The design and performance of high radiance, linear, Burrus type GaAs-GaAlAs double heterojunction LED's is described. Characteristics such as radiance, response time, spectral width, efficiency and reliability are considered. The properties of these surface emitting structures are contrasted with those reported for high radiance LED's having an edge emitting geometry. The coupling characteristics and total power available from both device designs when coupled to optical fibers typical of those employed in practical systems are described. Results are presented of measurements made of LED linearity as functions of structure, drive level and doping. Implications of these linearity measurements on the use of LED's for analog signalling are discussed. Circuit compensation techniques which have been employed to reduce the non-linearities in optical transmitters are briefly reviewed.