JP2012006791A - Method for producing optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical fiber preform stabilizable of characteristics of an optical fiber by making the growth rate of the optical fiber preform in an axial direction to suppress variations in ΔN (specific refractive index difference).SOLUTION: In the method for producing an optical fiber preform, the supply flow rate of H, which is a combustible gas, is controlled so that the growth rate of a glass fine particle deposit in an axial direction becomes constant instead of adapting to changes in the growth rate, and supply flow rate of GeCl, which is an additive, is controlled so as to be in proportion to that of H.

Description

  The present invention relates to an optical fiber preform manufacturing method for manufacturing glass particle deposits by depositing glass particles by the VAD method.

As a conventional method for manufacturing an optical fiber preform, there is known a manufacturing method in which glass fine particles are deposited by depositing glass fine particles by a VAD method (see Patent Document 1).
In the optical fiber preform manufacturing method described in Patent Document 1, the weight and growth rate of the glass particulate deposit are sequentially measured during the production of the porous preform, and the measurement increase per unit length of the glass particulate deposit is measured. The deviation between the weight and the target weight increase is fed back to the source gas, flammable gas, or auxiliary combustion gas, and the amount of glass particles deposited in the radial direction is adjusted to refract the core and cladding of the optical fiber preform. The relative refractive index difference (ΔN), which is the difference in rate, is stabilized.

By the way, in the optical fiber preform manufacturing process, when the core part is sooted to form the glass fine particle deposit, the core part burner and the clad part burner may be used. . In this case, the growth rate is calculated by monitoring the position of the tip of the core, but this growth rate may vary due to changes in deposition conditions and the like.
When the growth rate changes, the refractive index also fluctuates if an additive for adjusting the refractive index (for example, GeCl ₄ ) is constantly added at a constant flow rate regardless of the growth rate. Therefore, the axis of the manufactured optical fiber preform is changed. There is a disadvantage that the ΔN of the direction fluctuates and the characteristics of the optical fiber vary.

In order to solve this problem, a method of manufacturing an optical fiber preform is proposed in which the supply flow rate of GeCl ₄ for adjusting the refractive index is increased or decreased in proportion to the growth rate in the axial direction of the glass fine particle deposit (Patent Document 2). reference). As shown in FIG. 4, for example, when the growth rate increases, by increasing the supply flow rate of GeCl ₄ , variation in the axial direction of ΔN can be suppressed and made constant.

JP 2004-307235 A JP 2009-167029 A

  However, in the manufacturing method of the optical fiber preform described in Patent Document 2, there is a possibility that the outer diameter fluctuates. That is, if the growth rate varies, for example, if the growth rate is slow, the time for depositing soot per unit length becomes longer, so the amount of deposition per unit length increases and the soot diameter increases. When the soot diameter fluctuates in this way, there arises a disadvantage that the characteristics of the other optical fibers are not constant even if the fluctuation of ΔN is constant.

  The object of the present invention has been made in view of the above-described circumstances, and stabilizes the characteristics of an optical fiber by making the growth rate in the axial direction of the optical fiber preform constant and suppressing the fluctuation of ΔN. An object of the present invention is to provide a method for manufacturing an optical fiber preform capable of satisfying the requirements.

  The method for manufacturing an optical fiber preform according to the present invention capable of solving the above-described problem is a method for producing glass fine particles by supplying a raw material gas, a combustible gas, and an auxiliary combustible gas, and depositing the glass fine particles to produce glass fine particles An optical fiber preform manufacturing method for manufacturing a deposit, wherein the flow rate of the combustible gas is controlled so that the axial growth rate of the glass particulate deposit is constant, and the combustible gas The supply flow rate of the additive that adjusts the refractive index so as to be proportional to the supply flow rate is controlled.

According to the optical fiber preform manufacturing method configured as described above, the supply flow rate of the combustible gas is controlled so that the axial growth rate of the optical fiber preform is constant, and the supply flow rate of the combustible gas By controlling the supply flow rate of the additive (for example, GeCl ₄ ) so as to be proportional to the fluctuation of ΔN in the axial direction of the optical fiber preform, it is possible to stabilize the optical fiber characteristics. .

