JPS63291830A - Production of elliptical jacket type optical fiber reserving polarized plane - Google Patents

Abstract

PURPOSE:To obtain, in low costs, the title fiber of excellent extinction ratio by integrating a silica glass rod having the space, a jacket glass rod having the second space and a core rod into a solid rod and melt-drawing it. CONSTITUTION:(A) A silica glass rod 1 which has the first space 2 of elliptic section extending longitudinally along the center axis, (B) a jacket glass rod 3 of the same elliptic section as of the first space, containing boron and phosphorus and having the second space 4 of circular section and (C) a core rod 5 which is composed of a core containing Ge and having the same shape of cross section as of the second space 4 and a silica clad are separately prepared. The core rod 5 is inserted into the second space 4 and the glass rod 3 is inserted into the first space 2 to form an integrated parent material. Then, the parent material is melt-drawn into optical fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing an elliptical jacket type polarization maintaining optical fiber, and particularly to a method for manufacturing a fiber with excellent transmission characteristics at a high yield.

[Prior Art] Conventionally, an elliptical jacket type polarization maintaining optical fiber has been manufactured according to the following steps (1) to (2).

(2) A core rod consisting of a Ge-doped 5102 core and a silica cladding is stretched to a diameter of about 1#lII.

(2) B and P are deposited by the MCVD method on the inner wall of a starting quartz tube with a diameter of 16 mm and a wall pressure of about L5 am, which will become a support tube. This deposited layer becomes the elliptical jacket part.

■ After making this support tube into an oval shape by reducing pressure and heating, the core rod drawn in (■) is inserted into the tube, and the support tube is made into a round shape and a fiber base material.

■ This fiber base material is drawn to obtain an elliptical jacket type polarization maintaining optical fiber.

[Problems to be Solved by the Invention] However, the ovalization by the above step (2) is greatly affected by various factors such as the pressure reduction value, the heating temperature, the inner and outer diameters of the support tube, and the glass film pressure and composition of B and P. Even if any of these values changes slightly, the ellipticity will vary greatly. Therefore, there is a problem in that the reproducibility of ellipticity and the uniformity in the longitudinal direction are poor, and therefore the extinction ratio characteristics are deteriorated. One way to improve the extinction ratio is to increase the ellipticity and set the molar concentration of B high.
When the molar concentration of is increased, the viscosity decreases, making it even more difficult to make the elliptical shape uniform.

Furthermore, if the sizes of the core rod and starting quartz tube are made larger than the above-mentioned values, cracks are likely to occur when the core rod and the support tube are integrated, making it difficult to increase the length of the core rod by, for example, 10 mm or more.

Furthermore, there is a problem in that it is difficult to center the core rods when they are inserted, and the eccentricity of the fibers tends to increase.

Thus, an object of the present invention is to provide a manufacturing method capable of solving the problems of the above-mentioned prior art and producing an elliptical jacket type polarization-maintaining optical fiber that has excellent extinction ratio characteristics and can be extended in length with a high yield. It's about doing.

Means for Solving Problem E] In order to achieve the above object, the method for manufacturing an elliptical jacket type polarization maintaining optical fiber of the present invention has a core.

In a method for manufacturing an elliptical jacket type polarization maintaining optical fiber having a four-layer structure of a cladding, an elliptical jacket, and a support tube, a first cavity is formed in an elliptical shape on the central axis of a silica glass rod along its longitudinal direction. At the same time, a circular second cavity is formed along the longitudinal direction on the central axis of the glass rod for an elliptical jacket, which has the same shape as the first cavity and contains B and P. A core rod having the same shape as the second cavity and consisting of a Ge-containing core and a silica gland is inserted into the second cavity of the glass rod for steam oval jacket, and is inserted into the first cavity of the silica glass rod. This is a method of drawing lines after inserting it into the body and integrating it.

[Function] In this way, the base materials of the core rod, elliptical jacket, and support tube are each formed independently, and then integrated and drawn, so that the elliptical shape of the elliptical jacket can be easily made uniform.

