JPS63225207A - Method for fixing terminal of polarization plate maintaining optical fiber - Google Patents

Abstract

PURPOSE:To permit fixing of a stress-imparted polarization plane maintaining optical fiber into a ferrule without deteriorating the extinction ratio thereof by inserting the strand part of said fiber into the fine hole of the ferrule in the direction where the direction of the intrinsic compressive stress thereof is orthognoal with the opposite direction of grooves, then curing the adhesive agent in the grooves by heating. CONSTITUTION:The grooves 22 extending respectively in the longitudinal direction are formed in the opposite positions of the inside wall in the fine hole 20 of the ferrule 10 for an optical connector to be inserted with the strand part 18 of the stress-imparted polarization plane maintaining optical fiber and the strand part 18 of the optical fiber is inserted in the direction where the direction of the intrinsic compressive stress thereof is orthogonal with the opposite directions of both the grooves 2. The strand is then fixed by the adhesive agent in the grooves 22. There is no particular limitation for the sectional shape of the grooves 22 formed in the fine hole 20 for insertion of the stand. A thermally curing type adhesive agent consisting of epoxy, etc., is used as the adhesive agent. The fixing of the polarization plane maintaining optical fiber without deteriorating the extinction ratio and without impairing the excellent characteristics thereof is thereby permitted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for fixing the terminal of a polarization-maintaining optical fiber used for optical communications, optical sensors, etc. to a ferrule of an optical connector.

[Conventional technology] Connection between optical fibers or connection between optical fibers and light emitting
An optical connector is used for connection with a light receiving element and the like. This optical connector consists of a ferrule that holds and fixes the end of an optical fiber in a predetermined position with high precision, and an adapter that holds this ferrule.

The ferrule has a structure with a cylindrical hole in the center for inserting and accommodating the jacket part of the optical fiber, and a pore in the tip part for inserting the optical fiber strand, and is made of all stainless steel or alumina ceramic in the pore part. There are ceramic capillary types that use .

In any case, the commonly used method for fixing one end of an optical fiber to a ferrule is to insert the optical fiber element into the pore and fix the gap around the ferrule with an adhesive. As the adhesive, heat-curing epoxy adhesives are often used from the viewpoint of hardness and the like.

[Problem to be solved by the invention] Unlike ordinary optical fibers, stress-added polarization-maintaining optical fibers are forcibly subjected to internal stress, so when lateral pressure is applied from the outside, mode conversion occurs there. There is a problem that the extinction ratio deteriorates.

Therefore, when a heat-curing adhesive is used to fix a conventional optical fiber to a conventionally structured ferrule, the coefficient of thermal expansion of the adhesive and the coefficient of thermal expansion of the optical fiber become 1 when the temperature drops from the curing temperature to room temperature. A difference of ~2 orders of magnitude causes stress to act on the optical fiber, resulting in a disadvantage that the extinction ratio deteriorates.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method that eliminates the drawbacks of the prior art as described above and allows a polarization-maintaining optical fiber to be fixed to a ferrule without deteriorating the extinction ratio.

[Means for Solving the Problems] The present invention, which is capable of achieving the above-mentioned objects, is a method for improving the pore inner wall of an optical connector ferrule into which a strand of a stressed collapsed polarization-maintaining optical fiber is inserted. Grooves extending in the longitudinal direction are formed at opposing positions, and the strand of the optical fiber is inserted in such a direction that its inherent compressive stress direction is orthogonal to the opposing direction of the grooves. This is a method for fixing the terminal of a polarization-maintaining optical fiber configured to be fixed with adhesive.

There is no particular restriction on the cross-sectional shape of the groove formed in the pore for inserting the optical fiber part of the ferrule, and the adhesive used in the present invention is an epoxy-based isothermal curing type as in the past. be able to.

[Operation] The strand of the stressed collapsed polarization-maintaining optical fiber is inserted into the pore of the ferrule in a direction in which its unique compressive stress direction is orthogonal to the direction facing the groove, and the adhesive filled in the groove is applied. The end of the optical fiber can be reliably fixed to the ferrule by curing at a temperature and lowering the temperature to room temperature.

At this time, since the adhesive has a larger coefficient of expansion than the optical fiber, tensile stress is applied to the optical fiber in the opposing direction of both grooves. However, this means that compressive stress acts on the fiber optic fiber in the direction perpendicular to the direction in which the grooves face each other, and since this corresponds to the direction of the inherent internal compressive stress of the optical fiber, in the present invention, the extinction ratio is It will not deteriorate.

