JPH06219764A - Production of perform for dispersed shift fiber - Google Patents

Abstract

PURPOSE:To produce a preform for dispersed shift fiber having a stepwise refractive index profile by forming a center core and a side core by a concentric burner and to obtain a preform for dispersed shift fiber capable of readily controlling structure parameters of center core and side core. CONSTITUTION:A center core 1 is formed by a concentric burner 30 and successively a side core 4 is made by a concentric burner 40 to produce a preform for shift fiber having a stepwide refractive index profile. The concentric burner 30 for forming the center core consists of a raw material gas discharge nozzle 31 and an oxyhydrogen flame-forming gas discharge nozzle 32, which is divided into an inner layer 33 of a hydrogen gas flow, an intermediate layer 34 of an inert gas flow and an outer layer 35 of an oxygen gas flow and the flow rate of the oxygen gas discharging from the outer layer 35 is made >=2.7 times the flow rate of the hydrogen flow sent from the inner layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DSC (Dual Shape Core) having a stepwise refractive index profile.
VAD (Vapo
r Phase Axial Deposition)
In particular, the present invention relates to a method for manufacturing a base material for a dispersion shift fiber, which can simultaneously form a center core and side cores by a plurality of concentric burners and can easily manufacture one having predetermined structural parameters.

[0002]

2. Description of the Related Art In a typical SM (single mode) type optical fiber, the refractive index distribution of the core is a step type. A method and an apparatus for manufacturing such a porous base material for an SM optical fiber will be described with reference to FIG. In the figure, 1 is a porous base material composed of a core 2 and a clad 3, 11 is a starting material, 12 is a rotating / pulling device, 13 is a protective container, and 14 is an exhaust controller. In the radial direction inside the protective container 13, the core burner 1
5, first clad burner 16, second clad burner 1
7. A third clad burner 18 is arranged. The core burner 15 deposits and deposits fine particles of SiO ₂ generated from a mixed gas of SiCl ₄ and GeCl ₄ as a raw material gas on a starting material or a core porous body, and simultaneously generates Ge.
O ₂ is deposited on the fine particles of SiO ₂ , and S
desired refractive index of the core in an amount of GeCl ₄ with respect to LiCl ₄ is obtained. First, second and third clad burners 16, 1
7 and 18 are Si produced by using SiCl ₄ as a source gas
By depositing and depositing O ₂ particles around the core simultaneously, S
This is a method for obtaining a porous preform for an M-type optical fiber.

Particularly, in the core burner 15, since the diameter of the core porous body produced is as small as 10 mm or less, a burner capable of reducing the diameter is required. As a burner that responds to this request, the applicant has proposed a square burner (Japanese Patent Application Laid-Open No. HEI 1).
-208339 gazette). As shown in FIG.
The square burner 15 includes a raw material gas outflow nozzle 20, two inert gas outflow nozzles 21 and 22 provided at positions opposite to each other with the raw material gas outflow nozzle 20 interposed therebetween, and oxyhydrogen surrounding the three nozzles. A flame forming gas outflow nozzle 23. The oxyhydrogen flame forming gas outflow nozzle 23 includes an innermost layer 24 of an oxygen gas (O ₂ ) flow and an inert gas (Ar and He).
Only) flow intermediate layer 25, hydrogen gas (H ₂ ) flow outermost layer 2
It is divided into 6 layers.

By using this square burner 15, it is possible to obtain a good porous preform for SM optical fibers. However, as an improvement of this SM type optical fiber, a DSC type dispersion shift fiber having a stepwise refractive index profile as shown in FIG. 5 has been used. On the outer circumferences a1 and a2 of the center core 1 having a mountain-shaped refractive index change,
The side core 4 having a refractive index n1 is formed, and further the outer circumference a2
The cladding 3 having a refractive index of n2 (n1> n2) is formed on the surface of the cladding. This DSC type dispersion-shifted fiber has a characteristic that bending loss is small even if the mode field diameter is increased to about 9 mm, and it is becoming the mainstream at present.

As a method for producing the porous base material for the DSC type dispersion shifted fiber, a square burner is used for the core forming burner 15 shown in FIG. 4 for forming the center core, and the first clad burner 16 is used. Although a method of forming a side core using a concentric burner is conceivable, this method tends to have a stepwise refractive index distribution and is difficult to control.

