Laser Beam Combining and Cleanup via Stimulated Brillouin Scattering in Multi-mode Optical Fibers

摘要

The main objective of this thesis was to demonstrate the feasibility of combining and cleaning up multiple laser beams via Stimulated Brillouin Scattering (SBS) in a multi-mode optical fiber. Beam combining via SBS in an optical fiber is of interest because of the low SBS threshold power in an optical fiber allowing low power diode laser beams to be combined into one high power beam. SBS theory and some of the important historical results are described briefly. The experimental results clearly indicate that SBS in multi- mode optical fiber can indeed combine laser beams and clean up the beams at the same time. Both single-pass and ring-cavity geometries were used successfully. The SBS threshold power for the 9.5 micron diameter fiber was 26.5 +/- 0.5 mW for a single-pass setup and 19.7 +/- 0.5 mW for a ring-cavity setup. The SBS power conversion slope efficiency was measured to be 42% for the single-pass setup and 52% for the ring-cavity setup. The SBS signal exhibited both periodic oscillations and random amplitude fluctuations, which are believed to be due to low levels of power used for the experiment. The polarization of the SBS signal was the same as the input laser beam.