ABSTRACT
The interferometric fringe pattern of a Fiber Fabry Perot (FFP) sensor is modulated by change of the optical phase difference (OPD) induced by the measurand, such as displacement, temperature, strain and pressure. Absolute OPD demodulation is a universal method for readout of an FFP sensor, by which higher measurement accuracy could be obtained, compared with the intensity demodulation. A universal method for the OPD demodulation is to use the fast Fourier transform (FFT), since the reflected spectrum of the FFP cavity is a periodic curve in frequency domain. One of the most successful techniques for spectral interrogation of FFP sensors is based on the use of a tunable narrow bandpass filter. This chapter presents a multiplexing technique that allows for FFP sensors with different lengths to be arranged parallely by using an optical coupler. A multiplexing technique based on coarse wavelength-division multiplexing (CWDM) could be used to separate different sensors into their individual wavelength bands.
