JPH0784334B2 - Optical fiber manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an optical fiber, and more particularly to a novel method for producing an optical fiber from a base material for line drawing.

[Conventional technology]

An optical fiber is generally composed of a core, which is the center of the main optical transmission area at the center, and a cladding with a lower refractive index than the core, which is the same as that of the final optical fiber. An optical fiber preform composed of the core glass and the cladding glass was prepared, and the preform was drawn to obtain a fiber having a designed diameter ratio.

By the way, for example, in single mode fiber,
A ratio of core diameter to cladding diameter of about 115 is required.
Even if you try to obtain a large diameter ratio like this,
With the method of sooting by the VAD method, at best, only the base material with a ratio of about 1: 5 could be produced, so at the moment, make a glass body with a ratio of 1: 5, cover it with a glass tube (with a jacket) Also called), I got a ratio of 1:15.

Further, even in the so-called rod-inch-Yub method of inserting the core rod into the cladding pipe and heating and fusing the two together (collapse), it is possible to achieve a core: clad diameter ratio of 1:15 with one crap. Have difficulty. For example, when the outer diameter of the cladding pipe is about 25 mmφ, the core diameter is 1.67 mm.
The diameter is about φ, and during the collapsing process, the core rod is easily deformed to soften the core with a small heat capacity before the pipe is sufficiently heated, which causes eccentricity of the core after collapsing. easy. On the contrary, if the core diameter is about 5 mmφ where deformation is not a problem, then 75 mmφ is required for the outer diameter of the cladding pipe. Almost impossible with heating means. Therefore, even in the rod-inch uve method, if the diameter ratio is 1: 7 or more, soot is further attached to the outer periphery of the preform consisting of the core and the cladding obtained by the first rod-inch yuve, and the core-to-clad diameter ratio is 1 :. 7 or more, or by stretching the preform into a rod of small diameter,
Once again, the object was achieved by heating and fusing the glass pipe and the rod-inch-Yube method.

As described above, when trying to obtain an optical fiber preform having a large core: clat diameter ratio of about 1:15, the conventional method complicates the process and prevents the cost reduction of the fiber.

The present invention has been made in view of the above circumstances, and proposes a method capable of producing an optical fiber preform having a sufficiently large ratio of core diameter: cladding system without eccentricity in a simple one-step process. To aim.

[Means for solving problems]

The present inventors have completely changed the idea from the method of obtaining the wire drawing base material by additionally forming the outer peripheral portion so as to satisfy the set ratio with respect to the core rod of the conventional method. It was possible to solve the problems of the conventional method by opening the core and using the pipe-shaped preform with a reduced core cross-sectional area as it is as a wire drawing preform.

The present invention is to form a pipe-shaped base material by forming a hole penetrating in the longitudinal direction in a part of the core portion of an optical fiber base material having a core portion and a cladding portion, and then maintaining the inside of the pipe-shaped base material at a reduced pressure. The present invention relates to a method for manufacturing an optical fiber, which is characterized by drawing while drawing. The surface of the hole is preferably subjected to polishing treatment, and the ratio of the core area after opening to the area of the cladding is the ratio of the core area to the area of the cladding designed as a single mode fiber after the linear ratio. Opening to equality is a particularly preferred embodiment of the present invention, as it is easy to obtain a designed single mode fiber.

The pressure reduction inside the pipe-shaped base material during drawing can be realized by vacuum pumping or vacuum-sealing the base material.

The present invention will be specifically described below with reference to the drawings. In the present invention, first, a glass preform for optical fibers having a core portion 1 and a cladding portion 2 as shown in FIG. 1 (a) is prepared. This base material is produced by the known VAD method, MCVD method,
Any of a method of depositing glass soot such as an external method to make it into a transparent vitreous material, or a rod-inch tube method may be used. Next, as shown in FIG. 1B, a hole 3 penetrating the base material in the direction of the central axis is formed in the central portion of the core portion 1. Specifically, the holes are opened using an ultrasonic hole opener or the like. At this time, the cross-sectional area ratio of the two is calculated from the core: clad diameter ratio of the fiber design value, and the area ratio of the core portion and the cladding portion after the opening and subsequent polishing is made to match the above design value ratio. Do so. Next, the inner surface of the hole 3 is etched by, for example, optical polishing or heat treatment in a fluorine-based gas atmosphere, and then polished from the outer peripheral portion by means such as heating and smoothing.

