Recent advances in the semiconductor laser and photodetector state of the art has led to the development of small low cost, reliable laser transmitter and receiver modules (see Fig. 1). These modules are now being designed into a number of practical communication systems used for a wide variety of applications (see Figs. 2 and 3). These systems have been designed to transmit voice, computer data, and video sivals and offer a number of advantages over previous transmission methods including cost, security, simplicity, bandwidth and licensing requirements. Where atmospheric limitations are either absent or surmountable these optical communication systems offer the communication engineer a viable alternative.