JPS60103317A - Fiber type polarizer and its manufacture - Google Patents

Abstract

PURPOSE:To realize a fiber type polarizer by an easy method by drawing a desired part of a single-mode optical fiber into a biconical taper shape together with dummy fibers, and sticking a metallic film on the drawn part. CONSTITUTION:Dummy fibers 21 and 22 having no core are arranged is parallel at both sides of the single-mode optical fiber 1 to contact therewith and fixed temporarily on drawing tables 23 (23a and 23b). Then a part of the contact area is heated to fuse the fiber array, and one drawing table 23, e.g. 23b is moved in parallel in a Z direction to form a fused and drawn part 24 in the biconical taper shape. Then the fiber array is moved to a support plate 25 and fixed with an adhesive 26, and a metallic film 27 is vapor-deposited on the fused and drawn part 24 in a +y and a -y direction. Thus, the fiber type polarizer which has a high extinction ratio and small excessive loss is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a fiber polarizer used in the fields of optical fiber sensors and optical communications, and a method for manufacturing the same.

(Background Art) A polarizer is often required when constructing an optical fiber sensor or an optical circuit for optical communication. Using bulk type polarizers such as the Durham-Thomson prism has problems such as the inability to make optical circuits compact, lack of stability against mechanical vibrations, etc., and high cost.Fiber type polarizers have traditionally been used. is recommended.

An example of manufacturing a conventional fiber polarizer is shown in FIG. First, in FIG. 1a), the cladding part 1b of the middle part of the single mode original fiber is removed to the extent that the core part 1a is exposed, and a metal film 4 is deposited on the exposed surface 2 as shown in cross section 3. By doing this, a fiber-type polarizer is obtained. In the cross section 3, the polarized light component perpendicular to the metal film 4 is absorbed by the metal film 4 and disappears, whereas the polarized light component parallel to the metal film 4 passes through the exposed part without being absorbed by the metal film 4, i.e. It showed operation as a polarizer.

However, in this method of manufacturing a fiber polarizer, it is difficult to expose the core portion 1a with high precision. For example, when using a polishing method, if polishing is insufficient, the polarizer effect will be weak, and if polishing is excessive, the core portion 1a will be exposed with high precision. There was a drawback that part 1a was lost. Furthermore, in the first place, it was an extremely difficult operation to polish the single mode optical fiber 1 having an outer diameter of about 125μ7n.

In Figure 1b), two single mode optical fibers 1°1'
In order to reduce the splice loss caused by interposing the Kerr polarizing filter 5, which is intended to obtain a fiber-type polarizer as a whole by interposing and bonding the polarizing filter 5 between the end faces of the polarizing filter 5, the polarizing filter 5 is The thickness must be approximately 50 μm or less, and conversely, such a thin film structure has the problem that a sufficient polarizer function cannot be obtained.

(Problems to be solved by the invention) In order to solve the above-mentioned drawbacks of the conventional art, the present invention stretches a desired portion of a single mode optical fiber together with a dummy fiber into a piconic taper shape, adds metal to the stretched portion, and creates fiber-shaped polarized light. The drawings will be described in detail below.

(Structure and operation of the invention) FIG. 2 is an embodiment of the invention, and shows the manufacturing process of a fiber polarizer. First, a dummy fiber 2 which does not have a core part on both sides of the single mode optical fiber 10], , 2
2 and temporarily fixed on the stretching table 23a, 2.31). Next, a part of the contact area of the single mode optical fiber 1 and the dummy fibers 21 and 220 is heated to fuse these fiber rows, and the drawing table 23I) is moved in parallel in two directions to form a piconical fiber. A tapered fused and stretched portion 24 is formed. Next, the fiber array is transferred to the support plate B, fixed with adhesive 26, and then from the +y direction and the -y direction.
A metal film 27 is deposited on the fused extension portion 24 . FIG. 2d) is an enlarged sectional Tftr view of the fused and stretched portion 24. FIG. In the fused and stretched portion 24, the core diameter is small, so the propagating light spreads and propagates not only in the core portion but also in the crund portion, and reaches the region of the metal film 27. Therefore, in Fig. 2 d), the polarized wave component in the X direction is absorbed by the metal film 27 and disappears.
The structure shown in Figures 2c) and d) serves as a fiber polarizer.

Next, specific examples will be described. The single mode optical fiber used had an outer diameter of 125 μm, a core diameter of 8 μm, and a relative refractive index difference of 03% (the dopant in the core was GeO, and the length was about 1111 nm. The dummy fiber had an outer diameter of 125 μm and a 7 nm diameter).
A pure silica glass fiber having a length of approximately 5 ocIn was used. Arrange these fibers as shown in Figure 2a),
A part of it is heated and fused over about 2 lengths with a mini torch using oxygen/propane gas, and then the drawing table 23b is moved about 7 steps, and the fused and drawn portion 2
4 was formed. The dimensions of the waist part of the fused and stretched part were 201 tm in the X direction, and an Al metal film having a thickness of about 8 μrn in the X direction and 0.5 μnL in each of the y and X directions was deposited to obtain a fiber type polarizer. The characteristics of the fabricated fiber polarizer were transferred to LiNdJ with a wavelength of 1.32μ7n by OI2.
When evaluated using a laser, the extinction ratio, which is an index of polarizer function, was -18 dB, and the excess loss for X-direction polarization was as small as 1 dB.

In the above embodiments, M was used as the metal film, but in addition to this, C r + Au + A. It is also possible to use a metal film such as Ga or 1-1g, and instead of vapor deposition or sputtering, a plating method or a method such as coating a liquid metal such as Ga or 1-1g can be used to apply metal to the fused and stretched part. It is also possible to make it look old-fashioned.

