JPS6143683B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing optical fiber in a form suitable for communication cables.

If mechanical stress is applied to an optical fiber in the lateral direction, it will cause micro-fractures or micro-curvatures, increasing the transmission loss.If mechanical stress is applied in the longitudinal direction, the transmission loss will be significant, and especially if it breaks, the transmission loss will be extremely large. In any case, it is extremely fragile to mechanical stress.

A preferred embodiment of the invention provides a support that allows several optical fibers to be combined into a bundle, which is effective against the mechanical stresses experienced by the optical fibers as they pass through cable making machinery. It provides significant protection.

The present invention includes a central core wire surrounded by a twisted bundle of optical fibers, which core wire is supported by a support element or cord made of a material that has a high tensile strength and has little stretch under stress. A first sheath of a high modulus material containing the formed central strand and extruded around the strand to eliminate twisting forces on the core, and surrounding the first sheath. A second sheath made of a foamed or non-foamed material with a low elastic modulus extruded on the substrate, which acts as a buffer for the optical fiber twisted at a long pitch around the second sheath. It is.

The present invention will now be described in detail with reference to preferred embodiments thereof illustrated in the accompanying drawings.

The central wire has a strand 2 surrounded by two concentric sheaths 3 and 4. The stranded wire 2 serves as a support element. This strand is a cord made of a material with good tensile strength and little stretch. Suitable materials include aromatic polyamide thin wire, glass fiber, carbon fiber, and even metal wire if electromagnetic insensitivity is not required. This strand 2 resists the longitudinal tensile forces applied to the cable, and its dimensions are selected taking into account the magnitude of the expected force and the nature of the surrounding optical fiber bundle. Stranded wire 2
The inner sheath 3 in contact with is made of a high modulus extrudable material, such as polyamide, polyethylene terephthalate or high density polyethylene. This gives rigidity to the stranded wire 2, and since the optical fibers making up the bundle are wound in the same direction with long pitches and with low tension, the core wire can withstand the twisting force applied to the center core wire. Try to get it. The outer sheath 4 formed by extrusion around the inner sheath 3 is of a foamed or non-foamed material with a low elastic modulus, such as low density polyethylene, flexible vinyl polychloride or ethylene-vinyl copolymer. be. This acts as a buffer and absorbs the lateral pressure applied to the optical fiber. A plurality of elements, all or part of which are made of optical fibers, are arranged around this inner/exterior sheath 4. If some of these elements are optical fibers, the elements not used for transmission are metal,
Cable filler made of plastic or their composite wires.

The diameter of the central core 2 is chosen as a function of the elements forming the bundle or as a function of their number. The diameter of the first sheath 3 is determined as a function of the torsional strength of the strands 2 to be compensated and for the torsional forces exerted by the element 1 on the core wire 2 during assembly of the element 1. It is determined as a function of the torsional strength generated in

Taking an assembly of 18 optical fibers as an example, the diameter of the strand 2 is 0.7 mm, the thickness of the inner sheath 3 is 1.6 mm, and the thickness of the outer sheath 4 is 0.3 mm. The diameter of each optical fiber to be protected is 0.5
mm. The winding pitch of the optical fiber is approximately 400mm.

The optical fiber is formed by various elements including the optical fiber assembled around the central conductor, using known techniques such as tapes, layers of damping material or protective armor layers, Alupe type sealing barriers, etc. The outside is covered with a protective layer of The cable can be used alone or in combination with other similar cables to form other fiber optic communication cables by conventional cable technology.

[Brief explanation of the drawing]

The drawing is a cross-sectional view of a bundle of optical fibers 1 assembled around a center line in an embodiment of the invention. 1... Optical fiber, 2... Twisted wire, 3... First exterior, 4... Second exterior.

Claims (1)

[Claims] 1. In an optical cable that includes a central core surrounded by a bundle of optical fibers, the central core being formed by a supporting element or cord of a material with high tensile strength and little stress elongation, around the strands 2. a first sheath 3 of a high modulus material extruded to improve the torsional strength of said centerline; An optical cable characterized in that it includes a second sheath 4 of foamed or non-foamed material, which acts as a buffer for the pitch-stranded optical fibers 1.