JPH08119657A - Production of preforated preform of single mode optical fiber - Google Patents

Abstract

PURPOSE: To provide a process for producing a perforated preform of a single mode optical fiber which is flat in the curving shape of the refractive index direction in the radial direction of a core and is steep in the change in the refractive index at the core/clad boundary. CONSTITUTION: The perforated core 10 is deposited and formed by supplying a gaseous mixture contg. core raw materials and core additive raw materials from a torch 1 for the core and depositing core soot. A gaseous mixture contg. the core raw materials and core additive raw materials from a torch 3 for a skin layer is supplied onto the surface of the perforated core 10 to uniformly deposit the skin layer 11 thereon. Further, the clad layer 12 is formed on the skin layer 11 by supplying the clad layer raw materials from a torch 2 for the clad.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a single mode optical fiber porous glass preform by depositing glass particles obtained by flame hydrolysis of a gaseous glass raw material on a starting material.

[0002]

2. Description of the Related Art Generally, in an optical fiber, light propagates in the core while being totally reflected at the boundary between the core and the clad. The way of propagation varies depending on the refractive index distribution of the core, and when the core diameter is several tens of μm in both the step index type and the graded index type, the light path differs depending on the incident angle of light, and many optical paths occur. Further, when the outer diameter of the core is set to about 5 to 15 μm, the light travels straight through the core without being reflected at the boundary surface between the core and the clad, and has one optical path. Such an optical fiber is a single mode optical fiber.

Usually, in a single mode optical fiber, the refractive index of the core is higher than the refractive index of the clad by about 0.3% and is constant in the radial direction, and the refractive index changes at the boundary between the core and the clad. Is required to be steep. That is, when viewed as the entire fiber, it is necessary that the refractive index distribution in the radial direction of the fiber be step-shaped. In order to provide such a refractive index difference between the core and the clad, a method of mixing a material having a refractive index different from that of the core raw material is adopted in the core. Additives of this kind are hydrolyzed in the flame with the core raw materials to form oxides, which diffuse into the core as core soot accumulates and increase the refractive index of the core, resulting in a difference in the refractive index from the cladding. Cause Then, when designing or manufacturing the optical fiber, the refractive index difference or the core diameter is calculated from the curve shape of the obtained refractive index distribution, and the additional cladding deposition amount for obtaining the specified dispersion characteristics, the cutoff wavelength, etc. from the result is calculated. I have decided.

As a method of manufacturing the porous preform of such a single mode optical fiber, a shafting method (VAD) has been conventionally used.
Law; Vaper Phase Axial Deposition) is known. FIG. 3 is a schematic diagram for explaining the conventional VAD method. The core raw material (eg, silicon tetrachloride) and the additive raw material (eg, germanium tetrachloride) are used together with a combustible gas (hydrogen) and oxygen in the core torch 21. Supplied from
Then, the core raw material and the additive raw material are hydrolyzed in a flame to form a core soot, which is deposited in multiple layers to form the porous core 22. On the other hand, a cladding torch 23 is arranged on the downstream side in the moving direction of the base material, that is, above the core torch 21 in the figure, and the cladding layer raw material (for example, silicon tetrachloride) is supplied together with combustible gas and oxygen gas. It Then, it is hydrolyzed in the flame to form the cladding layer 24 on the porous core 22. Then, dehydration and clarification treatments (not shown) are performed to obtain a single mode optical fiber porous preform.

[0005]

However, in the above-mentioned conventional method for producing a single mode optical fiber porous preform by the VAD method, the torch structure, disposition position, temperature distribution on the preform surface, exhaust conditions, etc. Due to the influence, the diffusion of the additive into the core becomes non-uniform, and the concentration of the additive tends to decrease particularly in the peripheral portion of the core portion Ac. As a result, as shown in FIG. 4, the refractive index distribution in the core portion Ac is highest at the core center O (S1), gradually decreases toward the peripheral portion of the core portion Ac, and becomes minimum at a position close to the peripheral portion. (V1, V2) and small peaks (S2, S
3) has a shape having. Further, the change in the refractive index near the interface between the core portion Ac and the cladding portion Ec becomes gradual, and the rise angle θ2 is a relatively large obtuse angle.

