Demonstration of Spatial Mode Selection in a Coherently Combined Fiber Laser

Several physical mechanisms influence the self-phasing of passive coherently combined laser systems, including wavelength tuning, the Kramers-Kronig (KK) effect, the optical Kerr effect, regenerative feedback, and spatial mode selection. Beam recycling, a concept introduced in the modal analysis of a Michelson cavity, applies feedback to waste energy from the coherent combination process to introduce a second supermode in the cavity [1]. Experiments using a polarization-multiplexed cavity showed that the output power is less sensitive to gain arm path length changes when beam recycling is used [2]. Self-phasing mechanisms including beam recycling appear to have also been applied in a ring laser array [3]. Here, we present an experiment which isolates the beam recycling effect in a fiber laser with two separate gain media and show improved laser performance when recycling is implemented.