Photonic Nyquist folding receiver using optical pulses with discrete pulse position modulation

This paper presents a photonic Nyquist folding receiver (NYFR) architecture leveraging discrete pulse position modulation for efficient ultra-wideband radio frequency (RF) signal acquisition and processing. The proposed system integrates a mode-locked laser (MLL) with cascaded Mach-Zehnder modulators (MZMs) to generate non-uniform optical pulse trains with frequency-modulated sampling intervals. These non-uniform pulses serve as optical sampling signals to compress and capture wideband RF signals. The compressed signal is processed through a low-pass interpolation filter and under-sampled by a low-speed analog-to-digital converter, significantly reducing the hardware complexity associated with high-speed sampling. Digital signal processing is then applied to reconstruct the original signal from its folded spectral components across multiple Nyquist zones. The key innovation of this approach lies in its photonic implementation, which eliminates reliance on high-speed electronic pulse generators. The use of picosecond-scale optical pulse widths enhances the system's temporal resolution, enabling the processing of ultra-wideband signals. Experimental validation was conducted using a uniform optical pulse train at a 15-GHz repetition rate, and a digitizer with a 2-GS/s sampling rate, demonstrating the successful recovery of RF signals up to 7 GHz. Dual-tone and chirped signal tests further verified the system's robustness in handling diverse signal formats, with clear identification and reconstruction across multiple Nyquist zones. By employing high-speed photonic components as well as a signal reconstruction algorithm with much lower complexity than those in conventional compressive sensing, the proposed NYFR system achieves superior performance in broadband RF signal acquisition and holds significant potential for applications in communications, radar, and electronic warfare.