JPS60221337A - Preparation of optical fiber - Google Patents

Abstract

PURPOSE:To prepare optical fiber contg. little oxygen defficiency and little OH group formed therein by heat-treating optical fiber immediately after spinning in O2 atmosphere and allowing the fiber to contact with a clad material. CONSTITUTION:Optical fiber 12 drawn from a parent material 10 is introduced into a heating furnace 24 while flowing O2 continuously therethrough at ca. 600cc/min flow rate, and the fiber is heat-treated at ca. 1,200 deg.C then passed through a coater 14 to coat a clad material thereon. Since, by this method, oxygen defficiency in the fiber is reduced and the degree of increase of OH group is retarded even if diffusion of generated gaseous H2 occurred, improved optical fiber causing hardly increase of transmission loss for a long period is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing an optical fiber that can minimize the phenomenon of increase in transmission loss due to aging.

It has recently been found that transmission loss increases over time in optical fiber cables.

The reasons for this are currently thought to be as follows.

l] Hydrogen gas is generated due to hydrolysis or thermal oxidation of the plastic that is the constituent material of the optical fiber, and this hydrogen gas diffuses into the optical fiber, causing an increase in loss.

2) A part of the diffused hydrogen gas combines with -3'i-0 to form -8'1-OH, and a part is retained as hydrogen molecules in the network structure of the glass.

3) Hydrogen gas is generated not only from the above-mentioned plastics, but also when water enters an optical fiber cable made of different metals, forming a battery and generating hydrogen gas.

4) Even when the same amount of hydrogen gas is generated, the loss increase characteristics differ depending on the composition and composition ratio of the optical fiber. In other words, the increase in OH groups will not bond with hydrogen unless defective oxygen having dangling bonds exists in the glass in advance.

5) The number and type of defects strongly depend not only on the composition and composition ratio of the optical fiber, but also on the manufacturing method and manufacturing conditions.

This invention takes into account the above points 4) and 5),
The object of the present invention is to provide a method for manufacturing an optical fiber that can reduce oxygen defects in the optical fiber as much as possible.

Even if hydrogen gas is generated within the cable and diffused into the optical fiber, OH groups are not formed, thereby improving loss increase characteristics. be.

The λ Kawabe crush-spun optical fiber is characterized in that the optical fiber is heat-treated in an oxygen atmosphere before it comes into contact with the first coating material.

Conventionally, when manufacturing an optical fiber, an optical fiber 12 spun from a lU material lO is passed through a coater 14, a heater 16, a coater 18, and a heater as shown in Figure 1. 20 in turn and winding it onto the bobbin 22.

However, in the present invention, as shown in FIG. 2, the spun optical fiber 12 is passed through a heating furnace 24 before coming into contact with the coating material in the first coater I4. Further, oxygen is continuously flowed into the heating furnace 24.

As can be seen from the experimental results described later, the heat treatment temperature was 120
The temperature is around 0℃, and the oxygen flow rate is 1300cc/inch.
<Rei is appropriate.

Support 1 By changing the spinning speed, heat treatment temperature, and flow rate of the #element, the heat-treated optical fiber is coated with a primary coating (two layers of modified silicone resin and regular glue silicone resin) and a secondary coating of nylon. I used it as a core wire. Its specifications are shown in the following "Table 1".

The characteristics of increase in transmission loss in Table 1 were determined by an accelerated test method. That is, the produced optical fiber core wire was held in a 2006C oven for 2 hours, and the loss wavelength characteristics before and after the oven were measured using a monochromator. The value of loss increase is OH
This was determined based on the increase value at a wavelength of 1.39 pm, where the increase in loss due to groups is significant. Table 2 below shows the increase in loss when the heat treatment conditions are varied.

Table 2 (Note) The loss increase is the value at wavelength 1.3 Jt+ from "Table 2". In order to reduce the loss increase, the higher the temperature, the higher the oxygen flow rate, and the slower the spinning speed, the better for the heat treatment conditions. I understand that.

This invention was made based on the clarification of the cause of increase in transmission loss due to aging of optical fibers, which is caused by hydrogen scum generated within the optical fibers.

In the present invention, since the spun optical fiber is heat-treated in an oxygen atmosphere before it touches the first coating material, oxygen defects in the optical fiber are very small, and therefore the occurrence of Even if the hydrogen gas diffuses into the optical fiber, the amount of OH groups increases is very small.

Therefore, transmission loss does not increase significantly even after many years have passed since installation.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of a conventional primary coating; FIG. 2 is a detailed explanatory diagram of the present invention. 12: Optical fiber 14: First coater 24: Heating furnace Patent applicant: Fujikura Electric Wire Co., Ltd. Nippon Telegraph and Telephone Corporation Agent: Keiji Kunihira Figure 1

Claims (1)

[Claims] 1. A method for producing an optical fiber, which comprises heat-treating the spun optical fiber in an oxygen atmosphere before the fiber comes into contact with a first coating material.