  According to the method for manufacturing an optical fiber preform according to the present invention, the characteristics of the optical fiber can be stabilized by making the growth rate in the axial direction of the optical fiber preform constant and suppressing the variation of ΔN.

It is a block diagram of the manufacturing apparatus explaining the manufacturing method of the optical fiber preform which concerns on this invention. It is a relationship graph of combustible gas and the flow volume of an additive which shows one Example of the manufacturing method of the optical fiber preform which concerns on this invention. It is a relationship graph of the combustible gas and the flow volume of an additive which shows the comparative example with respect to FIG. It is a relationship graph which shows that (DELTA) N at the time of adjusting the supply flow rate of an additive with respect to the conventional growth rate does not fluctuate.

  Hereinafter, a method for manufacturing an optical fiber preform according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, a manufacturing apparatus 10 that performs the method of manufacturing an optical fiber preform according to the present embodiment suspends a support bar 12 from above a reaction vessel 11 and puts a dummy on the lower side of the support bar 12. A glass rod 13 is attached. Glass particulates are deposited on the dummy glass rod 13 to form a glass particulate deposit 14. The upper end of the support bar 12 is held by the lifting device 15 and is lifted and lowered by the lifting device 15 together with the rotation. The lifting / lowering device 15 has its pulling rate (growth rate) controlled by the control device 16.

A core burner 17 and a clad burner 18 are provided in the lower part of the reaction vessel 11, and the raw material gas is controlled from the gas supply device 19 controlled by the control device 16 to the burners 17 and 18 respectively. , A combustible gas, an auxiliary combustible gas, and an additive gas (for example, GeCl ₄ for adjusting the refractive index) are supplied.

  Further, the manufacturing apparatus 10 is provided with a growth rate measuring device 21 for measuring a pulling rate that is a growth rate of the glass fine particle deposit 14. The growth rate measuring device 21 is provided with, for example, a laser oscillator 22 that emits laser light that is detection light, and a light receiving unit 23 that receives the laser light from the laser oscillator 22 and emits a signal to the control device 16. An exhaust pipe 20 is attached to the central portion of the side wall of the reaction vessel 11.

  In the manufacturing procedure of the glass fine particle deposit 14, first, the support rod 12 is attached to the lifting device 15, and the glass rod 13 attached to the tip is placed in the reaction vessel 11. Next, while rotating the glass rod 13 by the lifting device 15, glass fine particles are deposited on the glass rod 13 by the core burner 17 and the cladding burner 18.

The glass particulate deposit 14 is pulled up by the lifting device 15 while monitoring the deposition state of the glass particulate deposit 14. At this time, the pulling rate is measured by the growth rate measuring device 21 and a signal is transmitted to the control device 16. The control device 16 controls the supply flow rate of the combustible gas (eg, H ₂ ) so that the growth rate measured as described later is constant, and is proportional to the supply flow rate of the combustible gas. Control the supply flow rate of the additive.

Next, the manufacturing method of the optical fiber preform of this embodiment will be described.
As described above, in the method of manufacturing the optical fiber preform according to the present embodiment, the raw material gas, the combustible gas, and the auxiliary combustible gas are supplied to generate the glass fine particles, and the glass fine particles are deposited. The supply flow rate of H ₂ , which is a combustible gas, is controlled so that the growth rate in the axial direction is constant. At the same time, the supply flow rate of GeCl ₄ as an additive is controlled so as to be proportional to the supply flow rate of H ₂ .

According to the manufacturing method of the optical fiber preform described above, the H ₂ supply flow rate is controlled so that the growth rate in the axial direction of the glass fine particle deposit 14 is constant, not according to the change in the growth rate, The supply flow rate of GeCl ₄ is controlled to be proportional to the supply flow rate of H ₂ . Thereby, the fluctuation | variation of (DELTA) N of the axial direction of the glass particulate deposit 14 can be suppressed, and stabilization of an optical fiber characteristic can be aimed at.

As a control of the flow rate of GeCl ₄ , when there is a sign that the growth rate in the axial direction increases, first, the supply flow rate of H ₂ is increased to suppress the increase in the growth rate and make it constant. At this time, the flow rate of GeCl ₄ is also increased in proportion to the increase in the supply flow rate of H ₂ . On the contrary, when there is an indication that the growth rate is lowered, the supply flow rate of H ₂ is decreased to keep the growth rate from being lowered and constant. At this time, the flow rate of GeCl ₄ is also decreased in proportion to the decrease in the supply flow rate of H ₂ .

