Squared peak-to-peak algorithm for the spectral interrogation of short-cavity fiber-optic Fabry-Perot sensors.

The cavity length of short-cavity Fabry-Perot (FP) sensors cannot be effectively interrogated using the conventional peak-to-peak method if the spectrum of the exciting source is not wide enough. In this paper, we propose a squared peak-to-peak algorithm for interrogation of short-cavity fiber-optic FP sensors. By squaring the DC-filtered reflection spectrum of an FP sensor in the frequency domain, we produce an additional peak, with which the cavity length of a sensor can be estimated using the same calculations as performed with the conventional peak-to-peak method. For investigation of the feasibility of this technique, we conducted simulations and practical experiments analyzing fiber-optic FP sensors with cavity lengths in the range of 15-25 µm. The maximum error in cavity length estimated using the proposed algorithm in experiments was 0.030 µm.

Fiber-optic, extrinsic Fabry-Perot interferometric dual-cavity sensor interrogated by a dual-segment, low-coherence Fizeau interferometer for simultaneous measurements of pressure and temperature.

A fiber-optic, extrinsic Fabry-Perot interferometric (EFPI), dual-cavity sensor made of sapphire was fabricated and interrogated by a dual-segment, low-coherence Fizeau interferometer to achieve simultaneous pressure and temperature measurements. The fiber-optic EFPI, dual-cavity sensor had an initial basal cavity length of 680 µm and an vacuum cavity length of 80 µm and was experimentally tested based on temperature and pressure measurements. It was demonstrated that simultaneous pressure and temperature measurement could be achieved in the respective pressure and temperature ranges of 0.1-3 MPa and 20-350 °C.