IMAGING AND PHASE SENSING WITH MULTIMODE OPTICAL FIBERS USING NONLINEAR OPTICS.

A double pass image transmission through a single multimode fiber is demonstrated, using a passive phase-conjugate mirror. We make use of degenerate four-wave mixing in the photorefractive BaTiO//3 crystal, requiring no external pumping. An application to interferometry based on phase effects is demonstrated, by implementing the multimode fiber-passive phase conjugating mirror system as one arm of a Michelson interferometer. Due to the unique properties of the self-pumped conjugator, nonuniform distortions caused by modal dispersion in the fiber and other aberrations are cancelled out, while uniform phase changes are detected.