JPS61132531A - Production of optical fiber - Google Patents

Abstract

PURPOSE:To produce a specific optical fiber composed mainly of SiO2 and added with fluorine, and having suppressed ultraviolet absorption peak caused by the addition of fluorine, by treating the preform or the optical fiber with deuterium gas. CONSTITUTION:In the production of an optical fiber consisting of at least two kinds of glass, i.e. a quartz-based core glass composed mainly of SiO2 and a clad glass composed mainly of SiO2 added with fluorine and having lower refractive index than the core glass, the optical fiber preform and/or the optical fiber are treated with deuterium gas. The ultraviolet absorption generated by the addition of fluorine is supposed to be caused by the presence of the non-crosslinked oxygen generated by the incision of the SiO2 network with fluorine resulting in the dissipation of Si in the form of SiF4. The ultraviolet absorption caused by the generation of the non-crosslinked oxygen can be suppressed by the deuterium gas treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing an optical fiber, and more specifically, to a method for manufacturing an optical fiber.
The present invention relates to a method of manufacturing a fiber containing z k 1 component and doped with fluorine, and the fiber according to the present invention can be advantageously used for communication optical fibers, image fibers, and the like.

[Conventional technology]

In recent years, the use of optical fibers has rapidly increased due to their many features such as light weight, low loss, and non-induction. The structure of an optical fiber has a part with a high refractive index called the core in the center.
It consists of a part with a low refractive index called the cladding on its outer periphery. The currently widely used fiber is SL
o.

The main component is gold, and various glass components are added to adjust the refractive index '1kvI4. Among these, fluorine is a component that lowers the refractive index and has recently become widely used, and is commonly used in cladding.

Conventionally, fluorine-doped fibers have particularly improved hydrogen resistance properties, and have therefore been used for long wavelengths such as 1.50 μm and 1.55 μm, which are affected by OH absorption and ``L absorption.'' However, the application range of the original fiber is With the expansion of wavelengths, wavelengths as short as α85 μm have come to be used.

As a conventional manufacturing method in which fluorine is added to sho as a main component, for example, 81(z,) is added to a plasma torch.

CC&'* #Os f supply, plasmate E11c
4 A method for producing +310xFy glass by reacting with t-oxidation and fluorine.

[Problems that the invention is about to resolve]

However, when manufacturing a fiber containing F-s1O as the main component and doped with fluorine using the conventional method, there are two manufacturing conditions:
It has become clear that an absorption peak exists in the ultraviolet region, and that the increase in loss due to absorption is over 100 aBAm near α4 μm.

An object of the present invention is to reduce the ultraviolet absorption peak that occurs due to fluorine addition. This reduction in ultraviolet absorption is also effective for manufacturing long wavelength fibers with extremely low loss.

[Means for solving problems]

The present inventors have arrived at the present invention as a result of research and study on the mechanism of ultraviolet absorption caused by fluorine addition.

That is, the present invention relates to the production of an optical fiber made of at least two kinds of glasses: a core of silica-based glass mainly composed of slo, and a cladding of glass having a low core-F refractive index containing 8109 Th as a main component and containing am fluorine. , provides a method for manufacturing a source fiber, characterized in that the base material for the source fiber or the optical fiber or both are treated with full deuterium gas.

The present invention will be explained in detail below.

The generation of ultraviolet absorption due to the addition of fluorine is due to the addition of L9810 to fluorine.
This is thought to be a defect caused by the network being disconnected and 81 being volatilized as 8iF4.

8101+2F, -420+81F4 ・-・II
(1) In the above formula (1), after the fluorine gas reacts with the Sin network, non-bridging oxygen is generated, and the presence of this non-bridging oxygen is considered to be the cause of ultraviolet absorption. Therefore, it can be seen that if this non-bridging oxygen is eliminated, the result will be ↓. The present invention is based on the discovery that deuterium gas treatment can completely reduce ultraviolet absorption due to the generation of L D and non-bridging oxygen.

It is thought that when non-bridging a-oxygen is generated and the glass is then treated in hydrogen gas, the non-bridging oxygen reacts with hydrogen as shown in formula (2) below to form an OH group.

20+H → 20H...---+2) As the concentration of non-bridging oxygen decreases, the concentration of ultraviolet absorption decreases. However, in long-wavelength fibers, hydrogen treatment results in OH
Absorption of groups may increase.

