Spectral Analysis of Brillouin Dynamic Grating Based on Heterodyne Detection

Spectral analysis based on heterodyne detection is used to investigate Brillouin dynamic grating (BDG) in a small-core polarization-maintaining optical fiber. Thanks to direct heterodyning of the readout and diffraction waves, essential BDG properties can be fully investigated. It is experimentally characterized that the BDG diffraction wave has an identical frequency downshift from the readout wave as the pump-probe frequency offset in the BDG generation, which straightforwardly verifies the theoretical estimation of the BDG's phase-matching condition for the first time to our best knowledge. The spectral analysis also confirms that the maximum power of the main peak changes in the same way with the stimulated Brillouin gain and has an exponential (linear) dependence on the pump (probe) power. (C) 2013 The Japan Society of Applied Physics