Ultralow-latency spectral-resolving for coherent ranging via an optical frequency-shifting loop computing system

Frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR) simultaneously measures distance and velocity with high resolution, precision, and sensitivity, enabling applications in autonomous navigation, robotics, and space-based sensing. The measurements rely on spectral analysis of beat frequency in the mixed signal, typically performed via digital Fourier transforms (FTs). However, electronic processing introduces microsecond-scale latency and is vulnerable to electromagnetic interference and cosmic radiation. Optical signal processing circumvents these limitations by exploiting light’s intrinsic high speed, broad bandwidth, and immunity to electromagnetic and radial disturbance. In particular, optical FT (OFT), enabled by space–time duality, performs real-time spectral analysis during propagation, enabling low-latency operation. Here, we demonstrate a photonic sensing-processing architecture that embeds an OFT architecture implemented by the frequency-shifting loop (FSL) directly into an FMCW LiDAR system. The FSL generates frequency-shifted signal replicas, emulating large dispersion for high-resolution spectral analysis with ultralow latency. Our system achieves a 40 GHz frequency-shifted span and offers 15 kHz spectral resolution, yielding a 7 mm ranging resolution, while slashing processing latency below 20 ns—orders of magnitude faster than digital FT. Detailed analyses and parameter optimizations are conducted to bridge the sensing and computing subsystems. Free-space experiments validate static ranging, 3-D mapping, and dynamic target tracking with millimeter-level distance and millimeter-per-second velocity precision. This work offers a compact, low-latency, and radiation-resilient solution for real-time LiDAR signal processing, promoting the convergence of optical sensing and processing systems.