Opposite ends of a fibre-optic cable have terminations 4 and 5 including a metal diaphragm 53 which is welded or brazed at its outer edge to the termination. The diaphragm 53 has a central aperture 54 into which extends the ends of a bundle 1 of optical fibres 2, the fibres being hermetically sealed together at their end and sealed in the aperture by a glass seal 55. The diaphragm 53 tapers in thickness from its outer edge to its central aperture where it is thinner and is flexible to accommodate relative displacement between the fibre bundle 1 and the sheath 3 of the cable.