JPS5946898B2 - Optical fiber manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in a method for manufacturing optical fibers using chemical vapor deposition (CVD).

Conventionally, to manufacture optical fibers, a raw material gas mixture of metal halide gas for glass formation and oxygen gas is supplied to a protective quartz glass tube in advance, and the mixed raw material gas is oxidized by heating from the outside of the quartz glass tube. After decomposing and depositing the generated nascent glass particles on the inner surface of the tube to form a cladding of a desired thickness, a rod-shaped core having a refractive index greater than the refractive index of the cladding is inserted into the inner peripheral surface of the cladding. The method used is to melt and spin a glass material with a triple lever structure.

However, in this method, since the core is inserted into a pre-formed cladding, the interface between the cladding and the core is unavoidably disturbed during spinning, impeding smoothness (parallelism) and resulting in optical transmission loss. There was a drawback to the large size of the optical fiber.

In addition, when forming a cladding on a protective quartz glass tube, it is gradually deposited and formed from the inner surface of the tube, so the nascent glass particles generated by oxidative decomposition cannot be used effectively.
There was a drawback that the efficiency of raw material gas and the efficiency of forming cladding were reduced. The present invention has been made in order to eliminate the above-mentioned drawbacks, and it is an object of the present invention to provide a method for manufacturing optical fibers with significantly improved optical transmission loss with high efficiency.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

First, the core 2 is concentrically inserted into the protective quartz glass tube 1 via three supporting jigs 3 protruding from near both ends of the tube 1 . Next, a raw material gas mixture of a metal halide gas for glass formation and oxygen gas is supplied between the core 2 and the quartz glass tube 1 from the direction of arrow A, and an oxyhydrogen flame burner or the like is supplied from the outside of the quartz glass tube 1. to oxidize and decompose the mixed raw material gas, and gradually deposit the generated fine glass particles (tin) on the outer surface of the core 2 and the inner surface of the quartz glass tube 1. A cladding having a refractive index smaller than that of the core is formed between the core and the core. Thereafter, an optical fiber is produced by melting and spinning a triple-structured glass material consisting of a core, a cladding, and a protective quartz glass according to a conventional method. Examples of core materials used in the present invention include quartz glass, SlO2 and GeO2, TiO2
, P2O3 or a mixture of two or more thereof. As the metal halide gas for glass formation used in the present invention, one is selected so that the nascent glass fine particles (cladding material) produced by oxidative decomposition have a refractive index lower than that of the core. Specifically, the core is treated with a refractive index improving component (
When forming a multi-component glass consisting of GeO2) and SiO2, silicon tetrachloride is used as the metal halide gas for forming the glass. On the other hand, when the core is formed from the above-mentioned multi-component glass or quartz glass, a mixed gas of silicon tetrachloride and boron trichloride or boron tribromide, which are refractive index lowering components, is used as the metal halide gas for forming the glass. Applicable. Note that the above mixed gas (for example, SiCl4 and BCl3) is used as the metal halide gas for glass formation.
When using borosilicate glass, if a high concentration borosilicate glass layer is formed directly on the quartz glass core, cracks may occur due to the significant difference in thermal expansion between the quartz glass and borosilicate glass.
This results in a decrease in the strength of the optical fiber after spinning. Therefore, when supplying the above-mentioned Sice4 and the mixed raw material gas of BCl3 and oxygen gas between the core and the protective quartz glass tube, the mixed raw material gas with a low BCl3 concentration is supplied first, and the BCl3 It is necessary to supply a highly concentrated raw material gas mixture. In the present invention, the mixing ratio of the glass-forming metal halide gas and oxygen gas is set so that the oxygen ratio is slightly larger than the theoretical oxidative decomposition ratio of each gas.

