JPS60215537A - Treatment of porous preform for optical fiber - Google Patents

Abstract

PURPOSE:To obtain an optical fiber having uniform clad thickness along its length, by passing an inert gas in a specific manner in the heat-treatment of a porous preform for an optical fiber in an atmosphere containing a chlorine-containing compound. CONSTITUTION:A porous preform 5 is lowered under rotation into the furnace core tube 12 containing the inner tube 14 (the sign 13 is electrical heater) to effect the heat-treatment. The preform is converted to transparent glass 5a gradually from its lower end. In the above apparatus, a process gas containing a chlorine compound is introduced from the inlet 16, passed through the annular path 15 countercurrently to the transfer motion of the preform 5, made to contact with the preform 5 at a high-temperature zone, and discharged from the outlet 18. Separately, an inert gas is introduced from the inlet 17, passed parallelly to the transfer motion of the preform 5, turned at the lower end of the inner tube 14, passed through the path 15, and discharged from the outlet 18.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for processing porous RQ material for optical fiber.

(Prior Art) A porous base material for an optical fiber produced by a VAD method, an OVD method, etc. is then subjected to heat treatment for dehydration and transparent vitrification.

Usually, the heat treatment in "-" is 11! The process is carried out in an atmosphere containing elementary compounds, and conventionally, a porous base material for an optical fiber is processed as shown in FIG.

In FIG. 1, a heating furnace 1 is equipped with an electric heater 2a and a quartz-based furnace core tube 2b. A gas outlet 4 is formed at the bottom.

When the porous m-material 5 is processed by this heating furnace l, a gas containing a single elemental compound is supplied from the gas population 3 into the furnace core tube 2b, and the porous m-material 5 inserted into the furnace core tube 2b is It is moved to the high-temperature part of the furnace tube 2b in a rotating state, and is sequentially heated from the end thereof to become transparent vitrified.

At this time, when the porous part 5h excluding the transparent vitrified part 5a is exposed to a chlorine compound (for example, 5OC12) for a long time, the chlorine compound and the dopant (for example, Ge02) in the porous 1'iJ material 5 are combined with the following formula. I reacted unnecessarily, like
The thickness of the cladding portion of the base material after being made into transparent vitrification becomes non-uniform in the longitudinal direction.

GeO+ 250111:l +GeCI2+ 2S0
22 (Objective of the Invention) In view of the problem described in -1-, the present invention provides a method for processing a porous preform for an optical fiber, in which the thickness of the cladding portion becomes uniform in the longitudinal direction.

(Structure of the Invention) The treatment method according to the present invention involves placing a porous In material for an optical fiber in an atmosphere containing a chlorine compound, and moving the porous base material in the atmosphere toward a high temperature part in the atmosphere. In the heat treatment method, a processing gas containing a chlorine compound is flowed in the high temperature part in the above atmosphere in the opposite direction to the moving direction of the porous base material, and the outer periphery of the porous base material in the atmosphere is heated in a direction opposite to the moving direction of the porous base material. The feature is that the inert gas flows in the same direction as the inert gas.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows an example of the apparatus used in the seventh aspect of the present invention, and the heating furnace 11 shown in the figure is equipped with a stone pod type furnace core tube 12 and an electric heater 13.

Inside the core tube 12, a stone pod type inner tube 14 is installed from its toe end to the heater region, and a gas passage 15 is formed between the inner tube 14 and the cores 1 and 12.

Further, a gas inlet 1117 is formed in the F section of the furnace core tube 12, and a gas inlet 1117 communicating with the inner tube 14 and a gas outlet 18 communicating with the waste flow path 15 are formed in the F section of the furnace core tube 12. It is formed.

When heat-treating the porous AI old material 5 using the apparatus shown in FIG. 2, the porous square material 5 inserted into the inner tube 14 of the heating furnace 1.1
Assuming that the rotational shape is 1, we move it downward,
At this time, chlorine compound-containing processing gas was supplied +JI from Kass population 16 into the core 'Ft' 1.2.

Inert gas is supplied into the inner pipe 14 from a gas pipe 1-11.7.

The conditions for heat-treating the porous +1'l material 5 are as follows, as an example.

l) Treatment temperature: 700° C. or higher, preferably a temperature at which the porous base material 5 can be completely transformed into transparent glass.

