Unlimited phase compensator for fiber-optic interferometric detection of slow temperature change

Measurement of slow temperature change by means of a Michelson-type fiber-optic interferometric sensor exploiting unlimited phase compensation is presented. A new simple phase demodulation system, based on a rotating half-wave retarder controlled by a feedback loop, permits real-time detection of a slowly induced phase change of any magnitude. A theoretical analysis of the demodulator is given, together with experimental data showing that a precision better than l/10 degrees C was achieved on a 1-h thermic cycle.