JPS60129711A - Formation of optical waveguide - Google Patents

Abstract

PURPOSE:To shorten a groove working time by employing anisotropic etching on RIE basis and isotropic chemical etching in combination for the groove work of a glass substrate. CONSTITUTION:A mask 2 is formed of a metallic protection film of Ni, etc., with etching resistance on a glass substrate 1 of quartz, etc., by photolithography, and anisotropic etching is carried out on RIE basis through a hole 3 to form a temporary groove 4 of depth d1. Then, the mask 2 is used for isotropic chemical etching using fluoric acid to shape the temporary groove 4, forming a groove 7 for an optical waveguide. The groove 7 is a sectioned in a channel shape having an arc of a radius (r) and has a size and a shape suitable for the joining of optical fibers. The mask 2 is removed and then a glass layer 8 having a larger refractive index than the substrate 1 is deposited by a CVD method; and its surface is polished and a glass layer 9 having a refractive index nearly equal to that of the substrate 1 is deposited to form the optical waveguide 8b. The isotropic etching is applied for the shaping, so the work time is shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a method for forming a multimode leading wavepath.

(Technical Background) Various methods for forming this type of leading wavepath have been proposed. For example, literature: [IEICE Technical Research Report 0 Q E 8O-135J (February 20, 1981)
Conventional methods, as typified by the method disclosed in Japan (Japanese Edition), involve a dry etching method (e.g., R
active fan etching, hereinafter referred to as RIE
), a groove with a square cross section is formed, and another glass material with a refractive index higher than that of the glass substrate is deposited in this square groove by a method such as CvD to form an optical waveguide. was forming.

By the way, the core diameter of the multimode optical fiber normally used for transmission is about 50 μm. For this reason, if a groove with similar dimensions suitable for bonding to an optical fiber is processed by etching only using the RIE method as described above, the processing speed of this RIE method is slow, so it is difficult to process the groove. The problem is that the questions take a long time.

Furthermore, since the walls and bottom surfaces of the grooves etched by this RIE method are optically rough, there is a drawback in that they are a major cause of transmission loss due to light scattering.

Furthermore, since etching by this RIE method is anisotropic etching, the cross-sectional shape of the processed groove, that is, the leading waveguide, becomes square.

For this reason, the bonding surface of the leading waveguide and the bonding surface of the optical fiber having a circular cross-sectional shape cannot be perfectly matched, and therefore, there is a disadvantage that splice loss occurs at the bonding portion due to the difference in cross-sectional shape. There is.

(Object of the Invention) An object of the present invention is to provide a method for forming a leading waveguide that eliminates the drawbacks of the above-mentioned conventional methods.

(Structure of the Invention) In order to achieve objective 1, the present invention combines anisotropic etching by RIE and isotropic etching by chemical etching when forming grooves on a glass substrate. The gist is what to do.

(Description of Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIGS. 1(A) to 1(C) are process diagrams for explaining an embodiment of the method for forming an optical waveguide according to the present invention, each of which is schematically shown as a cross-sectional view of the optical waveguide forming state at the main stage. This is an indication.

First, as shown in FIG. 1(A), a glass substrate 1 made of quartz or the like (with a refractive index of Ill) is prepared, and an underlying substrate 1 is deposited on this substrate 1 using the usual phosphorography technique. A mask 2 is formed to be used in etching the pattern. This mask 2 is made of, for example, an etching-resistant metal protective film such as Ni. 3 is a hole formed in this mask 2 (
or a window), and an optical waveguide is formed in a portion of the substrate l corresponding to this hole 3. The width W of this hole 3 is formed to be smaller overall than the width W2 (FIG. 1(C)) of the leading waveguide to be formed.

Next, as shown in FIG. 2, the substrate l having the mask 2 is subjected to anisotropic etching through the holes 3 of the mask 2 by RIE. In this case, it is preferable to use CF4 gas or a mixed gas of CF4 and oxygen. Through this anisotropic etching, a temporary structure 4 is formed on the substrate l with a width equal to the mask hole 3 and a depth d+, but the size of this temporary structure 4 is larger than the cross-sectional thickness of the optical fiber used. Formed small. Further, the cross-sectional shape of the etched temporary structure 4 has a so-called rectangular shape with rounded corners where the side surfaces and the bottom surface of the wall intersect.

