JPS63139025A - Production of optical fiber base material - Google Patents

Abstract

PURPOSE:To easily obtain the title inexpensive optical fiber base material by preparing a transparent glass base material, and etching the clad diameter against the core diameter with an etchant to an appropriate value. CONSTITUTION:The glass particle aggregate is sintered at high temp. and defoamed in the production of the optical fiber base material, and the process is carried out as follows: Namely, the clad part is formed so that the ratio of the clad diameter to the core diameter is made higher than the appropriate value to prepare the transparent glass base material, then the excess vitreous material of the clad part is etched with an etchant until the appropriate ratio of the clad diameter to the core diameter is obtained. An aq. mixed soln. of hydrofluoric acid and nitric acid is used as the etchant, and the aq. mixed soln. contg. 15-20% hydrofluoric acid and 15-20% nitric acid is preferably used.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing an optical fiber preform, and in particular, the present invention relates to a method for manufacturing an optical fiber preform, in which the optical fiber preform is entirely made of an aggregate of glass particles without using a quartz jacket tube. In the method of manufacturing an optical fiber preform by sintering and defoaming (hereinafter referred to as the total synthesis method), the excess cladding is etched to ensure an appropriate ratio of the core diameter to the cladding diameter. Regarding the method.

(Prior art) Conventional optical fiber base material is produced by heating high-purity glass forming raw material gas at high temperature using a glass particle synthesis torch to cause a hydrolysis reaction to synthesize oxide glass particles.
The glass particles are deposited and grown on the tip of the starting member that is rotated and pulled up, and the glass particle aggregate is then sintered in a high-temperature furnace and degassed to form the core part or core part. After obtaining a transparent glass base material that will form part of the cladding part, this transparent glass base material is stretched to an appropriate diameter, inserted into the cladding or a quartz jacketed tube that will become part of the cladding, and heated. However, a glass preform for optical fibers was manufactured by welding a jacket tube and transparent glass.

In this method, by adjusting the drawn diameter of the transparent glass preform, it is possible to obtain an optical fiber preform having an appropriate ratio of core diameter to cladding diameter. However, this method uses expensive quartz jacketed tubes, so
There is a problem that the manufacturing cost of the optical fiber preform is high, and there is also a problem that OHi contained in the jacket tube diffuses into the core portion, increasing optical loss of the fiber.

Therefore, a total synthesis method is used in which the optical fiber preform is manufactured entirely from glass particles without using a quartz jacket tube.

One of the total synthesis methods uses the transparent glass base material that forms the core and cladding parts as the optical fiber base material. This is a method of generating fine particle aggregates. That is, this is a method in which the preparation of a glass particle aggregate, the sintering in an oven, and the degassing treatment are each carried out only once to obtain a finished optical fiber preform.

Another total synthesis method involves further adhering glass particles onto a transparent glass base material, sintering them in a high-temperature furnace, and degassing them to achieve an appropriate ratio of the cladding diameter to the core diameter. This method is used as a finished optical fiber base material.

Although these total synthesis methods have the advantage of not using expensive quartz jacketed tubes, adjustments must be made to the thickness of the glass particle deposition to obtain an appropriate ratio of cladding diameter to core diameter. Furthermore, it is extremely difficult to obtain an appropriate ratio of the cladding diameter to the core diameter using this method, as the aggregate of glass particles undergoes significant shrinkage during the subsequent sintering and defoaming treatments. , and the yield is low.

(Problems to be Solved by the Invention) The present invention solves the problem caused by the above-mentioned total synthesis method, that is, it is impossible to reproducibly produce an optical fiber preform having an appropriate ratio of core diameter to cladding diameter. The object of the present invention is to provide a method for manufacturing an optical fiber preform easily and inexpensively.

(Means for Solving the Problems) The present inventors have completed the present invention as a result of intensive studies to solve the above problems.

The present invention provides a method for manufacturing an optical fiber preform by sintering a glass particle aggregate at high temperature and degassing it, in which the cladding portion is preliminarily adjusted so that the ratio of the cladding diameter to the core diameter is larger than an appropriate value. After forming a transparent glass base material, the excess glass in the cladding portion is etched and reduced using an etching solution until the ratio of the cladding diameter to the core diameter becomes an appropriate value. This is a method for manufacturing an optical fiber preform.

The configuration of the manufacturing method of the present invention will be further explained below.

