparent glass is used. can do. Further, by shortening the etching time, it can be applied to the production of a multi-mode glass waveguide.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of a glass waveguide according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a bulk density and an etching time.

[Explanation of symbols]

Reference Signs List 1 porous glass layer for core 2 quartz glass substrate 3 porous glass layer for high bulk density core 4 core pattern (porous glass layer for core after etching) 5 porous glass layer for cladding 6 core 7 cladding layer

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshikazu Kamoshida 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Prefecture Within the Opto-System Research Laboratories, Inc. (72) Inventor Hideo Otsuki Hitachi, Ibaraki Japan 5-1-1 Takamachi Inside Opto-System Laboratories, Hitachi, Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) C03B 19/14 C03B 20/00 C03B 37/00-37 / 16 G02B 6/12

Claims (2)

(57) [Claims] 1. A quartz-based porous glass layer for a core is formed on a quartz-based substrate, and the bulk density of the porous glass layer for a core is increased by heat treatment in a porous state, and then a core pattern is formed. Then, after forming the core pattern, a quartz-based porous glass layer for cladding is formed, and the core pattern formed by the porous glass layer for core and the porous glass layer for cladding are simultaneously vitrified. A method for manufacturing a glass waveguide. 2. A method for producing a glass waveguide, wherein the bulk density of the core porous glass layer increased by heat treatment is in the range of 0.8 to 1.5 g / cm ³ .