JPS6212628A - Production of optical fiber - Google Patents

Abstract

PURPOSE:To simultaneously, surely and stably, carry out drawing and collapsing and to obtain optical fiber in high production efficiency, by drawing a quartz tube which has piled specific synthetic glass on the inner face and sealed at one end, from the sealed end, while keeping the quartz pipe at given inner pressure. CONSTITUTION:The inner part of the quartz pipe 31 is piled with the synthetic glass layer 30 having higher refractive index than the quartz pipe by MVC method, et., in such a way that a ratio of the inner diameter/the outer diameter of the quartz pipe 31 becomes <=0.85 (the inner diameter is the inner diameter of the synthetic glass layer 30) and one end of the quartz pipe is sealed to form the sealed end 42 and the quartz pipe 31 is supported by the bearer 32 in the drawing furnace 33. Then, as a fixed amount of air inhalation is carried out by the suction pump 35 of the air inhalation system 50 connected through the joint part 40 to the open end 43 of the quartz pipe 31, an introduced amount of a gas consisting of Cl2, an inert gas, etc., is regulated by the the flow rate regulator 36 and pressure in the quartz pipe 31 is kept at 0--22mmH2O while detecting the inner pressure of the quartz pipe 31 by the differential pressure gauge 38, the optical fiber 41 is drawn from the above- mentioned sealed end 42, coated by the applicator 45 and taken up through the capstan 39.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention mainly relates to a method of manufacturing an optical fiber using an internal CVD method.

[Prior art]

Conventionally, there has been a method in which a synthetic glass with a higher refractive index than the quartz tube is placed inside the quartz tube to form a part commonly called a core, and this is collapsed at the same time as drawing in a drawing furnace to obtain an optical fiber. Are known. This method takes advantage of the fact that when the quartz tube is heated to a high temperature during wire drawing, it softens and as a result contracts due to surface tension, and has the advantage of high production efficiency since wire drawing and collapse are performed simultaneously.

However, in this method, the heating conditions required for collapse and the heating conditions required for drawing often do not necessarily match, and as a result, the center of the optical fiber does not solidify, leaving so-called crushed remains. , when solidifying, deformation such as deterioration of roundness occurs, resulting in a problem that collapse becomes unstable. Furthermore, if priority is given to heating conditions for collapse, there is also the problem that drawing conditions are restricted.

[Purpose of the invention]

In view of the above-mentioned problems, an object of the present invention is to provide an optical fiber manufacturing method that simultaneously performs drawing and collapse, in which both can be performed reliably and stably.

[Structure of the Invention] - In order to achieve the above object, the present invention includes a synthetic glass having a higher refractive index than that of the quartz tube attached inside the quartz tube, and collapses it while drawing it in a drawing furnace. In the method for manufacturing an optical fiber to obtain an optical fiber, the synthetic glass is inserted into the quartz tube so that the inner diameter/outer diameter value of the quartz tube is 0.85 or less, and then one end of the quartz tube is sealed. A sealed end is formed, and then the optical fiber is drawn from the sealed end while holding the quartz tube in a drawing furnace and maintaining the internal pressure of the quartz tube at 0 to -22 mmHgO. It is something to do.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, in the present invention, first, the quartz tube 3
For example, a synthetic glass layer 30 having a higher refractive index than the quartz tube 31 is placed inside the quartz tube 31. Using the lCV method, the quartz tube 31 is fitted inside so that the inner diameter/outer diameter value is kept to 0.85 or less (herein, the inner diameter refers to the inner diameter of the synthetic glass layer 30). Sealing is performed to form a sealed end 42 . Subsequently, the quartz tube 31 is placed in the support 3 in the drawing furnace 33.
2 and the other open end 43 of the quartz tube 31
The intake system 50 is connected to the intake system 50 via the connecting portion 40. Here, the intake system 50 includes piping 34 and 37 as shown in FIG.
and a suction pump 35 and a flow rate regulator 36 for introducing gas, which are respectively connected to the suction pump 3.
5 and the quartz tube 31.
and a setting device 44 that controls the flow rate regulator 36 by setting the amount of gas to be introduced, such as chlorine gas, inert gas, etc., based on the pressure indication value of the differential pressure gauge 38. Note that the pipes 34 and 37 are connected through a shield section 45. After connecting the quartz tube 31 and the intake system 50 in this way, the suction pump 35 takes in a certain amount of air, and the differential pressure gauge 38 detects the internal pressure of the quartz tube 31. 36 to adjust the amount of gas introduced, and maintain the pressure inside the quartz tube 31 at 0 to -22 mmH,O.