According to the present invention, a mixed raw material gas of silicon halide gas and oxygen gas for glass formation is supplied between the protective quartz glass tube and the core inserted concentrically into the tube,
By oxidizing and decomposing the raw material gas, a glass layer 4 can be gradually deposited on both the outer surface of the core 2 and the inner surface of the quartz glass tube 1 to form a cladding, as shown in the figure. Not only the interface between the tube and the cladding, but also the interface between the cladding and the core can be significantly smoothed (parallelized). As a result, when optical information is incident on an optical fiber obtained by melting and spinning this triple-structured glass material, the optical information is refracted at a constant state at the interface between the core and the cladding, and the light is Transmission loss can be significantly improved. In addition, by supplying a mixed raw material gas between the protective quartz glass tube and the core, the adhesion area of the nascent glass particles generated by oxidative decomposition increases, and the adhesion efficiency of the particles increases significantly. can significantly increase the formation rate, suppress the release of unattached fine particles, and, in turn, improve productivity and make effective use of raw materials.

Next, embodiments of the present invention will be described with reference to the above-mentioned drawings. Example 1 First, a protective quartz glass tube 1 with an inner diameter of 18H11φ was heated through a support jig 3 with a diameter of 5.0 mm. Quartz glass cores 2 having a diameter of φ were placed concentrically.

Next, Si is placed between the core 2 and the quartz glass tube 1.
Starting with the mixed raw material gas consisting of Cl4, BC'3 and 02, the BCl3 concentration in SiC24 and BCl3 is 1W1%.
3W1(Ff), 6W1(Ff)
f), 10W1%, 13W1% are heated while being supplied to oxidize and decompose each mixed raw material gas, forming a cladding in which the concentration of B2O3 is higher in the center in the radial direction, forming a triple-structured glass material. did. Thereafter, this glass material was melted and spun to obtain a core diameter of 50 μmφ, a cladding outer diameter of 90 μmφ, and a protective quartz glass tube with an outer diameter of 100 μmφ.
An optical fiber of φ was obtained. The difference in refractive index (Δn) between the core and cladding of the obtained optical fiber is 0.0007 to 0.
．． 01, and when optical information was introduced into this optical fiber, it was confirmed that there was little scattering of the optical information outside the optical fiber and that the optical transmission loss was extremely low.

Example 2 First, the inner diameter is 20? φ protective quartz glass tube 1
A core 2 of 7.0 HIIφ made of multi-component glass of SiO 2 and GeO 2 was placed concentrically through a support jig 3 .

Next, SiO2 is placed between the core 2 and the quartz glass tube 1.
2, the mixed raw material gas consisting of BCl3 and 02 is converted into SiCl
4 and BCl3 are heated while being supplied so that the concentration of BCl13 in BCl3 increases from 1 to 15W1%, and each mixed raw material gas is oxidized and decomposed to produce B2O toward the center in the radial direction.
A glass material with a triple structure was created by forming a cladding of borosilicate glass with a high concentration of 3. After that, this glass material is melted and spun to create a core diameter of 90 μmφ and a clad outer diameter of 1.
40μmφ and outer diameter of protective quartz glass tube 180μmφ
Obtained optical fiber. The obtained optical fiber core,
The difference in refractive index between the claddings (Δn) is 0.005 to 0.0
35, and the interface between the core and cladding was extremely smooth.

Also, when optical information is input into this optical fiber,
It was confirmed that there was little scattering of optical information outside the optical fiber, and that optical transmission loss was extremely low. As detailed above, according to the present invention, a glass layer is simultaneously deposited on both the outer surface of the core and the inner surface of the protective quartz glass tube to form a cladding.
By melting and spinning this, a highly practical optical fiber with significantly improved optical transmission loss can be obtained, and it is also possible to significantly improve productivity and effectively utilize raw material gas for cladding formation. It has a remarkable effect.

[Brief explanation of the drawing]

The figure is a sectional view showing the process of manufacturing a triple-structured glass material used in the method of the present invention. 1...Protective quartz glass tube, 2...Core.

Claims (1)

[Claims] 1. After inserting the core concentrically into a protective quartz glass tube, a mixed raw material gas of glass-forming metal halide gas and oxygen gas is supplied between the core and the quartz glass tube, and the mixed raw material gas is oxidized and decomposed to form a cladding having a refractive index lower than the refractive index of the core attached to the inner surface of the quartz glass tube and the outer surface of the core to obtain a triple-structured glass material,
A method for producing an optical fiber, which is characterized in that the glass material is then melted and spun according to a conventional method.