JPH02172838A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To stably and easily obtain the preform by vertically moving a perpendicularly installed glass rod back and forth while rotating the rod, then by spraying gaseous raw materials from a burner fixed perpendicularly to the rod to deposit fine glass particles thereon by each one layer. CONSTITUTION:A 'Pyrex(R)' glass tube is perpendicularly assembled in a housing tube B of a hermetic furnace 1 consisting of a spherical chamber of a reaction part A. The quadruple quartz tube burner 3 is horizontally fixed to the central side face of the chamber of the reaction part A and a discharge port 7 is disposed to the opposite part. The glass rod 2 for the core is passed through the center of the furnace and the upper part is fixed to a driving shaft. The glass rod is rotated at about 50rpm and while the glass rod is moved back and forth vertically at about 150mm/min speed, SiCl4 is fed together with an oxyhydrogen flame with gaseous O2 as a carrier gas into the reaction part from the burner 3 to deposit the fine Si glass particles by each one layer on the rod 2 to form the porous glass body 5. The glass body 5 is then heated to about 1500 deg.C in an atmosphere of He, etc., to form the transparent glass. The optical fiber preform is thus produced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an optical fiber preform, and in particular to a single-mode optical fiber preform that is large in size, has small variations in structural characteristics, has low loss, and has few disconnections. The present invention relates to a method for stably and easily manufacturing renovation products.

[Conventional technology and issues to be solved] Conventionally, in the manufacturing method of optical fiber preforms, a core or a rod consisting of a core and a cladding layer is installed horizontally, and the rod is rotated to move the gaseous glass raw material back and forth from side to side. introduced into a moving oxyhydrogen flame burner, and the glass particles produced by the flame hydrolysis are deposited on the rod.
This is done by creating a porous glass layer using the so-called external coating method, and then heating and melting it to make it transparent. For this reason, normally a rod 12 is arranged horizontally in a furnace 11 as shown in FIG. Flame from rod 1
2, and glass fine particles are deposited there as soot 14.

However, when manufacturing optical fiber preforms using such horizontal equipment, as the desired preform becomes longer and larger, even if the rod is straightened in advance, it becomes difficult to simply turn it horizontally. As the rod inevitably bends, the center shifts between the ends and the center, resulting in a difference in the deposited thickness, and this difference is accumulated over the course of repeated repetitions, resulting in a large difference in the amount of deposit, and the cladding in the longitudinal direction. There is a problem in that the thickness varies. In addition, this method has the disadvantage that the soot is destroyed due to repeated bending as the glass particles are deposited on the rod.Furthermore, in this conventional device, the burner rotates eight times from side to side, so the opening 15 Due to the large size of the preform, it is easy for outside air to flow in and dirt to enter, which causes the preform to contain foreign matter and air bubbles, which has the disadvantage of causing fiber breakage and transmission loss.

[Means for Solving the Problems] The present invention relates to a method for manufacturing an optical fiber preform that overcomes these disadvantages, and includes introducing a gaseous glass raw material into an oxyhydrogen flame burner to cause flame hydrolysis, In the method of producing an optical fiber preform by uniformly depositing the generated glass particles on the surface of a core glass rod by an external method to produce a porous glass body, and then turning this into transparent glass to produce an optical fiber preform, the rod is installed vertically. This was rotated and reciprocated up and down, and a burner fixed at right angles to the rod at the center of the moving part sprayed glass particles uniformly with flame to deposit the glass particles one layer at a time and integrate them. It is characterized by being heated as it is and becoming transparent vitrified.This deposition is also carried out in a vertical reactor with a reaction section A in the center and storage sections B above and below. The burner is characterized by having an insertion port C and an exhaust port for fixing each, and also ■ Inert gas is poured from both ends of the storage part and exhausted together with the reaction gas from the exhaust port to create a porous structure. It is characterized by obtaining a glass body.

That is, as a result of various studies on how to stably and easily obtain a large-sized, single-mode optical fiber preform with no longitudinal dimension change, the present inventors found that gaseous glass raw materials such as silicon tetrachloride In this method, glass particles obtained by hydrolysis in an oxyhydrogen flame are deposited on a glass rod for a core, and the resulting porous glass body is made into transparent vitrification. In order to deposit fine particles and obtain a porous glass body with a uniform deposition thickness, it is recommended that a rod be placed vertically in the furnace and rotated to move it up and down repeatedly. It was discovered that glass particles should be sprayed almost horizontally from an oxy-hydrogen flame burner fixed at right angles to this rod, and that the deposition should be carried out through a fixed exhaust port. In this case, introducing an inert gas into the reactor, which has a base material storage area for eight positions above and below the reaction area and the base metal, will prevent bubbles from being generated due to the inflow of foreign matter from the outside. The present invention was completed after confirming that rice can be harvested in this way.

This will be explained in detail below.

