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.