JPS60260442A - Preparation of fixed polarisation fiber - Google Patents

Abstract

PURPOSE:To prepare fixed polarisation fiber capable of obtaining high polarisation maintaining characteristics with high reproducibility by arranging a core glass rod and a stress generating glass rod appropriately in a quartz tube to make the quartz solid and to one body, and then drawing to wire. CONSTITUTION:A core glass rod 13 having a rectangular sectional shape with a core layer 11 having a circular sectional shape in the central part is prepd. by grinding a preform member 10 comprised of a core layer 11 and a clad layer 12. Then, a thermal stress generating glass rod 14 having higher coefft. of thermal expansion than the core glass rod 13 is arranged to the position facing oppositely to each other on both sides of the core layer 11 along a longer side of the rectangular section of the core glass rod 13, and the glass rod is inserted into a quartz tube 15. The inside of the quartz tube 15 is evacuated and solidified and integrated by heating. Obtd. rod is drawn at high temp.; thus, a fixed polarisation fiber 16 comprised of a core 11', clad 12', and a thermal stress generating layer 14' is prepd. Said thermal stress generating layer 14' faces the core 11' with a linear sectional shape 17 forming a structure strong to the shift of the thermal stress generating layer 14' from an axis of symmetry.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to optical fibers, and more particularly to a method for manufacturing a polarization-controlled fiber with good reproducibility that maintains the polarization state of signal light propagating within the optical fiber. It is.

In recent years, polarization-controlled fibers have been considered for application in optical sensors such as gyroscopes, and in coherent communication, which is ultra-high capacity communication, and prompt development is desired.

- Conventional technology Conventionally, as a manufacturing method of this kind of polarization-controlled fiber, as proposed in Japanese Patent Application Laid-Open No. 58-1-5+54-1, a method of manufacturing a glass to form a thermally stressed layer inside a quartz tube has been proposed. When forming a thin film layer and then heating the quartz tube to solidify it, the internal pressure of the quartz tube is made negative from atmospheric pressure, and the core layer is formed using the difference in viscosity between the core layer and the thermal stress layer. A method is used in which anisotropic stress is generated in the core after drawing by creating a difference in ellipticity between the wire and the thermal stress layer. : [Prior art 1]
Further, as another example, for example, Japanese Patent Application Laid-Open No. 57-2053
In Publication No. 33, stress-applying galanuloids 21, 22, and 23, 24 having different thermal expansion coefficients are arranged in opposing positions around a core base material 20 having a circular cross section, as shown in the second issue, and a quartz tube is used. A method is disclosed in which the fibers are inserted into a tube 25, heated to form a solid body, and then heated to a high temperature to be drawn into a fiber. : [Prior Art 2] Problems to be Solved by the Invention In the prior art described above, the ellipticity of the core layer and the thermal stress layer depends on the negative pressure value, the solidification temperature, and the quartz tube before solidification. It is strongly influenced by various factors such as the inner and outer diameters, the inner diameter of the core layer, and even the dopant composition of the core layer, and even if the values of any of these factors differ slightly, the obtained ellipticity will vary greatly. There was a problem that reproducibility was extremely poor.

In addition, in conventional technology 2, if the outer diameters of the four glass rods for applying thermal stress, which are placed opposite to each other around the core base material, are not exactly matched, the core material is solidified and integrated, and then heated at high temperature. In the cross section of the fiber shown in FIG. 3, thermal stress applying layers 31, 32 and 33. '34 causes axis deviation from the respective symmetry axes (x, y), and there is a problem that a polarization constant fiber having high birefringence cannot be manufactured with good reproducibility. Note that Shu is the core layer and A is the cladding layer.

Means for Solving the Problems and Effects The method for manufacturing the polarization constant fiber of the present invention will be explained with reference to factors a to d. Core layer 1 for single mode optical fiber
1 and a cladding layer 12,
For example, it can be created using the VAD method or the internal sealing method, as shown in Figure 1 a).
This preform base material 10'ii.

