JPH06199535A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To produce a optical fiber preform capable of keeping specific refractive index constant in the longitudinal direction. CONSTITUTION:The porous optical fiber preform composed of a core part 9a and a clad part 9b is produced by depositing a glass particulate for core formed by a core burner 5 and a glass particulate for clad formed by a clad burner 6 on the tip of a seed rod 3. The growth rate of the growing end of the core part 9a of the optical fiber preform is measured by using a flood lamp 11 and a light receiver 12 to input to a CPU 15 and a control signal to control the supply quantity of a gaseous starting material to the core burner 5 is given to a mass flow controller 13 from the CPU 15 based on the measured result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber preform manufacturing method for manufacturing an optical fiber preform by the VAD method (vapor phase axial attachment method).

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 4, in the manufacture of an optical fiber preform by the VAD method, as shown in FIG. 4, an opening 2 provided in an upper portion of a reaction vessel 1 and a lower portion of a seed rod 3 made of silica glass or the like. The seed rod 3 has a rotating / elevating mechanism 4 at its upper part.
The core burner 5 and the clad burner 6 are opposed to the lower end of the seed rod 3 in the reaction vessel 1, and the source gas (the source gas of the core burner 5 is SiCl ₄ , GeCl A gas obtained by vaporizing a raw material such as _4. The raw material gas of the clad burner 6 is SiCl.
Gas that vaporizes raw materials such as ₄ . ) And combustion gas (eg,
H ₂ and O ₂ ) are supplied together with a carrier gas (eg, Ar) and hydrolyzed in the flames 7 and 8 at the tips of the core burner 5 and the clad burner 6 to produce silica glass fine particles for the core and for the clad. While depositing silica-based glass fine particles on the lower end of the seed rod 3, the seed rod 3 is pulled up by rotating the seed rod 3 around the axis of the seed rod 3 by the operation of the rotation / elevation mechanism 4, and the core portion 9a and the clad are clad. This is performed by growing the optical fiber preform 9 including the portion 9b.
In addition, 20 is an exhaust port for discharging the exhaust gas in the reaction vessel 1.

The porous optical fiber preform 9 thus obtained is an optical fiber made of transparent glass obtained by repeating the steps of sintering and vitrification of silica glass fine particles and re-external attachment several times. It becomes the fiber base material.

One of the important characteristics of the optical fiber preform made of transparent glass thus manufactured is the relative refractive index difference (difference between the refractive index of the core and the clad, hereinafter referred to as Δ). There is.

One of the factors that influence the value of this relative refractive index difference (hereinafter referred to as the Δ value) is the vertically downward growth rate v of the optical fiber preform 9 during synthesis. .

[0006]

However, in the conventional method for producing an optical fiber preform, the growth rate v is changed with time due to changes in the internal pressure of the reaction vessel 1, the temperature of the air entering from the outside, the temperature of the carrier gas, and the like. Change, the Δ in the longitudinal direction of the optical fiber preform obtained by vitrification fluctuates, and there is a problem that uniform characteristics cannot be obtained in the longitudinal direction.

An object of the present invention is to provide a method of manufacturing an optical fiber preform capable of keeping the relative refractive index difference value constant in the longitudinal direction.

[0008]

Means for Solving the Problems To explain the means of the present invention for achieving the above-mentioned object, the present invention provides the tip of a seed bar with glass fine particles for core formed by a core burner and glass fine particles for clad formed by a clad burner. In the method for manufacturing an optical fiber preform, which is a porous optical fiber preform composed of a core part and a clad part, is measured on the growth rate of the growth end of the optical fiber preform to determine which one The amount of gas supplied to the burner is controlled.

[0009]

When the growth rate at the growth end of the optical fiber preform is measured in this way and feedback is applied to control the gas supply amount to either burner based on the measurement result,
The relative refractive index difference value can be kept constant in the longitudinal direction. Therefore, the characteristics in the longitudinal direction of the optical fiber preform can be kept uniform.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of an apparatus for carrying out a method for producing an optical fiber preform. In this embodiment, a projector 11 including a laser transmitter that emits a light beam 10 such as a laser beam that traverses the lower end of the core 9a is provided on one side of the lower portion of the optical fiber preform 9, and the optical fiber preform 9 is A light receiver 12 is provided at a position on the opposite side with respect to the pinch, which receives a light beam 10 that passes through without being blocked by the core portion 9a.

The core burner 5 and the clad burner 6 include
Mass flow controllers 13 and 14 are provided to control the flow rates of the respective gases supplied to them. In this figure, a mass flow controller 13, which controls the flow rate of each gas of the core burner 5 and the clad burner 6,
Only one each is shown on behalf of 14.

Further, these mass flow controllers 1
3, 14 are controlled by a signal from a CPU (central processing unit) 15. The CPU 15 uses the light receiver 1
2 gives a signal, and based on the result, the CPU 1
A control signal is supplied from 5 to the rotation / elevation mechanism 4 and the mass flow controllers 13 and 14 as described above.