As described above, it is desirable that the curve shape of the refractive index distribution of the optical fiber is a step type.
In the case of the refractive index distribution as shown in Fig. 3, the determination of the refractive index and the core diameter becomes inaccurate, the dispersion characteristics and the cutoff wavelength characteristics of the optical fiber are not stable, and as a result, there are problems such as frequent deviation from the standard. .

The present invention has been made to solve the above problems and drawbacks, and is a single mode in which the curve shape of the refractive index distribution in the radial direction of the core is flat and the refractive index change at the core / clad interface is sharp. An object is to provide a method for manufacturing an optical fiber porous preform.

[0008]

The above object of the present invention is to achieve the above object.
In a method for producing a single mode optical fiber porous glass preform by depositing glass fine particles obtained by flame hydrolysis of a gaseous glass raw material, a mixed gas containing a core raw material and a core additive raw material is produced from a core torch. While supplying to deposit the core soot to form a porous core, a mixed gas containing the core raw material and the core additive raw material is supplied from the torch for a skin layer on the porous core to deposit the skin layer, Further, it is achieved by a method for producing a single mode optical fiber porous preform, characterized in that the cladding layer raw material is supplied onto the skin layer from a cladding torch to deposit the cladding layer. Further, in the above, it is preferable that the mixed gas supplied from the core torch and the mixed gas supplied from the skin layer torch have the same composition.

[0009]

In the method for producing a single mode optical fiber porous preform according to the present invention, a skin layer formed from a gas composed of the same substance as the core forming gas is formed at the interface between the outer surface of the core and the clad. It is characterized by doing. This compensates for the decrease in the additive concentration in the core peripheral portion that occurs during core formation, and corrects the decrease in the refractive index due to the decrease in the additive concentration, thereby flattening the curve shape of the refractive index distribution in the core portion. Turn into. At the same time, since the refractive index in the peripheral portion of the core is increased, the difference from the refractive index of the clad becomes relatively large, and as a result, the change in the refractive index at the core / clad boundary becomes steeper. In particular, when the mixed gas supplied from the core torch and the mixed gas supplied from the skin layer torch have the same composition, the above-mentioned additive concentration can be more effectively compensated.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic diagram for explaining one embodiment of the method for producing a single mode optical fiber porous preform according to the present invention. As shown in the figure, in the method for manufacturing a single mode optical fiber porous preform according to the present invention, a skin layer torch 3 is disposed between the core torch 1 and the cladding torch 2.

From the core torch 1, a core raw material and a core additive raw material are blown together with a combustible gas and an oxygen gas onto the tip of a seed quartz rod (not shown). The core raw material is, for example, silicon tetrachloride, and the core additive raw material is, for example, germanium tetrachloride. Hydrogen gas is used as the combustible gas. Then, the core raw material (silicon tetrachloride) and the core additive raw material (germanium tetrachloride) are hydrolyzed in a flame to become a core component (silicon dioxide) and a core additive component (germanium dioxide), respectively. Are deposited in multiple layers as core soot to form the porous core 10.

A skin layer torch 3 is disposed downstream of the porous core 10 in the moving direction, that is, above the core torch 1 in the figure. From the skin layer torch 3, the core torch 1 is inserted. The same substance as the core raw material and the core additive raw material which are supplied, and a mixed gas including a combustible gas and an oxygen gas are blown onto the outer surface of the porous core 10. Then, the core component and the core additive component are generated by the hydrolysis in the flame, and are uniformly deposited on the porous core 10 to form the skin layer 11.

