Adaptive holographic interferometer based on optically addressed spatial light modulator for high-sensitivity optical fiber sensing

Adaptive holographic interferometry is a promising method for high-sensitivity phase-modulation measurements in the presence of slow perturbations from the environment. This technique is based on the use of a nonlinear recombining medium. We report the realization of an adaptive holographic interferometer relying on an optically addressed liquid crystal spatial light modulator operating at 1.55 mu m. The beam-coupling process that occurs in a GaAs-liquid crystal device, allows obtaining a phase-modulation sensitivity of 200 mu rad/sqrt (Hz) at 1 kHz. The interferometer behaves as an optical high-pass filter, with a cutoff frequency of approximately 10 Hz, thus, filtering slow-phase disturbances, such as due to temperature variations or low-frequency fluctuations, and keeping the detection linear without the need of heterodyne or active stabilization. Moreover, owing to the basic principle of holography, this technique can be used with complex wave fronts such as the speckled field reflected by a highly scattering surface or the optical field at the output of a multimode optical fiber. We demonstrate both theoretically and experimentally that using a multimode optical fiber as a sensing element, rather than a single-mode fiber, allows improving the interferometer phase sensitivity. Finally, we present a phase-optical time domain reflectometry (OTDR) optical fiber sensor using the adaptive holographic interferometer.