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

Abstract

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.