JPS5836942A - Manufacture of polarization retaining optical fiber - Google Patents

Abstract

PURPOSE:To obtain an optical fiber whose refractive index is not lowered at the central part by forming a quartz glass film contg. boron oxide on the inner wall of a round and hollow glass tube, evacuating the tube, and heating it from the outside to make the tube solid in an elliptical shape. CONSTITUTION:Quartz glass 2 contg. about 5% boron oxide is deposited on the inner wall of a quartz glass tube 1 having a round hollow part by a chemical vapor deposition method. The internal pressure of the tube 1 is made about 10mm.H2O lower than the external pressure, and the tube 1 is heated to about 1,900 deg.C. The boron oxide of high volatility in the innermost layer of the tube 1 is volatilized and scattered to form a thin layer of pure quartz, and by making the tube 1 solid in a flat shape, an elliptical pure quartz part 5 is formed at the central part. Thus, the refractive index distribution is not lowered at the core part 5, and a polarization retaining optical fiber with a small loss is obtd. by drawing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a polarization-maintaining optical fiber used in optical communications, optical sensors, and the like.

Optical fibers that guide light while preserving polarization have a high cost.Polarization preserving optical fibers, which have been developed in the past, are made using a method called chemical vapor deposition, which is a method called chemical vapor deposition, which is made by attaching the inner wall of a glass tube with a circular hollow part. Firstly, a low refractive index glass layer containing boron oxide is formed, secondly a high refractive index glass layer is formed,
More moths? 'The internal pressure of the x-tube is lower than the external pressure of the glass tube and the glass tube is heated from the outside so that the high refractive index layer becomes elliptical. It was manufactured by pulling.

An example of a cross-sectional view of a polarization-maintaining optical fiber having an elliptical core manufactured by the method described above is shown in FIG. The glass layer 3, 3, is a core portion with a high refractive index.The refractive index distribution in the cross section in the long axis direction of Figure 1 (ml) is 5 as shown in Figure 1 (b). The polarization-maintaining optical fiber having an elliptical shape produced by this method is produced by adding high refractive index contributing substances (germanium oxide, germanium oxide, Oxide monuments, etc.) are volatilized due to the high temperature, and a dip 4 in the refractive index, commonly called a center dip, is formed.
There was a problem in that the energy seeping out from the core portion 3 was particularly large in the short axis direction of the elliptical core, making it difficult to obtain a polarization-maintaining optical fiber with low loss. Therefore, an object of the present invention is to provide a method for manufacturing a low-loss polarization-maintaining optical fiber in which there is no drop in the refractive index at the center of the refractive index distribution, that is, less energy seeps out from the core. . The structure of the present invention is to form a quartz glass film containing boron oxide on the inner wall of a glass tube having a circular hollow part by chemical vapor deposition, and to control the internal pressure of the glass tube on which the glass film is formed from the external pressure of the glass tube. The temperature is low and the glass tube is heated from the outside.
This method of manufacturing a polarization-maintaining optical fiber is characterized in that the glass tube is shrunk into an elliptical shape to become solid, and a core in which boron oxide is volatilized is formed in the center.

Next, one embodiment of the present invention will be explained. The step of depositing a quartz glass layer containing boron monoxide on the inner wall of a quartz tube having a circular hollow portion is usually carried out by a chemical vapor deposition method. Typically an outer diameter of 14
A quartz glass containing 5% boron oxide is deposited on the inner wall of a quartz tube with a wall thickness of -1 l. Next, the internal pressure of the quartz tube is lowered by about l0 IEI water column pressure than the external pressure of the glass tube, and The quartz tube is heated until it reaches 1900t:'.

Then, the highly volatile boron oxide in the innermost layer of the quartz tube volatilizes and scatters, forming a thin layer of pure quartz.As the pressure is further reduced, the solid becomes flat, with an elliptical pure quartz part in the center. It is formed. The part where boron oxide has not volatilized has a refractive index that is about o, oos lower than the pure quartz part in the center, and becomes the nose part of the polarization-maintaining optical fiber. Then, the approximately 8-mm rod-shaped preform obtained in the above step is drawn to obtain a polarization-maintaining optical fiber. Since the core of the polarization-maintaining optical fiber manufactured by this method is made of pure quartz, there is no drop in the refractive index at the center. A cross-sectional view of this polarization preserving light 7-eyeper is shown in Figure 2 (-. In this figure, l is the outer quartz glass layer, 2 is the low refractive index glass layer containing boron oxide, and 5 is the glass layer where the boron oxide volatilizes. The core part is made of pure quartz produced from Kotok. Figure 2(b) shows the refractive index distribution of a cross section taken in the long axis direction of K112 ((Rotation). There is no dip in the refractive index distribution in the portion 5, so that less energy leaks out from the portion 5, and a polarization-maintaining optical fiber with low loss can be obtained.

In the above example, the quartz tube is solidified, and the rod-shaped preform is drawn to obtain a polarization preserving optical fiber. Good too.

As described above, according to the present invention, there is no dip in the refractive index distribution in the central core portion, and therefore less energy leaks out from the core portion, making it possible to obtain a polarization-maintaining optical fiber with low loss. effective.

[Brief explanation of the drawing]

Figure 1 (B) is a cross-sectional view of an example of a polarization-maintaining optical fiber manufactured by a conventional method, and Figure 1 (B) is a diagram showing the refractive index distribution of the cross section in the long axis direction of Figure 1 (B). , second
Figure (2) is a cross-sectional view of an example of a polarization-maintaining optical fiber manufactured by the method of the present invention, and Figure 2 (b) is a diagram showing the refractive index distribution of the cross section in the long sleeve direction of Figure 2 (supplementary figure 2). The symbols used in the drawings indicate the following: 1--Outer quartz glass layer, 2--Low refractive index glass layer, 3--Core portion with depression of the refraction wheel. 4-1. Core part with no drop in refractive index, 5.-1 drop in refractive index / Atsushi / B / Atsushi Z mouth

Claims (1)

[Claims] In a method for manufacturing an optical fiber that guides light while preserving polarization, a quartz glass film containing boron oxide is formed on the inner wall of a glass tube having a circular hollow part by chemical vapor deposition, and the quartz glass film is The internal pressure of the glass tube in which is formed is lower than the external pressure of the glass tube, and the glass tube is heated from the outside to shrink the glass tube into an oval shape and solidify it, forming a core in which boron oxide has volatilized in the center. A method of manufacturing a polarization preserving optical fiber, characterized in that: