olve in response to new opportunities and special needs. There are however two, perhaps three, market sectors of special Line plant for optical cables interest where a new fibre design might be justified. The first is in submarine cable systems where the benefit of lower loss means Generally it has proved feasible to adapt conventional cable hard- fewer underwater repeaters and potentially higher reliability. Some ware to the requirements of optical fibre. The preferred fibre joint- research into new glass compounds offering very low losses at long ing technique is by fusion of the two fibre ends, either in a gas flame wavelengths (10 um) has been reported. The second market sector or more commonly by an electric arc. Proprietary machines are is the proposal for optical links into telephone subscribers premises. available in which the fibre coatings are stripped, the fibre ends This application would probably benefit from larger core fibres cleaved, and fusion applied. Surface tension forces centre the mat- facilitating the design of the necessarily low cost optical devices and ing fibres with respect to the cladding surface diameters. Finally, the connectors. A third possible area is application in local area net- surface coatings are reinstated and the splice given mechanical works which is in some respects similar to the problem of subscriber support. Machines with various levels of automation are available connection. However, current sentiment seems to be in favour of and some provide light injection and detection (LID) SO that splice standard fibre for this application. loss can be minimised during the operation. It is common practice It is evident that any alternative fibre design in terms of operating to check splice losses by OTDR (optical time domain reflectometer) wavelength or core size, must be supported by a corresponding progressively as work proceeds along a route. range of transmitters, receivers, connectors and test equipment and The completed splice, with its reinforcement splint, must be that 