[Example] FIG. 1 is an explanatory diagram showing a state before fixing the polarization-maintaining optical fiber according to the present invention to a ferrule. The ferrule 10 has a structure including a large diameter cylindrical hole 16 for inserting and accommodating the jacket portion 14 of the optical fiber 12, and a small hole 20 formed at the center of the tip side for inserting and fixing the optical fiber bare side I8. .

The first point in which the present invention is significantly different from the prior art is that grooves 22 extending in the longitudinal direction are formed at opposing positions on the inner wall of the pore 20 (see FIG. 2).
.

As shown in FIG. 3, the stressed collapsed polarization maintaining optical fiber 12 has a core (light waveguide) 24 at the center of the strand 18.
is located, and stress applying portions 26 are provided on both sides thereof to create a difference in refractive index in the X-axis direction and the Y-axis direction. In this case, as shown by the white arrows, the direction of compressive stress is within the plane that includes the stress applying portions 26 on both sides (the horizontal direction in the figure), and the direction perpendicular thereto (the vertical direction in the figure) is the tensile stress direction. Become.

The second point in which the present invention differs from the prior art is that, as shown in FIG. It is inserted in the direction perpendicular to the groove 22 and fixed with the adhesive 28 placed in the groove 22.

'The adhesive 28 used here is a heat-curable epoxy adhesive with high hardness, as has been used in the past.

The adhesive 28 is heated and cured, and then the temperature is lowered to room temperature. At this time, since the coefficient of thermal expansion of the adhesive 28 is large, the groove 2
The adhesive 28 contracts within the grooves 2, and tensile stress is applied to the optical fiber strand 18 in the opposite direction of both grooves 22. Therefore, compressive stress acts in a direction perpendicular to the opposing direction of both grooves 22, and this direction coincides with the inherent internal compressive stress direction of the optical fiber element 18, so the extinction ratio of the polarization-maintaining optical fiber does not deteriorate. , the good properties are not impaired.

Various methods can be considered for forming grooves in the pores of the ferrule. For example, as shown in FIG.
Alternatively, as shown in FIG. 6, a monolithic ferrule 36 may be molded from the beginning, and grooves 40 may be formed by laser machining or the like on both sides of the inner wall of the pore 38 for inserting the cotton part.
may be formed.

[Effects of the Invention] As described above, the present invention forms grooves extending in the longitudinal direction on both sides of the inner wall of the ferrule into which the optical fiber strand is inserted, so that the unique compressive stress direction of the optical fiber strand is Since this is a method in which the optical fiber is inserted in a direction perpendicular to the facing direction of both grooves and fixed with the adhesive in the groove, a heat-curing adhesive is used, and its large coefficient of thermal expansion makes it possible to connect the optical fiber in the facing direction of the grooves. Even when tensile stress is applied, the direction of compressive stress perpendicular to it matches the direction of the inherent internal stress of the optical fiber element, so the extinction ratio does not deteriorate and the polarization maintaining optical fiber can be ferruled without losing its excellent properties. An effect that can be fixed is produced.

Further, in the present invention, since it is sufficient to insert the adhesive into the groove of the pore, the adhesion work becomes easy, and the positioning of the optical fiber element part can also be easily performed.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the state before fixing the polarization-maintaining optical fiber according to the present invention to a ferrule, FIG. 2 is a front view of the ferrule, FIG. 3 is an end view of the polarization-maintaining optical fiber, and FIG. A front view showing a state in which a polarization maintaining optical fiber is fixed to a ferrule, and FIGS. 5 and 6 are explanatory diagrams showing an example of forming grooves in the pores of the ferrule. DESCRIPTION OF SYMBOLS 10... Ferrule, 12... Polarization preserving optical fiber, 14... Jacket part, 16... Cylindrical hole, 1
8... Strand wire portion, 20... Pore, 22... Groove. Agent Shigeru Mi 1 Figure 1 Figure 3 Tensile stress direction

Claims (1)

[Claims] 1. Form grooves extending in the longitudinal direction at opposing positions on the inner wall of the pore of the optical connector ferrule into which the strand part of the stress-added polarization-maintaining optical fiber is inserted, and A method for fixing an end of a polarization-maintaining optical fiber, comprising inserting the fiber in a direction in which the specific compressive stress direction is perpendicular to the direction in which the two grooves face each other, and fixing the fiber with an adhesive in the groove.