JPS61226712A - Optical fiber coupler - Google Patents

Abstract

PURPOSE:To improve reproducibility and also improve mechanical strength by inserting plural optical fibers in a desired arrangement in a glass container which has a lower fusion point than the optical fibers in use, and heating the glass container and drawing the optical fibers and glass container axially almost at the same time. CONSTITUTION:Two optical fibers 1 and 2 are inserted into hollow glass pipes 3 and input port optical fibers 1-1 and 2-1 and output port optical fibers 1-1 and 2-2 are extended as shown by arrows 5-1 and 5-2 and arrayed linearly. The hollow glass pipes 3 are heated by a oxyhydrogen burner 4 and twisted at the same time as shown by the arrows 5-1 and 5-2 to contract and solder the center parts of the hollow glass pipes 3 to the optical fibers, thus forming a shape part 6 which is draw in a biconical tapered shape. The optical fibers 1 and 2 do not contact the flame of the oxyhydrogen burner and the array of the optical fibers never changes owing to the flame. Consequently, a polarization maintaining type single-mode optical fiber coupler which has a large extension ratio, low loss, and superior mechanical strength is manufactured with good reproductivity.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a single mode optical fiber coupler having linear polarization maintaining property, in which both the number of people and the number of output ports are n (n-≧2).
It is a turnip that consists of. This is a coupler suitable for optical fiber gyro systems.

[Background of the invention]

Single mode optical fiber couplers with linear polarization maintaining properties are expected to be applied to optical fiber sensors, optical fiber gyros, coherent optical communications, etc.

Reports on linear polarization-maintaining single-mode optical fiber couplers include 1. For example, [Linear-polarization-maintaining single-mode optical fiber coupler], Masao Kawachi, Institute of Electronics and Communication Engineers, Optical and Quantum Electronics Study Group, OQE 83-81, There are pages 23 to 30. This is shown in Figure 1.First, as shown in Figure 1(a), two optical fibers are arranged in one of the arrangements shown in Figures 2(a) to (c), and then as shown in Figure 1(b). As shown in FIG. 2, SiO2-based glass fine particles are thinly deposited on the side surfaces of the optical fibers arranged in order to aid in the fusion of the optical fibers.

However, the left-hand drawings in Figures 2 (a), (b), and (c) show the cross-sectional arrangement of the two fibers that allow linear polarization maintenance before fusing and stretching, and the right-hand drawings show the arrangement of the cross sections of the two fibers with arrows. , shows the cross-sections of the fused and drawn fibers that maintain linear polarization obtained by fusion and drawing of the two fibers on the left, and the first one.
In Figure (C), the optical fibers are fused in parallel by heating the above arrangement part with an oxygen-propane flame, and
This is a method of obtaining a coupler by stretching in the direction of the arrow as shown in d). This method achieves a large erasure ratio and low insertion characteristics. However, in order to obtain equal distribution characteristics with low insertion loss, the outer diameter of optical fiber is etched,
The diameter is about μmφ.

Therefore, when the optical fiber is stretched while being heated with an oxygen-propane flame, troubles such as unnecessary deformation or burnout of the optical fiber occur due to the flame, and it is difficult to manufacture the optical fiber with good reproducibility. In addition, troubles such as breakage of the fused/stretched portion are likely to occur when measuring the characteristics of the finished coupler or when handling it during transportation, resulting in mechanical strength problems.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polarization-maintaining single mode optical fiber coupler that solves the above-mentioned conventional problems.

In other words, it can be manufactured with good reproducibility, has high mechanical strength,
Another object of the present invention is to provide an optical fiber coupler with less contamination of impurities.

