JPS63176324A - Production of preform for optical fiber - Google Patents

Abstract

PURPOSE:To produce preform having a little core eccentricity and to contrive to improve in yield of preform production, by measuring eccentricity of core center based on a clad center and processing the clad part for correcting the amount of the core eccentricity. CONSTITUTION:Amount of divergence and direction of the divergence of the center of a core 11 of preform 10 for optical fiber from the center of an outer diameter, namely a clad center 13 of a clad 12 are measured and recorded. Depending upon the measurement and record, the preform is heated by using an oxyhydrogen flame by a processing burner 14 in the direction to reduce the core eccentricity. By this method, preform for optical fiber having a little core eccentricity can be produced and yield of preform production can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an optical fiber preform consisting of a core and a cladding, and (in particular, an optical fiber preform having a small eccentricity of the core center with respect to the cladding center. The present invention relates to a manufacturing method.

[Conventional technology]

Conventionally, methods for manufacturing optical fiber base materials include, for example, the VAD method (Vapor Phase Axial De
position: vapor phase axis method), MCVD method (Mo
dified Chemical Vapor Phas
eDeposition: fleshed chemical vapor deposition method),
OVD method
e OxidationDeposition: External vapor phase oxidation method), but in any of these manufacturing methods, the possibility of eccentricity of the core center with respect to the cladding center is unavoidable, and it is necessary to reduce this eccentricity in -a. Therefore, in the manufacturing process of each of the above-mentioned methods for manufacturing optical fiber preforms, methods are taken to suppress the causes of core eccentricity as much as possible. However, it is extremely difficult to manufacture a base material with a minimal eccentricity of the core, and it has been impossible to completely eliminate the occurrence of defective products as a base material. In addition, even if it is not a defective product, if the core has a large eccentricity, the splice loss will increase or the splice will be extremely difficult when the base material is drawn and made into a fiber. Selection is done in stages.

[Problem that the invention seeks to solve]

In conventional manufacturing methods for optical fiber base materials, if core eccentricity occurs at the stage of manufacturing the base material, even though it has been made into a base material, there is no technology to correct this eccentricity.
There is a problem that the selection of the base material is ephemeral and the yield from the base material to the optical fiber is poor.

[Means for solving problems]

The present invention solves the conventional problems and aims to correct the eccentricity of the core after it is made into a base material, thereby making it possible to improve the productivity of optical fiber manufacturing. The method for manufacturing the base material is characterized in that the eccentricity of the center of the core with respect to the center of the cladding is measured, and the cladding part of the glass base material is subjected to a correction process for the measured eccentricity of the core. The modification process is characterized in that it is performed by flame heating the outer periphery of the clad to evaporate the glass.

[For production]

In the production of optical fiber base materials, the present invention measures the eccentricity of the core with respect to the center of the cladding after the stage of producing a transparent glass base material, and if the eccentricity is large, it is physically applied to the transparent glass base material to reduce the eccentricity. The structure of the transparent glass base material is changed by modifying the structure of the transparent glass base material by, for example, evaporating the FF-7 gas on the outer periphery of the clad using fire, thereby producing a base material for optical fiber with less eccentricity of the core. This makes it possible to improve the manufacturing yield and reduce the manufacturing cost of optical fibers, resulting in significant economic effects. Examples will be described below based on the drawings.

〔Example〕

FIG. 1 is a diagram illustrating an outline of the main parts of an embodiment of the method for manufacturing an optical fiber base material of the present invention. 10 is a base material for an optical fiber, 11 is a core, 12 is a cladding, 13 is a cladding center, and 14 is a base material for an optical fiber using a flame, as an example of processing for correcting the misalignment between the cladding center 13 and the center of the core 11. This is a processing burner that evaporates the glass in the cladding 12 of No. 10 and performs correction processing.

As an example of the core eccentricity correction process in this example, structural change of the cladding part due to flame is shown as an example, but other methods include mechanically grinding the glass in the cladding area, or using chemical reactions to change the structure of the cladding part. Correction processing by etching is also included in the aspect of the present invention. However, in the case of the former type of machining, there is a risk of problems such as deterioration of the strength of the ground surface of the cladding and cracking due to residual strain, and in the case of the latter type of machining, there is a risk of problems such as cracking due to the deterioration of the strength of the ground surface of the cladding. In this case, the controllability of the amount of grinding and the direction of grinding is limited, and microfabrication is difficult. On the other hand, the modification process using flame in this example has no fear of mechanical strength deterioration, and microfabrication is easily possible by narrowing the flame or changing the heating time and amount. This is a preferred embodiment of the core eccentricity correction process of the present invention.

