Microwave Photonic Frequency Measurement With Large Bandwidth Enabled by Multiple Frequency-to-Time Mapping Curves

A microwave photonic frequency measurement system with a large bandwidth enabled by multiple frequency-to-time mapping (FTTM) curves is proposed and demonstrated. The optical sideband of the signal under test (SUT) is simultaneously mixed with the multiple frequency-sweeping optical sidebands generated from a semiconductor laser working in the period-one state. Multiple FTTM curves are achieved in a single channel due to the use of multiple frequency-sweeping optical sidebands and the square-law detection feature of the photodetector. The mixing products then pass through an electrical bandpass filter and an envelope detector to obtain electrical pulses at low speed. Multiple FTTM curves are exploited jointly to map the frequency of the SUT to the number and time locations of the generated electrical pulses, which can be captured with a low sampling rate. In this way, without introducing complex structures, the measurement bandwidth of the system can be effectively increased while guaranteeing the time and frequency resolutions. In a proof-of-concept experiment, four FTTM curves are realized by using the −1^st and the −2^nd-order frequency-sweeping optical sidebands. The instantaneous measurement bandwidth is extended to 39.8 GHz, with the working frequency range from 7.6 to 47.4 GHz and a root-mean-square error of 35 MHz. The frequency resolution is better than 50 MHz when the sweeping period is 50 μs.