The source points to lasers which are used mostly in all sorts of long distance fibre optic communications; more output power and narrow line width will definitely help in increasing the repeater spacing. The fibre is actually the heart of fibre optic communication systems and since the beginning of this era, research has been concentrated on making fibres with low loss described as dB/km. If it could be possible to make fibers with negligible loss, again a possibility is given to place repeaters at larger distances. The detectors: semiconductor detectors are used in all sorts of fibre optic communication. The quality of a detector is described by its ability in detecting a weak signal. Improvement in the detection system will help in extending the repeater spacing.