Transverse mode control by a self-imaging process in a multimode fibre laser using a single-mode feedback loop

Abstract

We propose new laser architecture to improve the spatial emission of a multimode fibre amplifier (MMFA) by using a self-imaging process. Interference between the different modes of the MMFA is filtered by a single-mode fibre section which serves as feedback in a unidirectional ring cavity. The laser self-adjusts its frequency to ensure self-imaging between opposite faces of the multimode fibre. The laser output pattern and longitudinal modes depend on the single-mode fibres' end face position with respect to the MMFA centre axis. As a proof of principle we report experimental results which are in good agreement with numerical simulations.