Phase-locking of two photonic crystal fibre lasers by mutual injection scheme

In recent years, exciting progress has been made in the upscaling of high-power fibre lasers, owing to the advance in cladding pump and fibre fabrication technologies. Especially, with the advent of photonic crystal fibres (PCFs), Yb-doped PCFs are rapidly being developed and utilised in the study of high-power fibre lasers, the reported output power of PCF laser having exceeded kW levels 1]. Compared with the conventional fibres, PCFs have many unique properties such as endless singlemode guiding, large singlemode area, small nonlinearity, and high numerical aperture of inner cladding, etc., which make PCFs especially suitable for producing high-power lasers with good beam quality. However, as in the case of the conventional fibre lasers, nonlinear effects and onset of catastrophic thermo-optical damage are the main limitations of the upgrading of high-power PCF lasers. Thus, coherent addition schemes are also desired for PCF lasers to achieve higher output power with higher brightness.