Coherent and incoherent beam combining and cleanup via stimulated Brillouin scattering in multi-mode optical fiber

Abstract

We present a simple technique for combining multiple laser beams into a single coherent beam and simultaneously cleanup the aberrations associated with the input beams. It is well known that the SBS process tends to produce a phase conjugate replica of the input (pump) beam in retro-reflection (called the Stokes beam) when excited in a bulk medium and a short (typically a few meters or less) multimode fiber. However, when SBS is excited in a long fiber the Stokes beam is no longer a phase conjugate replica of the pump beam due to the phase mismatch between the pump and the Stokes beams, but takes on an intensity profile corresponding to the fundamental fiber mode, irrespective of the pump beam profile. Thus when an aberrated pump beam is used to excite SBS in a multimode fiber, the SBS process has the effect of cleaning up the beam aberrations to produce a clean Gaussian-like Stokes beam.