JPS60200839A - Production of optical fiber retaining plane of polarization - Google Patents

Abstract

PURPOSE:To produce an optical fiber retaining its plane of polarization and having desired characteristics by setting conditions during the formation of an ellipse so as to control the ellipticity. CONSTITUTION:A jacket glass layer 2 and a clad glass layer 3 are formed successively and concentrically on the inner wall of a quartz glass pipe 1, and one end of the pipe 1 is sealed. The pipe 1 is evacuated to about -15mm.H2O pressure, a core rod 4 is put in the pipe 1, and they are melt-bonded together by moving an oxyhydrogen burner 6 from the bottom to the top to manufacture a base material for an optical fiber retaining its plane of polarization. The quartz glass pipe 1 has 5-15% ellipticity and the jacket glass layer 2 has >=30% ellipticity.

Description

[Detailed Description of the Invention] [Background and Objectives of the Invention] The present invention relates to a method for manufacturing a polarization-maintaining optical fiber. As a method for manufacturing a polarization-maintaining optical fiber, the core or cladding of the optical fiber is ovalized. A method of applying strain by utilizing the difference in thermal expansion between the core and cladding materials is known (Reference Electronics Letters, October 1979 issue, p. 677). In this method, after a central optical fiber is created, a portion of the 1 μlj surface is polished and drawn at a controlled temperature to create an optical fiber with an elliptical core. However, this method requires complicated steps such as polishing, and has the disadvantage that the outer diameter of the optical fiber cannot be circular. In addition, as a method using the rod-in-tube method, there is a method in which a core rod is placed in the center of a processed quartz tube, and a rod with a large coefficient of thermal expansion that creates strain symmetrically with the rod is placed in the center of the processed quartz tube. It was difficult to create the tube and each rod, and the rod that would cause strain could not be located near the core rod, making it impossible to achieve a short bond length.

The present invention was made in view of the above-mentioned situation, and an object of the present invention is to provide a method for manufacturing a polarization-maintaining optical fiber that can manufacture optical fiber preforms having various coupling lengths with low loss.

[Summary of the invention]

The method for manufacturing a polarization-maintaining optical fiber of the present invention includes sequentially forming a jacket glass layer and a cladding glass layer concentrically on the inner wall of a quartz glass tube, sealing one end of the quartz glass tube, and keeping the inside pressure lower than atmospheric pressure. When the silica glass tube is sequentially heated in the longitudinal direction to make it oval, and then a core rod is inserted inside and heated and fused to make it solid, the ellipticity of the quartz glass tube is 5 times ~
This is a method of forming a jacket glass tube with an ellipticity of 6 degrees or more by 15 degrees. That is, the present invention is a method in which the ellipticity can be controlled by setting conditions for ellipse formation, and a polarization-maintaining optical fiber having desired characteristics can be manufactured.

〔Example〕

The method for manufacturing a polarization-maintaining optical fiber according to the present invention will be explained below using an example with reference to FIG. In the figure, 1 is a quartz glass tube, 2 is a jacket glass layer, 6 is a clad glass layer, 4 is a core rod, 5 is a glass lathe, and 6 is an oxyhydrogen burner. 1 6 rrr installed on vertical and horizontal gas lathe 5
Inside the quartz glass tube 1 with m96X 1.5mm thickness, P
A 2O5B 20B S i Or2-based jacket glass layer 2 is formed to a thickness of 120 μm, and a p 2o 5-8i O2-based clad glass layer 3 is formed to a thickness of 20 μm on the inner periphery of the jacket glass layer 2, and one end is sealed to prevent internal pressure. 151
The rrIn water column is depressurized and heated by an oxyhydrogen burner 6 to form a quartz glass tube 1 into an elliptical shape. Elliptical shape has major axis 1
The 2-prong short axis is 10.5 cm. The elliptical silica glass tube 1 was positioned vertically as shown in the figure, the core rod 4 of 1 rran 96 was inserted, and the oxyhydrogen burner 6 was moved from the bottom to the top to fuse and integrate, thereby producing a polarization-maintaining optical fiber preform. Here, the ellipticity e of the quartz glass tube 1 is e - (major axis - short axis) / (major axis + short axis) x 100 = 6.7, and the jacket ellipticity of the base material is 40%. .

The bond length was 2.5 (extinction wavelength measured at 0.66 μm).

Figure 2 shows the ellipticity g (%) of the quartz glass tube 1 on the horizontal axis and the ellipticity (chi) of the jacket glass layer on the vertical axis, and shows the silica glass manufactured by the method shown in Figure 1.・This shows the relationship between the ellipticity and the jacket ellipticity. When the ellipticity of the quartz glass tube was 3 degrees or more, an elliptic jacket of 2 degrees or more was formed, and the bond length was 5 degrees or less (measured at a wavelength of 0.63 μm).

