JPS62162648A - Production of optical fiber - Google Patents

Abstract

PURPOSE:The preform for optical fiber is heated in a quartz tube reciprocating in the vertical direction to inhibit contaminants from furnace materials from depositing on the preform or on the resultant optical fiber whereby the strength of the drawn optical fiber is increased. CONSTITUTION:When the preform 1 is drawn into optical fiber 1A, a vertically reciprocating quartz tube is set on the axis of the furnace which is composed of carbon heaters 2 and carbon core tube 3. Then, the preform 1 is inserted into the quartz tube 10 and the objective optical fiber is formed by drawing. According to the process of the present invention, the fine particles or impurities flying out of the carbon core tube 3 and the carbon heaters 2 precipitate on the outer surface of the quartz tube 10 and carbon heaters 2 precipitate on the outer surface of the quartz tube 10 and the contamination of the preform 1 or the optical fiber 1A can be completely avoided. Thus, the resultant fiber is made free from impurities and damages and has increased strength. Moreover, the quartz tube 10 vertically reciprocates without local heating, resulting in prolonged life.

Description

[Detailed Description of the Invention] [Summary] When heating an optical fiber base material and drawing it into an optical fiber, impurities in the furnace material are removed by heating the optical fiber base material in a quartz tube that reciprocates in the vertical direction. , preventing it from adhering to the optical fiber base material or the optical fiber,
Improves the strength of drawn optical fiber.

[Industrial application field]

The present invention relates to a method of manufacturing an optical fiber.

For silica-based optical fibers, a rod-shaped optical fiber base material with a waveguide structure similar to that of an optical fiber is manufactured, and this optical fiber base material is heated to about 2000°C to soften it and have an outer diameter of 100 t.
tm-150 μm, and is manufactured by stretching it to a length of several tens of meters.

On the other hand, with the advancement of optical communication technology, optical fibers have come to be used for submarine cables, and optical fibers for submarine cables are more expensive than optical fibers used in optical equipment or optical fibers for land-based installations. Therefore, higher strength is required.

[Conventional technology]

FIG. 2 is a side sectional view showing a conventional optical fiber manufacturing method, and FIG. 3 is a perspective view of a carbon heater.

In FIGS. 2 and 3, the heating furnace that locally heats the optical fiber base material is made of carbon material, and includes a carbon heater 2 having staggered slots 7) 2A on the cylindrical wall, and , and cylindrical carbon furnace core tubes 3 mounted concentrically. The carbon heater 2 includes a pair of electrodes 2B, and is controlled to maintain the inside of the carbon furnace tube 3 at a desired temperature (for example, approximately 2000° C.) by applying electricity.

The carbon furnace core tube 3 makes the temperature distribution uniform. Note that carbon heater 2. In order to prevent consumption of the carbon furnace core tube 3, an inert gas such as nitrogen gas is injected into the heating furnace.

An optical fiber base material 1 with an outer diameter of several tens of G and a length of 100 G is vertically placed at the axial center of the heating furnace configured in this way.
When the optical fiber preform 1 is fed at a descending speed of about 100 yen/min, the lower tip of the optical fiber preform 1 is locally heated and softened to form a spindle shape, and an optical fiber L having a desirably smaller outer diameter than the tip is formed.
A is delineated.

Although not shown, the drawn optical fiber IA is primarily coated directly under the heating furnace, and then wound around a winding drum via a camp screen.

The optical fiber 18 manufactured in this way has a 0.5%
Most of them pass the screening test (applying an elongation of 0.5% to the optical fiber and inspecting the entire length of the optical fiber for the presence or absence of breakage), and are sufficient for use as optical fibers installed on land. It has strength.

As mentioned above, using the carbon heater 2 and the carbon furnace core tube 3 in the heating furnace makes it possible to use an optical fiber installed on land.
It is widely used because it has many advantages such as sufficient strength, simple furnace structure, low cost, and easy temperature control.

[Problem that the invention seeks to solve]

However, in the optical fiber obtained by the above-mentioned conventional means, due to high temperature heating during drawing, fine carbon particles or contained impurities fly out from the carbon heater, carbon furnace tube, etc. In the 2% screening test, several fractures were observed due to adhesion to the surface.

That is, the conventional optical fiber manufacturing method has a problem in that the reliability of the strength is low when applied to optical fibers for submarine cables, which require higher strength.

[Means for solving problems]

In order to solve the above-mentioned conventional problems, the method of the present invention, as shown in FIG.
A quartz tube 10 that reciprocates in the vertical direction is provided at the axial center of a heating furnace, and an optical fiber base material 1 is inserted into the quartz tube 10 to draw the optical fiber. It is.

