Robust Phase-Time-of-Flight Coherent LiDAR With Immunity to Random Initial Phase Variations

The ongoing technological advancements drive an ever-increasing demand for high-performance and cost-effective sensors, with light detection and ranging (LiDAR) being a primary focus. Phase-modulated continuous wave (PMCW) LiDAR has emerged as a competitive candidate owing to its coherent gain and interference robustness. Inspired by conventional time-of-flight (ToF) and PMCW schemes, this paper proposes and experimentally validates a robust phase-time-of-flight (PToF) coherent LiDAR with immunity to random initial phase variations. In the proposed architecture, a pulsed ranging signal is phase-modulated onto a continuous wave laser, and the echo is coherently detected with a local oscillator (LO) for precise ranging without quadrature coherent detection—retaining coherent detection advantages while maintaining low complexity comparable to direct ToF LiDAR. A triangular pulse modulation scheme optimized at integer multiples of the phase modulator's half-wave voltage is introduced to enable initial phase immunity. The system performance and its initial-phase-immunity property are rigorously evaluated through Cramér-Rao bound (CRB) derivations, Monte Carlo simulations and experimental validations. The experimental results demonstrate an achievable ranging precision of 7.3 mm, and a maximum deviation of 2.09 cm across all measured distances. Additionally, 3D imaging is realized via two-dimensional scanning. The proposed PToF LiDAR presents a viable pathway toward high-performance, cost-effective, and highly integrated LiDAR for practical applications.