The polarization maintaining optical fiber obtained under the above conditions can be applied, for example, to the measurement field. Also, quartz glass old 1
When the ellipticity of g=15% or more, the ellipticity of the jacket glass layer 2 does not increase further as shown in FIG.
The outer diameter cannot be made into a perfect circle during the welding process.

In forming the quartz glass tube 1 into an oval shape, an oxyhydrogen burner 6 is used.
However, in order to form a uniform ellipse in the longitudinal direction, the amount of heat given to the quartz glass tube 1 is optimized, and the ellipticity is controlled by the amount of reduced pressure. This amount of pressure reduction is -30
When ban Ag is exceeded, the silica glass tube 1 becomes extremely oval, and changes from hollow to solid. FIG. 3 shows the amount of pressure reduction on the horizontal axis and the ellipticity (ch) of the quartz glass tube on the vertical axis. Further, the ellipticity of the jacket glass layer 2 is determined by geometric constraints between the core rod 4 and the jacket glass layer 2, that is, the area of the jacket glass layer when solidified. The jacket glass layer 2 has a large coefficient of thermal expansion, and if the jacket glass layer 2 is made thicker, cracks will occur due to thermal strain.

Furthermore, the above phenomenon occurs in the rod-in-tube process, making it impossible to form a base material. Therefore, as a result of examining the diameter of the core rod 4 and the possible jacket glass layer 2 for forming the base material within a range where the ellipticity can be formed at 2o or more,
It was impossible to form the desired ellipticity unless the outer diameter of the core rod 4 was set to 6 degrees or less.

Because the diameter of core rod 4 is small, quartz glass G1 is used in the horizontal direction.
When the core rod 4 and the core rod 4 are fused and integrated, the core rod 4 is eccentric, so the heating source is moved from below to a vertical position. When forming the cladding glass layer 3, the refractive index is △n
= 0%, moreover, it forms a glass with higher viscosity than the jacket glass layer 2, and serves to suppress the eccentricity of the core rod 4 when the core rod 4 is fused and integrated. Therefore,
It is also necessary to form it when inserting a clad core rod.

However, the core rod 4 may be a core rod having a cladding layer 6. In this case, the interface between the core rod 4 and the cladding layer 6 has good uniformity, and loss can be reduced. Further, the jacket glass layer 2 is a glass containing B203, and the jacket glass layer 2 is a glass containing B203.
In addition to no 3 F 203 S io 2 series glass,
B10 B GeO2S to 2, B rho BP
P2QBSzO2, B 2OB-F-G e O2-8
i O2-based glass may also be used. The clad glass layer 6 needs to satisfy this range, with Δn=0.05% or less, and have a higher melting point than the jacket glass layer.

Therefore, as a glass, P , 05-8 io 2
, GeO2-”; io2, P 205 B 2Q 3
S to 2, B 20B G e Q! ! -8i0
2, B 2Q 3-F-P 205-8 i O2, B
203-F-G e O2-8i O2-based glass may also be used.

FIG. 4 is an explanatory diagram of the relationship between the jacket glass layer ellipticity and the coupling length of the polarization-maintaining optical fiber manufactured by the apparatus shown in FIG. 1, and polarization-maintaining optical fibers having various coupling lengths can be manufactured.

〔Effect of the invention〕

As described above, according to the method for manufacturing a polarization-maintaining optical fiber of the present invention, the manufacturing conditions of the optical fiber preform can be made clear, and polarization-maintaining optical fiber preforms having various coupling lengths can be manufactured with low loss. It is effective.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an apparatus for carrying out the method of manufacturing a polarization-maintaining optical fiber of the present invention, and FIG. 2 shows the ellipticity of the silica glass tube of the optical fiber base material manufactured by the method of FIG. 1 and the jacket glass layer. Figure 3 is an explanatory diagram of the relationship between the ellipticity of the silica glass tube, and Figure 4 is an explanatory diagram of the relationship between the ellipticity of the jacket glass layer and the bond length. be. 1; quartz glass tube; 2; jacket glass; 6;
Clad glass layer, 4; core rond. See 1 See 2 See the figure - Asahi A) Rashi 1 - ″I Shito Osu P1 Ki

Claims (1)

[Claims] (1) A jacket glass layer and a clad glass layer were sequentially formed concentrically on the inner wall of the quartz glass tube, one end of the quartz glass tube was sealed, and the inside was heated at a pressure lower than atmospheric pressure, and heated successively in the longitudinal direction to make it oval. Then, in the method of inserting a core rod inside and heating and fusing it to make it solid, the silica glass 'tW has an ellipticity of 5% to 15% and the jacket glass layer has an ellipticity of 30 cm or more. A method for manufacturing a polarization-maintaining optical fiber.