JPH0283504A - Optical fiber coupler - Google Patents

Abstract

PURPOSE:To prevent the leakage of a clad mode at an adhered point and to decrease an excess loss so as to improve transmission characteristic by housing the fusion-stretched part of are optical fiber coupler into a case for reinforcement and fixing this part to the case for reinforcement by using an adhesive agent having the refractive index lower than the refractive index of the clad of optical fibers. CONSTITUTION:The coating materials of the optical fibers 1, 1 are respectively removed from a part of the fibers to expose the clads 2, 2. These clads 2, 2 are partly joined and further the joint part is fused and stretched by an oxyhydrogen flame, etc., by which the fusion-stretched part 3 is formed. The fusion- stretched part 3 is housed into the case 4 for reinforcement consisting of a metal or glass, etc., and the part 5 near the fusion-stretched part 3 is fixed by the adhesive agent 6 into the case 4 for reinforcement. Since the fusion- stretched part 3 is fixed to the case 4 for reinforcement by using the adhesive agent 6 having the refractive index lower than the refractive index of the clad 2, the leakage of the clad mode at the adhered point is prevented.

Description

Detailed Description of the Invention "Industrial Field of Application" This invention is a flexible system used for branching or merging optical signals in systems using optical fibers such as optical fiber communications and optical fiber sensors. This invention relates to a stretched optical fiber coupler.

``Prior Art'' Conventionally, as this type of fused and drawn optical fiber coupler, the one shown in FIG. 1, for example, is known. In FIG. 1, the optical fiber coupler has a coating material removed from a portion of each of a pair of optical fibers 1 and 1 to expose a cladding 2.2, and a portion of the cladding 2.2 is coated with an adhesive or the like. The joint is then melted using an oxyhydrogen flame, etc., and stretched and tightened, thereby forming the fused and stretched portion 3! ,',? It has been accomplished. In such an optical fiber coupler, the fused and stretched portion 3 is usually housed in a reinforcing case 4 made of metal, glass, or the like.
It is fixed in the reinforcing case 4 to a portion 5 near the fused and stretched portion 3 with an adhesive 6.

"Problem to be Solved by the Invention" By the way, in the optical fiber coupler described above, the stretched portions 7 in the fusion-stretched portion 3 are stretched and have a small diameter, so that they are no longer in the original waveguiding state. As a result, in the optical fiber coupler, an increase in the propagation state in the cladding mode is likely to occur, and especially when a high refractive index adhesive is in contact with the stretched portion 7..., waveguide loss increases. It is more likely to occur.

In addition, in order to prevent such inconvenience, the stretched portion 7 of the fused and stretched portion 3...that is, the core portion other than the portion that has been stretched and has a small diameter, is reinforced with adhesive inside the reinforcing case 4. It is conceivable to fix the optical fiber coupler to the optical fiber coupler, but in that case, a sufficient length of the reinforcing case 4 (length in the axial direction of the optical fiber 1) would be required, making it difficult to downsize the entire optical fiber coupler. There are some inconveniences.

"Means for Solving the Problem" Therefore, in the optical fiber coupler of this invention, the fused and stretched portion is housed in a reinforcing case, and fixed to the reinforcing case using an adhesive having a lower refractive index than the cladding of the optical fiber. The above problem was solved by doing this.

"Example" The present invention will be explained in detail below.

The difference between the optical fiber coupler of the present invention and the conventional optical fiber coupler shown above is that the bone cement 6 is used to fix the fused and stretched part 3 to the reinforcing case 4, and has a refractive index higher than that of the cladding 2 of the optical fiber 1. The point is that a low amount of bone cement is used.

