Recent advances in optical fibre communications

Optical fibre cables are currently available having transmission losses of 3 dB/km and bandwidth x length products of 1 GHz km at an operating wavelength of 0.85¿m. At the longer wavelength of 1.3¿m attenuations as low as 0-5 dB/km, and repeater spacings of 50 km, have been demonstrated in the laboratory. The corresponding bandwidth of graded-index multimode fibres can be large, even with light-emitting diodes, while the combination of semiconductor lasers with single-mode fibres is capable of several hundred GHz km. Practical problems of cabling, jointing connectors, strength, sources and detectors are close to being solved.