Instantaneous Microwave Frequency Measurement Using Photonic Technique

We propose a novel photonic technique for measuring microwave frequency instantaneously over a wide bandwidth. In our approach, an optical carrier is divided into two parts. Both parts are modulated by an unknown microwave signal; one part is phase modulated while the other one is intensity modulated. The two differently modulated optical signals are then launched into single-mode fibers with the same lengths to introduce microwave signal power fading. After photodetection, the radio-frequency powers of the two parts are used to generate an amplitude comparison function which provides a frequency-to-power mapping. The proposed scheme is simple and is experimentally verified over a frequency range of 13.5 GHz with a measurement error less than $\pm$0.3 GHz.