JPH04310531A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To produce a porous optical fiber preform in high yield. CONSTITUTION:Flame containing glass soot is blasted from a core-forming burner and the glass soot is continuously deposited on a target 3 in axial direction to form a porous core member 4. A flame 6 containing glass soot is blasted from a clad-forming burner 5 to deposit the soot in the axial direction of the core member and form a porous clad member. In the above process for the production of an optical fiber preform, a porous clad member is formed by keeping the temperature of the flame 6 blasted from the clad-forming burner 5 to be lower at the tip end of the core member than at the other part.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical fiber preform for manufacturing optical fibers used for optical transmission and the like.

0002

[Prior art] Methods for manufacturing porous optical fiber preforms include internal attachment method (MCVD method) and external attachment method (OVPO method).
, axis method (VAD method), hybrid method (HVD method)
It has been known. Among these methods, the hybrid method forms an optical fiber preform consisting of a core member and a cladding member through a two-step process. That is, in the first step,
As shown in FIG. 4(a), a flame 2 containing glass particles is injected from a core forming burner 1, and a target 3 made of a quartz rod or the like is moved in the direction of the arrow. A porous core member 4 is formed by continuously depositing glass particles in the axial direction of the porous core member 3 . After that, in the second step, as shown in FIG. 4(b), while injecting a flame 6 containing glass fine particles from a burner 5 for forming the cladding part,
By reciprocating the core member 4 in the direction of the arrow,
Fine glass particles from a burner 5 for forming a cladding portion are deposited in the axial direction of the core member 4 to form a porous cladding member 7. As a result, a porous optical fiber preform 8 having a structure in which the core member 4 is arranged inside and the cladding member 7 is arranged outside is formed.

[0003] The optical fiber preform 8 thus formed is spun in the next drawing step to become an optical fiber core wire of a predetermined diameter.

By the way, when the radial refractive index distribution of the optical fiber preform 8 formed as described above is measured, the refractive index of the portion other than the tip 9 has a normal distribution as shown in FIG. 5(a). On the other hand, the tip part 9 has a
As shown in b), there is an abnormal distribution near the boundary between the core portion 4 and the cladding portion 7. For this reason, conventionally, the tip portion 9 having an abnormal refractive index distribution could not be used as a product.

[0005]

[Problems to be Solved by the Invention] However, even if the length of the tip portion 9 where the refractive index distribution is abnormal is approximately 5 to 15 mm, the weight of this portion is equal to the weight when spun into an optical fiber core. Converting to 12 to 13 km. For this reason, the yield was extremely low, which was a major factor in increasing costs.

The present invention has been made to solve the above-mentioned problems, and its technical problem is to provide a method for manufacturing an optical fiber preform that can produce a porous optical fiber preform with high yield. It is to provide.

[0007]

[Means for Solving the Problems] The method for manufacturing an optical fiber preform of the present invention is such that the temperature of the flame injected from the burner for forming the cladding portion is lower at the tip portion of the core member than at other portions. Thus, a porous cladding member was formed.

[0008]

[Example] FIG. 1 is a schematic diagram showing the configuration of an apparatus for carrying out the method for manufacturing an optical fiber preform of the present invention, in which the optical fiber preform is in a state before a cladding member is formed on the surface of a core member 4. It shows.

In FIG. 1, the optical fiber preform manufacturing apparatus of this embodiment includes a gas source 10 that supplies combustion gas to a burner 5 for forming the cladding portion, and a flow rate source 10 that adjusts the flow rate of the combustion gas. A regulating valve 11, a magne scale 12 for measuring the length L1 of the tip end 9 of the core member 4, which was conventionally removed;
Potentiometers 13 and 14 that vary and output the output voltage of this magnetic scale 12, this potentiometer 1
and a flow rate control section 15 that adjusts the opening degree of the flow rate control valve 11 based on the output voltages 3 and 14.