As shown by the dotted line in FIG.
A galanuloid 13 for the core having ltl- is prepared (FIG. 1b). After the grinding process, in order to smooth the surface of the ground surface, it is effective to perform etching in, for example, an HF solution, followed by fire arrow polishing.

Next, as shown in FIG.
Place it in a position facing each other on both sides.

The glass rod 14 for applying thermal stress is generally produced by a sealing method, but the method is not limited thereto. The glass rod 14 for applying thermal stress has a composition of Dovan which lowers the refractive index B201. F and a dopant that increases the refractive index Ge01 + P tOs r person 12
0a, Gazes, Tro! , SbgOs, etc., containing at least one kind of both dopant. For example, SiOg-BgOs-Ge01. Si
kOx-BgOs-PtOs, 5i02-1hOs-F
-GeOg, S+O*-GeOg-F, SICh-
PtO2-F, JO++-GeOx-PgOs-F
etc. apply.

The core glass rod 13 is inserted into the quartz tube 15 with the thermal stress applying rod 14 arranged thereon. It is also effective to heat-fuse the thermal stress applying rod 14t arranged on the core glass rod 13 before inserting it into the quartz tube 15.

After insertion into the quartz tube 15, it is desirable to reduce the pressure inside the quartz tube 150 to, for example, 300 mm Hg or less. ), heat the solid and integrate it.

The integrated rod is heated to a high temperature in a drawing furnace to produce a constant polarization fiber having the cross section shown in FIG. 1d. In FIG. 1d, there are 16 constant polarization fibers, 11' is the core, 12' is the cladding, and 14' is the thermally stressed layer.

As shown in FIG. 1d, the shape of the thermal stress adding layer 14' is such that the portion 17 facing the core 11' is linear in cross section because the entire plate-shaped core glass rod 13 is used. The structure is strong against deviations from the axis of symmetry of the thermal stress adding layer 14'.

Example Examples of the present invention will be described below.

Example 1: The outer periphery of a single mode optical fiber base material produced by the VAD method was ground to create a core glass rod having a rectangular cross section of 16 mm x 3 mm. 1 in the center.
It has a core layer doped with 2 mm of GeO2. The glass rod for the core of the sample has a refractive index difference △n = 0.2
It was 7chi.

After the grinding process, etching was performed in a 20% HF solution for 4 hours, and then the ground interface was smoothed by flame polishing with B2102 flame.

A 25-inch glass rod for applying thermal stress with an inner diameter of 9.5 mm and an outer diameter of 13 mm and an inner diameter of 9.5 mm, manufactured by the unidirectional CVD method (after being immersed in F bath solution for 48 hours and etched, the outer diameter of the layer was 6 mm). This glass rod for applying thermal stress was divided into two from the center line, and then placed on both sides of the core layer of a glass rod for a core with a rectangular cross section prepared separately, and both ends were attached to the glass rod for a core. They were fused and fixed. During this fusion and fixing, the center of the core layer and the center of the glass rod for applying thermal stress were aligned in a straight line.

With the glass rod for applying thermal stress in place, insert the combined rod together with the glass rod for the core into a quartz tube with an outer diameter of 18 mmφ and an inner diameter of 16.5 mmφ, and set f 45 inside the quartz tube.
The mixture was heated solidly with a Hz/Ch flame under reduced pressure to 0 mm Hy to be integrated. This solidified Rodswo H2102
The surface was smoothed by flame polishing twice at a burner travertine speed of 15 plates/min. The preform rod thus obtained was heated to 2100° C. in a carbon resistance furnace and drawn to have an outer diameter of 125 μmφ to form a fiber.

The polarization characteristics of the obtained fiber are determined by the wavelength of light λ = 1.15μ
When evaluated using m, a good value of birefringence B=3.5XIO was obtained. Transmission loss α is α = 1.3 dB
/ Kn'1 (λ = 1.15 IIm).

