Special issue paper. Principles of fibre-optical cable design

Much of the design and technology for fibre-optic cables is common to that used for conventional cables employing metallic conductors. The main concern relates to the inherent brittleness of the fibre material, and to the optical sensitivity to the mechanics of manufacture, installation and service. Necessary mechanical properties for the cabling of optical-fibre waveguides are obtained by the application of plastic coatings: this is an essential preliminary. A number of such coated fibres may then be combined together with a strength member which increases the tensile capability of the composite, using fillers and wraps to maintain the geometric register. This core unit may then be plastic sheathed, and it can be further provided with additional strength members, water barriers, etc. A number of such units may be combined to form a high-capacity unit cable. The basic design requirements involve protection of the fibres from tensile and radial stresses, adequate bend performance, and environmental protection. The limits on the design options which these requirements impose are discussed, and prototype cable designs and constructions are put forward.