When this state becomes stable, the sealed end 4 of the quartz tube 31
An optical fiber 41 is drawn from 2. Here, reference numeral 45 denotes a coating device for coating the optical fiber 41, and reference numeral 3
9 is a capstan used to take it out.

In addition, in FIG. 1, chlorine gas,
Although the pressure inside the quartz tube 31 is adjusted by introducing dry helium gas, argon gas, oxygen gas, etc., it goes without saying that the internal pressure may also be adjusted using the suction pump 35 alone. If there is an unstable factor such as pulsation in the suction pump 35, the suction pump 35 should always perform a certain amount of suction as shown in this figure, and the internal pressure of the quartz tube 31 should be constantly detected by the differential pressure gauge 38 to make fine adjustments. It is convenient to adjust the pressure by adjusting the amount of gas introduced by the flow rate regulator 36 because the minute pressure of 0 to -22 m@1ltO can be surely adjusted.

Here, as mentioned above, the inner diameter/outer diameter value of the quartz tube 31 is set to 0°85.
The reason why the internal pressure is set to 0 to -22 mmHxO will be explained below.

Generally, when the inside of the quartz tube 31 is made negative pressure, a force is applied to the tube in the direction of collapse due to the pressure difference between the outside and inside of the tube.1 Normally, the driving force for collapse is the surface tension of the molten glass, but in addition to the above-mentioned By generating a pressure difference between the outside and inside of the tube, the quartz tube 31 can be more easily collapsed.

However, if this differential pressure is too large, the collapse process of the quartz tube 31 itself is quite unstable, resulting in non-circularization. Therefore, of course there is an appropriate range for this differential pressure, but
This value is influenced by the dimensions of the quartz tube 310, particularly the inner diameter/outer diameter values, and the viscosity of the quartz tube 31. Naturally, the inner diameter/
The smaller the outer diameter value is, the smaller the hollow part inside the tube is, so the shrinkage rate of the quartz tube 31 during collapse is smaller, and therefore a tube with less deformation can be easily obtained. Therefore, even if the differential pressure is small, collapse is possible, and conversely, even if the differential pressure is too large, the shape does not occur to that extent. In other words, the range of differential pressure can be widened. Conversely, if the inner diameter/outer diameter value is large, the shrinkage rate is large, so
If the differential pressure is too small, it will collapse, and if it is too large, it will easily deform. In other words, the range of appropriate differential pressure becomes narrower. On the other hand, regarding viscosity, the 0 quartz tube 31 is affected by the viscosity of both the quartz tube 31 and the synthetic glass layer 30.
In the case of an ordinary quartz glass tube, its viscosity depends on the content of OH groups, and the lower the content, the higher the viscosity. The viscosity of the unidirectional synthetic glass layer 30 decreases when various dopants are added to the Stow, and the degree of viscosity is proportional to the amount of the dopant. A pipe with low viscosity is easily crushed but also easily deformed. Therefore, if the inner diameter/outer diameter values are the same, the differential pressure is determined by the smaller one.

