Fiber-optic extrinsic Fabry–Perot interferometer sensors with quadrature phase three wavelength demodulation

In this paper, a quadrature phase three-wavelength demodulation method for interrogating fiber-optic extrinsic Fabry–Perot interferometric sensors and dynamic signals is proposed. Three interference signals are obtained by selecting three sets of specific wavelength laser sources, two of which are symmetrical with the third signal. The linear fitting method is used to eliminate the direct current (DC) components of the two sets of signals, and two new quadrature signals are obtained. The phase signal demodulation of these two calibrated quadrature signals is then performed by the arctan algorithm. Experimental results show that the proposed method can accurately demodulate dynamic signals with different frequencies and modulation depths at different sensor cavity lengths. It is also important to mention that the proposed demodulation method avoids the assumption that the DC component and the alternating current amplitude of the interference signal are equal, thus it has a wide range of applications in three-wavelength demodulation.