Separate phase-locking and coherent combining of two laser diodes in a Michelson cavity

Abstract

We describe a new coherent beam combining architecture based on passive phase-locking of two laser diodes in a Michelson external cavity on their rear facet, and their coherent combination on the front facet. As a proof-of-principle, two ridge lasers have been coherently combined with >90 % efficiency. The phase-locking range, and the resistance of the external cavity to perturbations have been thoroughly investigated. The combined power has been stabilized over more than 15 min with an optical feedback as well as with an automatic adjustment of the driving currents. Furthermore, two high-brightness high-power tapered laser diodes have been coherently combined in a similar arrangement; the combining efficiency is 70% and results in an output power of 4 W. We believe that this new configuration combines the simplicity of passive self-organizing architectures with the optical efficiency of master-oscillator power-amplifier ones.

High-power operation of coherently coupled tapered laser diodes in an external cavity

“…Up to 12 W are extracted under the phase-locked operation of the bar and the front combination of the beams is currently under study. The concept of this architecture is suitable for different laser types 21,22 . However, the benefits of such rearside resonator architecture are highlighted in this experiment by the capability to use tapered devices reaching very high brightness per emitter, and also by avoiding any drop of the coherence at high currents.…”

Passive coherent combining of two tapered laser diodes in an interferometric external cavity

“…As a consequence, the electrical-to-optical efficiency of the phaselocked laser array is increased as compared to standard external cavity configurations, since losses are minimized on the useful output [3]. We have already demonstrated this configuration with two low-power ridge lasers [4]. In this contribution, this technique is applied to high-brightness tapered devices demonstrating the potential of extended-cavity phase-locking arrangements for high-power operation.…”