JPH02207202A - Method for manufacturing polarization-maintaining optical fiber coupler - Google Patents

Abstract

PURPOSE:To obtain excellent polarization maintaining characteristics at high yield by using a polarization maintaining optical fiber which is sectioned rectangularly and has its main axis of birefringence or fiber flank in parallel. CONSTITUTION:The preform for the optical fiber is drawn under constant conditions to obtain a rectangularly sectioned optical fiber 101 and, for example, two fibers 101A and 101B are used. The flanks of the fibers parallel to the main axes alpha and beta of birefringence are arranged in order and matched, the directions of the main axes of birefringence are aligned with each other, and their center parts are heated and fused by a burner 102, and further drawn. Consequently, the need for the complex alignment of the main axes of birefringence of the optical fibers in the fusion splicing and drawing stage is eliminated and the high-performance polarization maintaining type optical fiber coupler is easily obtained and manufactured economically at low cost.

Description

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

<Prior art> When using a polarization-maintaining optical fiber, which is a single-mode optical fiber that stably preserves linearly polarized waves along its principal axis, the optical circuit components connected to the fiber must also have direct polarization-maintaining properties. required.

Among these, polarization-maintaining optical fiber couplers are particularly important optical circuit components. This conventional polarization-maintaining optical fiber coupler is shown in FIG. Prepare polarization-maintaining optical fibers 13 and 14 from which the coating has been removed and which has a stress applying part 12 in the cladding part 11b around the core part 11a (two in FIG. 8) with a refractive index lower than that of the cladding part 11b. (8th
Figure (see al.). Next, these two polarization-maintaining optical fibers 13 and 14 are placed on the support stand 15, and each polarization-maintaining optical fiber 13 and 14 is rotated to form the stress applying section 12.
The birefringent principal axes α and β of the fiber determined by
(See Figure 8(b)). The polarization-maintaining optical fibers 13 and 14 whose principal axes of birefringence a and ρ coincide with each other are connected to the burner 1.
6, the support base 15 is heated in the axial direction (Fig. 8 (C)
), the two polarization-maintaining optical fibers 13 and 14 are fused and drawn, and then the ends of the fibers are split to obtain a polarization-maintaining optical fiber coupler. In the polarization-maintaining optical fiber coupler thus obtained, as shown in FIG. The light is also split into the other fiber at the same point, and is emitted from the fibers 13 and 14 as linearly polarized light 18 and 19, respectively.

In addition, when rotating the polarization-maintaining optical fiber described above to make the principal axis directions a and β of the polarized waves coincide, as shown in FIG.
The principal axis of birefringence α is determined by the stress applying section 12 using a microscope 22 by immersing the lens in a matching oil 20 and using light from a light source 21 as transmitted illumination.

While observing β, the polarization-maintaining optical fibers 13 and 14 are rotated, respectively, so that the principal axes of birefringence α and β are aligned so that they are parallel to each other.

<Problems to be Solved by the Invention> Generally, in order to obtain a polarization-maintaining optical fiber coupler that has a high ability to maintain the polarization plane of incident light even after splitting the light,
It is necessary to match the principal axes of polarization of the plurality of polarization-maintaining optical fibers used with high precision.

However, in the conventional method for manufacturing polarization-maintaining optical fiber couplers, in order to align a number of fibers whose axial directions of the birefringence principal axes determined by the stress-applying parts are not aligned, the stress-applying parts must be observed under a microscope. This method makes it difficult to arrange multiple ultra-thin diameter optical fibers with high precision, takes a long time, and tends to cause axis misalignment during fusing and stretching. It has become difficult to produce wave-holding properties with high yield.

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks, it is an object of the present invention to provide a method for manufacturing a polarization-maintaining optical fiber coupler with good polarization-maintaining characteristics at a high yield.