- Six preforms were manufactured in the same manner and their polarization characteristics were evaluated. As a result, all preforms had B=3.
It was within the range of 5±0.5×10 −4 and showed excellent reproducibility.

Example 2: A glass rod for a core having a rectangular cross section of 13 mm x 3 mm was prepared by grinding the outer periphery of a single mode optical fiber base material produced by the thickened CvD method.

It has a core layer doped with G60g'(i') with a diameter of 1.0 mm in the center. The glass rod for the core of the sample had a refractive index difference Δn=0.31%.

After the grinding process, etching in an HF solution and flame polishing using Ha102 flame were performed under the same conditions as in Example 1, and then the outer diameter smmφ was prepared on both sides of the core layer in the same manner as in Example 1. A glass rod for applying thermal stress was placed, and both ends were fused and fixed to form a combined rod assembly. This combination rod was inserted into a normal commercially available quartz tube with an outer diameter of 16 mm and an inner diameter of 14 mm, and the inside of the quartz tube was 360 mmH.
While the pressure was reduced to y, the mixture was heated with an 11*10x flame and solidified to integrate. This integrated preform was made into a fiber in the same manner as in Example 1, and its polarization characteristics were evaluated.

The evaluation results are that the wavelength of light λ=1.15, and the birefringence B=
4.2x10 good.

A good value was obtained. The transmission loss α is α=t, sdB/K
m (λ: 1.15 μm). Four preforms were made in the same manner, and the polarization characteristics of the drawn cores were evaluated. As a result, all preforms had a range of B = a, s ± 0.4 x 10-'. We were able to manufacture a polarization-constant fiber gold exhibiting high polarization-maintaining properties with excellent reproducibility.

Effects of the Invention According to the method of the present invention, stress-applying glass rods with a circular cross section are arranged at positions opposite to both (III) of the core layer of a flat glass rod for a core having a rectangular cross section. It is difficult for the symmetrical axial force island of the thermal stress application layer to shift, and high polarization maintaining properties can be obtained with good lid reproducibility.Furthermore, by using a plate-shaped glass rod for the core, the heat distribution facing the p1 core is prevented. Since the stress-applying layer is linear,
Addition of thermal stress.

It has the advantage of having a structure that is resistant to deviations from the symmetry axis of the layers, and is highly effective.

[Brief explanation of the drawing]

1A to 1D are diagrams for explaining the manufacturing method of the polarization constant fiber of the present invention, and FIGS. 2 and 3 are diagrams for explaining the conventional manufacturing method, respectively.010...Preform base material,
11... Core layer, 12. ...Flood layer, 13...
Glass rod for core, 14... Glass rod for applying thermal stress, 15... Quartz tube, 16... Constant polarization fiber,
ll', , core, 12'... cladding, 14', ,
, thermal stress application layer, processing...base material for core, 21-24.
・Glass rod for adding stress, 25...Quartz tube, processing・
...Core layer, 31-34...Thermal stress adding layer, Ah...
cladding layer. Patent Applicant Sumitomo Electric Industries Co., Ltd. Patent Attorney Hisashi Gobe Tamamushi □Figure 1a Figure 2Glass rod for 21, 22, 23, and 24 directions 1 Figure 3

Claims (1)

[Claims] In a method for manufacturing a polarization constant fiber in which a thermal stress layer is provided on the outer periphery of the core, a core galanuloid with a rectangular cross section containing a core layer with a circular cross section in the center is coated along the long side of the rectangular cross section. Stress-applying glass rods having a higher coefficient of thermal expansion than the core galanuloid are arranged at positions opposite to the core layer on both sides, and the core glass rod with the stress-applying glass rod is placed inside the quartz tube. A constant polarization fiber characterized by comprising the steps of: inserting the quartz tube into a quartz tube, heating the interior of the quartz tube to a reduced pressure state, and integrating the quartz tube into a solid body; then heating the quartz tube at a high temperature and drawing it into a fiber. Production method.