Single-Wavelength Passive Phase-Shifted Demodulation Technique With the Dual-Cavity and EFA for the Interrogation of EFPI Diaphragm-Based Fiber Sensor

A single-wavelength passive phase-shifted demodulation technique for the interrogation of a diaphragm-based fiber sensor is proposed. It is based on the configuration of the external Fabry–Perot interferometer (EFPI) with dual-cavity (DC) and the ellipse-fitting algorithm (EFA). The technique can address two main concerns: the orthogonality of the DC-EFPI must be matched, the direct current values and fringe visibility of the DC–EFPI must be excluded or normalized. Experiment results show that the proposed technique demonstrates high accuracy amplitude measurement of reflective surface vibration with a high dynamic range over 135 dB and good effectiveness with various initial phase differences apart from two areas around
0
and
π
rad. It is a successful solution for interrogating of diaphragm-based fiber sensors.