JPH0750213B2 - Broadband optical fiber coupler and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical fiber coupler used for branching an optical signal in an optical communication system or the like, and particularly to a broadband optical fiber having a small wavelength dependence of the optical branching ratio. The present invention relates to a coupler and a manufacturing method thereof.

(Prior Art) In recent years, various optical signal systems have been proposed and put into practical use due to the progress of optical signal transmission technology. Against this background, there is a demand for branching one or more kinds of optical signals propagating through one transmission path into a plurality of propagation paths, or superimposing one or more kinds of optical signals propagating through a plurality of transmission paths. It is increasing rapidly.

One of the parts that performs this function is an optical fiber coupler. The optical fiber coupler has the characteristics of low loss and excellent connectivity with an optical fiber that is a light transmission path. Although several methods of manufacturing an optical fiber coupler have been considered, the method of fusing and stretching has the highest productivity, and a sharp price reduction is expected.

Among optical fiber couplers, the optical branching ratio has little wavelength dependence, is suitable for branching optical signals, and has excellent compatibility with variations in light source wavelengths and with multiple wavelengths. It is an optical fiber coupler.

Broadband fiber optic couplers, as shown in International Application No. PCT / GB86 / 00445, mainly pre-stretch one of the two optical fibers, and then pre-stretch it and a second optical fiber. Although it is necessary to fuse and stretch the fiber, as a method for producing such an optical coupling portion, by a method similar to the method for producing an optical fiber coupler as shown in JP-A-61-113008,
By twisting the two optical fibers several times, the first
Of the optical fiber, the contact portion is fused while the front extending portion of the optical fiber and the second optical fiber are brought into stable contact with each other, and then the fused portion is extended to form the optical coupling portion.

However, in this case, it is necessary to provide a rotation mechanism on the support of the optical fiber, and the manufacturing device is complicated, the manufacturing time is increased, the positional accuracy of the optical fiber is lowered, and the optical loss is increased due to the twist. was there.

(Problems to be Solved by the Invention) The present invention has been made in view of the above circumstances, and a novel broadband optical fiber coupler with less optical excess loss due to variations in positional accuracy of optical fibers, and its efficient ,
And to provide a highly accurate manufacturing method.

(Means for Solving the Problem) The present invention is a method for manufacturing a wide-band optical fiber coupler, in which the first single-mode optical fiber is preliminarily required to have a required length rather than being fused by twisting as in the conventional method. The first single-mode optical fiber and the second single-mode optical fiber are crossed to each other to draw the front extension of the first single-mode optical fiber and the second single-mode optical fiber. By making them adhere to each other and then fusing and stretching the adhered portions, an optical coupling portion is formed and a broadband optical fiber coupler is manufactured.

Conventionally, in order to form an optical coupling portion of an optical fiber coupler by fusion drawing, it is necessary to stably bring two optical fibers into close contact with each other in advance. The method is as follows: (1) FIG. 3 (a) As shown in Japanese Patent Laid-Open No. 60-134208
A method of holding two optical fibers in parallel and closely contacting each other, and (2) as shown in FIG. 3 (b), JP-A-61-113008
There has been a method of twisting two optical fibers such as the above to bring them into close contact with each other.

Since the method (1) does not cause bending of the optical fiber, it is excellent in low loss and is particularly suitable for producing a single mode optical fiber coupler. Further, the method (2) has been applied to the production of a multimode optical fiber, in particular, an optical fiber star coupler by collective fusion, for stable adhesion of a large number of optical fibers.

As an optical fiber contacting method for manufacturing a broadband optical fiber coupler using a single-mode optical fiber, one optical fiber coupler is thinned by pre-stretching.
The method (1) cannot be applied, and the method (2) has been used.

However, when the wideband optical fiber coupler is manufactured by the method (2), there is a drawback that excessive loss is likely to occur due to bending of the optical fiber due to twisting, variation in positional accuracy of the optical fiber, and the like.