Specifically, based on a signal sent from the growth rate measuring device 21 to the control device 16, the control device 16 supplies H _{2 to} the gas supply device 19 when there is an indication that the growth rate is increased. A command to increase the flow rate and a command to increase the supply flow rate of GeCl ₄ in proportion to the supply flow rate of H ₂ is also provided.

When there is an indication that the growth rate is decreasing, the gas supply device 19 is instructed to decrease the supply flow rate of H ₂ , and the supply flow rate of GeCl ₄ also decreases in proportion to the supply flow rate of H _2. To command. Accordingly, while adjusting the supply flow rate of H ₂ maintaining the growth rate constant, by adjusting the supply flow rate of in proportion to the flow rate of H ₂ GeCl _4, the axial direction of the glass particle deposited body 14 of ΔN Variation can be suppressed.

(Example)
FIG. 2 is a graph showing an embodiment of the present invention. In addition, the vertical axis | shaft of FIG. 2 shows the normalized flow volume by making each flow volume at the time of a sooting start into 1. In FIG. The horizontal axis indicates time.
In this example, when there is an indication that the growth rate in the axial direction of the glass fine particle deposit is decreased (soot diameter becomes thicker), the growth of the glass fine particle deposit is started from the start of soot so as to make the growth rate constant. Accordingly, the supply flow rate of H ₂ , which is a combustible gas, is adjusted so as to gradually decrease. At this time, the supply flow rate of the additive, GeCl ₄ , is also adjusted to decrease in proportion to the supply flow rate of H ₂ .
As a result, the growth rate in the axial direction of the glass particulate deposit can be made constant, and the optical fiber preform manufactured by such a method has N = 100 (measured at 20 preforms and 5 points in the longitudinal direction). When the variation (standard deviation) of ΔN was obtained, the variation (variation) of ΔN could be suppressed within the range of 2.89 × 10 ⁻³ .

(Comparative example)
FIG. 3 is a graph showing a comparative example with respect to the above embodiment. In FIG. 3, as in FIG. 2, the vertical axis indicates the flow rate normalized with each flow rate at the start of sooting as 1, and the horizontal axis indicates time. In this comparative example, as in the case of the above example, there is a sign that the growth rate in the axial direction of the glass fine particle deposit is reduced (soot diameter becomes thicker). The supply flow rate of No. ₂ is adjusted to gradually decrease. At this time, the supply flow rate of GeCl ₄ was constant without adjustment. As a result, although the growth rate in the axial direction of the glass fine particle deposit can be made constant, a variation (standard deviation) in ΔN of N = 100 (measured at 20 base materials and 5 points in the longitudinal direction) was obtained as in the example. However, the variation (variation) in ΔN was 4.46 × 10 ⁻³ , which was greatly varied as compared with the above example.

In addition, the manufacturing method of the optical fiber preform of the present invention is not limited to the above-described embodiment, and can be appropriately modified and improved. In addition, the material, shape, dimension, numerical value, form, number, arrangement location, and the like of each component in the above-described embodiment are arbitrary and are not limited as long as the present invention can be achieved.
For example, in the above-described embodiment, the growth rate measuring device 21 is provided, and the flow rates of the combustible gas and the additive are adjusted with respect to the signs of fluctuations in the growth rate detected by the growth rate measuring device 21. It is also possible to adjust the additive gas in accordance with the adjustment of the raw material gas and the auxiliary gas.

14 Glass particulate deposit (optical fiber preform)

Claims (1)

A method for producing an optical fiber preform, in which a raw material gas, a combustible gas and an auxiliary combustible gas are supplied to produce glass fine particles, and the glass fine particles are deposited to produce a glass fine particle deposit,
Supply of an additive that controls the supply flow rate of the combustible gas so that the growth rate in the axial direction of the glass particulate deposit is constant and adjusts the refractive index to be proportional to the supply flow rate of the combustible gas. A method for manufacturing an optical fiber preform, wherein the flow rate is controlled.

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