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Photonic generation of radio-frequency signals has shown significantadvantages over the electronic counterparts, allowing the high precisiongeneration of radio-frequency carriers up to the terahertz-wave region withflexible bandwidth for radar applications. Great progress has been made inphotonics-based radio-frequency waveform generation. However, the approachesthat rely on sophisticated benchtop digital microwave components, such assynthesizers and digital-to-analog converters have limited achievable bandwidthand thus resolution for radar detections. Methods based on voltage-controlledanalog oscillators exhibit high time-frequency non-linearity, causing degradedsensing precision. Here, we demonstrate, for the first time, a photonicstepped-frequency (SF) waveform generation scheme enabled by MHz electronicswith a tunable bandwidth exceeding 30 GHz and intrinsic time-frequencylinearity. The ultra-wideband radio-frequency signal generation is enabled byusing a polarization-stabilized optical cavity to suppress intra-cavitypolarization-dependent instability; meanwhile, the signal's high-linearity isachieved via consecutive MHz acousto-optic frequency-shifting modulationwithout the necessity of using electro-optic modulators that have bias-driftingissues. We systematically evaluate the system's signal quality and imagingperformance in comparison with conventional photonic radar schemes that usehigh-speed digital electronics, confirming its feasibility and excellentperformance for high-resolution radar applications.

Photonic Generation of Radar Signals with 30 GHz Bandwidth and Ultra-High Time-Frequency Linearity