Instantaneous Frequency Measurement With Full FSR Range and Optimized Estimation Error

A photonic-assisted approach for instantaneous frequency measurement (IFM) based on a 1×4 Mach–Zehnder interferometer (MZI) structure is proposed and experimentally demonstrated. In this IFM method, a Mach–Zehnder modulator (MZM) in conjunction with an optical filter play the role of CS-SSB signal generator, mapping the unknown microwave into a tunable optical sideband. Due to the property of the subsequent 1×4 MZI structure, two amplitude comparison function (ACF) that convert the frequency information into optical power ratio can be established. A detailed theoretical analysis illustrates the realization of frequency measurement with a range of full free spectral range (FSR) and optimized estimation error by using these two ACFs. Simulation has been carried out to verify the mechanism, and the discussion about the merits of CS-SSB modulation and the applicable scenarios is also given. A proof-of-concept experiment is performed, in which the microwave frequency measurement from 7.5 to 20 GHz is demonstrated with an estimation error of less than 100 MHz.