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

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