High-Speed Distributed Sensing Based on Ultra Weak FBGs and Chromatic Dispersion

Abstract

A high-speed quasi-distributed fiber optic sensing technique is proposed. A sensing link consisting multiple identical fiber Bragg gratings (FBGs) was interrogated by a pulsed light source, and a dispersive unit at the receiver end was used to convert the wavelength shifts of the reflected pulses into time-delay changes. This Bragg wavelength-dependent time delay can be accurately calculated by a fast cross-correlation-based algorithm, enabling distributed high-speed sensing. This technique is experimentally demonstrated using a sensing link containing 2014 FBGs with a reflectance of about −35 dB. A wavelength resolution of 9.03 pm was achieved without any data averaging. Dynamic strain was applied to one of the FBGs, and corresponding wavelength variation was measured at a sampling rate of 20 kHz, obtaining a dynamic resolution of $\surd $ Hz.