Therefore, by replacing hydrogen with deuterium, the absorption is shifted from the light source wavelength to the longer wavelength side. In this case, 20 + D goose → 20D due to the reaction (3) below
・ ・ II Φ ・ (31 The reactions in (2) and (3) above are speeded up by increasing the temperature, so it is preferable to proceed at a high temperature.

Although deuterium gas treatment is possible at the base material stage, if it is done after drawing and forming into a fiber, deuterium gas will diffuse into the fiber within a short time. However, since fibers are usually coated with polymeric materials, it is difficult to heat them above 300°C.

Therefore, processing steps and processing conditions are selected according to the fiber structure and coating material.

〔Example〕

In the following Examples, the method of the present invention and its effects will be explained.

Example 1 A pure silica rod prepared by vAD method was clad with BLOxlPy glass having a 1.0% lower silica refractive index by plasma external deposition method. The obtained preform (base material) consisting of a core/clad two-layer structure was placed in a container in a T-electric furnace and heated at a temperature of aooc for 8 hours while flowing deuterium gas for 117 minutes. Then the preform and 9
A bare wire was obtained by drawing the wire. The bare wires were cut to a length of 50crR, tied into bundles of approximately 50,000 pieces, placed in a quartz tube with a diameter of 55cfIt, heated and integrated, and drawn again to form a 30,000 pixel image fiber A to L7? ,.

Image 7 shows a preform that is exactly the same as above, except that it is treated with deuterium for comparison.
Aipah B tot, l.

The transmission loss (aB/km) vs. wavelength (μm) characteristic t of the image fiber A and fabricated fiber B obtained above is shown in FIG. It is clear from Figure 1 that = sea urchin, without hydrogen treatment (B
) rarely had a loss of 250 dB/km at α40 μm, but in the method of the present invention (A), the loss was 80 aB
/km'4 width.

Example 2 A preform was prepared by forming a cladding of 5IO1Fy glass with a 19% lower refractive index on a pure silica rod prepared by the VAD method using a plasma external deposition method.This preform was drawn to form a wire. The strands were placed in a container in an electric furnace and heated at 500°C for 4 hours while flowing deuterium gas t-1115+. After taking out the strands from the container, they were cut into 40-length pieces and 15,000 pieces were made. After bundling, they were placed in a quartz tube, heated and integrated, and then drawn to form an image fiber.

Deuterium treatment for comparison? The transmission loss of the image fiber obtained under the same conditions except that
50 dB/km, but the one according to this example was 2
It was possible to reduce it to 5 dE/km.

Example 3 Pure silica soot gold was applied externally to a pure silica rod prepared by the VAD method using a flame hydrolysis method, and after dehydration, He, act, p,
It became transparent in the gas atmosphere. This glass barrel was further inserted into a quartz tube, heated and integrated, and then wire-drawn. This wire was placed in a container and heated to 200° C., then filled with deuterium gas and left for 4 hours. After that, I took it out of the container and measured the loss-wavelength characteristics, and found that it was 1.50μm (15dB/k
An ultra-low loss fiber of m was obtained.

〔Effect of the invention〕

The present invention has a great effect of completely reducing the ultraviolet absorption of an optical fiber containing alo as a main component and doped with fluorine. Such effects of the present invention are particularly effective in image fibers where transmission loss in the visible range is important. Since the image fiber has a small core diameter, the transmission loss of the cladding has a large influence, but this transmission loss can be reduced by one order of magnitude by optimizing the deuterium treatment conditions according to the present invention. Therefore, it is possible to use a single-digit long fiber according to the conventional method. It is also effective in long wavelength single mode fibers that require extremely low loss.

[Brief explanation of drawings]

w, Figure 1 is a graph showing the transmission loss wavelength characteristics of the image fiber, in which A shows the transmission loss of the fiber treated with 19 deuterium according to the present invention in Example 1, and B shows the transmission loss without deuterium treatment. shows.

Claims (1)

[Claims] 1. In the production of an optical fiber made of at least two kinds of glasses: a silica-based glass whose core is mainly composed of SiO_2, and a cladding whose refractive index is lower than that of the core and whose main constituent is SiO_2 and doped with fluorine, A method for manufacturing an optical fiber, which comprises treating a fiber base material, an optical fiber, or both with deuterium gas.