GB1562676A

GB1562676A - Optical fibre cable

Info

Publication number: GB1562676A
Application number: GB2061/78A
Authority: GB
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1978-01-18
Filing date: 1978-01-18
Publication date: 1980-03-12

Description

(54) OPTICAL FIBRE CABLE (71) We, STANDARD TELE PHONES AND CABLES LIMITED, a British Company, of 190 Strand, London, WC2R 1DU, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to optical fibre cables and in particular to cables of a flat construction.

According to the present invention there is provided a flat construction optical fibre cable containing only two optical fibres the cable having four elements held in side by side relationship in a common sheath of plastics material wherein the inner two elements of said elements are said optical fibres, each optical fibre being made of glass and being provided with one or more protective coatings, and wherein the outer two elements are electrical conductors.

There follows a description of a flat construction optical fibre cable embodying the invention in a preferred form suitable for data distribution in for instance short distance permanent wiring applications. The description refers to the accompanying drawing depicting the cable construction.

Referring to the drawing, a pair of single optical fibres 1, 2 are each provided with a primary plastics coating 3 that is applied to the freshly drawn fibre to protect its surface from atmospheric attack. Typically the fibres 1 and 2 have an internal waveguiding structure, and are made by the process described in British Patent Specification Serial No. 1,475,496, and have a core diameter of 30 Fum and an overall diameter of 100 ijm. If applied, the primary coating is typically a silicone resin, and is typically 35 ,um thick. The primary coated fibres are each encased in a secondary coating 4 having an external diameter of typically 1 mm. This coating is 4 may be an extruded coating of for instance polypropylene. Preferably the coatings 4 on the two fibres are provided with contrasting colours for identification purposes. In the case of fibres that do not have a primary protective coating the coating 4 is applied direct to the fibres themselves.

The two plastics coated single optical fibres are arranged side by side between a pair of electrical conductors 5, 6 which may also serve as tensile reinforcement members for the cable. For a number of applications where considerations of tensile strength are relatively more important than high electrical conductivity it is preferred to make the conductors 5 and 6 of a material other than copper, such as for instance steel. A preferred material is stranded brass plated steel such as is used for tyre cords. With a construction using fourteen 0.18 mm diameter strands of brass plated steel it was found that the electrical conductivity was in the region of 600 ohms per kilometre. In an alternative construction where each conductor was a 0.5 mm single solid strand of copper encased in a polypropylene sheath bringing the diameter up to 1 mm, the electrical conductivity was in the region of 90 ohms per kilometre. The stranded construction will generally be preferred where flexibility of the cable is particularly important, whereas a solid construction may be preferred when it is desired that the cable shall tend to retain its form after being bent.

An advantage of using a plastics sheath for the conductors is that it enables them to be colour coded. It also has the advantage that the conductors are provided with their own individual electrically insulating sheathing separate and additional to any insulation that may be provided by the cable sheathing. However, provided that the two optical fibres are colour coded, the electrical conductors can be distinguished from each other without themselves being colour coded. This is achieved by reference to their positional relationship with the two optical fibres.

The four elements comprising the sheathed optical fibres 1 and 2 and the conductors 5 and 6 are encased side by side in a common outer sheath 7 of suitable plastics material. In the case of a cable with each of the four elements having an overall diameter of about 1 mm the overall dimensions of the outer sheath 7 are typically 5 mm by 2 mm. A preferred material for the outer sheath is an ethylene vinyl acetate copolymer extruded around the elements in such a way as to leave three webs 8 separating the four elements off from each other. Preferably the extrusion is performed under conditions which will ensure that the sheath material is in intimate contact with the four elements but does not adhere to them. A preferred way of achieving this end is to use a lower melting point material for the outer sheath 7 than is used for the protective coatings 4.

WHAT WE CLAIM IS: 1. A flat construction optical fibre cable containing only two optical fibres the cable having four elements held in side by side relationship in a common sheath of plastics material wherein the inner two elements of said elements are said optical fibres, each optical fibre being made of glass and being provided with one or more protective coatings, and wherein the outer two elements are electrical conductors.

2. A cable as claimed in claim 1 wherein the two electrical conductors are plastics sheathed conductors.

3. A cable as claimed in claim 1 or 2, wherein the two electrical conductors are solid.

4. A cable as claimed in claim 1 or 2 wherein the two electrical conductors are stranded.

5. A cable as claimed in claim 3 or 4 wherein the electrical conductors are made of copper.

6. A cable as claimed in claim 3 or 4 wherein the electrical conductors are made of brass plated steel.

7. A cable as claimed in any preceding claim wherein the common sheath is formed with webs separating the four elements off from each other.

8. A cable substantially as hereinbefore described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. other without themselves being colour coded. This is achieved by reference to their positional relationship with the two optical fibres. The four elements comprising the sheathed optical fibres 1 and 2 and the conductors 5 and 6 are encased side by side in a common outer sheath 7 of suitable plastics material. In the case of a cable with each of the four elements having an overall diameter of about 1 mm the overall dimensions of the outer sheath 7 are typically 5 mm by 2 mm. A preferred material for the outer sheath is an ethylene vinyl acetate copolymer extruded around the elements in such a way as to leave three webs 8 separating the four elements off from each other. Preferably the extrusion is performed under conditions which will ensure that the sheath material is in intimate contact with the four elements but does not adhere to them. A preferred way of achieving this end is to use a lower melting point material for the outer sheath 7 than is used for the protective coatings 4. WHAT WE CLAIM IS:

1. A flat construction optical fibre cable containing only two optical fibres the cable having four elements held in side by side relationship in a common sheath of plastics material wherein the inner two elements of said elements are said optical fibres, each optical fibre being made of glass and being provided with one or more protective coatings, and wherein the outer two elements are electrical conductors.