Alignment tolerances of self imaging configurations for passive coherent beam combining

Abstract

We study guided self-imaging schemes useful to obtain Passive Laser Resonators Coupling (PLRC) for Coherent Beam Combining (CBC). Self-imaging schemes are well established methods for PLRC, but they are usually considered limited by large values of edge diffractive losses. In facts the Talbot effect (exact diffractive self-imaging) is obtained with infinite arrays only. This problem can be opposed by using a guided self-imaging that extends the finite array by means of a kaleidoscopic effect. This can be done in 2D with square or hexagonal symmetry or generating an infinite 1D array by winding up a linear array on a circle. In this case cyclic boundary conditions exactly produce an infinite array in the azimuthal direction. We report on numerical simulations performed to assess the coupling efficiency with particular attention to the alignment tolerance. Calculations are carried out with reference to a system of several fiber lasers. Our results indicate this as a viable solution for fiber lasers CBC.