Fourier-transform phase comparator for the measurement of extrinsic fabry-perot interferometric sensors

A Fourier-transform phase comparator is developed to measure fiber optic extrinsic Fabry-Perot interferometric sensors. The phase comparator is realized by comparing the phases of two whitelight spectra, which are obtained by scanning the wavelength of the light source. The changes of a cavity length, which are concerned in most applications, can be interrogated. A linear output is obtained, and a measurement resolution of 15 pm is experimentally achieved, which is very close to the theoretical value. The technique has high resolution and a large dynamic measurement range. In addition, the measurement is not affected by various imperfections of the sensor, light source spectrum profile, and the loss of leading fiber and connectors.