[Summary of the invention]

In the present invention, a plurality of optical fibers are inserted in a desired arrangement into a glass container whose melting point is lower than that of the optical fibers used. The glass container is then heated, and the plurality of optical fibers and the glass container are stretched almost simultaneously in the axial direction to form a glass container having a piconical tabular shape. Since the softening temperature and melting point of the glass container are lower than those of the optical fiber, the arrangement of the plurality of optical fibers is not disturbed during heating and melting, and the glass container can cover the fibers tightly.
The present inventor has experimentally discovered that it can be stretched. Moreover, since the coefficient of thermal expansion of the glass container is larger than that of the optical fiber, it is possible to suppress deterioration in polarization maintaining property due to stretching of the optical fiber.

In other words, when an optical fiber is densely covered with a glass container, stretched in the axial direction, and then cooled, compressive stress is applied to the optical fiber from its outer periphery, which acts to suppress the relaxation of stress characteristics caused by stretching the optical fiber. do. As a result, a linear polarization retention effect can be obtained. Furthermore, since the small-diameter piconic taper portion that couples and distributes light is covered with a glass container, the mechanical strength is reinforced.

Furthermore, handling of the optical fiber coupler becomes easier, and there is no need to worry about breakage. Here, the glass container is a multi-component low softening point glass, such as soda silica glass.

Potassium glass, soda/lime/silica glass, lead glass,
Neutral glass, Pyrex glass.

Borosilicate glass, phosphate glass, barium glass.

Lead alkali glass or the like can be used. Commercially available products include Corning's G-5, G-8, G6, and G.
--71, G-3718N, 705 A J
.

There are products with trade names such as 705A0.702P and 702EJ.

Another aspect of the present invention uses an optical fiber in which a cylindrical tube with markings on the outer periphery of the optical fiber is coated near both ends, and the main axis of the cross section of the optical fiber and the markings are approximately aligned. The goal is to create an optical fiber coupler. That is, an optical fiber coupler is made by arranging a plurality of optical fibers in one of the arrangements shown in FIG. 2 with reference to the markings. Here, the cylindrical tube above is metal.

Tubes made of materials such as glass, ceramics, and polymers can be used.

As described above, since the optical fibers can be stretched while maintaining the desired arrangement, it is possible to realize a polarization-maintaining single-mode optical fiber coupler without deterioration of the extinction ratio.

[Embodiments of the invention]

Figure 3 shows the manufacturing method and configuration diagram of the polarization-maintaining single-mode optical fiber coupler of the present invention. The optical fiber (silica glass fiber) used in the figure is called the PANDA type. This is an example in which the components are arranged as shown in Fig. 2(b).
), the optical fiber may be arranged as shown in
In addition to the NDA type, polarization-maintaining optical fibers called elliptical clad type, elliptical core type, etc. may also be used. In FIG. 3(a), 3 is a hollow glass having a melting point lower than that of the optical fibers 1 and 2 (in this case, a Pyrex glass tube was used), and 4 is a heating source (for example, an oxyhydrogen gas burner). , an oxy-propane gas burner, an electric furnace, a high-frequency heating source, a discharge device, etc. can be used, but in this case, an oxy-hydrogen burner was used.) First, two optical fibers 1 are placed in a hollow glass tube 3. ,2 is inserted. Next, input port optical fiber 1-1.2-1.
Arrange the optical fibers of the output port optical fibers 1-1 and 2-2 as shown in Figure 2 (b), pull them in the directions of arrows 5-1 and 5-2, and arrange them in a straight line. While heating the tube 3 with the oxyhydrogen burner 4, move the arrow 5-1.5-
By applying tension in two directions, the central part of the hollow glass tube 3 is contracted and fused to the optical fiber, as shown in FIG.
In addition, the shaped portion 6 is formed into a piconic tapered shape. In such a configuration, since the optical fibers 1 and 2 do not come into direct contact with the flame of the oxyhydrogen burner, the arrangement of the optical fibers does not change due to the flame.

In addition, since the hollow glass tube 3 has a lower melting point, it coats the optical fiber quickly, so the optical fiber arrangement is less likely to change when heated. The outer diameters of the optical fibers 1 and 2 may be reduced by etching in order to realize equal distribution characteristics with low insertion loss. , 2 may be interposed with fine powder or glass particles having a refractive index equal to or lower than the refractive index of the cladding portions 2 and 2.

