Polar-Encoded Coherent Spiking Pulse Train Generation in a Broadband Optoelectronic Oscillator

Coherent spiking pulse trains with polar-encoding capability are essential for near-field sensing and high-resolution ranging, yet their generation remains challenging. Here, we propose and demonstrate a method to generate such waveforms in a broadband optoelectronic oscillator. Our approach exploits the symmetric nonlinear dynamics of an intra-cavity dual-drive Mach-Zehnder modulator (DDMZM) biased on either side of its quadrature point. By injecting a tailored control signal, we dynamically shift the bias point of the DDMZM to achieve controlled spiking excitation and polar encoding. Simulations and experiments verify the scheme, producing bit-configurable, highly coherent spiking pulse trains with 3.3-ns pulse width, where coherence is confirmed via multi-pulse accumulation. Co-optimization of the control signal, the cavity length, and an extra-cavity bandpass filter enhances the sidelobe suppression ratio of the pulse-compressed output by >5.8 dB. A proof-of-concept radar ranging experiment further demonstrates high-resolution and robust detection performance of the generated spiking pulse trains under low signal-to-noise ratio (SNR) conditions. This work provides a practical solution for generating advanced coherent waveforms, highlighting its potential for near-field sensing.