JPS61227937A - Preparation of parent material for optical fiber - Google Patents

Abstract

PURPOSE:To prevent deformation and crack generation of a glass body by the effect of burner flame for cladding in a VAD process by blowing gas to the side face of a porous glass body for core. CONSTITUTION:Fine particles 5, 6 for core glass and clad glass synthesized each by a core burner 1 and a clad burner 2 are deposited on the top end on a rotating starting bar. Thus, a porous glass body 9 for core is grown in the axial direction and a porous glass for clad 10 is grown surrounding the glass body 9 for core. In this stage, the porous glass bodies are formed while blowing gas to the glass bodies 6 through nozzles 15 disposed at the opposite side to the burner 1. The porous glass bodies are then made transparent by heating.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a method for manufacturing a preform for a single mode optical fiber by a VAD method.

(Prior Art) A method of manufacturing a preform for a single mode optical fiber using the conventional VAD method will be described with reference to FIG.

In FIG. 2, Yuki is a burner for synthesizing glass fine particles for the core (hereinafter referred to as the burner for core), and 2 is a burner for synthesizing glass fine particles for the cladding (hereinafter referred to as the burner for cladding). A core glass raw material is fed to the core burner 1, and a clad glass raw material is fed to the clad burner 2 together with H2 and 02. The glass raw material for the core undergoes a flame hydrolysis reaction in the oxyhydrogen flame 5 formed by the burner 1 for the core, and becomes the glass fine particles 5 for the core. Glass particles for cladding 6 in hydrogen flame 4
becomes.

By pulling up the starting rod 8 while depositing glass particles on the tip of the non-starter @a which is attached to the rotary pulling device 7 and rotates nine times, the porous glass body 9 for the core and the cladding surrounding it are pulled up. The porous glass body 10 is formed in the axial direction. As the glass raw material for the core, Si(, /4 and, for example, GeCj14 is generally used to increase the refractive index of the core part, and as the glass raw material for the cladding, 8iC/4 is generally used. 11 is a reaction vessel, 12 is an adhesion deposition This is an exhaust pipe for discharging the glass particles 13 for the core, the glass particles 14 for the cladding, and waste gas that were not removed.

The thus produced porous glass body is subjected to a heating dehydration treatment and a heating transparentization treatment to obtain an optical fiber base material having a transparent core portion and a cladding layer. The base material is stretched to a predetermined diameter as necessary, inserted into a quartz glass tube and integrated, and then drawn to form a single mode optical fiber.

(Problems to be Solved by the Invention) The method for manufacturing a porous glass body for a single mode fiber using the conventional VAD method with the above configuration has two drawbacks as described below. Ta.

The first drawback occurs when trying to increase the production speed of porous glass bodies by increasing the total supply of glass raw materials for core and cladding in order to increase productivity. That is,
When the amount of glass raw material supplied is increased, it is necessary to simultaneously increase the flow rate of H2,02 gas in order to promote the reaction of the glass raw material. Also, in order to prevent the porous glass body from falling when broken, it is necessary to increase the bulk density of the porous glass body! However, if only the glass raw material is increased, the temperature of the surface of the porous glass body on which the glass fine particles are deposited decreases. The bulk density of the porous glass body is closely correlated with the temperature of the part where the glass fine particles are deposited.) When the temperature of the part where the glass fine particles are deposited decreases, the bulk density of the porous glass body decreases.) The porous glass body may crack or fall. becomes more likely to occur. Therefore, it is necessary to increase the flow rate of H2.02 gas to be supplied in order to increase the amount of glass raw material supplied and to prevent the porous glass body from cracking or falling at the time of death. For the above purpose, the amount of H2,02 supplied to the burner was increased, and as the core portion shown as 9 in Fig. 2 grew, it was strongly heated by the flame 4 of the cladding burner 2 and contracted and deformed. may occur. In extreme cases, the lucoa portion 9 may undergo a rapid temperature change due to heating by the flame 4 of the cladding burner 2, causing it to crack and fall. Therefore, in the conventional method, in order to achieve stable production, H2゜0 is supplied to the clad burner 2.
2. As a result, the amount of glass raw materials input was also limited, making it difficult and difficult to improve productivity.

