Efficiency analysis on coherent beam combination of fiber lasers using phase gratings

Abstract

Coherent beam combination (CBC) of fiber lasers has the potential to solve the power limitation in single fiber as well as maintaining good beam quality, which have been under intense research recently. Considering the advantage of high diffraction efficiency, compact volume and relatively easy to fabricate, phase grating has been considered as a promising combination component, and has been under intensive research recently. In this manuscript, take sine phase grating as an example, the combination efficiency in the case of phase error, incident angle error and laser intensity fluctuations will be detailed. Conclusions can be obtained from numerical calculating that the effect of incidence angle error and intensity fluctuation can be controlled within the specified range using off-the-shelf techniques. Nevertheless, the question whether the phase error can be controlled to be within 0.32 rad when scaled to high power level remains open due to the limited control bandwidth of existing phase stabilization system. For practical engineering in CBC using phase gratings, phase error control is the key component towards high efficiency.