High-speed quasi-distributed strain sensing based on time division multiplexing of fibre Bragg gratings

A high-speed quasi-distributed fibre optic sensing technique for strain is proposed and a proof-of-concept experiment is performed. The sensing link is formed by multiple fibre Bragg gratings and interrogated by a pulsed broadband source. A dispersive unit is used to translate wavelength variations to time-delay changes to enable high-speed sensing capability. As the gratings can be weakly reflecting and nominally identical in their reflection spectra, this technique has the inherent capability of high-capacity multiplexing. Linear and repeatable static strain response was achieved with a strain-delay conversion factor of -3.37 ps/epsilon and a resolution of 4.73 epsilon. Dynamic strain was successfully measured at a sampling rate of 7 kHz and dynamic resolution of 0.2 epsilon/Hz was obtained.