Incidentally, the eccentricity ε as an index of the amount of deviation between the core center and the clad center in the present invention is defined by the following equation.

δ Here, δ represents the amount of deviation between the core center and the cladding center, and D represents the cladding diameter.

Next, a specific example of the optical fiber base material manufactured according to the present invention will be described.

Specific Example 1: For an optical fiber base material having a diameter of 25 mmφ, the eccentricity of the swaged core was measured, and the amount and direction of deviation of the center of the core from the center of the outer diameter, that is, the center of the cladding, were recorded. Based on the results of this measurement and recording, correction processing was performed using an oxyhydrogen flame in the direction of reducing the eccentricity of the core. The processing burners used were concentric double pipes, and five processing burners having the double pipe structure were arranged at positions on the same circumference around the optical fiber base material as the workpiece. FIG. 2 shows an outline of the arrangement of processing burners in this specific example.

Reference numeral 20 indicates a workpiece of an optical fiber base material, and 21 indicates a processing burner. FIG. 3 is a diagram showing the relationship between the heating time by the processing burner and the processing amount of the cladding portion of the optical fiber base material.

The optical fiber base material in this specific example is GeO□-3i
20 liters of hydrogen per minute and 6 liters of oxygen per minute were flowed per processing burner.

When heating only one side of the workpiece, which is the base material for optical fiber, while moving the processing burner in the longitudinal direction of the workpiece at a speed of 50 mm per minute, the diameter of the base material for optical fiber of the workpiece was decreased by about 280 μm. By performing this correction process, the eccentricity of the core of the optical fiber base material of this specific example was 2.0%, but the eccentricity after the eccentricity correction process was corrected to 0.9%.

Concrete Example 2: An eccentricity correction process similar to that of Concrete Example 1 was performed on an optical fiber base material having a diameter of 60 mm and having the same material and structure as Concrete Example 1. However, the moving speed of the processing burner with respect to the optical fiber base material was 30 mm per minute. By applying this eccentricity correction process, the outer diameter of the optical fiber base material was slightly smaller by 0°5 mmN and the eccentricity was 2.0% compared to before the eccentricity correction process, but after the eccentricity correction process, the eccentricity was - It was revised to 1.2%.

In the above specific example, an oxyhydrogen flame was used as the flame for processing, but the flame is not limited to this, and gases such as methane and propane may also be used, and the number of burners for processing may vary depending on the number of burners required. The same effect can be obtained by appropriately selecting the amount of processing.

〔Effect of the invention〕

As described above, the present invention measures the eccentricity of the core center with respect to the cladding center at the optical fiber base material stage in the manufacturing process of the optical fiber base material, and reduces the core eccentricity obtained as a result of the measurement. By performing eccentricity correction processing on the cladding part of the optical fiber base material, it is possible to manufacture an optical fiber base material with less core eccentricity, improving the manufacturing yield of the optical fiber base material and reducing the manufacturing price of the optical fiber. The effect is remarkable.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating an overview of the method for manufacturing an optical fiber base material according to the present invention, FIG. 2 is a schematic diagram of an example of the arrangement of processing burners according to the present invention, and FIG. 3 is a diagram showing a workpiece to be processed by the processing burner. FIG. 3 is a diagram showing the relationship between heating temperature and processing amount. 10... Base material for optical fiber, 11... Core, 12...
...Clad, 13...Clad center, 14... Burner for processing, 20... Workpiece, 21... Burner for processing Outline explanatory diagram of the method for manufacturing a base material for fiber of the present invention No. 1
Fig. 2 1. Example of arrangement of machining burners according to the present invention using force Fig. 2 Fig. 3 showing the relationship between force time and processing amount

Claims (2)

[Claims] (1) In a method for manufacturing a glass base material for an optical fiber consisting of a core and a cladding, the eccentricity of the center of the core with respect to the center of the cladding is measured, and the measured eccentricity is applied to the cladding portion of the glass base material. A method for producing a base material for an optical fiber, the method comprising the step of performing correction processing. (2) The method for manufacturing an optical fiber base material according to claim 1, wherein the eccentricity correction process is performed by flame heating the outer peripheral portion of the clad to evaporate the glass.