<Means for Solving the Problems> The configuration of the first method for manufacturing a polarization-maintaining optical fiber coupler according to the present invention that achieves the above object uses a plurality of polarization-maintaining optical fibers, The multiple polarization-maintaining optical fibers are held together with their principal axes aligned, a portion of them is heated and stretched, and the central portions of the multiple polarization-maintaining optical fibers are fused together with their respective birefringence principal axes aligned.・In a method for manufacturing a stretched polarization-maintaining optical fiber coupler, a polarization-maintaining optical fiber having a rectangular cross section and whose main axis of birefringence is parallel to either side of the fiber is used. The second method for manufacturing a polarization-maintaining optical fiber coupler is characterized in that the central portions of the plurality of polarization-maintaining optical fibers are aligned in the direction of each birefringent principal axis of each optical fiber. In a method for manufacturing a polarization-maintaining optical fiber coupler, which is a polarization-maintaining optical fiber having a rectangular cross-section, either the birefringent principal axis or the side surface of the fiber is Using polarization-maintaining optical fibers with parallel polarization-maintaining optical fibers, a part of the axial direction of multiple wave-maintaining optical fibers is placed in a sleeve and fitted, so that these polarization-maintaining optical fibers are aligned in the direction of the principal axis of birefringence. The fitting holding portion is stretched.

<Example> A specific example of the method of the present invention will be described below with reference to the drawings.

The optical fiber preform used in this example is manufactured, for example, by the following method.

First, SiO is obtained, for example, by a hydrolysis method which is a known technique. By heating and making the soot porous base material transparent, a base material with fluorine added to the cladding portion is obtained. Alternatively, the base material is obtained by introducing the s1 halide, which is the starting material of 5102, into plasma and directly converting it into transparent vitrification.

Then, holes are formed along the axial direction using an ultrasonic hole punching material on both sides of the core in the radial direction of the single mode fiber base material manufactured using such known technology, and then stress is applied to the holes. Insert a glass member doped with B2O3 to form a stress-applying part, and further, make the cross-sectional shape rectangular so that the birefringence principal axis of the optical fiber determined by the stress-applying part is parallel to the side surface of the optical fiber base material. This was ground to obtain a base material for a polarization-maintaining optical fiber with a rectangular cross section used in this example.

In order to make a polarization-maintaining optical fiber coupler using the polarization-maintaining optical fiber preform in this embodiment, for example, the optical fiber preform is cotton-pulled under certain conditions as shown in FIG. A plurality of fibers 101 with a rectangular cross-section obtained by the above method, two fibers 10IA and 10IB in this example, are used, and one side of the fibers parallel to the principal axes α and β of birefringence are aligned and aligned. They may be aligned with their principal axes of refraction aligned, their central portions may be heated and fused using a burner 102, and further stretched.

After heating and drawing, it is necessary to separate both ends of the fiber into multiple fibers as necessary (see Figure 2), but this can be done by mechanical means using diamonds and stones or by using an etching solution. This can be achieved by chemical means. Furthermore, considering the strength of the separation fiber, it is possible to perform separation with high precision and high speed using a CO2 laser beam focused to a minute diameter. In this embodiment, a polarization-maintaining optical fiber coupler has been described, but the present invention can be widely applied to manufacturing components in which the cross-sectional directions of fibers are aligned.

In order to easily and accurately align the principal axes of birefringence, a plurality of base materials for polarization-maintaining optical fibers having a rectangular cross section are fused together with their principal axes of birefringence aligned, and then drawn. After that, the obtained fiber is cut and divided appropriately, and the central part of the divided fiber in the length direction is heated and stretched, and both ends of the divided fiber are stretched along the length direction. It may be manufactured by separating it into a plurality of fibers.

In this way, when a polarization-maintaining optical fiber coupler is manufactured by the method of the present invention, it takes less time and effort to align the birefringent principal axes than in the case of using a conventional polarization-maintaining optical fiber with a circular cross section. A high-performance polarization-maintaining optical fiber coupler can be obtained in a short time.

