Optical Phase Conjugation via Stimulated Brillouin Scattering in Multimode Optical Fiber

Abstract : The main objective of this thesis was to obtain phase conjugation of laser beam using the process of stimulated Brillouin scattering (SBS) in optical fiber and to characterize the parameters involved. SBS in fiber is used for several reasons: high conversion efficiency, nanosecond response time, only the signal beam is required and fiber has a lower SBS threshold and superior power handling capabilities compared to either crystals or liquids. SBS theory is briefly described along with some results from previous work. Experimental results show the multimode fiber losses at coupled powers below about 2 W to be 16.4 + or - 0.3 dB/km at 514.5 nm. The transmitted and backscattered power exhibited behavior similar to that previously reported for single-mode fiber. The SBS threshold power increased for shorter fibers and when index matching liquid was used. The Stokes shift was 32.78 + or - 0.02 GHz and the measured gain coefficient was 10.2 times 10(-9) cm/W with an error of 10%. Most importantly, nonlinear optical phase conjugation was demonstrated for the first time. The polarization state of the pump beam was not reproduced, however. In addition, the SBS power exhibited bursts of strong fluctuations.