JPS6159249B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an optical fiber preform, and more particularly to a method for manufacturing a polarization preserving optical fiber preform.

A polarization-maintaining optical fiber is one in which anisotropic strain is applied to the core, and birefringence generated by the photoelastic effect is utilized. FIG. 1 is a cross-sectional view of a polarization-maintaining optical fiber. The periphery of the core 1 is surrounded by an oval cladding 2, and the periphery of the cladding 2 is surrounded by a jacket 3. Since the area around the core 1 does not have a concentric structure, anisotropic strain occurs, and the amount of strain increases as the difference in coefficient of thermal expansion between the cladding 2 and the jacket 3 increases. The larger the value, the greater the distortion and the better the polarization characteristics.

In the manufacturing method shown in FIG. 1a, a glass film of cladding 2 is applied to the inner wall of a quartz glass tube, and then a core glass film is sequentially formed. Thereafter, the base material is manufactured by fusing under reduced pressure. That is, the base material is manufactured by the MCVD method, but this method has the drawback that it is difficult to manufacture a long polarization-maintaining optical fiber.

FIG. 1b is a cross-sectional view of another polarization-maintaining optical fiber. While accommodating the core 1 in the glass tube,
A pair of clads 2 are installed on the left and right sides. Thereafter, the pressure was reduced and the pieces were heated and integrated. By drawing this, a polarization maintaining optical fiber can be manufactured. However, when manufacturing using this method, cracks tend to occur due to differences in thermal expansion in each process, making the work difficult and reducing production efficiency.

An object of the present invention is to eliminate the drawbacks of the above-mentioned prior art, and to provide a method for manufacturing a polarization-maintaining optical fiber base material that has good polarization characteristics, can be controlled, is easy to manufacture, and is excellent in mass production. Its characteristics are: a process for obtaining a core porous base material; a process for obtaining an elliptical clad porous base material with this core porous base material in the center; and obtaining a transparent glass body using a jacketed cylindrical container.

FIG. 2 is a diagram showing a method for manufacturing a polarization-maintaining optical fiber, which is an embodiment of the present invention. Fig. 2a shows a state in which a core solution 5 containing SiCo(CH ₃ ) ₄ , H ₂ O, and CH ₃ OH mixed in a volume ratio of 1:4:4 is contained in a cylindrical container 4 made of quartz. . In FIG. 2b, the cylindrical container 4 containing the core solution 5 is placed in a dryer 7 and heated at 70° C. for 3 hours to gel.

The porous base material 6 is obtained by further keeping it at the same temperature for 5 days and taking it out from the cylindrical container 4.

Next, ellipticity (major axis - minor axis / major axis + minor axis) x 100
SiCo(CH ₃ ) ₄ and B
( _OCH3 ) ₃ and _H2O and _CH3OH in 1:0.08:4:
A porous base material 6 is placed in the center of the clad solution 8 mixed at a ratio of 4:4. This state is shown in FIG. 2c, the upper part of which is a cross-sectional view of the lower figure. This is heat treated in the same manner as in the previous step to obtain an elliptical clad porous base material 10.

Next, the same mixture as the core solution 5 is placed in a cylindrical container 14, and the elliptical clad porous base material 10 is placed in the center of the container as shown in FIG. 2d, and the jacket solution 11 is filled therein.

Further, a similar heat treatment is performed to obtain a porous base material 13 of a polarization preserving optical fiber.

Figure 2e shows the porous base material 13 of the polarization preserving optical fiber obtained as described above placed in a quartz tube and heated at 1 deg/min in an atmosphere of oxygen gas and chlorine gas from room temperature to 800°C in an electric furnace 12. Dry by raising the temperature at a rate of . Note that in this case, He gas and C ₂ gas may be used.

Fig. 2f shows that the polarization preserving optical fiber base material 13 obtained in Fig. 2e is placed in another electric furnace 16 and heated with He and C.
When the temperature is raised to 1300° C. and sintered for about 2 hours in a mixed gas of ₂ , a transparent glass body, that is, a polarization preserving optical fiber base material 15 is obtained. At this time, the opaque polarization preserving optical fiber base material 13 is manufactured by rotating and pulling it up.

The method for manufacturing the polarization-maintaining optical fiber preform of this embodiment is suitable for mass production as it is possible to manufacture a large number of optical fiber preforms at once. Wave characteristics can be easily controlled. Further, since the dimensions of the final transparent glass body are determined by the size of the cylindrical container 14, effects such as being able to obtain an optical fiber base material of arbitrary dimensions can be obtained.

In the above embodiment, as shown in FIG. 2f,
Although the polarization preserving optical fiber base material 13 is pulled up, it is also possible to lower the electric furnace 16.

Moreover, if the shapes of the elliptical containers 9 are different in ellipticity, base materials with different characteristics can be obtained.
Note that if the elliptical cladding portion is made of glass containing B ₂ O ₃ , it is necessary to provide a layer that does not contain B ₂ O ₃ between the core and the elliptical cladding. This is done in order to eliminate absorption loss of B--O especially when used in a long wavelength band (1.1 μm or more). In addition, colloidal silica of 30 mμ or less is used as the main raw material.

The method for manufacturing a polarization-maintaining optical fiber base material of the present invention has the advantage of easy control of polarization characteristics and excellent mass productivity.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a polarization-maintaining optical fiber;
The figures are cross-sectional views sequentially illustrating a method of manufacturing a polarization-maintaining optical fiber, which is an embodiment of the present invention. 1: core, 2: cladding, 3: jacket,
4, 14: Cylindrical container, 5: Core solution, 6: Porous core member, 7: Dryer, 8: Clad solution, 9:
Oval container, 10: Oval clad porous base material, 1
1: Jacket solution, 12, 16: Electric furnace, 1
3: Polarization preserving optical fiber porous base material, 15: Transparent glass body.

Claims (1)

[Claims] 1 A core solution containing Si(OCH ₃ ) ₄ or Si(OC ₂ H ₅ ) ₄ and one or more dopants for controlling the refractive index is placed in a cylindrical container, and the core solution is hydrolyzed, gelled, and dried to form a core porous material. A clad solution containing a dopant adjusted to have a refractive index lower than that of the core porous base material is placed in an elliptical container, the core porous base material is placed in the center, and gelation is performed. and drying to obtain an elliptical clad porous base material;
A solution prepared by adjusting a dopant to have a refractive index similar to that of the elliptical clad porous base material but with a different composition is placed in a cylindrical jacket container, and the elliptical clad porous base material is positioned at the center of the container. 1. A method for producing a polarization-preserving optical fiber base material, comprising the steps of gelling it, drying it, and sintering it to obtain a transparent glass body.