Next, as shown in FIG. 1(C), using the mask 2 as it is, chemically etching the Hibiki temporary structure 4 using hydrofluoric acid at Yη temperature to shape the temporary structure, and forming the leading waveform. A groove 7 is formed for this purpose. In this case, the concentration of hydrofluoric acid can be selected as required, but for example, the concentration is 50%. Since this chemical etching is isotropic etching, etching is performed in the direction of the side surfaces 5a, 5b and bottom surface 6 of the wall of the temporary structure 4, and the temporary structure 4 is processed and shaped. If r is the amount excavated from the wall surface (5a, 5b, 6) of the temporary structure 4 by this chemical etching method, the etching will be reshaped and finalized as shown in Fig. 1(C). The width W2 of the groove 7 thus obtained is Wl+2r, and the depth d2 is dl+r. Also, due to this chemical etching, the corner of the intersection of the side and bottom surfaces of the square temporary structure 4 (indicated by dotted lines in Figure 1 (C)) is removed, and the intersection point of both sides of this temporary structure 4 is centered. Therefore, the corner portion of the groove 7 finally obtained has a round U-shape as shown in the figure.

By controlling the processed J peak by this chemical etching, the cross section of the groove 7 is made to have a size and shape suitable for joining to an optical fiber.

The surface of the wall of the groove 7 obtained by this chemical etching is a smooth surface with optically good surface precision, which effectively reduces light scattering that adversely affects light transmission.

FIGS. 2(A) to 2(C) are process diagrams illustrating the process of depositing an optically transparent material suitable for light transmission into the groove thus processed to form an optical waveguide, which is the core part. It is.

As shown in FIG. 2(A), after removing the mask 2 on the substrate 1, the refractive index n of the glass substrate 1 is changed to a larger refractive index by using a conventional technique such as the CVD method. n2
A glass layer 8 is deposited.

Next, as shown in FIG. 2(B), the crow layer 8 (a portion of 8a and 8b) deposited on the surface of the substrate 1 and the surface 1a of the substrate 1 are removed by polishing, and the crow layer within 7 is removed by polishing. The portion 8b is left to remain, and the polished surface 1b is made into a smooth surface with optically good surface precision.

Next, as shown in FIG. 2(C), another glass layer 9 having a refractive index similar to that of the glass substrate 1 is deposited and formed by the GVD method, and the remaining glass layer portion 8b is formed as a leading waveguide. .

J-The material to be filled in the groove 7 described above should be optically transparent, have low absorption, and do not cause any actual damage to optical transmission.
For example, resin or the like may be used.

(Features and Effects of the Invention) As is clear from the series of explanations, according to the leading waveguide forming method of the present invention, the groove processing of the glass substrate at the time of optical waveguide creation is performed by an anisotropic etching process using RIE and a chemical etching process. This is done using an isotropic etching process. The etching speed of this chemical etching method is, for example, 10 to 20 times faster than that of the RIE method if hydrofluoric acid with a concentration of 50% is used.
Compared to the case where grooves are formed by etching using only the etching method, there is an advantage that the groove forming time can be shortened by two hours.

This chemical etching also improves the surface accuracy of the groove surface.
Compared to the case of etching using only the conventional RIE method, it is possible to obtain a smooth surface with high quality and optical quality, and therefore, there is no light scattering caused by the roughness of the surface of the optical waveguide as in the conventional method, and transmission loss is reduced. Further, by chemical etching, the cross-sectional shape of the groove can be changed from the conventional square shape to a rounded shape with no corners, such as a U-shape, or other shapes, such as a circular shape. Therefore, the advantage is that the connection with the optical fiber can be performed better than in the conventional case, and the connection loss can be significantly reduced.