FIGS. 4(a) to 4(f) show examples of glass containers used in the polarization-maintaining single-mode optical fiber coupler of the present invention.
Figure (a) shows a tapered hollow glass tube, and by making the inner diameter of the tube near the center slightly larger than the outer diameter of the optical fiber bundle to be inserted, the disorder of the optical fiber arrangement during heating is minimized. The structure is designed to eliminate this problem. In the same figure (b), a 68 is provided in the center of a hollow glass tube. This 68 is for promoting fusion and stretching of the optical fiber bundle within the hollow glass tube 3. That is, a part of the flame of the oxyhydrogen burner comes into direct contact with the optical fiber bundle. In addition.

Even if part of the flame of the oxyhydrogen burner directly contacts the optical fiber bundle, the arrangement will hardly be disturbed because the entire east part of the optical fibers is covered with the glass tube 3.

The figure (Q) shows a rectangular glass container, and the figure (d) shows a case in which the central part of the figure (Q) is tapered. Figure (e) shows a U-shaped glass container.

The containers shown in FIG. FIG. 6(f) shows a glass container with a structure close to an ellipse, which is also suitable for arranging optical fibers. In addition, the same figure (a), (c) - (
In the case of f), a 68 may also be provided as shown in FIG. 6(b).

FIG. S shows a schematic diagram of an optical fiber with a cylindrical tube used in the polarization-maintaining single mode optical fiber coupler of the present invention. (a) is a front view, (b) is a left side view, (C
) is a right side view. Reference numeral 1 denotes a polarization-maintaining single mode optical fiber, which may be an optical fiber made only of glass or an optical fiber partially coated with a polymer.

In the case of optical fibers coated with this polymer,
The optical fiber section 11 inserted into the hollow glass tube 3 and heated must be an optical fiber strand made only of glass, and the outer diameter of this section 11 has been reduced by etching as described above. In FIG. 5, 9-1 and 9-2 are cylindrical tubes with markings 10. This marking 10 and the main axis of the cross section of the optical fiber are approximately aligned. This cylindrical tube 9-1.9-2 is metal.

A tube made of glass, ceramics, or a polymer material such as nylon, vinyl chloride, silicone, or fluororesin, or a heat-shrinkable tube is used. The marking 10 is, for example, a V groove.

It may be a U-groove, a convex portion, etc., or a line drawn with a writing utensil, or even a marker attached. The positioning of this marker and the main axis of the cross section of the optical fiber is done by microscopic observation of the cross section of the optical fiber.6 Cylindrical tube 9-
1.9-2 is not limited to the vicinity of both end faces of the optical fiber, and may be located at any location other than the 11 portion.

FIG. 6 shows an embodiment of a manufacturing method for manufacturing a polarization-maintaining single mode optical fiber coupler using the two optical fibers with cylindrical tubes shown in FIG. Figure (a) is a front view, (
b) is a left side view. The markings on the cylindrical tubes 9-1 and 9-3 are aligned, and then the markings on the cylindrical tubes 9-2 and 9-4 are aligned so that each optical fiber is not twisted. These optical fibers are then inserted into the hollow glass tube 3, and the optical fiber coupler shown in FIG. 7 is produced in the same manner as in the case shown in FIG.

FIG. 8 shows another embodiment of the polarization-maintaining single mode optical fiber coupler of the present invention. The optical fiber used is an elliptical clad polarization-maintaining optical fiber. 12-1.12-
2 is a hollow glass tube that is connected together or is a separate hollow glass tube.

Furthermore, a metal tube, a ceramic tube, a polymer tube (for example, a heat-shrinkable tube made of a material such as silicone or fluorine) may be used.

