Power-Independent Microwave Instantaneous Frequency Measurement Based on Combination of Brillouin Gain and Loss Spectra

Photonics-assisted microwave instantaneous frequency measurement (IFM) is considered as a promising technique for detecting an unknown radio-frequency (RF) signal, which has advantages of broad frequency measurement range and fast processing speed. Up to date, there is no photonics-assisted IFM system that can essentially measure an unknown RF signal time-frequency information with power fluctuating seriously. Moreover, the measurement accuracy and frequency modulation recognition are not as good as those of traditional electronic methods. Here, we propose an IFM scheme based on the combination of Brillouin gain spectrum (BGS) and Brillouin loss spectrum (BLS), which is RF-power-independent with high measurement efficiency. The combination of BGS and BLS to construct the amplitude comparison function (ACF) can reduce the influence of RF signal power fluctuation within 21.27 dB by single-shot measuring. When an appropriate frequency interval with frequency domain monotonous power of microwave comb signal is modulated on the pump lightwave, the IFM accuracy of the unknown signal reaches about 1 MHz. After the initial calibration of the system, it can recognize the time-frequency variation of single tone signal, linear frequency modulated signal (LFM), nonlinear frequency modulated signal (NLFM), and Costas signal. This scheme will help to promote the application of the IFM in the field of spectrum reconnaissance and reception.