JP2603016B2 - Manufacturing method of optical fiber coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber coupler formed by heating and fusing a part of a plurality of polarization maintaining fibers to form an optical fiber coupler by stretching. It relates to a manufacturing method.

[0002]

2. Description of the Related Art A polarization maintaining optical fiber coupler is a device that splits and couples light while maintaining a polarization state between a plurality of optical fibers, and heats a part of the plurality of polarization maintaining optical fibers. It is manufactured by fusing and stretching. The portion where the glass diameter is reduced by fusion and stretching is called a tapered portion, and this portion is stored in a case after stretching.
Fixed.

An important characteristic parameter of a polarization-maintaining optical fiber coupler is crosstalk representing the degree of polarization maintenance. Crosstalk (CT) when X-polarized light enters the optical fiber coupler is: It is expressed by Equation 1. CT = 10 · log (Py / Px) [dB] (Expression 1) In Expression 1, Px is the optical power of the X-polarized light in the emitted light, and Py is the optical power of the Y-polarized light in the emitted light. To represent. The value of the crosstalk is usually a negative value, and the smaller the value, the better the polarization maintaining characteristic.

In order to obtain an optical fiber coupler having good crosstalk, it is necessary to align the polarization main axes of the optical fibers in the same direction when manufacturing the optical fiber coupler.

FIG. 2 is an explanatory view of a conventional method of aligning the polarization main axis directions of a plurality of polarization maintaining optical fibers. In the figure, 21 is a polarization maintaining optical fiber, 22 is a core, 23 is a clad, 24 is a stress applying section, 25 is a microscope, 26 is an illumination light source, and 27 is a rotary clamp. The polarization maintaining optical fiber 21 is cut and only a part is illustrated. Before fusing the two optical fibers 21, the direction of the stress applying unit 24 that determines the polarization main axis direction is confirmed while viewing the transmitted light from the illumination light source 26 with the microscope 25.
The rotation clamp 27 is rotated to rotate the optical fiber 21, and when the polarization main axes of the two optical fibers 21 coincide with each other, the rotation clamp 27 is fixed.

However, in this method, the degree of coincidence of the plurality of optical fibers in the direction of the principal axis of polarization is limited, and it is inevitable that a slight deviation of the principal axis of polarization remains. Furthermore, even if the directions of the principal axes of polarization of the plurality of optical fibers completely match before fusion, when the coupler becomes a coupler due to the twisting of the optical fibers generated in the fusion and drawing steps, the polarization principal axis becomes large. Direction mismatches,
There is a problem that the crosstalk of the coupler is deteriorated.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and it has been found that the polarization main axes of a plurality of optical fibers are incompletely aligned, and the optical fibers are generated during the fusion and drawing steps. It is an object of the present invention to improve the crosstalk of the optical fiber coupler by correcting the inconsistency in the direction of the principal axis of polarization after extending the coupler.

[0008]

According to the first aspect of the present invention, there is provided a method of manufacturing an optical fiber coupler in which a plurality of polarization-maintaining optical fibers are heated, fused and drawn to form a tapered portion. The method is characterized in that the fused and stretched optical fiber coupler is housed and fixed in a protective case or the like in a state in which the tapered portion is intentionally twisted. Item 1 is the invention according to Item 1, characterized in that, when a twist is applied to the tapered portion, the crosstalk of the optical fiber coupler is minimized by the twist.

When the torsion is applied to the tapered portion, the crosstalk of the optical fiber coupler may be monitored, and the torsion of the tapered portion may be adjusted to minimize the crosstalk.

[0010]

In the polarization maintaining optical fiber coupler, the principal axes of polarization are incompletely adjusted at the time of setting the fiber, or the principal axes of polarization are inconsistent due to twisting of the fibers in the fusion and drawing steps. In the conventional method of manufacturing a polarization maintaining optical fiber coupler, the mismatch of the main axes of polarization is neglected, which causes crosstalk degradation of the manufactured optical fiber coupler. Furthermore, since the degree of the mismatch of the polarization main axes changes every time an optical fiber coupler is manufactured, the crosstalk of the optical fiber coupler is not stable.

However, in the manufacturing method according to the present invention, the incomplete alignment of the principal axes of polarization of the set of optical fibers at the time of fusion and the inconsistency of the principal axes of polarization due to the twisting of the optical fibers in the fusion and drawing steps. Even in the case of occurrence, since the mismatch of the main polarization axes is corrected by twisting the tapered portion after the stretching, the deterioration of the crosstalk due to the mismatch of the main polarization axes can be recovered. Furthermore, even if the degree of mismatch of the main polarization axes varies in each manufacture, if this is corrected by the twisting of the tapered portion, the crosstalk after the twisting can be stably obtained.