It is clear that the present invention is not limited only to the embodiments described above. For example, chemical etching may be performed using something other than hydrofluoric acid; for example, an alkaline material can be used. In that case, the mask used must also be compatible with the etching process. In that case, it is possible to use an etching mask that has acid and alkali resistance from the beginning of the mask formation, or to remove the mask used for RIE etching and create a new alkali-resistant etching mask before chemical etching. An etching mask may also be provided.

Further, the mask may be a metal protective film other than the above-mentioned Ni.

Furthermore, the concentration of hydrofluoric acid can also be set to a concentration other than 50%.

[Brief explanation of drawings]

FIGS. 1(A) to (C) are process diagrams showing the steps of groove processing in the method for forming a leading waveguide of the present invention. FIGS. FIG. 4 is a process diagram showing the J-step of completing the guide waveguide by providing an optical material. l...Glass substrate (with refractive index nl), 1a...(glass substrate) surface 1b...(glass substrate) polished surface 2...mask, 3...(mask) hole or Window 4・
... Plate groove, 5a, 5b... (plate groove) side surface 6...
Bottom surface (of plate groove), 7... (for leading waveguide) groove 8... (
Glass layer 8a (with refractive index n2)...Glass layer portion 8b (on the substrate surface)...(
Glass layer portion (in the groove) or optical waveguide 9...another glass layer (provided on the polished surface). Patent Applicant: Oki Electric Industry Co., Ltd. Figure 1 Figure 2 L Itotori Yun Official Book 11/1 February 1, 1958 Commissioner of the Patent Office J'i Kazuo Sugi Tono 1° Haji 1 Indication Patent Application 1983 -237230 No. 29,
Name of the person who amends the leading wave path formation method 3 Relationship with Badge 1 Patent applicant address (〒-105) 1-7-12 Toranomon, Minato-ku, Tokyo Name (02+11) Oki Electric Industry Co., Ltd. Representative Hashimoto
Nankai O 4 Agent 170 廿 (988) 5583 Address 1-20-5 Higashiikebukuro, Toshima-ku, Tokyo Explanation column 1 Brief explanation of drawings and drawings 6 Person It j
As per Appendix E (1), the scope of claims in the specification is amended as follows. ``2. Forming a groove in a glass substrate with a refractive index nl as claimed in the claim, and forming a groove in a line groove with a refractive index nl.
2. When depositing the optical material (see above in 15) to form a guiding waveguide, the line grooves are first formed by anisotropic etching with a reactive gas on the substrate to form a temporary structure. and a step of shaping the temporary structure by isotropically etching the temporary structure using a chemical etching method, j (2), Specification, page 4. In the fourth line, change [on board l] to r
On the surface la of the substrate l, 1 is corrected, and in the 13th line, ``In Figure 2'' is corrected to 1 In Figure 1 (B)''. (3), ``Sides and bottom surface'' in the second line of page 5 is corrected to ``side surfaces 5a, 5b and bottom surface 6''. (4), page 6, line 3 to line 4, "becomes a corner part." One corner part 7a and 7b is rounded as shown in the figure, and the cross-sectional shape of the groove 7 is U-shaped. It becomes like this. ”, and in line 19 of the same line, “Crow layer 8 is J, 8 force lath layer 8 () The part of root surface 1a l: is 8a, the part inside i1ζ7 is 8b)” is corrected as A. (5), page 10, line 3 [7... (for leading waveguide)
Groove” then 1+’? a, 7b... Corner part J (of the groove)
join. (6) 3 Drawings Figure 1 (C) is corrected as shown in the attached drawing. Figure 1

Claims (1)

[Claims] A groove is formed in a glass substrate with a refractive index of n1, and h+E is formed in the groove.
When depositing an optical material with a refractive index of n7 (ill > I+2) to form a guiding wavepath, the grooves are first formed by anisotropic etching of the substrate using a reactive gas to form a temporary structure. 4. performing isotropic etching on the temporary structure using a chemical etching method to shape the temporary structure; A method for forming an optical waveguide with a ν characteristic.