JPS6214802B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL BACKGROUND OF THE INVENTION The present invention relates to optical fiber couplers, and more particularly to a method of manufacturing a low-loss fused biconical taper optical fiber coupler. Relatively low loss fused biconical taper (FBT…Fused Biconical Taper)
The manufacture of optical fiber couplers has been described in several publications. These documents include, for example,
DC Johnson, BS Kawasaki and KOHill, “Low-loss reflective star coupler for optical fiber distribution systems,” Applied Physics Letters, vol. 35(7), 479–
481 pages, October 1, 1979), EGRawson, AB
Nafarrate's "Star Coupler Using Fused Biconical Tapered Multimode Fiber"
(Electronics Letters Vol. 14 No. 9, April 1978
27), EGRawson, M. D. Bailey, “Bi-tapered star couplers with up to 100 fiber channels,” Electronic Letters, Vol. 15, No. 4,
July 5, 1979). According to these documents, an FBT coupler consists of twisting an arbitrary number N of optical fibers as a group over a certain length L, fusing the optical fibers together using a heat source, and simultaneously stretching the fibers. It is manufactured by forming a biconical taper of N fibers. Both reflective and transmitting star couplers can be fabricated using such methods. Typically, a coupler using an optical fiber system is required to have a uniform power distribution between the output ports of the coupler. Uniform distribution of power has not yet been reported for FBT star couplers with acceptable insertion losses using conventional manufacturing techniques such as those described above. This drawback is believed to be caused by the preferential recombination of light back into the pumped optical fiber of the coupler. The pumped optical fiber, hereafter referred to as the throughput fiber at the output end, always has a higher power level than the optical fiber taken out at any other tap;
This difference between the optical fibers tapped out and the throughput fibers depends on the number N of optical fibers in the coupler. In couplers with more than eight optical fibers, the throughput fiber has significantly more power (usually
50% or more). [Summary of the Invention] The object of the present invention is to overcome the above-mentioned drawbacks by eliminating the preferential recombination effect of throughput fibers and improving the overall uniformity of FBT couplers in two or more factors. An object of the present invention is to provide such an optical coupler. A feature of the present invention is to form a conventional low-loss fused biconical taper optical fiber coupler having N optical fibers, where N is an integer greater than 1;
A method of manufacturing a low-loss fused biconical taper optical fiber coupler includes the step of deforming the cores of N optical fibers in the minimum taper region of the coupler. As can be seen, the inventive technique involves deforming, stirring, and mixing the cores of N optical fibers in the minimum taper region of a conventional coupler, which annihilates the preferential recombination of the throughput fibers and reduces the overall Improve the uniformity of the FBT coupler by a factor of two or more. The above-mentioned and other objects and features of the invention will become more apparent from the following description in conjunction with the accompanying drawings. [Embodiments of the Invention] Before explaining the actual method and showing the experimental results, the terms used will be defined. Throughput factor T[I,J] = optical power loss from input port I to output port I where T[I,J] = +10logP[I,J]/P[J] where: P[I,J ] = port I for input port J
P[J] = Power injected into input port J Uniformity factor U[J] = Ratio of the difference between the maximum and minimum power to the maximum power for a given input port J U[J] = P[I ,J] _nax -P[I,J] _nio /P[I,
J] _nax ×100% The invention described herein uses standard conventional techniques (twisting and tapering) and tapers of conventional tapers to eliminate preferential recombination effects of throughput fibers. The present invention relates to a method for manufacturing an FBT coupler that transforms the area. The table shows the transmission data for a 32 port FBT transmission star combiner using standard conventional techniques for forming an FBT transmission star combiner. The port corresponding to the throughput port for each injected port is circled, indicating that the throughput fiber has clearly more power for either injected port than the fiber that taps out at all other taps. (For example, in the coupler shown here, output port 17 corresponds to input port 1, output port 18 corresponds to input port 2, etc.). Generally, the numbering method adapted here is such that ports i and i+N/2 are the same fiber (i=1, 2, . . . N/2). If port i is an input port, port i+N/2 is a throughput port, and vice versa.
Returning to the table, the uniformity factor U[I, J] for each input port is shown in the second row from the bottom of the table. These numbers range from 43% to 58%;
The highest output port in each case is the throughput port. The table shows the transmission characteristics of the same coupler after the tapered region has been modified by the technique described below according to the invention. As shown in this table, the optical signal level of the throughput port (circled) is reduced to the range of the port that is tapped. The uniformity factor is 24
It ranges from % to 30%. The factor limiting the uniformity factor is no longer the "throughput fiber effect" but other factors including (1) taper symmetry, (2) geometric tolerances of the optical fiber, and (3) errors in the measurement equipment. This is due to factors.

【table】

[Table] It is clear from the table that a coupler with a modified tapered region based on the principles of the present invention retains the desired throughput factor and significantly reduces the uniformity factor, thus narrowing the distribution range of the signal output. It is clear by and. This effect is very desirable from a system standpoint. The actual method will be explained below. As shown in FIG. 1A, N optical fibers 1 are fabricated using conventional techniques. That is, the optical fibers are heated with an oxypropane microtorch 2 or the like to twist and fuse the optical fibers, and at the same time, they are stretched in the direction of arrow F1 to form the minimum tapered region 3 as shown in FIG. 1B. form. In the next step, N optical fibers 1 are twisted and fused together.
The taper applying device (not shown) that performs the necessary tension in the F1 direction to give a taper to is reversed and the minimum taper region 3 is pushed in the F2 direction,
At the same time, this area 3 is heated with a microtorch 2 to deform the cores of the N optical fibers 1, thereby forming small glass spheres 4 as shown in FIG. 1C. Next, the small ball 4 in Figure 1C is the microtorch 2.
is heated by F3, and a tensile force is again applied in the direction of F3 to stretch the optical coupler until the desired optical coupler characteristics are obtained, as shown in FIG. 1D. Although the principles of this invention have been described above with reference to a specific device, such description is made by way of example only and does not limit the technical scope of this invention as set forth in the claims. It's not a thing.

[Brief explanation of the drawing]

FIG. 1 shows the states in successive steps A, B, C, and D in one embodiment of the method for manufacturing an optical coupler of the present invention. 1...Optical fiber, 2...Microtorch, 3...Tapered region, 4...Glass ball.

Claims (1)

Claims: 1. A plurality of optical fibers each having a core and a cladding surrounding the core, the optical fibers having a biconically shaped fused portion having first and second tapered regions; The biconically shaped fused portion has a ball-shaped deformed region between the first and second tapered regions, and the cores of the optical fibers are mixed in this ball-shaped deformed region. A low-loss fused optical fiber coupler with special features. 2, where N is an integer greater than 1, N optical fibers are simultaneously heated and stretched to form a small region of the fused biconical taper of N optical fibers; A small spherical deformed region of glass is formed between two biconically shaped tapered regions by pushing the region from both sides along the axial direction of the optical fiber, and the small spherical deformed region is heated and stretched. A method for manufacturing a low-loss fused optical fiber coupler, characterized in that it has a symmetrical appearance.