ACOUSTOOPTIC MODE-COUPLING OF PARTIALLY COHERENT-LIGHT IN 2-MODE OPTICAL FIBERS

An acoustic pulse propagating on a two-mode fiber can act as a beam sp litter in a scanning interferometer. When this device is employed in w hite-light interferometry, the effects of distributed coupling and dis persive interferometer arms need to be considered. A theory suitable f or treating acousto-optic interaction of partially coherent light in a moving interaction region was developed. It was found that differenti al optical dispersion should be negligible and the acoustic pulse leng th short. Also the coherence time should be short but long compared to the intermodal group delay difference over a pulse length. Experiment s with long acoustic pulses were performed, and fairly good agreement with theory was obtained.