Abstract

Few studies of the spatial beam profile of semiconductor lasers, and how they are effected by optical feedback, have been reported. This is despite the area of optical feedback in semiconductor lasers, particularly the effect on spectral content and noise, being a major area of research. Interest in the spatial beam profiles is increasing rapidly as broad area lasers, with their filamentary spatial profiles, are gaining as the preferred device for output power scaling in laser diodes [1], [2]. It is anticipated that through the use of tailored optical feedback, the beam quality may be improved. We report on the spatial beam characteristics of a standard, low power index-guided semiconductor laser (Hitachi HL8314). The results of three studies, including the effect of (i) focussing (fig. 1), (ii) tilting and (iii) aperturing the optical feedback field will be presented along with modelling using Gaussian beam propagation methods. All of the spatial beam profiles show that the beam profile is determined by interference of the emitted and optical feedback fields at the output facet of the laser diode. The importance of interference in determining the spatial beam profile has been shown before but here we demonstrate definitively that it is interference between the optical feedback field and the emitted field, rather than ghost reflections off intracavity optics, that determines the detailed profile. Results on how the output power of the system of laser diode with optical feedback varies as the spatial feedback field is tailored will also be presented.

© 2000 IEEE