Intrinsic fiber-optic ultrasonic sensor array using multiplexed two-wave mixing interferometry.

An intrinsic multiplexed laser interferometer is presented that allows for the simultaneous detection of acoustic waves by an array of fiber-optic sensors. The phase-modulated signals from each sensor are demodulated by use of an adaptive two-wave mixing setup. The light from each sensing fiber in the array is mixed with a reference beam in a single photorefractive crystal (PRC), and the output beams from the PRC are imaged onto separate photodetectors to create a multiplexed two-wave mixing (MTWM) system. The sensing fibers are embedded in graphite-epoxy composite panels, and detection of both acoustic emission and ultrasonic signals in these materials is demonstrated. The intrinsic MTWM system is an effective tool for the simultaneous demodulation of signals from a large fiber sensor array. Also, the adaptive nature of the MTWM setup obviates the need for active stabilization against ambient noise.