Fibre-optic cable assembly having a sheath with restrained expansion

A fibre-optic cable has a silica optical fibre within a fluoropolymer sleeve. The optical fibre extends between two couplings and is protected by a sheath that is fixed at each end to the couplings. The sheath comprises parallel silica filaments that extend between two braided aramid sleeves. The sheath is completed by an outer tube of a fluoropolymer resin extruded onto the braided sleeves so that its material flows through them and the filaments. The filaments restrain thermal expansion of the sheath to an expansion closely matched to that of the optical fibre.