Ultra-broadband and high-accuracy instantaneous frequency measurement based on frequency shift loop and stimulated Brillouin scattering

We propose an ultra-broadband and high-accuracy instantaneous frequency measurement (IFM) scheme based on frequency shift loop (FSL) and stimulated Brillouin scattering (SBS). The linear frequency modulation (LFM) signal with larger bandwidth is obtained by the FSL and is optically filtered by the SBS effect to construct a frequency-to-time mapping between the time difference of pulses and the frequency of the signal under test. The proposed IFM scheme is experimentally demonstrated. A 10-GHz LFM signal is extended to 80 GHz with a spectral flatness of approximately 1.32 dB by the FSL. The frequency measurement errors less than 12 MHz in 0-40 GHz and 5 MHz in 5-30 GHz are reached by exciting SBS through using the -1st modulation sideband and the -2nd modulation sideband, respectively. The frequency measurement resolution of multi-tone is about 100 MHz.