JPH03228003A - Production of fusion type optical branching/coupling device - Google Patents

Abstract

PURPOSE:To stabilize the heating range of optical fibers and to obtain the branching/ coupling device having a desired branching ratio and low loss by holding both ends of exposed clads with holding plates having a heat insulating function and heating and welding the clads between the holding plates. CONSTITUTION:Capillaries 4, 5 made of ceramics, etc., are inserted from both ends of the optical fibers 1, 2 and are fixed to both boundary parts of the clads and the coatings to array two pieces of the optical fibers 1, 2 in tight contact with each other. These fibers are then imposed on supporting bases and both ends thereof are pressed by the holding plates 6, 7 in such a manner that the clad parts with the coatings removed therefrom come into tight contact. The parts between the holding plates 6 and 7 are heated by a heating means 8, such as a gas torch or discharge, to weld the clads to each other and to apply a specified tension P. The holding plates 6, 7 at both ends are slightly parted from the optical fibers 1, 2 and while the fibers are heated, the fibers are stretched from both ends under the tension P applied thereon. The holding plates 6, 7 are thereafter completely separated and a semi-cylindrical reinforcing cover 9 consisting of quartz glass, etc., is imposed between the capillaries 4 and 5 and is fixed by adhering, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method of manufacturing an optical branching coupler for branching and coupling light in optical fiber communications, optical fiber sensors, and other optical signal processing.

"Prior Art" Optical branching couplers are important elements used in optical fiber communications, optical fiber sensors, and other optical signal processing.

A typical optical splitter coupler is made by peeling off the coating of two optical fibers 101 and 102 to expose the cladding, arranging them closely in parallel, and heating, fusing, and stretching a portion of them, as shown in Figure 4. be able to.

The necessary branching ratio is the bond length! That is, it can be obtained by adjusting the amount of stretching. The branching ratio η in that case can be given proximately by the following equation.

Here, I. is the detected value of the optical fiber 101, I.

is the detected value of the optical fiber 102, K is the coupling coefficient, and l is the coupling length.

The coupling coefficient depends on the wavelength of light, the core spacing of the coupling portion 103, the cross-sectional shape, the relative refractive index difference between the core and the cladding, and other factors.

By appropriately selecting the bond length l, a predetermined branching ratio η can be obtained. That is, by stretching, the diameter of the core in the cladding becomes smaller, the amount of light seeping out from the core increases, and the light gradually moves to the adjacent core, causing the light to be branched due to distributed coupling.

``Problem to be Solved by the Invention'' Conventionally, this type of optical branching coupler has two optical fibers 111 and 112 whose coatings have been peeled off in parallel and tightly attached using holders 114 and 115, as shown in section 5a. Arrange them.

Next, as shown in FIG. 5b, the optical fibers 111, 11
2 of the optical fiber 111112 by heating it with a slight tension P-P applied to it that does not stretch it.
Fuse the books. Thereafter, as shown in FIG. 5c, the film is further heated and stretched by applying a larger tension P-P to both sides, and the stretching is stopped at the required branching ratio.

As shown in the old method, the branching ratio η of such an optical branching coupler depends on the coupling length l. The heating range changes depending on conditions such as the environment and flame conditions, making it difficult to achieve reproducible fusion. Therefore, the bond length I for obtaining the necessary branching ratio η changes, and the taper shape due to stretching also changes, so that the loss between input and output also changes. In order to improve productivity and lower costs, it is essential to stabilize the heating range of optical fibers.

"Means and Effects for Solving the Problems" The present invention provides an Igr thermal function at both ends of the exposed cladding in order to stabilize the heating range of the optical fiber and obtain the required branching ratio and low-loss optical branching coupler. The cladding between the holding plates is heated and fused.

Further, in order to protect the fusion-stretched portion, a semi-cylindrical reinforcing cover was placed and fixed between the capillaries after fusion-stretching.

``Example'' The present invention has been made in view of the above circumstances, and its purpose is to keep the bond length constant by controlling the fusion length during fusion of optical fibers, and to reduce branching ratio, loss, etc. An object of the present invention is to provide a method for manufacturing a fusion type optical branching coupler with stable performance, reproducibility, and productivity, thereby reducing the cost of the optical branching coupler.

Next, an embodiment according to the present invention will be described with reference to FIGS. 1 to 3.

