Hybrid fiber-optic sensors using liquid-crystal light modulators and piezoceramic transducers

A new technique is described for linking remote sensors by multimode optical fibers. It combines two well-known technologies and is compatible with multimode optical multiplexing. At the sensing location, the output of a transducer (such as a piezoceramic hydrophone) is connected directly to a low-voltage liquid-crystal light modulator that is coupled to fiber-optic transmission lines by graded-index rod lenses. Transducer voltages as low as 10 microV produce intensity modulation of the fiber light. An optical hydrophone based on the technique demonstrated a minimum detectable pressure of 39 dB re 1 [equiation] at 500 Hz. The device performance was evaluated over the 8-45 degrees C temperature range. Sensitivity was found to decrease linearly by 0.2 dB/ degrees C over that range. The technique provides a means by which rugged nonmechanical sensors can be constructed that are suitable for incorporation into practical fiber-optic sensor systems.