Coherent Microwave Pulse Train Generation With Encoded Position and Phase in Actively Mode-Locked Optoelectronic Oscillator

An actively mode-locked optoelectronic oscillator (AMOEO) is proposed and demonstrated to generate coherent microwave pulse trains with encoded pulse position and phase. Through injecting a square-wave pulse into the AMOEO, localized oscillation is built up in the optoelectronic resonant cavity, which leads to the generation of coherent mode-locked pulse with ultrashort pulsewidth and extremely small duty cycle. The realization of pulse position and phase coding is based on adjusting the mapping relationship between the external driving signal and the amplitude–phase feature of the mode-locked pulse via a dual-drive Mach–Zehnder modulator (DDMZM) used as a dynamic regulation device in the oscillation cavity. Both simulation and experiment are carried out to verify the feasibility of this scheme. Coherent microwave pulse trains with a pulsewidth of 50 ns and a 3-dB bandwidth of 30 MHz are generated in a frequency tuning range of several gigahertz. By designing the time–frequency characteristic of the injection signal, various encoded microwave pulse trains are generated, including position-coded and phase-coded ones. The generated microwave pulse trains are used to realize radar ranging. Accurate distance measurements within a detection range of 30 m are achieved by using either a 9-bit linearly chirped position-coded microwave pulse train or a 13-bit Barker phase-coded one. Benefiting from its low cost and high controllability, this scheme is promising for anti-jamming radar and wireless communication applications.