Optical fiber communication cables and method and apparatus for assembling same

Claim 2

An individually armoured fiber optic of micro dimensions comprising a fiber optic element (12) intimately surrounded by a protective layer (13) and together forming a fiber optice core (11), and a seamed metal sheath (14) surrounding said core and providing an armour therefor, characterised in that said sheath (14) is of a high strength metal drawn about said core and having an external diameter not greater than 0.05" (1.72 mm) and an internal diamter such that the ratio of the external diameter of the core to the internal diameter of the sheath, if removed one from the other, is at least 0.6:1, the longitudinal edges of said seam (15) being defined by opposing, non-linear deformed edges (16) and (17) extending along the length of the sheath on the opposite sides of the seam and whose thickness, measured from the outside of the sheath to the inside, is greater than the drawn thickness of said sheath intermediate those edges.

Claim 3

A fiber optic according to claim 1, characterised in that the ratio of the external diameter of the core (11) to the internal diameter of the sheath (14), if removed one from the other, is at least 0.7:1.

Claim 4

A fiber optic according to claim 1 or 2, characterised in that In the assembled state, the outside diameter of the core (11) is slightly less than the internal diameter of the sheath (14).

Claim 5

A fiber optic according to claim 1 or claim 2, characterised in that in the assembled state, the external surface of the core (11) is in intimate contact with the internal surface of the sheath (14).

Claim 6

A fiber optic according to claim 4, characterised in that the material of said protective layer (13) of the core (11) is extruded into and between the opposed edges (16, 17) of tne seam (15) of the sheath (14), thereby to seal the core (11) hermetically inside the sheath (14).

Claim 7

A fiber optic according to claim 1, 2, 3 or 4, characterised in that the core (14) is hermetically sealed by a line of solder along the length of said seam (15).

Claim 8

A fiber optic according to any of claim 1-6, characterised in that said edges (16, 17) of the seam (15) intermesh and that the sheath has a yield strength of at least 50 ksi (345 MPa).

Claim 9

A fiber optic according to any one of the preceding claims, characterised in that the sheath (14) is formed of a copper alloy.

Claim 10

A fiber optic according to claim 8, characterised in that said alloy is in the full hard condition.

Claim 11

A fiber optic according to any one of the preceding claims, characterised by a further, insulative coating (19) formed externally about said sheath (14).

Claim 12

A fiber optic cable comprising a plurality of individually armoured fiber optics (10) according to any one of claims 1-9 arranged in parallel array.

Claim 13

A cable according to claim 11, characterised in that it comprises a plurality of strands (28) arranged in a bundle (27'), at least one strand (10') comprising a fiber optic according to any one of claims 1-9 and at least one other strand (28) comprising a strand of metal or plastics material.

Claim 14

A cable according to claim 12, characterised in that said strands (28, 10') are all of the same external dimension.

Claim 15

A cable according to claim 12, charaterised in that said bundle comprises a plurality of strands (28) of metal or plastics material each having an external diameter greater than that of said fiber optic (10), and wherein said fiber optic(s) (10) is or are located in the interstices (29) between said metal or plastics strands (28).

Claim 16

A cable according to claim 11, characterised in that said array of fibre optics (10) is enclosed within a common outer sheathing (21, 22, 23, 24).

Claim 17

A cable according to claim 12, 13 or 14 characterised in that said bundle (27) of strands (28) is located within a common outer sheathing (34) completely surrounding said bundle.

Claim 18

A cable according to claim 15 or 16, characterised in that said outer sheathing is multi-layered structure.

Claim 19

A method of fabricating an individually armoured fiber optic as claimed in claim 1, characterised by feeding a strip (32') of high strength metal to a die (36), said strip having generally parallel linear edges (16, 17) along both sides, drawing the strip through the die whilst simultaneously laying therein a fiber optic core (11) comprising a fiber optic element (12) embedded in an outer protective layer (13), the die serving to form said strip (32') as it passes therethrough into a sheath (14) surrounding the core and having an external diameter not greater than 0.05 " (1.72 mm), and an internal diameter such that the ratio of the outside diameter of the core (11) to the inside diameter of the sheath is at least 0.6:1, the strip 32' having an initial dimension such that its transverse cross-sectional area exceeds the cross-sectional area of the sheath after drawing, whereby as the strip is drawn through the die the longitudinal edges (16, 17) of the strip are deformed to provide a seam (15) defined on opposite sides by non-linear edges whose thickness measured from the outside of the sleeve to the inside is greater than the drawn thickness of the sheath.

Claim 20

A method according to claim 18, as applied to the fabrication of a fiber optic required by any one of claims 2-5 or 7.

Claim 21

A method according to claim 18 or 19, characterised in that after drawing through the die the sheath (14) is sealed along the length of the seam (15) by applying a line of solder therealong.

Claim 22

A method according to claim 18, 19 or 20, characterised in that after passage through the die an insulative coating layer is formed in the external surface of the sheath.