Transverse dynamics of speckles in output radiation of optical fiber and determination of intermode dispersion generated under probing of laser diode with GHz frequency deviation

摘要

We have observed for the first time the dynamics of a speckle field generated in bulk scattering partly ordered media or low-mode optical fibers probed by a laser diode ( = 654 nm) and a compact diode-pumped YAG:Nd laser ( = 532 um) in the regime of frequency tuning. The dynamic coherent speckle-photo-chromic effect can be observed provided that the deviation of the probing radiation frequency is comparable with or greater than the effective phase delay difference between modes in the optical fiber of between waves in the random scattering medium. Using the proposed photochromic speckle technique, it is possible to determine the intermode dispersion of fibers with a length on the order of one meter and the dispersion of phase delay in test fluoroplastic structures in the regimes of several fold scattering (for a sample thickness of 10-20 μm) or multiple scattering (for a thickness of up to ~ 2 cm).