JPS593033A - Manufacture of base material for optical fiber - Google Patents

Abstract

PURPOSE:To manufacture a base material for a high-quality optical fiber having uniform quality in the growing direction when a base material for an optical fiber is grown by hydrolyzing gaseous starting materials, by controlling the surface temp. of a base material so as to keep it constant. CONSTITUTION:Oxygen, hydrogen, an inert gas and gaseous starting materials for a base material for an optical fiber are spouted from a burner 2 for an oxyhydrogen flame in a reactor 1, and a base material 10 for an optical fiber is grown on a support rod 3 by hydrolyzing the gaseous starting materials. The temp. of the surface 6 of the base material 10 is measured with an infrared thermometer 18, and the signal is inputted in a control circuit 19. The circuit 19 controls the output power of a heater 9 so as to make the difference between the measured value and the set temp. value to zero, and the surface temp. of the growing base material 10 is kept constant by regulating the temp. of excess gas 7 passing through the heater 9. A base material for a high-quality optical fiber having uniform quality in the growing direction can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD OF THE INVENTION The present invention relates to an improvement in a method for manufacturing optical fiber preforms.

Background of the technology The production of the base material for optical fiber is carried out in a reaction vessel 1 as shown in the figure.
A glass raw material and a refractive index control raw material for changing its refractive index are blown upward to achieve a predetermined spatial distribution from an oxyhydrogen flame burner 2 having a plurality of nozzles arranged below, and are hydrolyzed. Glass fine particles produced by the reaction are deposited on the lower end of the support rod 3 facing the oxyhydrogen flame burner 2, and as they grow, the support rod 3 is rotated and pulled up to obtain the optical fiber preform 10.

In the production process of the optical fiber base material 10 shown in the prior art and problem diagram,
It is very effective to maintain a uniform temperature on the surface of the base material 10, especially on the surface of the base material growth surface 6 at the bottom end of the base material where glass fine particles are being deposited, in order to obtain a high quality base material. It becomes a means. However, the temperature of the base material growth surface 6 on the base material surface during which glass particles are being deposited is due to fluctuations in the flame 4 formed by the oxyhydrogen flame burner 2 9 and changes in the cooling effect of the outside air on the outer surface of the reaction vessel 1. Change in the temperature of the gas inside the reaction vessel 1 2 Change in the temperature distribution of the gas around the base material 10 due to a change in the flow state of the gas inside the reaction vessel 1 The influence of changes in the flow rate of the exhaust gas 8, etc. will vary. Conventionally, as a means to keep this fluctuation constant, it has been possible to control the base material directly by manipulating the amount of hydrogen or oxygen supplied from the oxyhydrogen flame burner 2, or by using an external heat source such as a tungsten lamp, CO, or laser cape. A method of controlling the temperature of the growth surface 6 has been proposed, but the former is undesirable because it directly affects the glass particle generation reaction occurring within the flame 4 and the shape of the flame itself. There are problems in that the influence is local, and that it is undesirable to incorporate it into a company's equipment because there are significant restrictions on operational stability, shape, and material of the reaction vessel 1.

Purpose of the Invention The purpose of the present invention is to control the temperature of gas (hereinafter referred to as surplus gas) supplied from a location different from the burner that blows glass raw materials into the reaction container. By controlling the surface temperature of the optical fiber base material being produced at a constant level, the quality of the multi-optic fiber base material in the longitudinal direction, that is, the growth direction, can be maintained uniformly, and a high quality optical fiber base material can be obtained. It is in. This will be explained below with reference to the figures.

Embodiments of the Invention In the present invention, the temperature of the base material growth surface 6 is controlled to be constant by controlling the temperature of the excess gas 7 supplied into the reaction vessel 1 using a heater 9 as shown in the figure. According to the method of the present invention, the temperature of the base material growth surface 6 can be controlled indirectly via the flame 4 or by heat conduction of the base material 10 from the vicinity of the base material growth surface 60. There is no runner-up to worry about. In the figure, 11α to 11d are ports for supplying oxygen, hydrogen, raw material gas, and inert gas to the oxyhydrogen flame burner 2. 12 is a cleaning tower for neutralizing mainly hydrogen chloride gas contained in the exhaust gas 8; 16 is a nozzle that sprays a neutralizing liquid; 14 is a pump that sends the neutralizing liquid to the nozzle 16; 15 is a neutralizing liquid It is a receiving tank.

