Half century of semiconductor lasers in photonics

We look back the history of semiconductor lasers toward future starting from the middle of the 20th century. In 1958, A. L. Shawlow and C. H. Townes proposed “Optical Maser”, that is about 40 years later after the concept of “Induced Emission” by A. Einstein and several years after A. W. Overhauser recognized the population inversion. Few years after this proposal, lasers have been realized. For semiconductor optical devices, J. von Neumann predicted that the semiconductor could be an optical amplifier in 1953. First semiconductor “lasers” were realized almost simultaneously and independently with GaAs substrate by R. N. Hall et al., T. M. Quist et al., and M. I. Nathan et al., respectively, and with GaP by N. Holonyak. Jr et al. in 1962. These semiconductor lasers consisted of homo-junction structure. Therefore, the lasing operation was achieved only under pulsed operation.