The reactor used in the method of the present invention has a burnaro, a distance between the deposition surfaces necessary for blowing the flame at the outlet of the gas stream during the reaction, and a distance between the deposition surfaces.
A reaction part with a large diameter in consideration of radiant heat, and 8 on the top and bottom.
The reactor consists of a small-diameter housing that protects the rods during deposition from the outside air.Inert gas is supplied into the furnace, but this inert gas is purified by passing through a filter. Air, nitrogen, helium, argon, etc. may be used, and this supply is carried out through gas inlets provided at the upper and lower parts of the reactor, and an exhaust port is provided at the center of the reactor and is used by fixing it.

In the method of the present invention, a gaseous glass raw material is introduced into an oxyhydrogen flame burner, and glass fine particles are formed by the flame hydrolysis, which may be performed by a known method. silicon tetrachloride,
It is sufficient to use a gasifiable silicon compound containing trichlorosilane, etc. The burner is a concentric ring-shaped burner that supplies this gaseous glass raw material from the center and supplies oxygen gas and hydrogen gas from the periphery. You can use something.

Since the preform obtained by the method of the present invention is dimensionally stable in the longitudinal direction, the rod on which the glass particles are deposited is a glass rod consisting of a core portion or a partially clad portion designed in advance as a single-mode optical fiber. The starting material is one that is centered straight. This rod is installed vertically in the furnace, and during operation, the speed is set at 5 to 80 rpm, for example, in order to deposit the fine glass powder uniformly.
After rotating the rod to make sure that there are no irregularities, twists, or bends along its entire length, it is necessary to repeatedly move the rod up and down in order to uniformly adhere the fine glass powder to the entire length of the rod.

In addition, since the blowing of glass fine powder onto this rod allows the fine glass powder to be deposited layer by layer uniformly and accurately over the entire length of the rod, it is necessary to repeatedly move the glass powder up and down as described above. It is necessary to fix an oxyhydrogen flame burner at right angles to the rod so that the fine glass powder is blown from directly beside the rod. It can be assumed that the

Next, this will be explained based on the attached drawings.

FIG. 1 shows a longitudinal sectional view of an optical fiber preform manufacturing apparatus according to the method of the present invention. This device consists of a reaction part and a storage part, and can be used as a single piece or as a piece that can be divided. Inside the closed furnace 1, a rod 2, which is the starting material, is held vertically. 2 is rotated at 5 to BO rpm by an external drive during furnace operation,
At the same time, it is repeatedly moved up and down, and the speed of this movement can be determined experimentally by considering the size of the starting member and the state of destruction of the soot. A gaseous glass raw material such as silicon tetrachloride and oxyhydrogen are sent to an oxyhydrogen flame burner 3, and a flame 4 is blown onto the rod, and the glass produced by hydrolysis in this oxyhydrogen flame is Fine powder is deposited on this rod 2 and a porous glass body (soot) 5 is formed. Since the rod moves up and down as it rotates, the porous glass body 5 is formed almost uniformly on the rod 2. Since the rods are held vertically, even if the rods are long, unevenly distributed gravity is not applied to the central part, and furthermore, even when porous glass bodies are deposited, the rods do not bend or bend. Porous glass bodies have the advantage that the central axis of the flame and the central axis of the rod do not deviate, so the amount of deposition remains constant, there is no difference in the amount of deposition in the longitudinal direction, and there is no variation in the thickness of the deposit. gender is given. In addition, this furnace has openings for inserting the burner and exhaust pipe, and inert gas supply ports 6 are provided at the top and bottom, through which inert gas is introduced, and these are exhausted from the exhaust port. Since it is discharged to the outside through the pipe, this has the advantage of eliminating the contamination of foreign matter and foaming that flow in from the outside.

[Example] Next, examples of the present invention will be given.

Example As the closed furnace 1 shown in Fig. 1, the inner diameter of the reaction section was 280 m.
A spherical Pyrex chamber with a diameter of mφ was prepared, and a Pyrex glass tube with an inner diameter of 180 mmφ and a length of 800 mm was vertically assembled into the chamber as a storage part by slotted jointing. A quadruple-tube quartz burner is fixed horizontally on the side of the center of this spherical Pyrex chamber, and the inner diameter 10
An exhaust port with a diameter of 0 mm was made, and a five-English tube with an outer diameter of 98 mm was inserted into the port and connected to the outside air exhaust duct.

The glass rod for the core has an outer diameter of 17.7mmΦ and a length of 62
0mm, 17mmΦ x 200mmL on both ends
A quartz dummy glass is welded to the top, and a 15mm
Φx ao.

A mmL quartz rod was fixed and passed vertically through the center of the closed furnace, and the upper part was fixed to the drive shaft. This silica glass rod is designed as a single mode optical fiber core in the 1.3 μ band, and has a refractive index difference of 0.34% due to germanium doping, and a ratio of core diameter to cladding layer made of silica glass of 0.34%. 205, the outer diameter of the glass rod is finished to within ±100 μm. In addition, this rod is installed via a quartz glass dummy in the rotating part of a vertical pulling machine that has a weight weighing function.
Since it is not rotated at rpm, the movement of the central axis due to eccentricity of the rod and vertical B movement is within ±0.5 mm. Further, as a measuring device for fiber design, a Preform Analyzer model P-101 manufactured by York Co., Ltd., UK was used, and an outer diameter measuring device manufactured by Anritsu Electric Co., Ltd. was used to determine the accuracy of the shaft.

