JPH03154012A - Manufacturing method of optical fiber coupler - Google Patents

Abstract

PURPOSE:To obtain the optical coupler in which the wavelength dependency of a branching ratio is small in a wider area by using optical fibers whose outside diameter is 125 - 400mum, and also, whose outside diameters are different from each other, an optical fibers to be welded. CONSTITUTION:At the time of forming an optical coupler by welding and drawing two pieces of optical fiber glass 1, 2, fibers which have outside diameters d1, d2 (d1>d2) of different sizes, and also, whose outside diameters are 125 - 400mum are used. In order to make the wavelength dependency of a branching ratio small, it is better to use the fiber whose outside diameter is large, but when it exceeds 400mum, flexibility of the optical fiber decreases, and its handling is made difficult, therefore, the upper limit comes to 400mum. Also, as the outside diameter difference, a difference of 5 - 20mum is provided. As a result, the coupler in which the wavelength dependency of a branching ratio is small can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing an optical fiber type coverlet used in the fields of optical communication, measurement, etc.

(Prior Art) In constructing an optical communication system, an optical data link network, etc., an optical branching device that distributes optical signals emitted from a light source at a desired ratio is an important component. One type of optical splitter is an optical fiber coupler, which usually consists of twisting multiple optical fibers together or fusing them in parallel, then heating and melting them using a heat source such as an acetylene burner. A tapered portion is formed by stretching this under constant tension.

Most optical fibers used in normal optical communications have an outer diameter of 125 μm, and the above-mentioned optical fiber coupler is also manufactured using this 125 μm optical fiber. Manufacturing an optical fiber coupler by combining this 125 μm optical fiber and a single mode optical fiber with a smaller outer diameter was proposed at the 1989 Institute of Electronics, Communication and Information Engineers Autumn Conference, presented by Mr. Juuchi, Mr. Hanabusa, and Mr. Noda, C-207r. "Broadband Optical Fiber Coupler". Although the branching ratio of this optical fiber coupler is approximately constant with respect to wavelength, as shown in FIG. 4, the branching ratio exhibits wavelength dependence over a wide band.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for manufacturing an optical fiber coupler in which the branching ratio is not wavelength dependent in a wider band. It is something to do.

(Means for Solving the Problems) The present invention provides a method for manufacturing an optical fiber coupler in which two optical fibers are fused and stretched, and the optical fibers to be fused have an outer diameter of 125 μm or more and 400 μm or less. This is characterized by the use of optical fibers with different outer diameters.

(Function) The present invention allows two optical fibers having different outer diameters to be fused and bonded together.
This is based on the discovery that the wavelength dependence of the branching ratio of an optical fiber coupler obtained by stretching is related to the absolute value of the outer diameter. When two optical fibers with different diameters are used, an optical fiber coupler with a constant branching ratio over a wider band can be obtained.

(Example) FIG. 1 is a schematic diagram of a fused portion of an optical fiber for explaining an example of the manufacturing method of the present invention. In the figure, 1 and 2 are the glass portions of the optical fibers, 3 and 4 are the primary coatings of the respective optical fibers, 5 is the burner, and 6 is the flame.

Parts of the coatings 3 and 4 of the two optical fibers are removed to expose the glass parts 1 and 2, which are gripped by a stretching stage (not shown) and heated by a burner 5 while being pulled with a constant tension to fuse them. , stretch.

The outer diameter of the glass portion of the optical fiber used and the wavelength dependence will be explained. Two optical fibers of d type and d2 (at > da), which have different outer diameters due to drawing, were prepared and combined to produce a prototype optical fiber coupler. Let Po be the manual power of one optical fiber, Pl be its output power, and P2 be the output power of the other optical fiber.

Measure PL and P2 at different wavelengths to determine the wavelength stability ω of the branching ratio. ,,(from the value that minimizes the insertion loss P2-P0, 0
．． The wavelength width increased by 5 dB) was evaluated.

The optical fiber is an optical fiber made of quartz doped with germanium. The target branching ratio is 80%, and the outer diameter difference (dt-d2)/dt is 0.08. The combinations of the outer diameters of the prototypes are shown in Table 1: o 60 μm;
The cutoff wavelength of the 125 μm and 250 μm optical fibers was 1.1 to 1.2 μm, and the MFD (mode field diameter) was 9.5 to 9°9 μm. 55μm, 115μm
The optical fibers of m and 230 μm are respectively 60 μm and 1
The same base material from which 25 μm and 250 μm optical fibers were drawn was used.

In Table 1, Figure 2, the wavelength is plotted on the horizontal axis and the insertion loss is plotted on the vertical axis, and the wavelength dependence is considered. FIG. 3 shows ω versus the outer diameter of the optical fiber. , is the value of .

As is clear from these experimental results, as the outer diameter of the optical fiber increases, ω. It can be seen that the value of , becomes larger and the branching ratio with respect to wavelength becomes more constant. Therefore, it is better to have a larger outer diameter of the optical fiber;
If it exceeds .mu.m, the flexibility of the optical fiber decreases and it becomes extremely difficult to handle, so the upper limit is 400 .mu.m.

(Effects of the Invention) As is clear from the above description, according to the present invention, there is an effect that it is possible to manufacture a single mode optical fiber coupler in which the wavelength dependence of the branching ratio is extremely small.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a fused portion of an optical fiber for explaining an example of the manufacturing method of the present invention, FIGS. 2 and 3 are explanatory diagrams of the characteristics of the optical fiber coupler according to the present invention, and FIG. The figure is an explanatory diagram of the characteristics of a conventional optical fiber coupler. 1.2...Glass part of optical fiber, 3, 4...Coating, 5...Burner, 6...Burner flame.

Claims (1)

[Claims] In a method for manufacturing an optical fiber coupler in which two optical fibers are fused and stretched, as an optical fiber to be fused,
A method for manufacturing an optical fiber coupler, characterized in that optical fibers having an outer diameter of 125 μm or more and 400 μm or less and having different outer diameters are used.