JPS59152234A - Preparation of parent material for optical fiber - Google Patents

Abstract

PURPOSE:In preparation of a parent material for single mode optical fiber by vapor-phase axial deposition (VAD method), to obtain a parent material capable of forming an optical fiber having low loss, by setting a partition wall between a part for forming a porous parent material for core and a part for forming a porous parent material for clad. CONSTITUTION:The flame flow 2 of the torch 1 for synthesizing fine particles for core is blown on the starting material 11 (the sign 12 is a rotary pulling device) in the reactor 15, the fine particles 3 of glass contained in it are attached and piled on the material to form the porous parent material 9 for core. The flame flow 6 of the torch 5 for synthesizing fine particles for clad is blown on the material, the fine particles for clad contained in it is attached and piled on the parent material 9 to form the porous parent material 10 for clad. In the above-mentioned method, the partition wall 16 is made between a part for forming the parent material 9 and a part for forming the parent material 10, so that prepared excess fine particles for core and prepared excess fine particles for clad are discharged from the exhaust vent 14 and the exhaust vent 13 separately, respectively, without blending.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a base material for a single mode optical fiber by the vapor phase axial deposition method (VAD method). 1. Refer to FIG. 1 for a conventional manufacturing method of this type. The explanation is as follows.

In FIG. 1, a core particulate synthesis torch 1 is equipped with H2 gas for combustion and 0.00000000. The glass-forming raw materials 5ift, , G60!4 sent together with the gas form a flow of core glass fine particles 3 inside the flame stream 2 by a flame hydrolysis reaction, and at the same time adhere to the tip of the rotating starting material 11. The particles are deposited to form a core porous base material 9 which is an aggregate of glass particles. In addition, glass fine particles 7 for cladding are synthesized inside the flame stream i by the fine particle synthesis torch 5 for back cladding, and adhere and deposit on the surface of the porous base material 9 for core formed in the above step, forming the core part and the cladding glass particles 7. A porous matrix 10 having layers is prepared.

The porous base material 10 produced in this way was
A transparent preform for optical fiber is obtained by heating at a temperature of ~1600°C.

According to such a conventional method, the core fine particle synthesis torch 1
Among the glass particles 3 and 7 synthesized by the cladding particle synthesis torch 5, surplus particles 4 and 8 that have not been deposited are exhausted to the outside of the reaction vessel 15 from the exhaust port 3. However, at this time, the core surplus fine particles 4 and the cladding surplus fine particles 8 are not completely separated and exhausted, and most of the core surplus fine particles 4 are on the surface of the core porous base material 9 and the cladding. The excess fine particles 4 for the core and the surplus fine particles 8 for the cladding are mixed together and reach the exhaust port through a part of the surface of the porous body.
8 to the outside of the reaction vessel 15.

Therefore, as shown in FIG. 2, a base widening of the refractive index distribution exists at the boundary between the core and the cladding in the optical fiber base material produced in this manner. In single-mode optical fibers, where loss increases due to the effect of optical power spread on the cladding layer, in the case of a refractive index distribution with a base spread as shown in Fig. 2, the effect of optical power spread on the cladding layer is reduced. Because of this, it is difficult to reduce loss and the thickness of the cladding layer must be increased.
There are problems such as ``31.''

Therefore, a manufacturing method has been proposed that solves the above-mentioned problems by aiming at a step-type refractive index distribution, which is the ideal form of the refractive index distribution of a single mode optical fiber. One method is to install two exhaust ports as shown in Figure 8.

This is a way to That is, an exhaust port 14 for exhausting only the core surplus fine particles 4 and an exhaust port 3 for exhausting only the cladding surplus fine particles 8 are provided, and each surplus fine particle is exhausted individually. Another method is as shown in Figure 4.
Inert gas is blown out from the gas blowing nozzle 17 onto the surface of the formed porous base material 9 for the core 1, and the surplus fine particles 4 for the core are removed by the gas flow]8.
This is a method of preventing the excess fine particles 8 for cladding from being mixed with the excess fine particles 8 for cladding.

The present inventors have studied these two proposed methods, that is, the methods shown in FIG. 8 and FIG. Therefore, it became clear that there was still a skirt spread at the edge of the phage rad boundary of the optical fiber base material.

The present invention is characterized in that a partition wall is provided between the core porous base material forming section and the cladding porous layer forming section, and excess fine particles for the core and excess fine particles for the cladding are completely separated and exhausted. The purpose is to provide a method for manufacturing an optical fiber base material having a step-type distribution structure, which is the ideal form of the refractive index distribution of a single mode optical fiber, by preventing the refractive index distribution of the base broadening at the core-clad boundary. It is in. The present invention will be described in detail below with reference to the drawings.

FIG. 5 shows an embodiment of the present invention, which differs from the conventional method in that a partition wall 16 is provided between the core porous base material deposition section and the cladding porous layer deposition section. The core surplus fine particles 4 and the cladding surplus fine particles 8 are exhausted from the exhaust ports 18 and 14, which are separated by the partition wall 16, respectively.

According to such an apparatus configuration, the surplus fine particles 4 that were not deposited as the porous base material 9 for core are
Surplus for cladding transmitted through the surface of! There is no mixing with II fine particles, and therefore it is possible to obtain an optical fiber base material having an almost perfect step-type refractive index distribution.

