High-Speed Interrogation of a Fiber Grating Sensor based on Wavelength-to-Time Mapping and a Fabry-Perot Configuration

Abstract

A novel approach to interrogate a fiber grating sensor based on spectral-shaping and wavelength-to-time mapping is proposed and simulated. In the system, two chirped fiber Bragg gratings (CFBG), with one used as a reference grating and the other one as sensing grating, are employed to form a Fabry-Perot (FP) interference structure, used as the spectral-shaping filter. The filter can be modeled as a two-tap delay-line filter. An optical pulse from a mode-locked laser source is reflected and spectrally shaped by the FP structure, and then the shaped spectrum is mapped to the temporal domain by a dispersive element. When the sensing CFBG is experiencing a strain, its wavelengths will be changed, leading to different interference spectra. Using Fourier transform, the frequency of the generated microwave waveform can be achieved, from which the wavelength shift of the sensing grating and the applied strain can be demodulated. A mathematical model to describe the microwave waveform generation is developed, by which the interrogation principle is analyzed. Numerical simulations are implemented to verify the proposed approach. The results present that the sensitivity of the system is 0.014 GHz/μe.