An Interrogation Technique of FBG Cascade Sensors Using Wavelength to Radio-Frequency Delay Mapping

A technique is proposed to interrogate a distributed \nphotonic sensor composed of seven standard fiber Bragg gratings \nin cascade. A microwave-modulated optical signal is launched into \nan FBG cascade and subsequently undergoes dispersion in standard \nsingle-mode fiber, so that the different Bragg wavelengths are \nmapped into the radio-frequency (RF) delays that determine the \npeaks in the electrical impulse response of the optical link. Shifts \nin Bragg wavelengths have been determined from the shifts in the \nimpulse response s peaks by recording the link s RF response in \nthe range dc-20 GHz using a vector network analyzer (VNA), and \nthen performing its inverse Fourier transform. A resolution of 14 \npm is experimentally demonstrated after zero-padding the VNA \ntraces.