On the other hand, when the viscosity increases, it becomes difficult to deform, but it also becomes difficult to collapse.If the inner diameter/outer diameter values are the same, the differential pressure can be specified as the larger one. Based on this premise, the following experiment was conducted to determine the above-mentioned inner diameter/outer diameter value and differential pressure range. Experiment 1 As a pipe with low viscosity, the content of OH groups (water content) was approximately 20.
1 mol of P2O is placed on the inner surface of the 0ppm natural quartz tube 31.
% doped Sl islands as synthetic glass 1i30, the cross-sectional area ratio is 3.3:1. Several types were manufactured with different inner diameter/outer diameter values. These are heated to approximately 2100°C in a drawing furnace 33 and drawn into wire, with an outer diameter of 125 μm.
- optical fiber 41 was obtained. At this time, the internal pressure of the quartz tube 31 was set to ~OmaHzO, and the pressure was gradually reduced to negative pressure, and samples were taken each time to measure the shape. The drawing speed is approximately 80
−7 minutes, the drawing tension was approximately 10 g. The result was as shown by the solid line ABC in FIG. Here, the outside (11) part of A-B is the part where there was a crushed residue inside the quartz tube 31, the outside (13) part of A-C is the part that is so deformed that it cannot withstand use, and the part A-B-C The inside (12) part is a good part with no remaining crushing or deformation.

Experiment 2 As a highly viscous tube, the content of OH groups (water content) is approximately 1
A synthetic glass layer 30 of pure 5ift was attached to the inner surface of a pp+m anhydrous quartz tube 31 so that the cross-sectional area ratio was 3.3:t,o, and several types with different inner diameter/outer diameter values were manufactured. Hereafter, in the same manner as in Experiment 1 above, the outer diameter was 125 μm.
- optical fiber 41 was obtained. At this time, the internal pressure of the quartz tube 31 was set to ~OmmHzO, and the pressure was gradually reduced to negative pressure, and samples were taken each time to measure the shape. The result was as shown by the dotted line D-E-F in FIG. Here, outside of D-H (
11) Part is the part where the crush remains in the quartz tube 31, E-F
The outer (13) portion of D-E-F is a portion that is severely deformed and cannot be used, and the inner (12) portion of D-E-F is a good portion with no remaining crushing or deformation.

As shown in FIG. 2, the inner diameter/outer diameter value of the quartz tube 31 is 0.
．． When the internal pressure is 85 or less and the internal pressure is 0 to -22 mmH*O, drawing and collapse can be stably performed simultaneously and satisfactorily. Note that when the inner diameter/outer diameter value of the quartz tube 31 is 0.1 or less, the hollow portion of the quartz tube 31 is substantially small, so the effect of the present invention is not great in this range of 0.1 or less. Very little.

(Effects of the Invention) As described above, by defining the inner diameter/outer diameter value and the inner pressure of the quartz tube within a predetermined range as in the present invention, drawing and collapse can be performed simultaneously and efficiently.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the manufacturing method of the present invention, and FIG. 2 is a graph showing the manufacturing conditions of the present invention. 30 - Synthetic glass layer 31 - Quartz tube 33 - Drawing furnace 35
~ Suction pump 36 ~ Flow rate regulator 42 ~ Sealing end 43 ~
Open end 50 ~ Intake system Fig. 1 Fig. 2 Internal pressure (mm H201

Claims (3)

[Claims] (1) A method for manufacturing an optical fiber in which a synthetic glass having a refractive index higher than that of the quartz tube is attached inside the quartz tube, and the synthetic glass is collapsed while being drawn in a drawing furnace to obtain an optical fiber. After installing the synthetic glass inside the tube so that the inner diameter/outer diameter value of the quartz tube is 0.85 or less, one end of the quartz tube is sealed to form a sealed end, and then the quartz tube is wired. The quartz tube is kept in a furnace, and the internal pressure of this quartz tube is kept at 0 to -.
A method for manufacturing an optical fiber, comprising drawing the optical fiber from the sealed end while maintaining the temperature at 22 mmH_2O. (2) Suction the gas inside the quartz tube from the open end of the quartz tube using a suction pump to reduce the internal pressure of the quartz tube to 0 to -22 mmH_
2. The method for manufacturing an optical fiber according to claim 1, wherein the optical fiber is controlled to 2O. (3) A flow rate regulator for gas introduction is provided in the middle of the pipe connecting the open end of the quartz tube and the suction pump, and the flow rate regulator adjusts the amount of gas introduced to maintain the internal pressure of the quartz tube from 0 to -22 m.
3. The method for manufacturing an optical fiber according to claim 1 or 2, wherein the optical fiber is controlled to mH_2O.