In the optical fiber coupler of the present invention, quartz-based or multi-component glass-based optical fibers are used as the pair of optical fibers 1, 1, and the coating material is removed from a portion of each of these optical fibers 111 to form a cladding 2.2. is exposed, a portion of these clads 2.2 are joined, and the joined portion is further fused using an oxyhydrogen flame or the like and the extended portion is tightened, thereby forming the fused extended portion 3. This fused and stretched part 3 is housed in a reinforcing case 4 made of metal, glass, etc., and a portion 5 near the fused and stretched part 3 (a portion with a normal clad diameter) is reinforced with a bone cement 6. It is fixed inside the case 4. Here, as the bone fixing agent 6, one having a refractive index lower than that of the cladding 2 is used, and for example, one made of a silicone resin or a resin containing fluorine molecules is preferably used.

According to such an optical fiber coupler, since the fused extension part 3 is fixed to the reinforcing case 4 using the adhesive 6 having a lower refractive index than the cladding 2, leakage of the cladding mode at the bone attachment site is prevented. be done.

In addition, when fixing the melt-stretched part 3 to the reinforcing case, the stretched part 7, which has been stretched to a small diameter, may be bonded as shown in FIG. It becomes possible to shorten the length of the reinforcing case (the length in the axial direction of the optical fiber 1), and the overall size of the optical fiber coupler can be reduced.

In addition, in the above embodiment, a pair of optical fibers! ,
Although a 2×2 type optical fiber coupler formed by fusing and drawing 1 is shown, the present invention is not limited thereto, and an nXn type optical fiber coupler may be made using three or more optical fibers.

(Experimental Example) Hereinafter, the optical fiber coupler of the present invention will be specifically explained with reference to Examples.

A core doped with germanium is used as an optical fiber l.
A pair of single mode optical fibers were fused and stretched (1 ml) to form a fused and stretched portion.

This fused and stretched part? The specimen was housed in a +It strong case, and the vicinity of the fused and stretched portion was fixed to the inner surface of the case using two types of bone cement, hard and soft, with a refractive index lower than that of the cladding.

Five of each of the two types of optical fiber couplers were produced in this way, and the increase in loss, ie, excess loss, caused by bonding each with bone cement was measured, and the average values are shown in Table 1.

In addition, the fused and stretched parts were formed in the same way as above, and two types of adhesives, hard and soft, with a higher refractive index than the cladding were used to fix the fused and stretched parts to the reinforcing case, and the conventional optical fiber capacitors were fixed to the reinforcing case. Five pieces were prepared, and the excess loss was measured, and the average value is shown in Table 1.

Table 1: EPO-TEK328 (product name), J:,
HiEI'0-TEK353ND (trade name) is an adhesive manufactured by Eboxy Technorono (USA), and X-38-089 (trade name) and 0F-20 (trade name) are adhesives manufactured by Shin-Etsu Chemical Co., Ltd.

Moreover, nd in the table indicates the refractive index.

The results shown in Table 1 confirm that the product of the present invention, which uses an adhesive with a lower refractive index than the cladding, has sufficiently lower excess loss than the conventional product, regardless of the hardness (hardness or softness) of the adhesive. It was done.

``Effects of the Invention'' As explained below, the optical fiber vacabra of this invention has
Since the fused and stretched part is fixed to the reinforcing case using a bone cement with a refractive index lower than that of the cladding, it is possible to prevent the leakage of Talarado mode at the bone attachment point, thereby reducing excessive loss. Be able to improve the transmission characteristics.

In addition, since leakage of the Talarado mode is prevented, the stretched and reduced diameter part of the melt-stretched part may be bonded to the reinforcing case, and in that case, the length of the 'PIli strong case can be shortened. As a result, the entire optical fiber converter can be made smaller.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams related to the present invention, and both are schematic configuration diagrams of an optical fiber coupler. l... Optical fiber, 2... Clad,
3... Melting and stretching portion, 4... Reinforcing case, 6... Adhesive.

Claims (1)

[Claims] Two or more optical fibers having partially removed coating materials are arranged in parallel, the exposed claddings of these optical fibers are fused to each other, and the fused portion is further stretched to form a fused and stretched portion. The fused and stretched optical fiber coupler is characterized in that the fused and stretched portion is housed in a reinforcing case, and fixed to the reinforcing case using an adhesive having a lower refractive index than the cladding of the optical fiber. Optical fiber coupler.