The present invention is not limited to the above embodiments. For example, the number of glass containers is 2! Containers larger than J may be grooved, and glass containers, metals, and ceramics.

It may also be combined with a container made of high molecular weight polymer or the like. Three or more optical fibers may be inserted into the glass container.
In addition to the polarization-maintaining single mode optical fiber described above, an ordinary single mode optical fiber or a multimode optical fiber may be used as the optical fiber, and an optical fiber coupler may be used. In the method shown in Fig. 3, the optical fiber bundle is twisted in advance before heating, and then, at the same time as heating, while further twisting,
If stretching is applied in two directions, insertion loss can be lowered.

It is possible to make a distribution optical coupler. 9-1 again
9-4 may have a rectangular outer shape or a triangular shape other than a cylindrical tube.

〔Effect of the invention〕

According to the present invention, the extinction ratio is large and the loss is low.

A polarization-maintaining single-mode optical fiber coupler with excellent mechanical strength can be manufactured with good reproducibility. As a result, significant cost reductions can be achieved.

[Brief explanation of drawings]

Figure 1 shows a conventional method for manufacturing a linear polarization-maintaining single mode optical fiber coupler, Figure 2 shows a conventional optical fiber arrangement that allows direct ms wave maintenance, and Figure 3 shows a polarization-maintaining single mode optical fiber coupler according to the present invention. An example of the manufacturing method and a block diagram of a mode optical fiber coupler, FIG. 4 is an example of a glass container used in the polarization-maintaining single-mode optical fiber coupler of the present invention, and FIG. 5 is a polarization-maintaining type of the present invention. A schematic diagram of an optical fiber with a cylindrical tube used in a single-mode optical fiber coupler, FIG. 6 shows a method for manufacturing a polarization-maintaining single-mode optical fiber coupler of the present invention, and FIGS. 7 and 8 show a method of manufacturing a polarization-maintaining single-mode optical fiber coupler of the present invention. This is an example of a wave-maintaining single mode optical fiber coupler. l l, l-2, 2-1, 2-2, 1... optical fiber, 3... hollow glass tube, 4... heating source, 5-1.
5-2... Arrow indicating the stretching direction, 6... Piconical taper part, 7... Taper part, 8... Hole, 9-l,
9-4...Cylindrical tube, 10...Indication, 11.・、
C length of optical fiber) <b)

Claims (1)

[Claims] 1. An optical fiber bundle consisting of a plurality of optical fibers is inserted into a glass container whose melting point is lower than the melting point of the optical fibers, and by heating the glass container and stretching the optical fiber bundle in the axial direction, An optical fiber coupler characterized in that the stretched optical fiber bundle is covered with a glass container. 2. The optical fiber coupler according to claim 1, which is obtained by heating a glass container and stretching both the glass container and the optical fiber bundle in the axial direction. 3. An optical fiber coupler according to claim 1 or 2, characterized in that a polarization-maintaining single mode optical fiber is used as the optical fiber. 4. In the optical fiber coupler according to any one of claims 1 to 3, the glass container may include a hollow glass tube, an elliptical glass tube, a rectangular glass container, a U-shaped glass container, or a plurality of glass containers in the shape of a square. An optical fiber coupler characterized by being used in combination with. 5. The optical fiber coupler according to claim 4, characterized in that at least one hole is provided in the heated portion of the glass container. 6. In the optical fiber coupler according to claim 3, the fibers are heated and stretched so that the optical fiber shapes in the cross section of each of the plurality of optical fibers are arranged in either parallel or orthogonal to each other. Optical fiber coupler. 7. In the optical fiber coupler according to claim 6, the vicinity of both ends of the plurality of optical fibers is covered with a container with marks for indicating the main axes in the cross section of the optical fibers,
An optical fiber coupler characterized in that a plurality of optical fibers are arranged based on this marking. 8. An optical fiber coupler according to any one of claims 1 to 7, characterized in that a cylindrical container is inserted between the glass container and the optical fiber bundle.