Here, the core raw material and core additive raw material supplied from the core torch 1 and the skin layer torch 3
It is more preferable that the core raw material and the core additive raw material supplied from the same are made to be the same substance and have the same composition. As a result, when the skin layer 10 is deposited on the porous core 10, the compatibility at the boundary between the two and the mutual diffusion of core additive components become uniform, and the porous core 10
Since the skin layer 11 and the skin layer 11 are uniformly continuous, the refractive index distribution in the core can be made more uniform, and the mechanical strength of the core can be increased.

Next, the clad layer 12 is formed by blowing a clad layer raw material (eg, silicon tetrachloride), a combustible gas, and an oxygen gas from the clad torch 2 onto the outer surface of the skin layer 11.
By forming, a single mode optical fiber porous preform is obtained. The porous base material thus obtained is further dehydrated and clarified to produce a preform.

FIG. 2 shows the refractive index distribution of the single mode optical fiber porous preform obtained by the manufacturing method according to the present invention. As shown in the figure, in the porous base material according to the present invention, the refractive index in the core part Ac is uniform, and the change in the refractive index in the vicinity of the interface between the core part Ac and the clad part Ec is close to a rising angle θ1. Shows a sharp change, and has a step-like refractive index distribution curve shape.

[0016]

As described above, in the method for producing a single mode optical fiber porous preform according to the present invention, the interface between the outer surface of the core and the clad is made of a gas composed of the same material as the core forming material gas. It is characterized by forming a generated skin layer. This compensates for the decrease in the additive concentration in the core peripheral portion that occurs during core formation, and corrects the decrease in the refractive index due to the decrease in the additive concentration, thereby flattening the curve shape of the refractive index distribution in the core portion. Can be converted. At the same time, since the refractive index of the core peripheral portion is increased, the difference from the refractive index of the cladding is relatively increased, and as a result, the refractive index change at the core / cladding boundary portion can be made steeper. In particular, when the mixed gas supplied from the core torch and the mixed gas supplied from the skin layer torch have the same composition, the above-mentioned additive concentration can be more effectively compensated. As a result, it is possible to accurately calculate the core diameter and the refractive index difference, and as a result, it is possible to manufacture a high-quality single mode optical fiber porous preform having stable dispersion characteristics and a cutoff wavelength.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a method for producing a single mode optical fiber porous preform according to the present invention.

FIG. 2 is a diagram showing a refractive index distribution of a single mode optical fiber porous preform manufactured according to the present invention.

FIG. 3 is a diagram showing a method for manufacturing a conventional single mode optical fiber porous preform.

FIG. 4 is a diagram showing a refractive index distribution of a single mode optical fiber porous preform manufactured by a conventional manufacturing method.

[Explanation of symbols]

 1 torch for core 2 torch for clad 3 torch for skin layer 10 porous core 11 skin layer 12 porous clad layer

[Procedure amendment]

[Submission date] February 22, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

Here, the core raw material and core additive raw material supplied from the core torch 1 and the skin layer torch 3
It is more preferable that the core raw material and the core additive raw material supplied from the same are made to be the same substance and have the same composition. As a result, when the skin layer 10 is deposited on the porous core 10, the compatibility at the boundary between the two and the mutual diffusion of core additive components become uniform, and the porous core 10
And the skin layer 11 becomes possible to continuously uniformly, as possible out that a more uniform refractive index distribution in the core portion.

Claims (2)

[Claims] 1. A method for producing a single mode optical fiber porous glass preform by depositing glass fine particles obtained by flame hydrolysis of a gaseous glass raw material, wherein a core raw material and a core additive raw material are prepared from a core torch. Is supplied to form a porous core by depositing a core soot, and a skin is provided by supplying a mixed gas containing the core raw material and the core additive raw material from the skin layer torch on the porous core. A method for producing a single-mode optical fiber porous preform, comprising depositing a layer and further depositing a cladding layer raw material from a cladding torch on the skin layer to deposit the cladding layer. 2. The single mode optical fiber porous body according to claim 1, wherein the mixed gas supplied from the core torch and the mixed gas supplied from the skin layer torch have the same composition. Method of manufacturing base material.