Although this embodiment has been explained using two polarization maintaining optical fibers, it goes without saying that three or more optical fibers can also be used, and in the case of multiple fibers, it takes more effort than before. Never.

Next, an embodiment of the second manufacturing method of the present invention will be described with reference to the drawings.

In this embodiment, the aforementioned polarization-maintaining optical fibers 10IA and 10IB having a rectangular cross section are used, and the same reference numerals are given to the overlapping members, and the explanation thereof will be omitted.

As shown in Fig. 3, the polarization-maintaining optical fibers 10IA, 10] and B, each having a rectangular cross section, are aligned so that their side surfaces are aligned, and the principal axes of birefringence a and β are parallel to each other. .

A sleeve 32 having a concave cross section and an opening 31 is fitted into a part of these optical fibers in the axial direction, and the sleeves 32 are bundled by a cover 33 that closes the upper edge of the opening 31. The optical fibers 10IA and 10IB are fitted and held. In this state, as shown in FIG. 4, the support stand 34 is placed on the left and right support stands 34, and while the sleeve 32, which is the fitting part, is heated with a burner 35, the support stand 34 is moved in the left and right direction in FIG. Move each polarization-maintaining optical fiber l0
I.A.

101B and the sleeve 32 are heated and stretched while being integrated, and then the respective ends of the polarization maintaining optical fibers 101A and 10IB are divided to obtain a polarization maintaining optical fiber coupler.

FIG. 5 shows the sleeve 32 according to this embodiment as described above.
and an optical fiber 10IA in the lid part 33.

101B is shown in a fitted state.

Here, the sleeve 32 and the optical fiber 10IA.

101B This relationship is shown as follows.

The length of the long side of the cross section of optical fibers 10IA and 10IB is 4
1. The length of the short side is 42. The length of one side of the inside of the sleeve 32 is l! 3. If the length of the other side is 14, li is 2)
'3F'4 has the relationship -11=2x.

Birefringence principal axes α and β of the optical fibers 101A and 10IB
For example, it is a straight line passing through the centers of the two stress applying parts 12, 12, and the main axes α and β are always parallel to the side surfaces of the optical fiber.

Therefore, the optical fiber l in which the straight line passing through the two stress applying parts 12, 12 (principal birefringence axes α, β) and the long side of the cladding 1lbO of the optical fibers 101A, l0IB are parallel.
0IA.

101B, and a polarization maintaining optical fiber 101A having a rectangular cross section is attached to a sleeve 32 having a concave cross section.

By storing 101B, two optical fibers 101A,
It becomes possible to partially align the birefringence principal axes a and β of 10IB, and the complicated alignment work required in the past becomes unnecessary.

Incidentally, when combining a plurality of optical fibers, it is possible to make the length of the sleeve 32 14 longer according to the number of optical fibers.

Furthermore, the side surfaces in the longitudinal direction of the optical fibers 10IA and 10IB and the main birefringent axes α and β, which are composed of the stress applying parts 12 and 12, are shaved parallel to each other (this is done at the stage of manufacturing the fiber base material, so it is possible to achieve high precision). It becomes easier to perform axis alignment, and therefore the properties of the connector are also improved.

In this example, the polarization-maintaining optical fiber with a rectangular cross-section was made by polishing and grinding the base material so that the principal axis of birefringence was parallel to the side surfaces, and was drawn at a certain temperature. The method is not limited to this.

Test example Next, test examples showing the effects of the present invention will be explained.

Core layer 1- with GeO added to the center by VAD method
1. A porous preform having a cladding layer made of 8102 soot on the outside was heated and integrated to obtain a preform for a single mode optical fiber.

This optical fiber base material (outer diameter: 19 mm, length: 250 mm)
) using an ultrasonic drilling machine to drill 5 m on both sides of the core in the radial direction.
A hole of mφ was formed. Next, the inside of this hole is mechanically polished,
Smoothed by vapor phase etching. After that, a BO-doped SiO glass rod (Sin2 glass) with an outer diameter of 7.5 mm was prepared by the vapor phase filling method, and the refractive index difference Δ-=0.60
%) was inserted into the hole.

