JPS60246239A - Manufacture of polarization stabilized optical fiber - Google Patents

Abstract

PURPOSE:To obtain the titled optical fiber having excellent transmission characteristics, in high reproducibility, by grinding a specific V-shaped groove to a clad, putting a stress-imparting glass rod into the groove, inserting the assembly in a quartz tube, collapsing and integrating by heating, and drawing the product. CONSTITUTION:The glass rod 1 is made of the core 2 having high refractive index and the clad having lower refractive index than the core and placed at the outer circumference of the core. A pair of V-shaped grooves are formed to the clad by grinding at the opposite positions around the core. The opening angle theta of the groove against the core 2 is 90 deg.<theta<150 deg., and the ratio of d/a is 1.5<d/ a<5 wherein (d) is the distance between the center of the core 2 and the apex of the opening angle theta and (a) is radius of the core 2. A glass rod 3 for imparting thermal stress and having higher thermal expansion coefficient than the clad is fixed in the groove, and the whole assembly is inserted into the quartz tube 4 to form the preform (c). The preform is collapsed and integrated by heating and drawn to obtain the titled optical fiber (d).

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an original fiber, and more particularly to a method for manufacturing a polarization constant optical fiber that maintains the polarization state of signal light propagating within the original fiber. Polarization-controlled optical fibers are expected to be applied to sensors such as gyroscopes, and to coherent communications, which are ultra-high-capacity communications.

BACKGROUND OF THE INVENTION A conventional method of manufacturing this kind of polarized optical fiber f is to form a glass thin film layer on one htl of a quartz tube, as described in, for example, Japanese Unexamined Patent Publication No. 15041/1982. After that, when heating the quartz tube to solidify it, the internal pressure of the quartz tube is made negative from atmospheric pressure, and the difference in glass viscosity between the core part and the thermal stress layer is used to make the thermal stress layer 6 as shown in Figure 2V. A method has been adopted in which the core 2 is made into an ellipse and anisotropic stress is generated in the roughly circular core 2.

In FIG. 2, 20 is an optical fiber and 4 is a quartz tube.

(Prior art 1) As another method, for example, Japanese Patent Application Laid-Open No. 57-20565
As described in Publication No. 3, stress applying glass rods 6 having different coefficients of thermal expansion were arranged around the glass rod 1 for the core as shown in FIG. 6 α, and inserted into the stone A tube 4. A method has been proposed in which a polarization-constant optical fiber 60 as shown in 51 kl b K is manufactured by heating, solidifying, and then drawing. In FIG. 6 α, 5 is a quartz iron, 2 in FIG. 6 is a core, and 31 is a thermal stress layer. (Prior Art 2) Problems to be Solved by the Invention In the method according to Prior Art 1, the ellipticity of the core and thermal stress layer is determined by the negative pressure value with respect to the atmospheric pressure during heating, the intermediate ignition temperature, and the temperature before intermediate ignition. Inner and outer diameter of quartz tube.

This is greatly influenced by various factors such as the inner diameter of the core and the dopant composition of the core, and even a slight difference in any of these values results in a large difference in the ellipticity that can be achieved, resulting in a problem of poor reproducibility.

In addition, in the method according to Prior Art 2, it is difficult to arrange the glass rods for applying stress in ideal opposing positions without any "gap" around the glass rod for the core. There is a problem in that the thermal stress layer of the fiber is deviated from the axis of symmetry, resulting in poor reproducibility of polarization holding characteristics.

Means/Function for Solving the Problems The present invention has the following configuration in order to arrange the thermal stress layer around the glass rod for the core with good reproducibility. FIGS. 1A to 1D are diagrams for explaining the main parts of each process of the present invention.

FIG. 1 α shows a sectional view of a glass rod 1 for the core. A V-shaped groove having an opening angle θ with respect to the core 2 is cut and provided on the side surface of the glass rod 1 for the core at a position opposite to each other with the core 2 at the center (FIG. 1b).

Next, a glass rod 5 for applying thermal stress, which has a coefficient of thermal expansion larger than that of quartz, is fixed and disposed so as to be inscribed in and interposed in this double-shaped groove. If the diameters of the glass rods for applying thermal stress are equal, the glass rods can be fixed in line contact at two points within the V-shaped groove and arranged at desired positions. Note that by grinding the outer periphery of the glass rod for the core, it is possible to easily provide a V-shaped groove facing the core with extremely high precision. Glass port for applying thermal stress (6) A glass rod for a core with a rad fixedly disposed within a V-shaped groove is inserted into the quartz tube 4 (FIG. 1C). Thereafter, the quartz tube is heated, centralized and integrated, and drawn to form a fiber (FIG. 1d). 51 is a thermal stress layer, and 10 is the obtained polarization constant optical fiber.

As the thermal stress imparting layer, G-
□! , PgOs, IhOs, Ti1t,
It is desirable to add at least one of AL*Os + C; axOsr 5bzO11, etc. Further, the refractive index of the thermal stress imparting layer is desirably approximately the same as or smaller than the refractive index of silica glass in order to prevent the occurrence of cladding modes within the optical fiber. Therefore, with a dopant that lowers the refractive index, 17 and B20
．． , F and the other dopant mentioned above are desirably present together.

Next, the opening angle θ of the two-shaped groove shown in Fig. 4, the core radius α,
By varying the distance 2d between the apex positions of the V-shaped grooves, polarization-constant optical fibers according to the present invention in which the V-shaped grooves were provided in the glass rod for the core were prepared, and the birefringence (4') properties were measured.