As shown in FIG. 1a, two optical fiber parts 2 are prepared in which the protective coating of a certain range of the optical fiber parts 2 is peeled off to expose the cladding. Capillaries 4 and 5 made of, for example, ceramics are inserted from both ends of the optical fibers 1 and 2 and fixed at both boundaries between the cladding and the covering, and the two optical fibers 1 and 2 are brought into close contact in parallel.

Then, as shown in Figure 1b, place it on a support stand,
Both ends of the cladding portion from which the coating has been peeled off are pressed down with holding plates 6 and 7 shown in FIG. 2 so that they are in close contact with each other. At this time, a slight tension is applied to the holding plates 6 and 7 and the optical fiber heart 2 so as not to cause stretching due to heating. The holding plates 6 and 7 are preferably made of a material that is heat resistant and has low thermal conductivity for insulation purposes, such as porous ceramics.

As shown in FIG. 1C, the clads are fused together between the holding plates 6 and 7 by heating means 8 such as a gas torch or electric discharge, and a constant tension P is applied. At this time, the heat fusion range is limited by the interval between the retaining plates 6 and 7 because the retaining plates 6 and 7 have a heat insulating effect and only the heated portion is heated. Further, the shape of the holding plate may be other than that shown in FIG. 2 as long as it can properly hold the optical fiber.

Next, as shown in FIG. 1d, the holding plates 6 and 7 at both ends are slightly separated from the optical fiber part 2, and stretching is performed while applying tension P from both ends while heating. At that time, the heating range is similarly limited by the holding plates 6 and 7, but the heating range may be different from that during fusion.

Incidentally, the heating source may be movable or fixed, as long as it does not cause microquenching and does not contain impurities, and can perform fusion stretching with low loss.

To adjust the stretching, light is applied manually to one end of the optical fiber 1, and the output from the two optical fibers 1 and 2 is monitored at the other end, and the stretching is performed when the required branching ratio η is reached. stop working.

After that, as shown in Fig. 1e, the holding plates 6 and 7 are completely separated from the optical fibers 1 and 2, and a reinforcing cover 9 such as semi-cylindrical quartz glass is placed between the capillaries 4 and 5 and fixed by adhesive etc. do. In that case, it is preferable to use a material for the reinforcing cover 9 that has approximately the same coefficient of linear expansion as the optical fiber.

Thereafter, it is removed from the jig and placed in a protective cover 10 as shown in FIG. 3 to complete the optical branching coupler.

``As described above, the method for manufacturing a fusion-type optical branching coupler of the present invention allows the cladding of optical fibers to be brought into close contact with each other by a holding plate having a heat insulating function, and the distance between the holding plates is almost fused. Since the length and heating range during stretching can be specified, the fusion length and stretching heating range can be specified, making it possible to manufacture a reproducible optical branching coupler.

Further, in the present invention, the optical fibers are aligned in advance using capillaries, and once the processing is completed, the reinforcing cover is fixed between the capillaries on the spot, and the reinforcing cover can be safely removed with the reinforcing cover fixed. In addition, once the reinforcing cover is fixed, it can be sent to final processes such as attaching the protective cover. That is, it is possible to reduce the yield of the product, and it is possible to manufacture the product in a short time, thereby reducing the price of the product.

Furthermore, the present invention can contribute to miniaturization of optical couplers by optimizing the fusion length and stretching length by adjusting the distance between the holding plates, thereby limiting the heating fusion and stretching range.

[Brief explanation of drawings]

Figure 1 is a schematic diagram explaining the manufacturing process of the present invention, Figure 2 is a front view of the holding plate used in the manufacturing step 1 in Figure 1, and Figure 3 is a fusion bond manufactured by the manufacturing method of the present invention. FIG. 4 is a front view of the fusion-type optical splitter and coupler, and FIG. 5 is a schematic M showing the manufacturing process of a conventional fusion-type optical splitter and coupler. 2... Optical fiber = 5... Capillary 7... Holding plate 8... Heating means 9... Reinforcement cover 10... Protective cover

Claims (2)

[Claims] (1) A fusion-type optical branching coupler made by fitting and fixing a capillary to the boundary between the cladding and coating of multiple optical fibers each having an exposed cladding portion, and fusing the exposed cladding. A method for manufacturing a fusion type optical branching coupler, characterized in that both ends of the exposed cladding are held by holding plates having a heat insulating function, and the cladding between the holding plates is heated and fused. (2) The method for manufacturing a fusion-type optical branching coupler according to claim 1, wherein a semi-cylindrical reinforcing cover is placed and fixed between the capillaries after the fusion-stretching.