Reference-Free Photonic-Assisted Microwave Frequency Measurement With Stimulated Brillouin Scattering and Bipolar Pulse Detection

We demonstrate a photonic-assisted microwave frequency measurement (MFM) system based on frequency-to-time mapping (FTTM) principle with multi-tone identification capacity. An amplitude-modulated linear frequency modulation (AM-LFM) wave is used as the scanning signal, allowing the system to generate negative reference pulses without the need for an external reference source. With the positive signal pulses generated by a stimulated Brillouin scattering (SBS)-based microwave photonic filter (MPF), whose passband is controlled by the signal under test (SUT), a bipolar signal output is formed. This simplifies the discrimination between the signal pulses and reference pulses, leading to more robust and efficient subsequent digital signal processing. Furthermore, switching between the working points of the modulator extends the measurement range by enabling the utilization of both the upper and lower scanning sidebands. Experimental results show that when scanning speed is 5 GHz/μs, frequency measurement errors of less than 20 MHz, RMS errors of less than 6 MHz, and a frequency resolution of 60 MHz can be achieved over a measurement range of 1-34 GHz.