The second drawback of the conventional method is that among the core glass fine particles 5 formed by the core-forming agent 1, those 15 that have not adhered and deposited are not promptly discharged through the exhaust pipe 12, and the cladding surface As a result, in the fabricated optical core injector base material, the boundary between the core and the cladding becomes unclear. As shown in Fig. 3, in the refractive index distribution, a slope (hereinafter referred to as skirt wave force) of the refractive index distribution occurs in the cladding layer around the core.
In single-mode optical fibers, where the transmission loss increases due to the influence of the power spread of light to the cladding, if there is a base broadening of the refractive index distribution as shown in Figure 3, the power of light to the cladding increases. Since the influence of power spread becomes larger, it becomes necessary to increase the thickness of the cladding part, which has been difficult to reduce loss.

The purpose of the present invention is to overcome the drawbacks of the conventional methods described above, improve the speed of fabricating a porous glass body, and create a single-mode original fiber with excellent transmission characteristics and a refractive index distribution structure without base broadening. It is an object of the present invention to provide a method for producing a new preform for a fiber-formed fiber.

(Means for Solving the Problems) As a result of intensive research, the present inventors found that as a means to overcome the above-mentioned drawbacks of the conventional method, by blowing gas on the side surface of the porous glass body for the core, In addition to preventing strong heating of the porous glass part for the core by the flame of the cladding burner, the gas is also blown from the opposite side of the porous glass body from the core burner to prevent the gas from adhering to the core part. The method of the present invention has been achieved, which prevents the core glass fine particles from flowing along the surface of the cladding part and promptly discharges the glass fine particles.

That is, in the present invention, glass fine particles for the core and for the cladding synthesized by the burner for the core and the burner for the cladding are deposited on the tip of the rotating starting rod, and the porous glass body for the core and the porous glass body for the core are deposited in the axial direction. A porous glass body for cladding that bends the glass body is simultaneously grown to form a porous glass body having a core portion and a cladding portion, and then the porous glass body is subjected to heating dehydration treatment and heating transparentization treatment. In a method for manufacturing an optical fiber base material, the method is such that the core burner is located within a plane substantially including the axis of the core burner and the axis of the porous glass body, and on the opposite side of the core porous glass body from the core burner. This method of manufacturing an optical fiber preform is characterized in that a porous glass body is formed while blowing gas from a nozzle onto a side surface of a porous glass body for a core.

The entire method of the present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of the present invention, which differs from the conventional method in that the core burner is made of a porous glass body and a gas blowing nozzle 15 is provided on the opposite side 11. Gas is supplied to the nozzle 15 and the core porous glass body 9 is
The point is to spray gas onto the sides of the Note that illustration of the reaction container is omitted. However, FIG. 1 is only for illustrating the gist of the present invention, and does not limit the detailed arrangement relationship or dimensions of the 17 burners and nozzles. According to the method shown in FIG. The area near the boundary of the base material is cooled by the gas blown out from the nozzle 15, and the temperature of this area decreases.
It is possible to prevent the porous base material for the core from deforming, cracking, or falling without ever increasing the temperature.

Furthermore, the flow of gas blown out from the nozzle 15 (indicated by a shaded area 16 in the figure) prevents the core glass fine particles 13 that have not been deposited on the core porous glass body 9 from reaching the cladding surface. If this is not possible, immediately remove the exhaust pipe 12.
A part of the glass material for the core does not adhere to the surface of the porous glass body 10 for the cladding, and the fourth
As shown in Fig. 5, it is possible to obtain a base material for a single mode optical fiber with almost no base widening of the refractive index distribution.

I can do that. As for the type of gas to be blown, N2 gas, 02 gas, inert gas, air, etc. are preferable because they are easy to handle, but there is no problem with using any gas as long as it does not remain permanently in place.

In addition, a new exhaust pipe 12'' was installed to discharge the glass fine particles 14 for cladding that did not adhere and accumulate as shown in FIG.
It is also preferable to provide fr-.