Further, when the two optical fibers are crossed and brought into close contact with each other as in the conventional general method of manufacturing an optical fiber coupler that does not perform pre-stretching, the intersection of the two optical fibers is located at a specific place. It is difficult to determine, and it is necessary to control the position of the intersection. However, in the method for manufacturing a broadband optical fiber coupler according to the present invention, when the front extending portion of the first optical fiber and the second optical fiber are crossed, The position of the intersection has the advantage that it is automatically aligned with the reduced-diameter front extension.

(Example) As a method of manufacturing a broadband optical fiber coupler, first, only the first optical fiber was stretched by about 4 mm to prepare a front stretched portion. Next, the front extending portion of the first optical fiber and the second optical fiber were cross-adhered.

FIG. 1 shows a contact portion (intersection portion) when the front extending portion of the first optical fiber and the second optical fiber are brought into close contact with each other by the method of the present invention. Since the position of the intersecting portion is self-controlled by the front extending portion only by intersecting the two optical fibers, it is not necessary to perform special position control. Next, by applying a fixed (for example, about 10 g) tension to one end of the two optical fibers in the lengthwise direction and fixing them, the adhesion at the intersection is stabilized and the bending habit of the optical fibers is corrected. Then, fusion was performed in that state, and stretching was performed while applying a tension of 0.2 to 10 g. Stretching was performed using an LD light source with a wavelength of 1.3 μm, while inputting light from one end of the first optical fiber and monitoring the output from the two optical fibers at the other end, with an optical branching ratio of 50:50.
I adjusted it to be. After stretching, the optical fiber coupling section
It was fixed to the quartz substrate using an ultraviolet curing adhesive.

FIG. 2 shows the measurement result of the wavelength dependence of the optical branching ratio at this time. In the wavelength range of 1.2 to 1.7 μm, almost flat branching characteristics around 50:50 were obtained. In this case, the optical signal loss increase of the optical fiber coupler is about 0.2 at the wavelength of 1.3 μm.
It was dB.

(Effect of the Invention) As described above, when the broadband optical fiber coupler is manufactured by the method of the present invention, it is not necessary to perform fusion splicing of two optical fibers while twisting, and the twisting speed can be controlled. Since it is unnecessary, there are advantages such as an increase in bending transmission loss of the optical fiber due to twisting and a decrease in factors causing an excessive loss of the optical fiber coupler due to variations in the positional accuracy of the optical fiber, and a stable low loss optical fiber coupler. Can be manufactured. Further, the cost of the optical fiber coupler can be expected to be reduced by simplifying the structure of the manufacturing apparatus and the manufacturing process.

[Brief description of drawings]

FIG. 1 is a diagram showing a contact portion of the first embodiment when the front extending portion of the first optical fiber and the second optical fiber are brought into close contact by the method of the present invention, and FIG. 2 is the first embodiment of the present invention. A wavelength characteristic diagram of the branching ratio of the broadband optical fiber coupler manufactured by the method shown in the embodiment, FIG. 3 (a) is an explanatory view of a conventional method of closely adhering two optical fibers in parallel, and FIG. 8] is an explanatory view of a conventional method for applying a twist to bring two optical fibers into close contact with each other. 1 ... Optical fiber, 2 ... Front extension part 3 ... Optical fiber holding part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toichi Noda 1-1-6 Uchiyuki-cho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (56) Reference JP-A-54-6563 (JP, A) JP Sho 62-210409 (JP, A) JP-A-1-161306 (JP, A) Special Table Sho 63-501527 (JP, A)

Claims (2)

[Claims] 1. A first single-mode optical fiber, a part of which is drawn, and a second single-mode optical fiber, which crosses and is in close contact with the drawing part, and the crossing part is fused and drawn. A broadband optical fiber coupler, characterized in that it forms an optical coupling portion. 2. A first single-mode optical fiber is stretched in advance to a required length, and the first single-mode optical fiber and the second single-mode optical fiber are crossed to each other to form the first single-mode optical fiber. An optical coupling part is formed by bringing the front extension part of the one-mode optical fiber into close contact with the second single-mode optical fiber, and then fusing and extending the contact parts of these two single-mode optical fibers. A broadband optical fiber coupler manufacturing method comprising: manufacturing a broadband optical fiber coupler.