High-Accuracy Multiple Microwave Frequency Measurement with Two-Step Accuracy Improvement Based on Stimulated Brillouin Scattering and Frequency-to-Time Mapping

A photonic-assisted multiple microwave frequency measurement approach based on stimulated Brillouin scattering (SBS) and frequency-to-time mapping with high accuracy and a wide frequency measurement range is reported. A frequency sweeping signal is modulated on an optical carrier that is shifted by the Brillouin frequency shift as a frequency sweeping optical probe wave. The unknown microwave frequencies are modulated on the original optical carrier to pump a length of single-mode fiber. Thanks to the SBS effect, the Brillouin gain spectrum is detected by the frequency sweeping optical probe wave. After the optical signal from the probe branch is detected at a photodetector, the amplitude of the direct-current component will be much increased at the exact time when the SBS gain generated by the unknown signal overlaps with a specific optical wavelength of the frequency sweeping optical signal. Therefore, the unknown microwave frequencies are mapped to the time domain. More importantly, by introducing a two-step accuracy improvement, including the reference calibration and the curve smoothing, the measurement accuracy of the proposed approach is greatly improved compared with most of the available approaches. An experiment is performed. Microwave frequency measurement from 6 to 18 GHz is demonstrated with a measurement error of less than ±1 MHz.