GaAs-Ga1-x Alx As double heterojunction material was grown by liquid phase epitaxial technique, and small area high radiance light emitting diodes are made. The radiation power is above 100W/sr.cm2, output power of the tail fibre (inner diameter 60m N.A.=0.17) is 200W, and extrapolated life reaches 105 hours. It is already being used in the 1.8km 8.448 Mb/s PCM-120 route optic fibre telephone communication system. Analysis is made on the operational characteristics of the diodes. Factors affecting its proper use and approaches for improvement are discussed.