[0012]

FIG. 1 is an explanatory view of an embodiment of a method for manufacturing an optical fiber according to the present invention. In the figure, 1 is a light source, 2 is a polarizer,
3a is a main line incident side rotary clamp, 3b is a branch line incident side rotary clamp, 3c is a main line output side rotary clamp, 3d is a branch line output side rotary clamp, 4a and 4b are stretching optical fiber clamps, 5 is an analyzer, and 6 is power. A meter, 7 is an optical fiber at the end of the coupler, and 8 is a tapered portion of the coupler. The figure shows a state in which the stretching step has been completed.

After the coupler is stretched, the stretching optical fiber clamps 4a and 4b are removed to allow the optical fiber to freely rotate, and then the rotating clamps 3a to 3d are rotated.
This rotation applies a twist to the tapered portion 8 of the coupler. One optical fiber of the coupler is a main optical fiber, test light is incident on the main optical fiber from the light source 1 via the polarizer 2, and the emitted light is measured by the power meter 6 through the analyzer 5 to calculate the crosstalk CT. I do. The light emitted from the branch optical fiber may be measured. In this manner, by applying a twist to the tapered portion 8, it becomes possible to correct the mismatch in the direction of the main polarization axis caused during the adjustment of the main polarization axis or in the fusion and stretching steps. Crosstalk can be improved. In an improved state,
By accommodating and fixing the tapered portion in the case, a polarization maintaining optical fiber coupler having good crosstalk can be manufactured.

According to the embodiment described above, 0.85 μm
Polarization maintaining optical fiber coupler was manufactured. The used optical fiber is a polarization maintaining optical fiber UV strand having a cutoff wavelength of 0.82 μm. After the two optical fibers are fused and drawn to produce a coupler, in the system shown in FIG. 1, the drawing optical fiber clamps 4a and 4b are opened so that the tapered portion 8 can freely rotate. By rotating the rotary clamps 3a to 3d, the tapered portion 8 was twisted. FIG. 3 shows the measurement results of the crosstalk. From this experimental result, it was confirmed that the crosstalk could be improved by twisting the tapered portion 8.

Further, after the coupler was manufactured, the tapered portion was twisted while monitoring the crosstalk, and the tapered portion was housed and fixed in a case in a state where the crosstalk had an optimum twist angle. With this method, 20 polarization-maintaining optical fiber couplers were manufactured, and for each coupler, the crosstalk before the twist was applied to the tapered portion and after being housed and fixed in the case with the twist was evaluated. The results are summarized in a frequency distribution diagram in FIG. 4. By adding a twist to the tapered portion, the crosstalk is improved, and the variation of the crosstalk for each coupler is reduced. Was confirmed.

It should be noted that the present invention is not limited to the above-described embodiment, and various methods can be employed as long as the tapered portion can be twisted after coupler stretching. Further, an optical fiber coupler having desired crosstalk can be manufactured.

[0017]

As is apparent from the above description, according to the method for manufacturing a polarization maintaining optical fiber coupler according to the present invention,
Reproduces a polarization maintaining optical fiber coupler with good crosstalk because the crosstalk can be improved even if the polarization main axes are not properly aligned or the polarization main axes are mismatched during the fusion and stretching processes. There is an effect that it can be manufactured with good efficiency.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of a method for manufacturing an optical fiber of the present invention.

FIG. 2 is an explanatory diagram of a method of aligning a polarization main axis direction of a polarization maintaining optical fiber.

FIG. 3 is a diagram showing a measurement result of crosstalk due to a twist applied to a tapered portion of a prototype optical fiber coupler.

FIG. 4 is a frequency distribution diagram for evaluating the crosstalk of a prototype optical fiber coupler.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Polarizer 3a, 3b, 3c, 3d Clamp 4a, 4b Stretching optical fiber clamp 5 Analyzer 6 Power meter 7 Optical fiber of coupler terminal 8 Coupler taper part

Claims (2)

(57) [Claims] 1. A method for manufacturing an optical fiber coupler in which a plurality of polarization-maintaining optical fibers are heated to be fused and stretched to form a tapered portion, wherein the fused and stretched optical fiber coupler has a tapered portion. A method for manufacturing an optical fiber coupler, wherein the optical fiber coupler is housed and fixed in a protective case or the like while being intentionally twisted. 2. The method of manufacturing an optical fiber coupler according to claim 1, wherein, when a twist is applied to the tapered portion, crosstalk of the optical fiber coupler is minimized by the twist.