JPH0243510A - Production of polarization maintaining coupler - Google Patents

Abstract

PURPOSE:To obtain the polarization maintaining coupler which maintains the low deterioration of an extinction ratio, decreases a light loss and has excellent environmental characteristics by partly removing clads and stress imparting parts from the section of respective optical fibers to a half moon shape and adhering the fibers by heating and melting. CONSTITUTION:Two pieces of the polarization maintaining fibers F, F' which are subjected to an etching treatment and are individually produced are so fixed to a fiber holder that the etching surfaces E come into contact with each other and the fibers are paralleled. The etching surfaces E are fully or partly heated and melted by an oxyhydrogen burner, etc., and are adhered to each other to form a coupling part B. The stress imparting parts 4, 4' joined to the two cores exist in the integrated clad. Since the respective fibers are horizontally chipped, the fibers cannot rotate freely with each other at the time of heating and melting and the stress imparting parts 4, 4' exist uniformly on both sides of the core. The clad does not exist between the two stress imparting parts 4, and 4' which are joined. Since the dispersion of the stress directions is obviated in this way, the deterioration of the extinction ratio is obviated and since the excess stress imparting parts do not exist between the cores, the polarization maintaining coupler having the small light loss is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a polarization-maintaining coupler, and in particular, to a method for manufacturing a polarization-maintaining optical fiber that maintains polarization characteristics by manufacturing two polarization-maintaining optical fibers each having a stress-applying portion on both sides of the core within the cladding. The present invention relates to a method for manufacturing a polarization preserving cover, which is characterized in that the polarization preserving cover is bonded by heating and melting the cover while it is being held.

The polarization-maintaining coupler of the present invention is suitably used as an optical component for splitting and combining light in the fields of optical communications and optical sensors.

Polarization maintaining fiber is known as one type of optical fiber. Polarization-maintaining fibers can maintain and transmit linearly polarized light within the fiber, so they are useful as fibers for optical circuits that handle polarized light, and as fibers for coherent optical communications that use the phase and frequency of light as information. As shown in Figure 5, the polarization maintaining fiber F has a stress imparting portion 4 symmetrical by doping boron on both sides of the core 3 within the cladding 2 having a protective coating 1 made of silicone resin or ultraviolet curing resin. It is designed to preserve the polarization in the optical fiber.

Optical components that separate and combine light are needed in the fields of optical communications and optical sensors. Among these optical components, polarization-preserving couplers (splitters), which split light while preserving its polarization state, can eliminate noise caused by changes in polarization, increasing the amount of information transmitted in optical communications, and are useful in sensors. has excellent features such as improving the clarity of optical interference.

It is known that polarization can be preserved as described above using polarizing filters, polarizing prisms, etc., but these measures lead to the complexity of devices, and there will be a demand for higher performance in the future. cannot handle fiber optic devices.

As a method of fabricating a polarization-maintaining coupler from only the polarization-maintaining fiber itself without using a polarization filter or a polarization prism, a polarization-maintaining optical fiber F, as shown in FIG.
A method of manufacturing a polarization-maintaining coupler is known in which the protective coating is removed, two F's are bundled as is, and a joint is formed by melt-stretching. However, in this method, the cross section of the melt-stretch joint B where light is coupled becomes as shown in FIG. Deterioration of extinction ratio occurred.

In addition, the spacing between the cores of the two fibers is 1.
In some cases, the stress imparting portion is located between two cores, which often results in a large optical loss.

Another method for creating a polarization-maintaining double-layer is to embed each polarization-maintaining fiber in a synthetic resin, polishing the sides of the polarization-maintaining fiber together with the synthetic resin, and then placing the two sides facing each other with the synthetic resin so that their polished surfaces touch. Methods of making wave-preserving Kabras are known. However, with this method, the polished surface of the polarization maintaining fiber becomes rough, resulting in increased optical loss. If a matching liquid with a refractive index is used to alleviate this roughness, the environmental temperature characteristics will deteriorate. Furthermore, there were many problems with packaging and fixing methods, such as the optical branching ratio changing even if the relative positions of the two polarization-maintaining fibers changed slightly.

As the practical use of optical fibers and their various applications progresses, polarization-maintaining fibers are becoming more and more popular. There is a need to establish a simple and reliable method for producing a polarization-preserving splitter that has low optical loss, excellent environmental characteristics, and can withstand outdoor use.

Hikari 1p11 As a result of repeated studies, the inventors of the present invention have solved the above-mentioned drawbacks by removing part of the cladding and stress-applying parts so that the cross-section of each optical fiber becomes half-moon-shaped, and then bonding them by heating and melting. The degree of light coupling can be freely adjusted by melting and drawing after heating and fusing.