FIG. 5 shows the measurement results of the beat length when d/a was fixed at 4.5 and θ was varied. 90° from the figure θ<15
It can be seen that the range of 0° is the region exhibiting maximum birefringence.

FIG. 6 shows the measurement results when θ was fixed at 120° and the ratio of d/α was varied. From the figure, it can be seen that it is desirable that d/α be 5. However, when d/a < 1.5, a phenomenon was observed in which the transmission loss value rapidly increased. Therefore 1.
It is desirable to manufacture the film in the range of 5<d/α.

Note that the wavelength λ of light in this measurement is 0.85 μm.

Examples Example 1: According to the present invention, a glass base material for a single-mode light beam with a core diameter of 1.5 m'frLφ and a cladding diameter of 1t5 yarn, manufactured by the VAD method, was heated to θ-120°ld/c.
A V-shaped groove L-2 was formed by grinding. In addition, the core part has G-
01 is added, and the refractive index difference between the core and cladding layer is 0.27.
%Met. The V of the glass rod with this two-shaped groove ground.
B20B made with MCVD method in the shape groove: 14m01
%, F:0-2u)L%+GaO@:4mol% A thermally stressed glass rod (outer diameter 6 mmφ) was interposed and fixed, and the tip portion was heat-fused.

Furthermore, the entire body was inserted into a quartz tube with an outer diameter of 'l'1 rran tlr and an inner diameter of 16.5 myinφ, heated to a high temperature with an H2102 flame, solidified, and the integrated glass rod was powdered to determine the transmission loss and polarization characteristics. was evaluated. the result,
Transmission loss is 1.2 d for light with wavelength λ-1, 15 μm
Good characteristics with a B/hmr beat length of 3 mm were obtained.

In addition, seven optical fiber base materials were fabricated using the same method, drawn and made into fibers, and the characteristics were evaluated. As a result, the transmission loss was 1.2 ± 0.2 dB/hrn, and the beat length was 6 ± 0. ，
Extremely high portraiture of 5 mm was confirmed.

Example 2: Core diameter 1.0% produced by MCVD method. A glass base material for a single mode optical fiber I with a diameter of 1 mm and a cladding diameter of 15.5 mm was ground in the same manner as in Example 1, and
°.

A V-shaped groove of d/α-3 was formed. The refractive index difference between the co-f part and the cladding layer was 0.26%. The same glass rod for applying stress as in Example 1 was interposed and fixed in the two-shaped groove, and the outer diameter was 2.
It was inserted into a quartz tube with a diameter of 2 mmφ and an inner diameter of 16 mrrLφ, heated to form a solid body in the same process as in Example 1, and then wire-drawn. For the obtained polarization-controlled optical fiber, the wavelength λ−
As a result of characteristic evaluation using 1.15 μm light, the transmission loss was 1.
．． Good characteristics of 6 dB/km and a beat length of 5 mm were obtained.

Similarly to Example 1, seven optical fiber base materials were prepared for Example 2, and the fibers were drawn and evaluated. As a result, the transmission loss was 1.6 ± 2 dB/km,
It was confirmed that the beat length was 5±9.5 mm and the reproducibility was good.

Effects of the Invention As detailed above, according to the present invention, it is possible to manufacture polarization-controlled optical fibers with excellent transmission characteristics and high reproducibility, which can be applied to optical sensors and coherent communications for ultra-high capacity communications. It is highly effective in applications such as

[Brief explanation of drawings]

Figures 1 α to d are diagrams illustrating the main parts of the manufacturing process of the present invention, Figure 2 is a conventional example, and Figure 5 α, b + 71 and other examples (7) shows the configuration of a polarization-controlled optical fiber according to a conventional example. Diagram to explain, 4th
The figure is a diagram illustrating a configuration example of a polarization constant optical fiber according to the present invention, and FIGS. 5 and 6 are diagrams showing measurement results of birefringence and transmission characteristics of the polarization constant optical fiber according to the present invention. . 1... Glass rod for core, 2... Core, 6...
・Glass rod for applying thermal stress, 4...Quartz tube, 1o・
...Constant polarization optical fiber, 61...Thermal stress layer, 5...
Quartz rod, 50...Constant polarization optical fiber patent applicant Sumitomo Electric Industries Co., Ltd. Representative Patent Attorney Hisashi Tamamushi Gobu (8) Dan-J-Ryo 6 Soe Muroro

Claims (1)

[Claims] The cladding of the glass rond is composed of a core having a layer with a high refractive index in the center and a cladding having a refractive index lower than the refractive index of the core on the outer periphery of the core, at positions opposite to each other with the core as the center. , the opening angle θ with respect to the core is 90°〈θ〈150
°, and the distance d from the core center to the apex of the opening angle
A V-shaped groove with a ratio of 5 to the radius α of the core is 1.5<d/α, and a stress-applying glass rond having a thermal expansion coefficient higher than that of the cladding is interposed in the V-shaped groove. The entire glass rond with the stress-applying glass rond interposed in the V-shaped groove is inserted into a quartz tube, and the quartz tube containing the glass rond with the stress-applying glass rond interposed in the V-shaped groove is heated. 1. A method for producing a polarization-constant optical fiber, comprising the steps of integrating the fiber into a solid body, and then drawing the fiber.