Rear-side resonator architecture for the passive coherent combining of high-brightness laser diodes

Abstract : We describe a new coherent beam combining architecture based on passive phase-locking of emitters in an extended cavity on their rear facet, and their coherent combination on the front facet. This rear-side technique provides strong optical feedback for phase-locking while maintaining a high electrical-to-optical efficiency. Two high-brightness high-power tapered laser diodes are coherently combined using a Michelson-based cavity – the combining efficiency is above 82% and results in an output power of 6.7 W in a nearly diffraction-limited beam with an M²4σ ≤ 1.2. A semi-active automatic adjustment of the current enhances the long-term stability of the combination, while the short-term stability is passively ensured by the extended cavity. This new laser configuration exhibits the simplicity of passive self-organizing architectures, while providing a power conversion efficiency of 27% that is comparable to master-oscillator power amplifier architectures.