Accurate monitoring of an interferometric fiber-optic sensor with a multimode semiconductor laser

A technique for monitoring interferometric sensors by correlation of the op tical signal hom the sensor with the signal from a phase-modulated referenc e interferometer is described. The technique is applied to temperature meas urement with a fiber Fabry-Perot sensing head. We extend the 7 degrees C un ambiguous measurement range obtained with a 1.3-mu m laser diode as the Lig ht source to 43 degrees C by adding a second laser diode emitting at 1.55 m u m. Experimentally, a rms phase-measurement error of +/-0.28 rad, correspo nding to a temperature error of +/-0.32 degrees C, was achieved with a low- quality multimode Fabry-Perot laser. The phase error was improved to +/-0.1 4 rad, corresponding to a temperature error of +/-0.16 degrees C, by use of a distributed-feedback laser diode. (C) 1999 Optical Society of America.