(Example) Example 1 81R4ft75667min, GaC in core burner 1
6cc of l2 for 1 minute, H2 gas 2.5 II 7 minutes, 02
Gas 8 J/min and Ar gas 543/min were supplied, and 131014 was supplied to cladding burner 2 at 800 cc/min.
H2 gas 20J/min, 02 gas 2s 47min and mr
Gas is supplied at 15 J/min to form core glass particles 5 and cladding glass particles 6t, and a porous material with an outer diameter of 115 nφ having a core portion and a cladding portion is placed at the tip of a starting quartz rod 8 of 18N1φ which is rotated at 30 rpm. The glass body was formed at an axial growth rate of 55jIII1 hr. At this time, as shown in Fig. 1, the core burner 1 is a porous glass body 9 for the core.
A quartz glass nozzle 15 with an inner diameter of 5 φ was installed on the opposite side of the core porous glass body 9 to spray N2 gas at a flow rate of k104/min. In addition, if the nozzle 15 is not provided under exactly the same glass particle synthesis conditions, the cladding burner 2
The core porous glass body 9 contracted and deformed due to the flame 4, and a stable porous glass body could not be formed. The porous glass body thus obtained is Hθ:, C/=99=1
After heat dehydration treatment was performed in an electric furnace heated to 1050C in an atmosphere of 1000C, transparent vitrification treatment was performed in an electric furnace at HelOO% and 1650C. As a result, an optical fiber preform having the refractive index distribution shown in FIG. 5 was obtained. After forming the base material into a fiber, it was drawn to a predetermined diameter so that the core diameter was 7.8 μm.
0 ppm) and integrated into the outer diameter f 25
The fiber obtained as a result of drawing at ttm has a transmission loss value of 0.396B/Km at a wavelength of 1.3μm,
The absorption loss due to OH group at 1.59 μm is α86B /
Km was excellent.

Comparative Example 1 When the nozzle 15 was not used under the conditions shown in Example 1, porous glass suspension # could not be obtained, so the refractive index shown in FIG. Create a base material for an optical 7-eyeper with a distribution and make it into a fiber,
The transmission loss was measured. As a result, the transmission loss at 1.3 μm is 0.7 dB/K+a, 1.39
The absorption loss due to OH group at μ+11 is 8 (IB/
Km was inferior to that of the example.

At this time, the heating dehydration treatment, transparent vitrification treatment, wire drawing conditions, core diameter, and cladding diameter were the same as in the examples, so the deterioration in transmission loss was due to the expansion of the refractive index distribution seen in Figure 6. It was assumed that this was caused by In addition, when producing the porous base material, 40cc/40cc of Sin/4 was added to the core burner 1.
Min, Ge Oj! 4 at 3.8cc/min, H2 gas 2.
2) 7 minutes, 02 gas 8J/min, Ar gas 3 no/min, BIOI f400cc7 for cladding burner
12 minutes of H2 gas. , e7 min 02 gas for 1017 min,
Ar gas was supplied at 62/min, and the outer diameter was 80. A porous glass body having a diameter of φ was formed at an axial growth rate of 35 w/hr.

(Effects of the Invention) As explained above, the method for assembling an optical fiber preform of the present invention prevents the deformation of the porous glass body for the core due to the flame of the burner for the cladding, which occurs when the creation speed of the porous glass body is increased.
It is an extremely excellent material that can improve both manufacturing efficiency and quality because it can prevent cracking and falling, and it can also reduce the widening of the base in the refractive index distribution and produce a single mode optical fiber with excellent transmission characteristics. This is a method.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing one embodiment of the present invention, Figure 2 is a diagram showing a method for manufacturing a porous glass body for single mode optical fiber using the conventional VAD method, and Figure 3 is a diagram showing a method for manufacturing a porous glass body for a single mode optical fiber using the conventional VAD method. FIG. 4 is a graph showing a refractive index distribution with a base expansion, FIG. 4 is a graph showing a refractive index distribution with almost no base expansion obtained by the present invention, and FIG. 5 is a graph showing a refractive index distribution obtained in an example. The graph shown in FIG. 6 is a graph showing the refractive index distribution obtained in the comparative example.

Claims (1)

[Claims] (1) On the tip of a rotating starting rod, deposit glass particles for the core and cladding synthesized using a burner for the core and a burner for the cladding, respectively, and form the porous glass body for the core and the porous glass body for the core in the axial direction. An optical fiber base material in which a surrounding porous glass body for cladding is simultaneously grown to form a porous glass body having a core part and a cladding part, and then the porous glass body is subjected to heating dehydration treatment and heating transparentization treatment. In the manufacturing method, gas is supplied to the core from a nozzle arranged in a plane substantially including the axis of the core burner and the axis of the porous glass body and on the opposite side of the core porous glass body from the core burner. 1. A method for producing an optical fiber preform, comprising forming a porous glass body by blowing onto a side surface of the porous glass body.