In the method of manufacturing an optical fiber base material by sintering a glass particle aggregate at high temperature and degassing it, the cladding portion is formed in advance so that the ratio of the cladding diameter to the core diameter is thicker than an appropriate value. To create a transparent glass base material, we create a glass particle aggregate so that the cladding diameter is larger than the appropriate ratio of core diameter to cladding diameter, sinter this in a high-temperature furnace, and degas it. After processing to obtain a transparent glass base material, measure the refractive index distribution of this transparent glass base material to determine the core diameter and obtain the appropriate rad diameter, or Then, fine glass particles are attached so that the cladding diameter is larger than the appropriate value for the ratio of core diameter to cladding diameter, and it is sintered again in a high-temperature furnace and degassed to create a transparent glass base material. After obtaining the rad diameter, the refractive index distribution is measured in the same manner as described above, the core diameter is determined, and the appropriate rad diameter is obtained.

The etching solution used in the present invention is a mixed aqueous solution of hydrofluoric acid and nitric acid, and a mixed aqueous solution of 15 to 20% hydrofluoric acid and 15 to 20% nitric acid is particularly preferably used.

(Function) According to the present invention, since an accurate core diameter is measured in advance and an appropriate rad diameter can be determined from this value, the excess cladding portion can be etched until an appropriate rad diameter is obtained. This has the effect of making it possible to easily and efficiently manufacture an optical fiber preform with excellent reproducibility and having an appropriate ratio of the rad diameter to the core diameter.

(Examples) Hereinafter, the present invention will be further explained based on Examples, but the present invention is not limited only to these Examples.

Example 1 A method for manufacturing an optical fiber preform having a core diameter to cladding diameter ratio of 1:1.25 will be described.

Glass fine particle aggregates with core and cladding diameters of about 60 mm and about 80 mm, respectively, were prepared by the vapor phase attachment method. This is sintered in an electric furnace heated to 1500°C,
A transparent glass base material was obtained by defoaming treatment. When the refractive index distribution of this was measured using a spatial filtering method, the core diameter was 31 mm and the cladding diameter was 41 mm.

Therefore, the appropriate rad diameter is 31 Xl, 25 = 38
．． It turns out that 75 mm is sufficient. Therefore, when the transparent glass base material was immersed in an etching aqueous solution containing 15% HF and 15% HNOz for 4 days, the cladding diameter was reduced to 40 mm. Further, as a result of immersion in the same etching aqueous solution for 5 days, the cladding diameter could be reduced to 38.75 mm. As can be seen from the examples, it was possible to obtain an optical fiber preform in which the ratio of the core diameter to the cladding diameter was exactly 1:1.25.

Example 2 A method for manufacturing an optical fiber preform having a core diameter to cladding diameter ratio of 1:15 will be described.

Glass fine particle aggregates having core diameters and cladding diameters of about 15 mm and about 120 mm, respectively, were prepared by a vapor phase axial attachment method. This is sintered in an electric furnace heated to 1500°C,
A transparent glass base material was obtained by defoaming treatment. The outer diameter of this glass base material was approximately 58 mm. This was accurately stretched to an outer diameter of 20 mmφ using a glass lathe, and glass fine particles were further deposited on the outer periphery to give an outer diameter of about 94 mm.

This was sintered again in an electric furnace heated to 1500°C, and subjected to degassing treatment to obtain a transparent glass base material.

When we measured the refractive index distribution using the spatial filtering method, we found that the core diameter was 2.6 mm and the crund diameter was 39 mm.
, 6n++n. Therefore, it was found that the appropriate land diameter is 2.6 x 15 = 39 mm.

The transparent glass base material obtained therein was mixed with 15% HF, HNo,
As a result of immersion in a 15% etching aqueous solution for 40 hours, the cladding diameter could be set to 39 mm. As can be seen from the example, the ratio of the core diameter to the cladding diameter is exactly 1=15.
could be used as an optical fiber base material.

(Effects of the Invention) As explained above, the optical fiber preform manufactured by the present invention has the following properties by etching the cladding part.
Since the ratio of the cladding diameter to the core diameter can be adjusted accurately, the reproducibility is high (the effect of being able to manufacture with high yields has a large economic contribution).

Claims (1)

[Claims] In a method of manufacturing an optical fiber preform by sintering a glass particle aggregate at high temperature and degassing it, the cladding portion is formed in advance so that the ratio of the cladding diameter to the core diameter is larger than an appropriate value. After creating a transparent glass base material,
A method for manufacturing an optical fiber preform, comprising etching and reducing excess glass in the cladding portion using an etching solution until the ratio of the cladding diameter to the core diameter reaches an appropriate value.