A scalable instantaneous frequency measurement system based on single branch AC/DC detection

Abstract

A scalable instantaneous frequency measurement (IFM) system based on single branch AC/DC detection is proposed and analysed. The techniques of polarization-multiplexing and time delay are employed to realize the correlation between the amplitude comparison function (ACF) and unknown signal frequency. It is worth mentioning that the ACF is built through the AC and DC power of the same photocurrent, which means only single detection link is needed. This way can potentially improve the system accuracy by not introducing excessive optoelectronic devices. The measurement range can be tunable by changing the value of electrical time delay line. To extend the measurement range and improve the system resolution, several repeatable modules are adopted to build different ACF curves. Through our analysis, jointly using multiple ACF curves could bypass a trade-off between the measurement range and the system accuracy in IFM system. The measurement range of the system is extended beyond the restriction of monotonic region in single ACF and the system error, especially in low frequency could also be improved. A detailed theory deduction is carried out and simulation has been performed to verify the system principle. The result shows that in one module structure, a root mean square error (RMSE) of less than 65.8 MHz over 0–20 GHz is achieved. In two-module structure, a lower RMSE of 53.9 MHz over 0–20 GHz are given.