Coherence-multiplexed fiber-optic sensor systems for measurements of pressure and temperature changes

A digital demodulation method for read-out of phase changes induced in coherence-multiplexed sensors based on highly birefringent fibers is described. The method employs the fringe counting principle and enables registration of the phase shifts simultaneously induced in two multiplexed sensors with a maximum frequency of 10 kHz and resolution of 1/4 of the interference fringe. The performance of three multiplexed systems interrogated using the proposed detection method is investigated. The first system is composed of two serial multiplexed sensors serving for measurements of pressure and temperature changes in the same location, while the two other systems are composed of two parallel or serial multiplexed temperature-compensated sensors serving for pressure measurements at different locations.