JPH01321411A - Production of fiber type optical coupler - Google Patents

Abstract

PURPOSE:To produce the optical coupler with good polarization maintaining characteristics and a high yield by heating and stretching the longitudinal central part of divided fibers and separating both ends thereof to plural pieces of fibers along the longitudinal direction. CONSTITUTION:Two pieces of glass base materials 14, 15 for straight polarization maintaining optical fibers having stress imparting parts 12, 13 in the clad part 11 are heated and fused by aligning the double refractive main axes thereof and are further heated and drawn by using a drawing chamber 16 to obtain the fiber 17 having a very small sectional area. The fiber is thereafter cut to a desired length and is divided. The central part 18 of the fiber 17 is stretched under heating. The fused parts at both ends of the fiber 17 are then separated to obtain two pieces of the fibers 19, 20. The good polarization maintaining optical fiber type optical coupler is obtd. with the good reproducibility in this way and the economical production of said coupler at the high yield is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application> The present invention relates to a method for manufacturing a fiber-type optical coupler used in optical communications, optical fiber sensors, and the like.

<Conventional technology> When using a direct-S damage-maintaining optical fiber, which is a single-mode optical fiber that stably preserves linearly polarized waves along its principal axis, side waves are also directly transmitted to the optical circuit components connected to the fiber. Retention is required. Among these, fiber-type optical couplers are particularly important optical circuit components, and conventionally a structure shown in FIG. 2 has been proposed. In FIG. 2, the linear polarization maintaining optical fiber has a cladding portion 4b surrounding a core portion 4a.
The two linear polarization maintaining optical fibers 1 .
By stretching, a direct Sat wave optic coupler is produced. The linearly polarized light 8 incident on the fiber 1 is transmitted along the fiber birefringence main axis, is split into the other fiber at the fusion/stretching section, and is emitted from the fibers la and 2a as linearly polarized lights 9 and 1o, respectively.

<Problem to be solved by the invention> In order to maintain good polarization maintaining characteristics of a fiber type optical coupler,
It is necessary to align the fiber birefringence principal axes 6a and 6b in parallel with high precision. This fiber arrangement operation is performed by observing the position of the stress-applying portion under a microscope.

However, with conventional coupler manufacturing methods, it is difficult to arrange multiple ultra-thin diameter optical fibers with high precision, and it is difficult to arrange them with high precision.
Axis misalignment tends to occur during stretching, making it difficult to produce good polarization maintaining properties at a high yield.

Therefore, in view of the above-mentioned drawbacks, the present invention provides a method for manufacturing a fiber type optical coupler with good polarization maintaining characteristics at a high yield.

Means and Effects for Solving the Problems> The present invention, which achieves the above-mentioned objects, uses a glass base material for a plurality of direct-S flaw-maintaining optical fibers having a stress-applying portion in the cladding portion, in which the direction of the principal axis of birefringence is oriented. The fibers are aligned, fused, and drawn to form fibers, and then the obtained fibers are cut and divided, and the central part of the divided fibers in the length direction is heated and stretched, and both ends of the divided fibers are lengthened. The fiber is separated into a plurality of fibers along the longitudinal direction.

As shown in FIG.
．． 13 (preform) (Fig. 1(a)
(see Fig. 1(b)), and then heated and fused using a drawing tower 16 to obtain a fiber 17 with a small cross-sectional area (see Fig. 1(b)). (C)
).

Thereafter, the fiber 17 is cut into desired lengths and divided into parts (FIG. 1(dl)), and then the central portion 18 of the fiber 17 is heated and stretched (FIG. 1(e)).

Then, the fused portions at both ends of the fiber 17 are separated to obtain two fibers 19 and 20.

In this method, the large-diameter preform base material is arranged and heat-fused so that the principal axes of birefringence are aligned, making it possible to achieve highly accurate axis alignment.

The preform base material usually has a diameter of 10IllI11 to 151 m, and it is easy to align the principal axes of birefringence while observing the position of the stress applying portion on the end face of the base material. Furthermore, it is also possible to detect and align the stress applying portion by observing it from the side through a polarizing plate. In any case,
Since positioning can be performed with an accuracy of 1/100 mm or more, it is not necessary to use special equipment to achieve alignment accuracy of 1 degree or less. □Also, in the process of heating and drawing the preform base material and heating and stretching a portion of the obtained fibers, since a plurality of fibers have already been fused together, the process can be easily drawn. Conventionally, a special jig was required to fix the small-diameter fiber in order to prevent axis misalignment, but even with this, axis misalignment still occurred. Since it is formed into a fiber, axis misalignment can be prevented.

In the present invention, after heating and drawing, it is necessary to separate both ends of the fiber into a plurality of fibers, which can be achieved by mechanical means using diamonds and stones or chemical means using etching liquid. be able to. In addition, considering the strength of the separation fiber, CO
□ High-precision and high-speed separation is possible using laser light. In the present invention, a coupler for a direct 1s wave-maintaining optical fiber has been described, but the present invention can be widely applied to manufacturing parts in which the cross-sectional directions of fibers are aligned.

Practical example: While observing the position of the stress applying part on the end face of two linear polarization-maintaining optical fiber preform base materials (diameter: 15 mm x length: 300 mm) using an ITV, align the birefringent principal axes, After the sides of both base materials were brought into contact and fixed, they were heat-fused using an H2102 burner. After that, after connecting a dummy rod for wire to one end of the preform mother i, the wire drawing furnace (drawing temperature 1900℃)
) was drawn to have a major axis of 250 μm and a minor axis of 125 μm (see FIG. 1(C)). The obtained fiber was cut and divided into 200 mm lengths, and the central portion of the fiber was heated and drawn using an H2102 microburner. In this case, the core diameter is 65 μm, the difference in refractive index relative to the core part is +0.38%, the diameter of the stressed arch is 20 μm, and the distance between the center of the stress applying part and the center of the core is 16
It became μm.

Thereafter, CO2 laser light was moving and irradiated onto the side fused portions at 50 mm from both ends of the fiber to separate them. When 10 optical couplers were fabricated using this process, the average insertion loss was 0.
．． 10 dB and an average crosstalk of -29.5 dB, good characteristics were obtained with good reproducibility.

<Effects of the Invention> As explained above, if the manufacturing method according to the present invention is used, there is no need to align or fuse the birefringent main axis of the fiber itself, so it is possible to produce a good polarization-maintaining optical fiber type optical coupler. It becomes possible to manufacture economically with good reproducibility and high yield.

[Brief explanation of the drawing]

FIG. 1 (al to fl is an explanatory diagram of the method of the present invention, and FIG. 2 is an explanatory diagram of the conventional method. In the figure, 11a is a core part, 11 is a cladding part, 12.13 is a stress applying part, 14 .15 is the preform, 16 is the drawing furnace, 17, 19, and 20 are the fibers, and 18 is the central part.

Claims (1)

[Claims] A plurality of glass preforms for linear polarization-maintaining optical fibers having a stress-applying part in the cladding part are fused together with their birefringent principal axes aligned, and then drawn to form a fiber, and then the obtained fiber is cut and divided. A fiber-type optical coupler characterized in that the longitudinal center portion of the split fiber is heated and stretched, and both ends of the split fiber are separated into a plurality of fibers along the length direction. manufacturing method.