The material of the partition plate may be any material as long as it has heat resistance of about 500° C. or higher, such as glass plates, ceramics, etc. Next, examples of reaction conditions in Examples of the present invention will be described.

For core particle synthesis torch 1, 5iOt, , GeC
t.

A raw material gas 11 mixed at a ratio of 9a:7 (mo1%) was fed together with 250 cc/min of He gas for carrier at a flow rate of 100 cc/min.
2 gas 8 l/min, 0□ gas 6 l/min XI
(Flame hydrolysis is performed with a flame stream 2 composed of e-gas at 1 l/min to generate a core glass fine particle stream 8, which is sprayed onto the tip of the starting R starting material 11 rotating at 15 rpm to form a core glass particle stream 8. A porous base material 9 was formed. When the core porous base material 9 passed through the partition plate 16 and grew to the position of the cladding fine particle synthesis torch 5, SiCl 4 was heated to 80
Carrier Hel gas 850 at a flow rate of 0 cc/min
Co/min and feed it into a 2'' rad fine particle synthesis tool 5.

61//n] Soil n102 Gas 7 l/min, l
(Flame hydrolysis is performed by a flame flow 6 composed of e-gas at 1 l/min to generate a glass particulate flow 7 for the cladding, and this is blown onto the surface of the porous base material 9 for the core to form a cladding layer. A porous base material 10 having a core portion and a cladding layer was produced at a speed of 52 r.

During the above process, the excess fine particles 4 for the core are passed through the exhaust port 14, and the excess fine particles 8 for the cladding are passed through the exhaust port 13 into the reaction vessel 1.
The mixing phenomenon of excess fine particles 4 for the core and excess fine particles 8 for the cladding, which had conventionally occurred, could be completely prevented.

The porous base material 10 thus obtained was heated to 1500°C.
It was heated at a temperature of ~1600°C to obtain a transparent optical fiber base material.

The refractive index distribution of this optical fiber base material is shown in FIG. As is clear from FIG. 6, there was hardly any widening of the refractive index distribution at the boundary between the core and the cladding, and the refractive index distribution had an almost perfect step-type refractive index distribution.
! ...(7) Table 1 also shows the single-mode optical fibers fabricated according to the present invention and the single-mode optical fibers fabricated by the conventional methods, that is, the method shown in Figure 1, the method shown in Figure 3, and the method shown in Figure 4. The results of examining the content of OH groups in optical fibers at a wavelength of 1.39 μm are shown.

Table 1 These optical fibers differed only in the method of preparing the porous base material, and all other steps, such as the transparent vitrification method, the jacket tube used, and the drawing method were all the same. As is clear from Table 1, the OH group content of the optical fiber obtained by the present invention was lower than that of the conventional method. Since the refractive index distribution is step-type, the power spread of light to the cladding layer is less than that of optical fibers obtained by conventional methods, so it can be used as part of the cladding layer. This means that the increase in loss due to the influence of the jacket tube (which has a large number of OH groups) is smaller than in the conventional method.

As explained above, the method for manufacturing an optical fiber preform of the present invention is characterized by providing a partition between the core porous preform forming section and the cladding porous layer forming section. The base spread of the refractive index distribution at the boundary of the cladding can be suppressed, and the spread of optical power to the cladding layer in the 10 single mode optical fiber can be significantly suppressed compared to optical fibers produced by conventional methods. Therefore, there is an advantage that it is easy to realize a low loss single mode optical fiber.

[Brief explanation of drawings]

Figures 1, 8, and 4 are diagrams showing the configuration of an apparatus for explaining the conventional method of manufacturing a base material for single mode. A diagram ′ showing an example of the refractive index distribution of a base material for optical fiber. FIG. 5 is a diagram showing an example of manufacturing a preform according to the present invention, and FIG. 1 is a diagram showing a refractive index distribution of a preform for a single mode optical fiber manufactured according to an embodiment of the present invention. 1... Fine particle synthesis torch for core, 2... Flame flow, 3
...5 Glass fine particles for core, 4... Surplus fine particles for core, 5... Fine particle synthesis torch for cladding, 6... Flame flow, 7... Glass fine particles for cladding, 8... For cladding Excess fine particles, 9...Porous base material for core, 10.
...Porous base material, 11...Starting material, 12...Rotation-
Lifting device, 1.) 18, 14...Exhaust port, 15
... Reaction container, 16 ... Partition plate, 17 ... Gas blowing nozzle, 18 ... Gas flow. Figure 1 ε f. JP-A-59-152234 (4) Figure 3 □ Figure 4

Claims (1)

[Claims] 1 Synthesize glass fine particles for the core using a fine particle synthesis torch for the core, deposit a porous glass body for the core on the tip of a rotating support rod, grow it in the axial direction, and at the same time synthesize glass for the cladding using a fine particle synthesis torch for the cladding. After synthesizing fine particles and depositing them around a porous glass body for a core to form a porous glass body having a core portion and a cladding portion, single mode light is applied to heat the porous glass body. In the method for manufacturing a fiber base material, a partition wall is provided between a core porous glass body accumulation part and a cladding porous glass body accumulation part, and excess fine particles for the core and surplus fine particles for the cladding 1 are separated by the partition wall. A method for producing a base material for a single mode optical fiber, characterized in that exhaust is exhausted from separate exhaust ports.