On the other hand, there is a method of manufacturing a porous base material for GI (Graded Index) type optical fiber as a method for easily making the refractive index distribution into a square distribution shape. The above-mentioned SM for manufacturing method and device of conventional porous preform for GI type optical fiber
The difference from the method for manufacturing the porous optical fiber preform for optical fibers will be mainly described. In the arrangement shown in FIG. 4, the core burner 15 also uses a concentric burner as shown in FIGS. The concentric burner is composed of a raw material gas outflow nozzle 31 provided in the center and an oxyhydrogen flame forming gas outflow nozzle 32 provided around the source gas outflow nozzle 31, and the oxyhydrogen flame forming gas outflow nozzle 32 is An innermost layer 33 of a gas (H ₂ ) flow, an intermediate layer 34 of an inert gas (only Ar and He) flow,
Similar concentric burners are used for the first clad burner 16, the second clad burner 17, and the third clad burner 18 which are partitioned into three layers of the outermost layer 35 of the oxygen gas (O ₂ ) flow. The raw material gas flowed out from the raw material gas outflow nozzle 31 is usually a mixed gas of SiCl ₄ and GeCl ₄ from the core burner 15, and clad burners 16, 17, 1.
From 8 is SiCl ₄ gas.

[0007]

In this method for producing a porous preform for a GI type optical fiber, the refractive index distribution tends to have a square distribution shape. However, in the conventional method, the core becomes thicker so that the DSC type dispersion is obtained. It was difficult to apply to the production of the porous base material for shift fibers. Therefore, we tried to reduce the soot diameter by reducing the nozzle diameter of the burner, especially the diameter of the raw material gas outflow nozzle, but the soot diameter is smaller than when using a conventional burner, but it is remarkable. No effect was obtained. The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to form a center core and side cores by a concentric burner and to provide a dispersion having a step-type refractive index profile. It is an object of the present invention to provide a method for manufacturing a base material for a shift fiber, which is capable of easily controlling the structural parameters of the center core and the side cores.

[0008]

A method of manufacturing a dispersion shift fiber preform according to the present invention, which achieves the above object, is a dispersion having a stepwise refractive index profile in which a center core and a side core are formed by a plurality of concentric burners. A method of manufacturing a base material of a shift fiber, wherein a concentric burner for forming a center core comprises a raw material gas outflow nozzle provided in the center and an oxyhydrogen flame forming gas outflow nozzle provided around the source gas outflow nozzle. The oxyhydrogen flame forming gas outflow nozzle is divided into three layers, an inner layer of hydrogen gas flow, an intermediate layer of inert gas flow, and an outer layer of oxygen gas flow, and the flow rate of the oxygen gas flow out of this outer layer flows out from the inner layer. Of the flow rate of the hydrogen gas flow to 2.7
This is a method characterized in that the number is twice or more.

[0009]

[Function] By setting the flow rate of the oxygen gas flow flowing out of the outer layer to be 2.7 times or more the flow rate of the hydrogen gas flow flowing out of the inner layer, the oxygen gas flow velocity becomes a value of a certain value or more, and the oxygen gas flow to the inner layer of the oxygen gas flow is increased. Wraparound occurs, and as a result, the oxyhydrogen flame flow is reduced in diameter. Therefore, the glass fine particles obtained by the reaction of the raw material gas and the oxyhydrogen flame are confined in a narrow space, and the diameter of the obtained center core can be reduced.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a method and an apparatus for manufacturing a dispersion shift fiber preform of the present invention. The concentric burners 15 and 16 in FIG. 1 are for forming a center core and side cores, respectively, and are both concentric burners, and FIG. 2 is a sectional view thereof.

In FIG. 1, concentric burners 15 and 16 are provided.
The structure is similar to the conventional one in the arrangement of the nozzles. Of these, the concentric burner 15 for forming the center core has a small diameter of the raw material gas outflow nozzle. From the source gas outflow nozzle at the center of the concentric burner 15, SiC
The mixed gas flow of l ₄ and GeCl ₄ is discharged, and the oxyhydrogen flame forming gas discharge nozzle is provided with an inner layer of the hydrogen gas (H ₂ ) flow, an intermediate layer of the inert gas flow (Ar and He), an oxygen gas flow It is characterized in that it is partitioned into three outer layers of (O ₂ ), and the flow rate of the oxygen gas stream flowing out of this outer layer is 2.7 times or more the flow rate of the hydrogen gas stream flowing out of the inner layer.

The concentric burners 30 and 40 are composed of circular source gas outflow nozzles 31 and 41 at the center, and oxyhydrogen flame forming gas outflow nozzles 32 and 42 concentric with the source gas outflow nozzles 31 and 41. The oxyhydrogen flame forming gas outflow nozzles 32 and 42 include the innermost layers 33 and 43 of the hydrogen gas flow, the intermediate layers 34 and 44 of the inert gas flow, and the outermost layer 3 of the oxygen gas flow.
It is divided into three layers of 5,45.

