JPS5933883B2 - How to form an optical fiber connection groove - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a connection guide groove of a connection device suitable for holding optical fibers constituting a part of an optical transmission line so that their end surfaces face each other and are optically coupled. It is something.

When constructing an optical communication system using optical fibers, it is extremely important to accurately butt the mutual end faces of the optical fibers and connect them with low loss.

There are two types of optical fiber connections: permanent connections and removable connector connections.For the former, the V-groove connection method, which has relatively low connection loss, is widely used. There is.

That is, the V-groove connection method for optical fibers involves forming a highly precise V-shaped guide connection groove on a connection board, aligning the optical fibers to be optically connected within the guide connection groove, and poking their mutual end faces. Optical fiber connections with extremely low connection loss are possible with a simple configuration that is fixed with adhesive or the like, and by forming at least one V-shaped guide connection groove on the connection board, multiple optical fibers can be connected. A configuration that connects them all at once has also been proposed. By the way, as a conventional method for forming a guide connection groove of a connection substrate used in the V-groove connection method, as shown in FIG. After applying a resist film 2 and masking the area other than the area where the V-shaped groove is to be formed on the connection substrate 1 as shown in FIG. By anisotropically etching the exposed surface layer region of the substrate 1 with an etching solution consisting of an aqueous solution, a guide groove 3 having a V-shaped cross section surrounded by <111> planes is formed. However, since wet chemical etching is used to form such V-shaped grooves, management of etching solutions and etching conditions is complicated, and it is difficult to form guide grooves with high precision and good reproducibility. Furthermore, if the guide groove to which the optical fiber is to be connected is V-shaped, the optical fiber is placed along the two-wire contact with the cross-shaped side wall of the guide groove. Unless it is formed with very high accuracy in the longitudinal direction, such an L-shaped guide groove has the disadvantage that it is not possible to connect optical fibers with high optical axis alignment accuracy and low loss. The present invention has been made in view of the above-mentioned drawbacks of the conventional art, and its purpose is to form a U-shaped guide groove in a connecting device for optically connecting optical fibers by abutting their mutual end faces to form a U-shaped guide groove with good controllability by plasma etching. Another object of the present invention is to provide a novel method for forming an optical fiber connecting groove, which allows optical fibers to be connected with high precision and with low loss.

Embodiments of the present invention will be described in detail below with reference to the drawings.

3 to 6 are cross-sectional views of essential parts showing an embodiment of the method for forming an optical fiber connection groove according to the present invention in the order of steps.

First, as shown in FIG. 3, the surface of the connection substrate 21 made of mirror-polished silicon is completely thermally oxidized to form a thick silicon oxide film (S
iO2)22 is formed. The reason why this thick SiO2 film 22 is formed is that when the surface of the connection substrate 21 made of silicon is mirror-polished, defects such as mechanical strain and penetration of fine particles of the polishing agent occur in the surface layer. Due to this fact, when the surface of the substrate 21 in this state is etched, the surface is etched non-uniformly and the etched surface becomes rough, making it difficult to obtain a flat surface. Therefore, in this embodiment, the defective surface layer of the substrate 21 is treated with Si by thermal oxidation.
By etching the desired etched portion of the substrate 21 subsequent to the etching of the SiO2 film 22, a flat etched surface can be obtained.
By thermally oxidizing the surface of 1, a thick SiO2 film of at least 5000λ or more is formed, as is clear from the relationship between the thickness of the SiO2 film formed on the silicon substrate and the etching surface roughness shown in FIG. . Next, a photoresist film 23 is deposited on the SiO2 film 22.

Thereafter, as shown in FIG. 4, the photoresist film 23 on the region of the connection substrate 21 where the guide groove 25 for holding the optical fiber is planned to be formed is selectively removed to form an opening 24, and then the opening 24 is formed. The SiO2 film 22 and the connection substrate 21 are etched using the photoresist film 23 having 24 as a mask and etching the SiO2 film 22 and the connection substrate 21 at 0.6T0rr using carbon tetrafluoride (CF4) gas as a base gas and adding a trace amount (5% or less) of 02 gas. Perform plasma etching using gas. At this time, the oscillation frequency is 13.56, high frequency power of 200 W is applied, the degree of vacuum during etching is 0.5 to 1.0 T0rr, the substrate temperature is preferably about 80°C, and the etching is performed at a depth of Although etching tends to be substantially isotropic in the direction, the amount of side etching in the vicinity of the mask opening 24 is large, about 10 times the width of the opening 24, and this amount of side etching is larger than the width of the etching groove. 5, a U-shaped guide groove 25 having a semicircular cross section is formed with high precision, as shown in FIG. After that, if the photoresist film 23 used as a mask is removed, for example 13
An optical fiber connection plate is obtained in which a U-shaped guide groove 25 having an opening width of 01 tm and a depth of 60 ttm is formed. Further, in the case of such a connecting plate, it is possible to accurately arrange the optical fiber 26 having a diameter of, for example, 125 μm in the guide groove 25 so as to make large surface contact with the side wall surface thereof.
FIG. 8 shows the etching rate at each etched portion when forming the above-mentioned guide groove 25. In the figure, A is the etching rate curve for the SiO2 film 22, and B is the etching rate curve for the SiO2 film 22 directly below the mask opening 24. In the etching speed curve for the substrate 21, C is an etching speed curve in the depth direction, and D is a side etching speed curve near the bottom of the etching groove. As is clear from the above description, according to the method for forming an optical fiber connection groove of the present invention, the guide connection groove of the connection device that holds the optical fibers abutting each other for optical coupling is arranged so that the optical fibers are brought into contact with each other by surface contact. Since it is formed in a U-shaped cross section with good controllability and high precision by plasma etching so that it can be arranged, the connecting device in which the U-shaped guide connection groove is formed according to this embodiment is used.
By arranging the end faces of the optical fibers to be connected in the guide connection groove and fixing them with adhesive, etc., it is possible to easily connect the optical fibers stably with high precision and low connection loss. It has great practical effects.

In the above-mentioned embodiment, an example was explained in which three guide grooves were formed on the optical fiber connecting device plate.
The present invention is not limited to this, and it goes without saying that one or more can be formed all at once.
It goes without saying that the present invention can be applied to the formation of variously modified optical fiber guide grooves such as branch grooves or cross-shaped grooves for optical directional coupling.

[Brief explanation of drawings]

1 and 2 are main part sectional views explaining a conventional method for forming a guide groove of an optical fiber connection plate, and FIGS. 3 to 6 are one embodiment of the method for manufacturing an optical fiber connection plate according to the present invention. FIG. 7 is a graph showing the relationship between the thickness of the SiO2 film formed on the silicon substrate and the etching surface roughness according to the present invention, and FIG. 8 is a cross-sectional view of the main part showing an example in the order of steps. 3 is a graph showing the etching speed at each etched portion of FIG. 21 is a connection substrate, 22 is a silicon oxide film, 23 is a photoresist film, 24 is an opening, 25 is a guide groove having a U-shaped cross section, and 26 is an optical fiber.

Claims (1)

[Claims] 1. A step of forming an oxide film of at least 5000 Å or more on the surface of a connecting device that holds optical fibers constituting a part of an optical transmission path so that their end faces face each other and are optically coupled; a step of coating a photoresist film on the connected device and selectively removing the photoresist film on a region of the device where an optical fiber holding groove is to be formed to form an opening; A method for forming an optical fiber connecting groove, comprising the step of forming a guide groove having a U-shaped cross section for connecting and holding an optical fiber on the connecting device by plasma etching using a resist film as a mask.