Moreover, even if the core rod is made thicker, cracks do not occur, and it becomes possible to make the core rod longer.

[Examples] Examples of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a process diagram showing a method of manufacturing an elliptical jacket type C wavefront preserving optical fiber according to an embodiment of the present invention. First, on the central axis of a silica glass rod 1 having a diameter of 50all and a length of 10c11, a long axis diameter of 30 mm is placed along the longitudinal direction.
An elliptical first cavity 2 having a minor axis diameter is, (ellipticity 33%) is formed by drilling.

Next, 8 with a diameter of 305111 and P-containing glass rod 3
The outer part of the silica glass rod 1 is ground to match the shape of the first cavity 2 of the silica glass rod 1. Here, the molar concentration of B is about 8 mo 11%, and P is doped so that the refractive index of the glass rod 3 has the same value as silica. A circular second cavity 4 having a diameter of 5511 is formed along the longitudinal direction on the central axis of the glass rod 3 which has been formed into an ellipse in this way by drilling.

Furthermore, a core rod made of a Ge-doped core and a silica cladding with a relative refractive index difference of 0.4% is stretched to an outer diameter of 5# to form a stretched core rod 5. Here, the core diameter after stretching is set to 1°25 tan.

Silica glass rods formed as described above 1. After cleaning the glass rod 3 and the drawn core rod 5, the drawn core rod 5 is inserted into the second cavity 4 of the glass rod 3 as shown in FIG. Insert it inside and integrate it. As a result, a fiber preform as shown in FIG. 2 is formed.

This fiber preform is drawn to obtain an elliptical jacket type polarization maintaining optical fiber.

When an elliptical jacket type polarization maintaining optical fiber with a length of 10 cm was manufactured in the above manner, the transmission loss was 5sIi at wavelength t! 0.22dB/noodle at R, extinction ratio -38d
The bond length was 1.5 mm (converted to 0.63 μs) and the eccentricity was 0.1- or less.

Note that instead of the glass rod 3 serving as the elliptical jacket, a quartz tube with B and P deposited on the inner wall by the MCVD method and carved can also be used.

[Effects of the Invention] As explained above, according to the present invention, the following excellent effects are exhibited.

(1) The elliptical shape of the elliptical jacket can be easily made uniform, and the extinction ratio characteristics are improved.

(Wa) Even if the core rod is made thicker, cracks will not occur and it is possible to make it longer.

(31 By making the core rod thicker, the influence of fluctuations at the interface between the core rod and the elliptical jacket is alleviated, and lower loss is achieved.

(4) Since the manufacturing speed is improved, costs can be reduced.

(5) Since the glass rod to be drilled is large, it can be easily centered, and the eccentricity of the fiber can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing a method for manufacturing an elliptical jacket type polarization-maintaining optical fiber according to an embodiment of the present invention, and FIG. 2 is a sectional view of a fiber preform produced in the embodiment. In the figure, 1 is a silica glass rod, 2 is a first cavity, and 3 is a silica glass rod.
4 is a glass rod, 4 is a second cavity, and 5 is a stretched core rod.

Claims (1)

[Claims] In a method for manufacturing an elliptical jacket type polarization maintaining optical fiber having a four-layer structure of a core, a cladding, an elliptical jacket, and a support tube, a first cavity is formed in an elliptical shape on the central axis of a silica glass rod along its longitudinal direction. and a circular second cavity is formed along the longitudinal direction on the central axis of the glass rod for an elliptical jacket, which has the same shape as the first cavity and contains B and P. A core rod having the same shape as the second cavity and consisting of a Ge-containing core and a silica cladding is inserted into the second cavity of the glass rod for an elliptical jacket, and these are inserted into the first cavity of the silica glass rod. 1. A method for producing an elliptical jacket type polarization-maintaining optical fiber, which comprises inserting it into a cavity, integrating it, and then drawing it.