Real-Time FFT Analysis for Interferometric Sensors Multiplexing

In this paper, a theoretical and experimental study of two interferometric sensor multiplexing schemes has been carried out by means of the fast Fourier transform (FFT) analysis. This study addresses one of the main drawbacks of photonic crystal fiber (PCF) sensors, that is, its multiplexing capability. Using a commercial optical interrogator combined with a simple FFT measurement technique, the simultaneous real-time monitoring of several PCF sensors is achieved. A theoretical analysis has been performed where simulations matched with the experimental results. For the experimental verification, highly birefringent (HiBi) fiber sections that operated as sensing elements were multiplexed and tested in two configurations. Due to the FFT analysis, both multiplexing schemes can be properly interrogated by monitoring the FFT phase change at the characteristic spatial-frequency of each sensor. For this purpose, a commercial interrogator and a custom Matlab program were used for computing the FFT and for monitoring the FFT phase change in real time (1 Hz).