Also in such an optical fiber preform manufacturing apparatus, the optical fiber preform 9 is manufactured by using the core burner 5 and the clad burner 6 and by using the rotation / elevation mechanism 4 as in the conventional example. . At this time, the projector 11 is arranged so as to cross the lower end of the core portion 9a in the lower portion of the optical fiber preform 9.
A light beam 10 is emitted from a light source and is received by a light receiver 12.
As the growing end of the optical fiber preform 9 grows, the light beam 1
When a part of 0 is cut off and the power received by the light receiver 12 is reduced to half from the full power, rotation from the light receiver 12
A command is issued to the elevating mechanism 4, and the optical fiber preform 9 is pulled up until the light receiving power of the light receiver 12 is restored to full power. At this time, the CPU 15 to which the signal from the light receiver 12 and the signal from the rotation / elevation mechanism 4 are given, the amount of pulling up calculated from the number of rotations of the motor of the rotation / elevation mechanism 4 is calculated in the time required for pulling up Then, the growth rate in the longitudinal direction of the optical fiber preform 9 per unit time is calculated.

On the other hand, assuming that the length L in the longitudinal direction of the portion of the optical fiber preform 9 which is generated by the core burner 5 and hits the core portion 9a is constant, the time required to pull up only the portion L is the growth rate. Inversely proportional to. Further, it is assumed that a constant amount of GeO ₂ is supplied into the core portion 9a per unit time,
Ge is included in the core portion 9a in the longitudinal direction L.
Considering that it is proportional to the amount of ₂ , Δ is proportional to the time required to pull up the optical fiber preform 9 by L and is inversely proportional to the growth rate of the optical fiber preform 9 in the longitudinal direction. Therefore, in order to keep Δ as constant as possible, it is necessary to adjust the input amount of GeCl ₄ in an amount inversely proportional to the growth rate.

Based on these conditions, C is adjusted so that the amount of GeCl ₄ charged is adjusted so as to be constant at a desired Δ.
A control signal is sent from the PU 15 to the mass flow controller 13, and the optical fiber preform 9 is manufactured while controlling the mass flow controller 13. Δ in the longitudinal direction of the optical fiber preform manufactured by the conventional method as a comparative example, the variation of the growth rate, and Δ in the longitudinal direction of the optical fiber preform produced by the method of the present invention, the variation of the growth rate, It is shown in FIGS. 2 and 3.

The variation Δ in the longitudinal direction of the optical fiber preform manufactured by the conventional method and the variation of the growth rate show large fluctuations as shown in FIG.

On the other hand, the variation Δ in the longitudinal direction of the optical fiber preform manufactured by the method of the present invention and the variation of the growth rate are as shown in FIG. It was reduced to 1/3 of the variation.

Table 1 shows the comparison results of the characteristics of the optical fiber preform manufactured by the conventional method and the characteristics of the optical fiber bare wire, where Δ is the variation in growth rate, σ of dispersion and bending loss.

[0019]

[Table 1] As is clear from Table 1, according to the method of the present invention, various characteristics are improved as compared with the conventional method.

In the above embodiment, the feedback from the growth rate of the optical fiber preform in the longitudinal direction is applied to the mass flow controller 13 for adjusting the input amount of GeCl ₄ .
The mass flow controller 13 that controls the amount of hydrogen, the amount of oxygen, and the amount of argon supplied to the core burner 5, or the mass flow controller 14 that controls the amount of each gas supplied to the clad burner 6, etc., is fed back to any factor affecting Δ. Good.

[0021]

As described above, in the method of manufacturing the optical fiber preform according to the present invention, the growth rate at the growth end of the optical fiber preform is measured and the gas supply amount to the burner is controlled by the measurement result. Since the feedback is applied, the relative refractive index difference value can be kept constant in the longitudinal direction. Therefore, according to the present invention, it is possible to suppress variation in characteristics of the optical fiber preform in the longitudinal direction, and it is possible to efficiently manufacture an optical fiber having desired characteristics.

[Brief description of drawings]

FIG. 1 is a side view showing a schematic configuration of an example of an apparatus for carrying out a method for producing an optical fiber preform according to the present invention.

FIG. 2 is a characteristic diagram showing variation in Δ value and growth rate in a longitudinal direction of an optical fiber preform manufactured by a conventional method.

FIG. 3 is a characteristic diagram showing variations in Δ value and growth rate in the longitudinal direction of the optical fiber preform manufactured by the method of the present invention.

FIG. 4 is a side view showing a schematic configuration of an example of an apparatus for performing a conventional optical fiber preform manufacturing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction container 2 Opening part 3 Type rod 4 Rotation / lifting mechanism 5 Core burner 6 Clad burner 7,8 Flame 9 Optical fiber base material 9a Core part 9b Clad part 10 Exhaust port 11 Emitter 12 Light receiver 13,14 Mass flow controller 15 CPU

Claims (1)

[Claims] 1. A porous optical fiber preform comprising a core portion and a clad portion is manufactured by depositing core glass fine particles formed by a core burner and clad glass fine particles formed by a clad burner on the tip of a seed rod. In the method for producing an optical fiber preform, the growth rate of the growth end of the optical fiber preform is measured, and the gas supply amount to any of the burners is controlled by the measurement result. Production method.