OPLL-based reconfigurable broadband LFM waveform generation via heterodyne-beating

A wideband programmable linearly frequency modulated (LFM) signal is highly desired in modern radar systems to adapt to variable environments and achieve high detection resolution. However, conventional digital microwave generation has restrictions on operation band and bandwidth. Current optical microwave generation has provided solutions to the dilemma of electronic devices, meanwhile arising new problems like insufficient time-bandwidth product and dependence on high-frequency or high-rate RF sources. Here, utilizing heterodyne-beating two phase-locked lasers, we present a new LFM signal generation method with no aid of high-frequency or high-rate electronics, featuring simple structure, large bandwidth and adjustable parameters. A frequency -swept laser (FSL) and a frequency-fixed laser (FFL) combined with a voltage-controlled oscillator are phase locked to the same oscillator to reduce phase fluctuations and employed for heterodyne-beating. An LFM waveform with an instantaneous bandwidth of 7.3 GHz cross X and Ku band is developed. The reconfigurable capability is also investigated, the bandwidth, central frequency and pulse width of the LFM signal are programmed by merely adjusting the central frequency of the FFL, voltage amplitude and the period of a low-frequency driving voltage signal driving the FSL. Measured results validate the effectiveness and prospect of the approach.