After performing the above processing, the pipe-shaped base material obtained was
After being set in the drawing furnace 6 as shown in FIG. 6 (c), one end of the drawing furnace 6 is connected to the vacuum pump 5 by the connecting tool 4 to reduce the pressure inside the pipe-shaped base material to 0.1 to 20 torr while the drawing furnace 6 Heat to draw and draw fiber. Alternatively, the pipe-shaped base material is sealed in a state where the inside of the pipe-shaped base material maintains a reduced pressure, and this is drawn. As shown in FIG. 2 (a), such vacuum sealing of the base material is performed by holding the base material on a lathe 7 and attaching a rotary joint 8 at one end, and first depressurizing the inside of the base material with a pipe 5. While pulling, heat one end from the outside to fuse,
After that, the pressure is reduced by the vacuum pump 5, and when the internal pressure becomes 0.1 to 20 torr, preferably 10 torr or less, the other end is heated to cause fusion as shown in FIG. 2 (b).

[Action]

According to the present invention, the core cross-sectional area: clad cross-sectional area ratio can be adjusted to a desired value by drilling the core portion in the base material having a diameter ratio of about 1: 5 to 1: 7 obtained by the prior art. Therefore, the base material before drilling may be prepared, for example, by a simple rod-inch uve method using a large-diameter core material that does not cause core deformation. And the diameter ratio is 1:
You can get about 15 preforms. By drawing this pipe-shaped preform, an optical fiber having a desired diameter ratio and no eccentricity can be obtained. Moreover, since a stable core diameter can be obtained in the longitudinal direction of the fiber, the transmission loss of the fiber can be reduced. Therefore, the method of the present invention is advantageous in the production of a single mode fiber having a large cladding system compared to the core diameter,
Of course, it can be advantageously used as a general manufacturing method for optical fibers.

〔Example〕

Example 1 A pure silica glass rod having a diameter of 9 mmφ serving as a core was inserted into the hollow portion of a fluorine-added quartz glass pipe having an outer diameter of 35 mmφ and an inner diameter of 10 mmφ (fluorine addition amount: 0.9% by weight, relative refractive index difference: 0.3%). In this state, the pipe was heated from the outside to fuse them together to obtain a glass preform. A hole having a diameter of 8 mm and penetrating the base material was opened at the center of the glass base material using an ultrasonic perforator. Next, the inner surface of this hole was polished by heat treatment in an SF ₆ atmosphere, and the diameter of the hole was expanded to 8.7 mmφ. The inside of the hole of the obtained pipe-shaped base material was depressurized to P = 500 mmHg with a vacuum pump, and heated to 2010 ° C in a drawing furnace to obtain a tension of
g, wire drawing speed 100m / min, and outer diameter 125mμ, core diameter 8.3μm, core diameter: cladding diameter (ratio) ≈ 1:15, single-mode fiber with 0.3% relative refractive index difference between core and cladding. Was given. The transmission loss of this fiber is 01 at a wavelength of 1.55 μm.
A very good result of 9 dB / km was shown.

〔The invention's effect〕

The present invention provides a core fiber that is small relative to the diameter of the cladding or the outer diameter of the fiber, and has a stable core diameter in the longitudinal direction of the fiber and a fiber that has a low loss without eccentricity of the core. This is an epoch-making manufacturing method. It is of course advantageous to use it for the production of ordinary fibers, but especially when it is used for the production of single mode fibers, a great effect can be obtained in terms of quality and production cost.

[Brief description of drawings]

FIGS. 1 (a), (b) and (c) are schematic diagrams for explaining each embodiment of the present invention, and FIGS. 2 (a) and 2 (b) illustrate another embodiment of the present invention. It is a schematic sectional drawing.

Claims (5)

[Claims] 1. A pipe-shaped base material having a hole penetrating in a longitudinal direction in a part of a core portion of an optical fiber base material having a core portion and a cladding portion, and the inside of the pipe-shaped base material is decompressed. A method for producing an optical fiber, which is characterized in that drawing is performed while maintaining 2. The method for producing an optical fiber according to claim 1, wherein the surface of the hole is subjected to polishing treatment. 3. The hole is formed so that the ratio of the core area after the opening: the area of the cladding is equal to the ratio of the core area designed as a single mode fiber after drawing: the area of the cladding. A method for manufacturing an optical fiber according to claim 1 or 2. 4. The method for producing an optical fiber according to claim 1, wherein the reduced pressure inside the pipe-shaped base material is maintained by vacuum pumping. 5. The method for producing an optical fiber according to claim 1, wherein the reduced pressure inside the pipe-shaped base material is maintained by vacuum sealing the base material.