2) Processing gas SOCl2, CI, , CCl2, NOCI, etc.
A gas mixture of chlorine compounds and helium that has the ability to volatilize dopants.

3) Inert gas helium, or helium and other inert gases (Ar,
Mixed gas with N2).

However, a substance that does not volatilize the dopant, such as 02 or a chlorine compound containing 02, may be mixed.

4) Base material movement speed 1000mm/hour or less.

Note that the porous base material 5 is made of Ge, P, B, AI,
It contains oxides such as Sb as Dopan I.

Further, as shown in FIG. 3, it is desirable that the distance between the lower end of the porous ff85b in the porous material 5 and the lower end of the inner tube 14 is about 5 cm.

When the porous material 15 is heat-treated in the furnace core tube 12 as described above, a processing gas is supplied to the high temperature section 19 of the furnace core tube 12, and in this state, the porous base material 5 is dehydrated sequentially from its end. treatment and transparent vitrification treatment, but at this time, porous f! Since the porous portion 5a of the jm material 5 is covered with an inert gas, the porous portion 5a is not exposed to the processing gas, and therefore the dopant does not volatilize from the porous portion 5a. The length of the base material after the treatment is −L
The refractive index distribution over the direction is maintained in a predetermined uniform state.

Next, specific examples and comparative examples of the method of the present invention will be explained.

By the VAD method using a known multi-tube burner, S i
A porous 8I material 5 made of OG e O2 system and having an outer diameter of 55 mm was prepared and heat treated using the apparatus shown in FIG. 2 under the following conditions.

Temperature of heating furnace 11: 1450'C! Processing gas: He l0j2/min and S + CI 214
127 minutes is supplied from the gas inlet 16. Inert gas: Hefl//minute is supplied from the gas port 17. Moving speed: 360 mm/hour. The outer diameter of the bar after the above treatment is about 22 mm, and As a result, a refractive index distribution with a clear interface between the core and cladding parts was obtained.

Furthermore, the thickness of the cladding portion in the treated base material -1- was highly uniform as shown by the dotted line in Figure 5.

Note that the thickness of the cladding portion in FIG. 5 is calculated to correspond to the value when the outer diameter of the core portion is 50 pLm.

Comparative Example When the same porous RII 44 as in the specific example was heat-treated using the apparatus shown in FIG. The base material was treated.

In the case of this treated matrix, the refractive index distribution was as shown in FIG. 4, but the thickness of the cladding part in the treated matrix was less uniform, as shown by the solid line in FIG.

(Effects of the Invention) As explained below, when using the method of the present invention, 1±, when a porous base material is heat treated in an atmosphere containing an IJI elementary compound, while covering the outer periphery of the porous base material with an inert gas. By processing this, it is possible to make the thickness of the cladding portion uniform over the length direction, and also to make the refractive index distribution in the longitudinal direction uniform.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram schematically illustrating a conventional method for treating I-shaped materials, and FIG. 2 is an explanatory diagram schematically illustrating a method for treating I-shaped materials according to the present invention.
Figure 3 is a partially enlarged view of Figure 2, Figure 4 is a refractive index distribution diagram of the treated base material, and Figure 5 is the longitudinal measurement of the thickness of the cladding part of the treated base material. FIG. 5 Porous base material 11 Heating furnace 12 Working furnace core tube 13-φ Electric heater 14 Inner tube 5 Gas flow path 16 Gas inlet 17 for processing gas ...Gas inlet for active gas 19... High temperature section agent Patent attorney Yoshio Saito 1st round Figure 2 41!0 Figure 5 = xoIV Condolences J-Kyo

Claims (1)

[Claims] Porous 1 for optical fiber? 11 materials! In a method in which the porous base material is placed in an atmosphere containing an elemental compound and is heat-treated without moving the porous base material in the atmosphere toward a high temperature part in the atmosphere, the high temperature part in the atmosphere contains a one elemental compound. The processing gas is caused to flow in the opposite direction to the moving direction of the porous matrix, and the porous pores in the atmosphere are allowed to flow. A method for processing a porous base material for an optical fiber, which includes flowing an inert gas around the outer periphery of the material with jlτ in the same direction as the moving direction of the RJ material.