This manufacturing apparatus is constructed based on the analysis result that the abnormality in the refractive index distribution at the tip 9 of the optical fiber preform is due to the surface temperature being higher than other parts when forming the cladding member. It is what was done. That is, as a result of measuring the surface temperature distribution in the axial direction when the core member 4 passes through the flame of the burner 5 for forming the clad member when forming the clad member, as shown in FIG. The temperature at the tip part 9 is approximately 700°C, whereas the temperature at the other part 9 is approximately 700°C.
The temperature exceeds 700℃ and even reaches 800℃. There is a tendency that the tip is the highest, and as it approaches the predetermined length L1, the temperature converges to about 700°C. It is thought that the abnormality in the refractive index distribution of the tip 9 is caused by the Ge component in the flame being volatilized due to its surface temperature being abnormally high. Therefore, in order to make the surface temperature of the tip 9 equal to that of other parts, when the flame 6 is injected to the tip 9, the amount of combustion gas is reduced so that the temperature of the flame 6 is lowered. It is designed to adjust.

Next, a method for manufacturing an optical fiber preform using the manufacturing apparatus having the above configuration will be explained. First, the core member 4 is formed in the same manner as in the conventional method. Next, a cladding member is formed on this core member 4 using a burner 5 for forming a cladding member, and the position of the flame 6 of the burner 5 is measured using a magne scale 12. The measurement result is the potentiometer
The flow rate is inputted to the flow rate control section 15 via the data meters 13 and 14. The flow rate control unit 15 controls the flame 6 measured by the Magne scale 12.
Until the position reaches the predetermined length L1, the flow rate q of the combustion gas input to the burner 5 changes from q1 to q2 (
The opening degree of the flow rate regulating valve 11 is adjusted so as to gradually increase toward q1<q2). As a result, the temperature of the flame 6 becomes lower in the range of the tip 9 up to the predetermined length L1 than in other parts, and changes with the characteristics shown in FIG. 2(a). That is, the surface temperature is made uniform at approximately 700° C. at any location in the axial direction of the core member 4. As a result, the refractive index distribution in the tip 9 after forming the cladding member can be made as normal as in other parts, and the tip 9, which could not be used as a product in the past, can be It can be used for drawing core wire. This improves the yield of the fiber preform and makes it possible to greatly contribute to cost reduction.

0012

As described above, the method for manufacturing an optical fiber preform of the present invention allows the temperature of the flame injected from the burner for forming the cladding to be lower at the tip of the core member than at other parts. As a result, the refractive index distribution after forming the cladding member is almost uniform in all parts in the axial direction. It can be used to draw the line. This improves the yield of fiber preform and
This makes it possible to greatly contribute to cost reduction.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing the configuration of an apparatus for implementing the optical fiber preform manufacturing method of the present invention.

FIG. 2 is a characteristic diagram showing control characteristics of flame temperature and combustion gas flow rate of a burner for forming a cladding member in the present invention.

FIG. 3 is a characteristic diagram showing the surface temperature distribution in the axial direction of the base material in a conventional manufacturing method.

FIG. 4 is an explanatory diagram for explaining a conventional optical fiber preform manufacturing method.

FIG. 5 is a characteristic diagram showing the refractive index distribution of the tip and other parts of an optical fiber preform formed by a conventional optical fiber preform manufacturing method.

[Explanation of symbols]

1 Burner 2 for forming core member
,6 Flame 3 Target 4
Core member 5 Bar for forming cladding member
Na 7 Clad member 8
Optical fiber base material 9
Tip part 10 Gas source 11 Flow rate adjustment valve 12 Magne scales 13, 14
Potentiometer 15 Flow rate control section

Claims (1)

[Claims] Claim 1: A flame containing glass particles is injected from a core forming burner, and the glass particles are continuously deposited in the axial direction of the target to form a porous core member. In the method for manufacturing an optical fiber preform, the cladding part is formed by ejecting a flame containing glass fine particles from a burner for forming the cladding part and depositing them in the axial direction of the core member to form a porous cladding member. Production of an optical fiber preform, characterized in that the temperature of the flame injected from a burner is lower at the tip of the core member than at other parts to form a porous cladding member. Method.