Based on the above findings, the present invention provides: 1) A method for manufacturing a polarization maintaining coupler by bundling two polarization maintaining optical fibers each having a stress imparting portion on both sides of the core within the cladding. A method for manufacturing a polarization preserving coupler, characterized in that the cladding and a part of the stress-applying part are removed so that the cross section has a half-moon shape, and are bonded by heating and melting, and 2) in item 1), heating the optical fiber. The present invention provides a method for manufacturing a polarization preserving cover which involves melting and adhering and stretching the heated and melted portion in the longitudinal direction.

Methods for producing a half-moon-shaped cross section include: a) etching using an etching solution such as hydrofluoric acid or a mixture of hydrofluoric acid and an etch bit inhibitor; and b) attaching the fiber to a compound that hardens or softens depending on the temperature. It is preferable to adopt a method in which the cross section of the optical fiber is made into a semicircular shape by embedding and polishing, and an optical fiber with a semicircular cross section is obtained by removing the compound, and c) a method in which the optical fiber is polished with a circular grindstone while being stretched on a fiber holder. .

First, a method for manufacturing a polarization-maintaining fogger using an etching method will be described.

The protective coating 1 of the polarization maintaining optical fiber F as shown in FIG. 5 is removed with a razor or the like, and the removed portion is cleaned with a solvent such as acetone. For example, the polarization maintaining fiber F is attached to an optical fiber fixing device 10 as shown in FIG.
I was once criticized. Next, while observing the polarization-maintaining fiber with a microscope, loosen the clamp and position the polarization-maintaining fiber so that the plane passing through the core of the polarization-maintaining fiber and the center of the stress-applying parts on both sides is horizontal. After adjusting the position by rotating around the fiber axis, it is fixed and fixed. This can be easily accomplished, for example, by adjusting the rotation of the fiber so that the two stress-applying parts are in the farthest position under microscope observation with the microscope barrel in a vertical position from above the fiber. .

Thereafter, as shown in FIG. 2, a small amount of an etching solution 15 such as hydrofluoric acid or a mixture of hydrofluoric acid and an etch bit inhibitor (for example, ammonium fluoride) is poured onto the etching solution table 14 to increase the surface tension of the etching solution. Use it to form a droplet shape as shown. The polarization-maintaining fiber, which was rotated and fixed after position adjustment, is set there so that approximately the lower half of the fiber is immersed in the etching solution, and the portion immersed in the etching solution is etched. Figure 2 (showing Mako's appearance).

Because the etching liquid is raised in the shape of a water drop, the fiber is etched in a parabolic shape in the longitudinal direction of the polarization maintaining fiber, and when the two etched fibers are later bundled and fused, the etched The cores of the two fibers are closest to each other at the central portion in the longitudinal direction. In addition, polarization maintaining fiber is
Since the two stress applying parts are set horizontally, the etched surface seen in cross section is parallel to the straight line connecting the core and the center of the two stress applying parts.

In order to speed up the etching rate, it is also possible to heat the etching solution to a temperature below the decomposition temperature of the etching solution (approximately 50° C. in the case of the above-mentioned hydrofluoric acid type).

Thereafter, as shown in Figure 1 &, the two individually fabricated etched polarization maintaining fibers F and F' are aligned so that the etched surfaces E are in contact with each other and the fibers are parallel to each other. is fixed to the fiber holder. In addition, 2
If there is a space-time contact between the etched surfaces of the etched polarization-maintaining fibers, the two fibers may be bundled with a thin string on both sides of the etched portion, or they may be bonded with adhesive. good.

In this state, the two etched polarization-maintaining fibers are bonded to each other by heating and melting the entire or part of the etched surfaces with a hydroxide bar or the like to form a joint B. The state is shown in FIG. 1(a).

There is a stress imparting portion of 4.4° that is integrated with the two cores within the integrated cladding.

Since each fiber is cut horizontally, it can freely rotate with respect to each other during heating and melting, so that no positional deviation occurs, so that the stress-applying parts are evenly located on both sides of the core, and the cladding and stress-applying part Since it is joined in the state of almost half,
There is no cladding between the two stress-applying parts being joined. Therefore, since the stress direction is not dispersed, there is no deterioration of the extinction ratio, and since there is no extra stress-applying portion between the cores, it is possible to manufacture a polarization-maintaining coupler with small optical loss.

In addition to the above-mentioned etching method, methods for obtaining a fiber with a half-moon cross section include, for example, 1) embedding the fiber in a compound that hardens or softens depending on the temperature, polishing the fiber to make the cross section into a half-moon shape, and removing the compound; Alternatively, 2) a method in which the optical fiber is stretched on a fiber holder and polished with a circular grindstone to obtain the desired half-moon-shaped fiber can also be adopted.