Using a drawing machine, the composite optical fiber base material is
While heating and integrating, the outer diameter is 125μmφ x 70μmφ
A polarization-maintaining optical fiber with a rectangular cross section was obtained.

This optical fiber was cut and divided into 200 mm lengths and coated with 40 mm.
was removed. Next, the two optical fibers 201A are inserted into the opening 41 of the sleeve 42 having a concave cross section as shown in FIG.
, 201B was inserted, and the upper edge of the opening 41 was closed with the lid 43 to hold the optical fibers 201A and 201B (sixth
(See figure (a)). In this state, the sleeve 42 is
6, 46, and the light from the monitor M was incident only on the end of the optical fiber 201A (the left end in the figure). On the other hand, an optical power meter PApP8 was connected to the other ends of the two optical fibers 201A and 201B (right end in the figure).

Next, the sleeve 42 portion is heated with the H2102 micro burner 47, and the sleeve 42. The lid part 43 and the two optical fibers 201A and 201B were drawn while being heated and integrated (the drawing tension during this drawing was 50 g or more).

During this hot rolling fl, an optical power meter PA is used.

The output of the two optical fibers 201A, 201B is constantly monitored by P, and the output of the two optical fibers 201A, 201B is
Stretching was stopped when the outputs of 201B became equal.

When we prototyped 5 connectors and evaluated their characteristics, the average loss was 0.12 dB, and the average crosstalk was -29 dB for the ■→■ route.

Regarding the path from ■ to ■, good characteristics with an average of -30 dB were obtained with good reproducibility.

<Effects of the Invention> As explained above, according to the method of the present invention, there is no need for complicated alignment of the principal birefringence axes of optical fibers during the fusing and drawing stages, so that high-performance polarization-maintaining optical fibers can be produced. The fiber connector can be easily obtained and economically manufactured at low cost.

[Brief explanation of the drawing]

FIGS. 1 and 2 are schematic views of an embodiment of the first manufacturing method of the present invention, and FIGS. 3 to 5 are schematic diagrams of an embodiment of the second manufacturing method of the present invention. The schematic drawings, FIGS. 6 to 7, are the schematic drawings and FIGS. 8 to 10 related to one test example, respectively.
Each figure is a schematic diagram of a conventional example. In the drawing, 101A, 10IB, 201A, and 201B are polarization-maintaining optical fibers, α and β are birefringent principal axes, 32.42 is a sleeve, 33.43 is a lid, and 102.47 is a burner.

Claims (1)

[Claims] 1) Using a plurality of polarization-maintaining optical fibers, holding them together with their principal axes of birefringence aligned, and heating and stretching a part of them to form a plurality of polarization-maintaining optical fibers. In a method for manufacturing a polarization-maintaining optical fiber coupler, in which polarization-maintaining optical fibers having a rectangular cross-section 1. A method for manufacturing a polarization-maintaining optical fiber coupler, characterized in that a polarization-maintaining optical fiber is used, the main axis of birefringence being parallel to either side of the fiber. 2) In a method for manufacturing a polarization-maintaining optical fiber coupler in which a plurality of polarization-maintaining optical fibers are mutually fused and stretched with their central portions aligned in the direction of each birefringence principal axis of each optical fiber, Using polarization-maintaining optical fibers having a rectangular cross-section and whose main axis of birefringence is parallel to either side of the fiber, a part of the plurality of polarization-maintaining optical fibers in the axial direction is made into a sleeve. A method for manufacturing a polarization-maintaining optical fiber coupler, which comprises: inserting and fitting the polarization-maintaining optical fibers, holding them aligned in the birefringent principal axis direction, and stretching this fitted holding portion. .