Abstract

We are exploring power scale-up of semiconductor lasers through the use of arrays of amplifiers and coherent beam combining. In this paper we report 93%-efficient interferometric beam combining of the output of two saturated amplifiers yielding 372 mW in a single diffraction-limited lobe. A single mode semiconductor laser was amplified in a single stage and divided into two beams of 53 and 71 mW. Each beam was injected into a 10-stripe gain guided amplifier array having dimensions of approximately 100 μm wide by 250 μm long. Each amplifier had antireflective coatings (R~2%) on the front facet and high reflectivity mirrors (R~99%) on the rear facet. The output from the double-pass amplifiers produced 206 mW and 195 mW in the respective central lobes. Relative phase control was implemented by a mirror mounted on a piezoelectric stack before the beams were recombined at a common beam splitter. Proper adjustment of the relative phase resulted in a single beam having an output power of 396 mW with 94% or 372 mW, in a single diffraction-limited lobe. The corresponding single-lobe combining efficiency is 93%. The out-of-phase far-field profile was also recorded and indicated some mode mismatch as well as less than ideal coherence. Based on this data, we have shown that higher saturated gain may be achieved with multi-element systems.

© 1992 Optical Society of America