After it is installed in the chamber, the hole between the top and bottom is closed except for the hole that the dummy passes through, clean air is blown from near the hole between the top and bottom to prevent outside air from entering, and the entire length of the glass rod is heated with acid. Fire polished with hydrogen flame.

Next, silicon tetrachloride is sent together with an oxyhydrogen flame from a quadruple tube burner, using oxygen gas as a carrier, and silica glass particles are sprayed onto the glass rod. At this time, the glass rod is rotated at 50 rpm and moved vertically by 150 mm/
The silica glass particles were deposited layer by layer by repeated movement at a speed of 1 minute. At this time, the amount of oxyhydrogen and silicon tetrachloride will be changed as the soot diameter increases. At the start, the amount of silicon tetrachloride will be small, and as the soot diameter increases, the amount of silicon tetrachloride and the amount of oxyhydrogen will be increased. and finally stc
I142og/min, H, 50j2/min, 0.25fi/
minutes. This reaction was continued for 12 hours, and the entire length was repeated about 130 times until the amount of deposited silica particles reached the target value, and then the reaction was stopped and the resulting porous glass body was examined. Outer diameter is 109
．． The diameter was 0 mm, the total weight was 4,114 g, and the average soot density was 0.496 g/cc.

Next, this porous glass body was zone-melted in an electric furnace heated to 1,500°C through which a mixed gas of helium and chlorine was passed, and the result was that it had an outer diameter of 58.1 mm and was transparent, with no bubbles or foreign matter. A glass ingot was obtained, which was heat-processed to have an outer diameter of 30 mm, and the stationary portion was made into a glass fiber with a diameter of 125 μm using a wire drawing machine, and structural fluctuations over its entire length were examined. The most common way to determine variations in the cladding is to examine variations in the designed cutoff wavelength (λC) and mode field diameter (ω).
When I checked the 10 points, this one had an average of λ, :=
The deviation (maximum and minimum value difference) was 23 nm, and the eccentricity was excellent with an average of 0.14 μm.

Comparative Example Using the horizontal external device shown in Figure 2, fine silica glass particles were deposited on the quartz rod for the core used in the example to create a porous glass body, which was then treated in the same manner as in the example. When an optical fiber was made from a glass ingot, the average cutoff wavelength of this material was λ. is 1.17
7μm1 deviation is 154nm, eccentricity is average 0.77
μm1 maximum was 2.7 μm.

In addition, in this horizontal external device, the opening 16 required for eight shifts of the burner 13 has a width of 40 mm and a length of 800 mrn.
Hydrochloric acid gas inside the room leaked out and an odor wafted into the room, so in order to suppress this, the exhaust was made stronger, but the flame of the burner fluctuated greatly, and it took more than 15 hours for the soot to accumulate, which caused the soot to accumulate after vitrification. Many air bubbles were generated in the transparent glass ingot.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of an optical fiber preform manufacturing apparatus according to the method of the present invention, and FIG. 2 is a longitudinal cross-sectional view of an optical fiber preform manufacturing apparatus according to a conventionally known method. ... closed furnace, 2 ... core part, 3 ... oxyhydrogen flame burner 4 ... oxyhydrogen flame, 4 ... porous glass body, 6 ... inert gas inlet, 5. ...Gas exhaust port, 12...rod, 6...opening. No. 1 Amendment Procedures December 22, 1999 2゜Name of the invention Name related to the case concerning the person amending the manufacturing method of optical fiber preforms (2

Claims (1)

[Scope of Claims] 1. Gaseous glass raw materials are introduced into an oxyhydrogen flame burner and subjected to flame hydrolysis, and the resulting glass fine particles are uniformly deposited on the surface of a glass rod for a core by an external deposition method to form a porous glass body. In this method, a rod is installed vertically, the rod is rotated and reciprocated up and down, and a burner is fixed at right angles to the rod in the center of the moving part. A method for manufacturing an optical fiber preform, which is characterized in that glass particles are deposited layer by layer by uniformly spraying raw material gas together with flame from a flame, and the glass particles are heated while being integrated to form transparent glass. 2. This deposition is carried out in a vertical reactor with a reaction section in the center and storage sections above and below, and the reaction section is characterized by having a burner insertion port and an exhaust port and fixing each of them. A method for manufacturing an optical fiber preform according to claim 1. 3. The method of manufacturing an optical fiber preform according to claim 1, wherein the porous glass body is obtained by injecting an inert gas from both ends of the storage part and exhausting it together with the reaction gas from an exhaust port.