A technique for monitoring interferometric sensors by correlation of the optical signal from the sensor with the signal from a phase-modulated reference interferometer is described. The technique is applied to temperature measurement with a fiber Fabry–Perot sensing head. We extend the 7 °C unambiguous measurement range obtained with a laser diode as the light source to 43 °C by adding a second laser diode emitting at . Experimentally, a rms phase-measurement error of , corresponding to a temperature error of , was achieved with a low-quality multimode Fabry–Perot laser. The phase error was improved to , corresponding to a temperature error of , by use of a distributed-feedback laser diode.
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