JPH0225850B2 - - Google Patents

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. Background and Purpose It has recently been found that transmission loss increases with time in optical fiber cables.
The reasons for this are currently thought to be as follows. (1) Hydrogen gas is generated by 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) Part of the diffused hydrogen gas is −|Si |−O
It combines to form -|Si|-OH, and some of it is retained as hydrogen molecules in the network structure of the glass. (3) Hydrogen gas can be generated not only from the above-mentioned plastics, but also when water gets into optical fiber cables made of dissimilar metals, hydrogen gas is generated by forming a battery. (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, when increasing the number of OH groups, they do not bond with hydrogen unless a defective oxygen having a dangling bond is already present in the glass. (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 aims to provide a method for manufacturing an optical fiber that can reduce oxygen defects in the optical fiber as much as possible, particularly in consideration of the above points (4) and (5). This prevents the formation of OH groups even when hydrogen gas is generated within the cable and diffuses into the optical fiber, thereby improving the loss increase characteristics. It is. Structure of the invention The spun optical fiber is characterized in that, before it touches the first coating material, it passes through a heating furnace in which oxygen is continuously flowed, so that it is heat-treated in an oxygen-only atmosphere. More detailed explanation of the configuration When manufacturing optical fibers, conventionally "Figure 1"
An optical fiber 1 spun from a base material 10 as shown in FIG.
2 is sequentially passed through the coater 14, heater 16, coater 18, and heater 20, and then wound onto the bobbin 22. However, in the present invention, as shown in "Figure 2",
The spun optical fiber 12 passes through a heating furnace 24 before contacting the coating material in the first coater 14. Further, oxygen is continuously flowed into the heating furnace 24. As you can see from the experimental results below, the heat treatment temperature was about 1200℃, and the oxygen flow rate was 600c.c./min.
About that amount is appropriate. Example: By changing the spinning speed, heat treatment temperature, and oxygen flow rate,
The heat-treated optical fiber was coated with a primary coating (two layers of a modified silicone resin and an ordinary adhesive silicone resin) and a secondary coating of nylon to obtain an optical fiber core. Its specifications are shown in the following "Table 1".

[Table] The transmission loss increase characteristics were determined by an accelerated test method. In other words, the fabricated optical fiber core wire is
The sample was kept in an oven at 200°C for 2 hours, and the loss wavelength characteristics before and after the oven were measured using a monochromator. The value of increase in loss was determined from the increase value at a wavelength of 1.39 μm, where the increase in loss due to OH groups is significant. The following "Table 2" shows the values of increase in loss when the heat treatment conditions were varied.

[Table] (Note) The loss increase is the value at a wavelength of 1.39μm. From "Table 2", to reduce the loss increase,
It can be seen that the higher the temperature, the higher the oxygen flow rate, and the slower the spinning speed, the better the heat treatment conditions. Effects of the Invention The present 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 gas generated within the optical fibers. In the present invention, before the spun optical fiber touches the first coating material, it passes through a heating furnace in which oxygen is continuously flowed and is heat-treated in an oxygen-only atmosphere. There are very few oxygen vacancies in the optical fiber, so even if the generated hydrogen gas diffuses into the optical fiber, the amount of OH groups will increase to a very small extent. As a result, transmission loss will not increase significantly even after many years have passed since installation.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a conventional primary coating, and FIG. 2 is an explanatory diagram of a heat treatment according to the present invention. 12: Optical fiber, 14: First coater, 2
4: Heating furnace.

Claims (1)

[Claims] 1. The spun optical fiber is characterized by being passed through a heating furnace in which oxygen is continuously flowed before coming into contact with the first coating material, and being heat-treated in an atmosphere containing only oxygen in the heating furnace. , a method for manufacturing optical fibers.