Optical multiple fiber

Details Optical multiple fiber Optical multiple fiber

1983-11-01

1987-09-01

Sikes, William L.

350 9624, 350 9626, 350 9627, 350 9629, G02B 606

Patent

active

046905006

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
The present invention relates to an optical multiple fiber (hereinafter simply referred to as "multiple fiber") having a construction that a multiplicity of silica glass optical fibers are fused together with each other and more particularly to a multiple fiber, each optical fiber of which consists of a pure silica glass core and a cladding layer thereon made of a silica glass containing a dopant and having a lower refractive index than pure silica glass.
2. Background Art
The above-mentioned multiple fiber which consists of optical fibers each having a core of pure silica glass retains desirable properties such as excellent heat resistance and radiation resistance inherent in pure silica glass, and therefore is useful as an image-guide for monitoring the inside of a high-temperature furnace, a nuclear reactor, and the like.
Generally, a silica glass multiple fiber is produced by bundling a multiplicity of optical fiber preforms or materials obtained by drawing the preform to reduce it in diameter (hereinafter, those two materials are generically referred to as "preform" simply) and drawing the resulting bundle at a high temperature, whereby each preform is reduced in diameter into an optical fiber and simultaneously adjacent optical fibers are fused together with each other.
As compared with the pure silica glass of the core, the dopant-containing silica glass of the cladding layer has a very low softening point and a very low resistance to deformation in softened state. For that reason, in the case of a multiple fiber produced by the above-mentioned drawing method, as illustrated in FIG. 1, the core 2 of each optical fiber 1 included in the multiple fiber retains a circular cross section similar to that of the core of the preform, while the cladding layer 3 on the core 2 is deformed to acquire a hexagonal outer shape in cross section and the cladding layer 3 having such outer shape is fused together with the cladding layers of the adjacent optical fibers, most of the optical fibers thus being arranged in such a manner that hexagons are most closely packed.
However, the production of the multiple fiber of silica glasses is very difficult as compared with multiple fibers of multi-component glasses because the softening point and melt viscosity of silica glass are much higher than those of multi-component glass. It is only recently that it became promising to produce such a silica glass multiple fiber. Under these circumstances, there are few studies dealing with such problems as how to improve various properties required for multiple fiber, such as image-transmitting capacity.
The present inventors have found that the sectional structure of each optical fiber included in a silica glass multiple fiber, especially the interrelationship between the core diameter and the cladding layer thickness, has a great influence on the various properties of the multiple fiber, including the image-transmitting capacity. This finding and an intensive study based thereon have led to the present invention.


DISCLOSURE OF THE INVENTION

The present invention provides a multiple fiber comprising a multiplicity of optical fibers fused together with each other, each optical fiber comprising a pure silica glass core and a cladding layer thereon made of a dopant-containing silica glass and having a thickness which satisfies the following equation (I): D.sub.1 is the outer diameter of the core in .mu.m.
In the above, the cladding layer thickness T.sub.1 means the shortest distance between a side of the hexagon defined by the contour of the deformed cladding layer and the core surface, as illustrated in FIG. 2.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a multiple fiber in accordance with the present invention, illustrating the disposition of optical fibers therein.
FIG. 2 is a cross-sectional view of an optical fiber included in a multiple fiber in accordance with the present invention and having a two-layer construction.
FIG. 3 is a cross-sectional view of a multiple f

REFERENCES:
patent: 2992516 (1961-07-01), Norton
patent: 3436142 (1969-04-01), Siegmund et al.
patent: 3502455 (1970-03-01), Gardner
patent: 3554720 (1971-01-01), Crepet
patent: 4613205 (1986-09-01), Seiji et al.
patent: 4615583 (1986-10-01), Tsuno et al.
Kaiser et al. "Low Loss Single Material Fibers Made of Pure Fused Silica" Bell Tech Jour., vol. 53, No. 6, 8/74, pp. 1021-1039.
Utsumi, A., et al., "Modified Rod-in-Tube Method for Low Loss Step-Index Optical Fiber", Topical Meeting on Optical Fiber Transmission, Washington, D.C., Mar. 1979.
Utsumi, A., et al., "Fiber Optics in Adverse Environments II", SPIE, 506 (1984), 176-183.
Shintani, S., et al., "Silica Glass Imageguides and Their Applications", JARECT, vol. 17, Optical Devices & Fibers (1985), 320-332.
"Diaguide Scope, A New Industrial Fiberscope for Upto 100 m Span", Dianichi-Nippon Cables, Ltd., Dec. 1982.

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