By the way, an optical fiber demultiplexer based on melt-drawing is known as an optical fiber demultiplexer.

In this method, parts of two optical fibers are heated and stretched in a molten state, so that the two are connected at the stretched portion. Two optical fibers are placed in parallel and in contact, and a predetermined width portion is locally heated and thermally fused. Thereafter, the heat-sealed portion is stretched from both sides to form a biconical stretched portion that is thin in the center and has tapered portions on both left and right sides. In the narrowed central portion, the cores of the two optical fibers are spaced closer together than their original spacing within the integrated cladding. The center-to-center distance between the cores and the length of the light coupling portion can be changed depending on the amount of stretching. The principle of the optical fiber demultiplexer is that the stretched portion of the single mode fiber produced by the melt-drawing method has a tapered shape, so the coupling length changes depending on the wavelength, resulting in periodic optical coupling with respect to the wavelength. The reason is that this cycle can be adjusted by taking responsibility. Therefore, also in the present invention, it is preferable to use this method to adjust the degree of bonding.

As shown in FIG. 3, light is input from the light source 20 into one of the polarization maintaining fibers F, and while the output light from both side wave maintaining fibers F and F' is monitored by the detectors 22 and 24, burners, heaters, etc. The joining part C is heated and fused by the heating means 26.
At the same time, the core is thinned by pulling the polarization-maintaining fiber in the longitudinal direction, and heating and stretching are stopped when a predetermined optical output is output to the double-side wave-maintaining fiber.

Since the two polarization-maintaining fibers are integrated by melting the fiber glass, no mutual positional change occurs, and a polarization-maintaining fiber with excellent environmental characteristics can be produced.

1. By etching the sides of the polarization-maintaining fibers, the rotation of each polarization-maintaining fiber is stopped, and there is no stress-applying part between the cores of the polarization-maintaining fibers, and stress is applied in one direction. As a result, a polarization-maintaining coupler with less deterioration of extinction ratio and less optical loss can be obtained.

2. Since the glass of the polarization-maintaining fiber is fused and bonded, there is no mutual positional change between the fibers at the optical coupling part, making it possible to produce a polarization-maintaining fiber with excellent environmental characteristics.

Figure 1 is a cross-sectional view of two polarization-maintaining fibers with a semicircular cross section bundled together.

FIG. 1(a) is a cross-sectional view of the fiber of FIG. 1 after being heat-fused.

FIG. 2 is a schematic front view of an etching apparatus comprising an etching table and an optical fiber fixing device having a clamp for fixing the polarization maintaining fiber in a proper position.

FIG. 3 is an explanatory diagram showing an outline of polarization-maintaining fiber melt-drawing.

FIG. 4 is a cross-sectional view of a polarization-maintaining fiber coupler manufactured by a conventional melt-drawing method.

FIG. 5 is a cross-sectional view of a polarization maintaining fiber.

F, F’: polarization maintaining fiber 1: Protective coating 2.2゛: Cladding 3.3゛: Core 4.4゛: Stress imparting part B: Joint part E: Etched surface 11.12: Clamp 14: Etching table 158 etching liquid 20: Light source 22. 24: Detector 26: Heating means Figure 2 Day Figure 3 Hi Figure 1 Day Φ Figure 1 (a) Tate 4 Figure 5

Claims (1)

[Claims] 1) In a method for manufacturing a polarization maintaining coupler by bundling two polarization maintaining optical fibers having stress imparting parts on both sides of the core in the cladding, each optical fiber has a semicircular cross section. A method of manufacturing a polarization-preserving coupler, which comprises removing a part of the cladding and a stress-applying part and bonding them by heating and melting. 2) The method for manufacturing a polarization maintaining coupler according to claim 1, wherein the optical fiber is bonded by heating and melting, and the heating and melting portion is stretched in the longitudinal direction. 3) A method for manufacturing a polarization maintaining coupler according to claim 1 or 2, wherein an optical fiber having a semicircular cross section is produced by etching using an etching solution. 4) The method for manufacturing a polarization preserving coupler according to claim 3, wherein the etching solution is hydrofluoric acid or a mixed solution of hydrofluoric acid and an etch pit inhibitor. 5) The optical fiber is embedded in a compound that hardens or softens depending on the temperature, the optical fiber is polished to have a semicircular cross section, and the compound is removed to produce an optical fiber with a semicircular cross section.
A method for manufacturing a polarization preserving coupler as described in . 6) A method for manufacturing a polarization maintaining coupler according to claim 1 or 2, wherein an optical fiber having a semicircular cross section is produced by polishing the optical fiber with a circular grindstone while the optical fiber is stretched on a fiber holder.