Next, a concrete example of the present invention for manufacturing a preform for dispersion-shifted fibers by the apparatus of FIG.
Description will be made in comparison with the conventional example. Table 1 shows the structures and dimensions of the concentric burners of the examples of the present invention, comparative examples, and conventional examples. The type is conventionally used for manufacturing the GI type optical fiber preform, and the type is used for manufacturing the dispersion shift fiber preform of Examples and Comparative Examples. Table 2 shows
It is a table which shows the soot diameter of the center core and the growth rate of the soot obtained by the manufacturing conditions of the Example of this invention, a comparative example, and a prior art example.

[0014]

[Table 1]

[0015]

[Table 2]

FIG. 3 shows the relationship between the ratio A / B of the oxygen gas flow rate A to the hydrogen gas flow rate B in Table 2 and the soot diameter of the center core and the soot growth rate. Comparative Examples 1 and 2 use a burner of a type having a small nozzle diameter, and the soot diameter is 22.5 mm although it is smaller than that of a burner of a conventional type.
Could not be thinner than. Therefore, as a result of intensive studies, it was found that the ratio A / B of the oxygen gas flow rate A to the hydrogen gas flow rate B affects the soot diameter and the growth rate as described above. As is clear from Table 2 and FIG. 3, the ratio A / B of the oxygen gas flow rate A to the hydrogen gas flow rate B is 2.
When it is 7 or more, the soot diameter is remarkably reduced and the growth rate is stabilized.

[0017]

As described above, the method of manufacturing the base material for dispersion-shifted fiber according to the present invention is such that the flow rate of the oxygen gas flow flowing out from the outer layer of the oxyhydrogen flame forming gas outflow nozzle in the concentric burner for the center core is the hydrogen flowing out from the inner layer. The flow rate of the gas flow is 2.7 times or more, and when the oxygen gas flow rate becomes a certain value or more, the oxygen gas flow wraps around into the inner layer, and as a result, the oxyhydrogen flame flow has a small diameter. Turn into. For this reason, the glass fine particles obtained by the reaction of the raw material gas and the oxyhydrogen flame are confined in a narrow space, the diameter of the obtained center core can be made thin, and the growth rate is stable. The manufacturing conditions of the side cores are set so that the porous base material for dispersion-shifted fiber can be easily manufactured and the structural parameters such as Ra defined by a1 / a2 and RΔ defined by Δ1 / Δ2 are appropriate. It can be changed and the desired base material for the dispersion shift fiber can be easily obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a method for manufacturing a base material for a dispersion shift fiber of the present invention.

FIG. 2 is a cross-sectional view of a concentric burner used for manufacturing a base material for a dispersion shift fiber of the present invention.

FIG. 3 is a graph showing the relationship between the ratio of the oxygen gas flow rate to the hydrogen gas flow rate, the soot diameter of the center core, and the soot growth rate in Examples and Comparative Examples of the present invention.

FIG. 4 is a diagram showing a method for manufacturing an optical fiber porous body by the VAD method.

FIG. 5 is a graph showing a relationship between a refractive index and a fiber radius in a DSC type dispersion shift fiber.

FIG. 6 is an explanatory diagram showing a method for manufacturing a porous base material for an SM optical fiber.

[Explanation of symbols]

 1 Center core 4 Side core 30,40 Concentric burner 31,41 Raw material gas outflow nozzle 32,42 Oxygen hydrogen flame forming gas outflow nozzle 33,43 Hydrogen gas outflow nozzle 34,44 Inert gas outflow nozzle 35,45 Oxygen gas outflow nozzle

Claims (1)

[Claims] 1. A method for producing a base material of a dispersion-shifted fiber having a stepwise refractive index profile by forming a center core and side cores with a plurality of concentric circular burners, the concentric circular burner for forming a center core being the center. The gas outflow nozzle for forming an oxyhydrogen flame is provided around the raw material gas outflow nozzle and the gas outflow nozzle for forming an oxyhydrogen flame, and the oxyhydrogen flame forming gas outflow nozzle is an inner layer of the hydrogen gas flow and an intermediate layer of the inert gas flow. A dispersion shift fiber characterized by being divided into three outer layers of oxygen gas flow, and the flow rate of the oxygen gas flow flowing out of this outer layer is 2.7 times or more the flow rate of the hydrogen gas flow flowing out of the inner layer. Base material manufacturing method.