FIG. 3 is a cross-sectional structural diagram showing another embodiment of the present invention, in which a birefringent optical fiber having a stress applying portion is used as a single mode optical fiber.

■ A part of the tapered part is fused and stretched to form an iconic taper structure, and the metal film 27 is placed in the fused and stretched part. The right side of Figure 3 shows the fused and stretched part. It is an enlarged cross-sectional view of a stretched part.The birefringent original fiber 31 is oriented in its main axis direction 3.
3 and the dummy fiber 21 has the property of stably maintaining linearly polarized waves along the orthogonal directions.
.

That is, in FIG. 3a), the linearly polarized wave incident along the principal axis direction 33 of the birefringent optical fiber 31 is absorbed by the metal film 27 at the fused and stretched portion and disappears, whereas the linearly polarized wave incident along the principal axis direction 33 In addition, the linearly polarized wave in the orthogonal direction passes through the fused and stretched portion without being absorbed by the metal film 27, and even if the birefringent optical fiber arm before and after the fused and stretched portion is bent or twisted, it remains straight. There is no concern that the polarization will shift, and there is an advantage that the degree of freedom in configuring an optical circuit incorporating a fiber polarizer is increased.

Figure 3 b) and c) are birefringent optical fibers: 31,
This is a case where a fiber having stress applying parts 32c on both sides of the core part 31a is used, and also the main J (i direction: 3:3
By paying attention to the direction of , it is possible to obtain the same operation as in the case of FIG. 3, 1). - Regarding Fig. 3 1)), a more specific example of production will be described.

The stress-applied birefringent optical fiber used has an outer diameter of 125μ?
71. The core diameter is 8p, nt, and the relative refractive index difference is 03chi,
15 μm apart on both sides of the core, inner diameter: 30/υ
Under a polarizing microscope of No. 71, a dummy fiber was placed between the birefringent optical fibers, immersed in a refractive index matching liquid, and the stress-applying part was looked through, so that the main axis direction was adjusted to the third direction.
They were arranged as shown in Figure 1)). A portion of these fiber arrays was heated with a mini-torch to evaporate the refractive index matching liquid, and at the same time, the core ink was fused and stretched. Finally, the fiber array was transferred to a support plate, and a liquid metal containing Qa and In was applied to the fused and stretched portion to form a fiber-shaped polarizer. X
When the directional polarized wave was incident, it passed through the fusion and stretching part with only a loss of 0.8 dB, whereas the It was revealed that the molecule exhibits an extinction ratio of about -20d13. Moreover, this extinction ratio was stably maintained even when the birefringent optical fiber arm on either the input side or the output side was subjected to normal bending or the like.

In the present invention, it is also possible to increase the number of dummy fibers, and in the example of FIG. 4a), the birefringent optical fiber 310
Two dummy fibers on each side 41°42, /13
, /M is arranged. Furthermore, Fig. 4b) is an example in which dummy fibers 45 and 46 having rectangular cross sections are used, and the examples of Fig. 4a) and b) have higher extinction ratios than those in Fig. 3. (approximately -30 dB).

It is preferable that the dummy fiber has a refractive index equal to or lower than the cladding part of the single mode optical fiber to be used (. Glass fibers with a refractive index substantially lower than that of silica glass can also be used. Dummy fibers are used.
If the dummy fiber has a refractive index part equal to or higher than the core part of the single mode optical fiber, the propagating light will transfer to the dummy fiber at the fusion-stretching part, which is undesirable.

(Effects of the Invention) As described above, according to the present invention, a fiber polarizer having a high extinction ratio and low excess loss can be realized by a simple method, and can be used for optical fiber sensors and coherent optical communications. It is expected that it will be useful in the field of application.

[Brief explanation of the drawing]

Figures (a) and (1)) are examples of manufacturing a conventional fiber polarizer, Figures 2 (a) to (d) are manufacturing process diagrams for the fiber polarizer of the present invention, and Figure 3 ( a) to (C) are diagrams showing examples of fiber polarizer configurations using birefringent optical fibers,
FIGS. 4(a) and 4(I) are diagrams showing another embodiment of the present invention. ■, 1'...Single mode optical fiber, 2...Exposed part,
:3...Cross section, 4...Metal film, 1a...Core part,
Ib cladding part, 5... polarizing filter, 21,
22... Dummy fiber, 23a, 23b... Stretching table, 24... Fusion drawing part, 25... Support plate, 26...
・Adhesive, 27 ・Metal film, 3j ・Birefringent optical fiber, 3+a ・Core part, 32b ・Clad part, : 32c 4 parts, 33 ・Main axis direction, 41
, 42.43. 411 r 45 r lH juice/dummy fiber. Patent Applicant Nippon Telegraph and Telephone Public Corporation Patent Application Agent Megumi Yamamoto - Bottom 40 a)

Claims (3)

[Claims] (1) A single-mode optical fiber, a dummy fiber without a core portion that contacts the single-mode optical fiber in parallel and sandwiches the single-mode optical fiber, and a fused-stretched portion in which the contact portion is fused-stretched into a tapered shape. and a metal film attached to the outer periphery of the fused and stretched portion. (2) The single mode optical fiber is a birefringent optical fiber, and the birefringent optical fibers are aligned and fused and stretched so that the main axis direction is coincident with or perpendicular to the plane formed by the birefringent optical fiber and the dummy fiber. A fiber-type polarizer according to claim (1), characterized in that: (3) A single-mode optical fiber and a dummy fiber without a core are brought into contact with each other in parallel, the contact portions are heated and fused, and the single-mode optical fiber is then sandwiched between the dummy fibers. 1. A method for producing a fiber polarizer, which comprises fusion-stretching the fiber into a tapered shape, and then attaching metal to the fusion-stretching portion.