[Effect]

According to the method of the present invention, the carbon particles or impurities ejected from the carbon furnace core tube 3 and the carbon heater 2 adhere to the outer circumferential surface of the quartz tube 10, so that they do not adhere to the optical fiber IA or the optical fiber base material 1. There is no fear of it happening.

Therefore, there is no possibility that impurities other than quartz may be contained in the drawn optical fiber IA, and there is almost no occurrence of scratches, so that the strength of the optical fiber IA is improved.

Furthermore, since the quartz tube 10 reciprocates up and down, local high temperatures are prevented, resulting in a long life.

〔Example〕

The method of the present invention will be specifically explained below with reference to the illustrated examples. Note that the same reference numerals indicate the same objects throughout the figures.

FIG. 1 is a side sectional view of one embodiment of the method of the present invention, in which the heating furnace includes a carbon heater 2. Carbon furnace tube 3. It is composed of a lower seal tube 4 disposed at the lower part of the carbon furnace core tube 3, and a quartz tube 1o that is disposed concentrically within the carbon furnace core tube 3 and reciprocates up and down.

Further, the entire heating furnace is installed in an atmosphere of an inert gas such as nitrogen gas.

The lower seal tube 4 has a cylindrical shape made of quartz and has an inner diameter approximately the same as that of the carbon core tube 3, and is configured to inject an inert gas, such as nitrogen gas, from the tube wall. It prevents the consumption of 10.

The quartz tube 10 has a cylindrical shape in which the inner diameter of the hollow hole is sufficiently thicker than the outer diameter of the optical fiber preform 1 (and the length is sufficiently longer than the carbon core tube 3).

The means for imparting vertical reciprocating motion to the quartz tube 10 is as follows.

The upper part of the quartz tube 10 is gripped by the gripper 11, and the gripper 11
Provide a vertical screw hole at the end of the A screw shaft 12, which is rotated forward and backward by a motor (not shown), is mounted so as to be screwed into this screw hole, and in order to prevent the gripping tool 11 from rotating in a horizontal plane, a A guide bar 13 is provided to loosely pass through the insertion hole of the gripper 11.

With this structure, when the screw shaft 12 is rotated forward, for example, the quartz tube 10 descends, and when the screw shaft 12 is rotated in the reverse direction, the quartz tube 10 rises.

The reciprocating speed of this quartz tube 10 is approximately five times faster than the feeding speed of the optical fiber preform l. That is, the portion of the tube wall of the quartz tube 10 corresponding to the carbon heater 2 is constantly moving. ``Therefore, the quartz tube 10 is prevented from becoming locally heated, and there is little risk that the quartz tube 10 will become soft or deformed (and damage is prevented).

As mentioned above, the optical fiber preform 1. The outer periphery of the portion of the optical fiber IA that is locally heated to a high temperature by the carbon heater 2 is protected by a quartz tube 10. therefore,
The carbon particles or impurities ejected from the carbon furnace core tube 3 and the carbon heater 2 adhere to the outer peripheral surface of the quartz tube 10 and do not adhere to the optical fiber 18 or the optical fiber base material 1.

Note that the components of the quartz tube 10 are scattered and the optical fiber base material l,
Alternatively, even if it adheres to the optical fiber LA, it will melt because it has the same composition as the surface of the optical fiber. Therefore, no scratches will occur.

Therefore, there is no possibility that impurities will be contained in the drawn optical fiber IA, and there will be almost no scratches, thereby improving the strength of the optical fiber IA.

In addition, as a result of a 2% screening test of the optical fiber drawn by the method of the present invention (conducted with an optical fiber length of 5 km), no breakage was observed.

〔Effect of the invention〕

As explained above, in the method of the present invention, impurities in the furnace material are removed from the optical fiber preform by heating the optical fiber preform in a quartz tube that reciprocates up and down.

Alternatively, adhesion to the optical fiber is prevented, which improves the strength of the drawn optical fiber, and has excellent practical effects such as extending the life of the heating furnace.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of one embodiment of the method of the present invention, FIG. 2 is a side sectional view showing a conventional optical fiber manufacturing method, and FIG. 3 is a perspective view of a carbon heater. In the figure, ■ is the optical fiber base material, IA is the optical fiber, 2 is the carbon heater, 3 is the carbon core tube, 4 is the lower seal tube, 10 is the quartz tube, 11 is the gripping tool, 12 is the screw shaft, and 13 is the guide Show bar.

Claims (1)

[Claims] In drawing the optical fiber (1A) from the optical fiber preform (1), the optical fiber is placed at the axial center of a heating furnace that softens the tip of the optical fiber preform (1) and spins it. A quartz tube (10) through which the base material (1) is inserted and which reciprocates in the vertical direction is provided in the hollow part.
A method of manufacturing an optical fiber, the method comprising drawing the optical fiber.