16 is an exhaust fan, and not only the exhaust gas 8 but also all the surplus gas 7 are sucked into the exhaust fan 16. A chuck 17 rotates the support rod 6 and moves it upward in accordance with the deposition rate of the glass particles. 18 is a thermometer for detecting the temperature of the base material growth surface 6, and usually an infrared radiation thermometer is used.

A control circuit 19 controls the output power of the heater 9 so that the deviation between the output value of the thermometer 18 and the set value becomes zero. Although it is important to reduce the thermal inertia of the heater 9 in order to speed up control responsiveness, there is a structural upper limit. Therefore, when a control system with very quick response is required, the method using the configuration shown within the broken line in the figure is advantageous. A gas merging section 21 is provided in the middle of a pipe 20 connecting the heater 9 and the reaction vessel 1, and surplus gas 7α passing through the heater 9 and surplus gas 7b not passing through the heater 9 are merged. By changing the mixing ratio of the surplus gases 7a and 7b by changing the opening degree of the flow rate control valve 22 provided in the pipe for the surplus gas 7b, the temperature of the surplus gas 7 flowing into the reaction vessel 1 is controlled as a result. do. 26 is a motor that drives the flow control valve 22, and 24 is an agitator that efficiently mixes the surplus gases 7a and 7b. It is clear that this method makes it possible to realize a control system with very quick response.

Next, when performing temperature control on the base material growth surface 6, there are cases in which the configuration within the dashed line is not used (CASB), a case in which this configuration is used (CASEB), and a case in which no temperature control is performed at all (CASE C). ) for optical fibers under 6 conditions.
The results of manufacturing the base material are shown in the table. The table shows the stability of quality in terms of band characteristics, and also shows the temperature fluctuation range of the base material growth surface 6 in each CASH for reference.

Air was used as the surplus gases 7.7α and 76.

In CASE A and B in the table, the temperature of the excess air at the inlet of the reaction vessel is 20 to 50°C.

In E and C, the amount of surplus air was 50 tA+. Furthermore, the following conditions were the same for CASE A, E, and C.

(1) Matsuful shape: 300'°" x 800mm
H''(Jh' (2) Burner supply gas: H,, 4V min*os+7t1miny Ar; 21/min+5tC14
: 1.7 town/molecule G a C70: 0-3 V min (3) e Property shape: 50mm ”=x 400 m
mLe'''Lg'' (4) Growth rate: Q, 5 ft'/min Effects of the Invention As described above, the present invention can reduce the surface temperature of the forming base material at or near the area where the granular glass is being deposited. By supplying surplus gas from a location different from the location where the burner that blows the glass material is installed, and controlling the temperature of the surplus gas to a constant temperature, the base material for optical fiber can be heated in a stable manner. The quality in the growth direction can be maintained uniformly, and a high-quality optical fiber base material can be obtained, which is a remarkable effect.

[Brief explanation of drawings]

The figure is a schematic diagram showing a method for manufacturing an optical fiber base material of the present invention. 1... Reaction vessel, 2... Oxyhydrogen flame burner, 3...
Support rod, 4... Flame, 5... Exhaust pipe, 6... Base metal growth surface, 7° 7a, 7b... Surplus gas, 8... Exhaust gas, 9... Heater, 10... Base material, 11 cL to 1
1d... Boat, 12... Washing tower, 16... Neutralizing liquid spray nozzle, 14... Pump, 15... Receiving tank,
16...Exhaust fan, 17...Chuck, 18...
・Thermometer, 19... Control circuit, 20... Piping, 21
...Gas confluence section, 22...Flow rate control valve, 23...
Motor, 24... Agitator patent applicant Sumitomo Electric Industries Co., Ltd. Patent attorney Tamamushi, Hisa Gobe

Claims (2)

[Claims] (1) A glass raw material gas is ejected from an oxyhydrogen burner to undergo flame hydrolysis, and granular glass produced by the flame hydrolysis is deposited in a rod shape to produce a porous optical fiber base material in a reaction vessel. In the method for manufacturing an optical fiber base material, the surface temperature of the part of the forming base material where the granular glass is being deposited or the vicinity of the part is detected, and the core surface temperature is measured in the reaction vessel by the oxyhydrogen burner. 1. A method for manufacturing a base material for Hikari 7 Eyepa, characterized in that the temperature is controlled by the temperature of gas supplied from a location different from the ejection location. (2) Control of the surface temperature includes means for heating or cooling the gas, and means for merging gas different from the gas from the middle of piping connecting the means for heating or cooling the gas and the reaction vessel. 2. The method of manufacturing an optical fiber preform according to claim 1, further comprising: and means for adjusting the flow rate of the different gases.