High-speed fibre Bragg grating sensor interrogation using dispersion- compensation fibre

Introduction: Fibre Bragg gratings (FBGs) have proved themselves as the ideal candidates for measuring strain and temperature in smart structures, civil engineering or other harsh environments. The advantages of the FBG sensor over conventional electrical sensors include small size, light weight, immunity to electromagnetic interference, low cost and other inherent advantages of fibre-optic sensors. FBG emerges as one of the most successful fibre-optic sensors owing to its wavelengthencoded nature which makes it insensitive to intensity fluctuation caused by losses in the connection fibre and connectors [1]. The key technology for an FBG sensor system is the interrogation of the shift of the Bragg wavelength reflected from an FBG. Various approaches to realise FBG interrogators have been developed, including those based on scanning filters, tunable lasers, interferometry, a discriminator using the power ratios of optical filters, a holographic grating based spectroscopic charge coupled device (CCD), long period gratings and chirped FBGs [2]. High-speed interrogation of FBG sensors in the order of megasamples per second is desirable in some applications where fast dynamic system response measurement is required. Most reported methods, however, interrogate FBGs at less than 1000 samples per second. Some schemes for high-speed interrogation were proposed recently, based on arrayed waveguide grating and shortpulse interferometry [3, 4]. In this Letter, we propose and demonstrate a novel FBG sensor interrogation system [5] using an electro-optic modulator (EOM) and a dispersion compensating module to convert wavelength to time measurement, and the system can interrogate FBGs at speed in the order of megasamples per second.