Ghost frequency-time comb LiDAR in the single photon regime

We experimentally demonstrate a feasible approach to light detection and ranging for low-reflecting targets using a ghost frequency-time comb (GFC). The continuous wave (CW) output beam of a fiber ring laser with half a million cavity modes is split into two paths: one at full intensity to an analog detector near the laser source, and the other sent to the target and reflected back to a single photon avalanche diode. Using a “hybrid detection scheme” with mixed analog and single-photon detectors, we calculated the second-order temporal correlation to reveal a GFC with as few as 937 total detected photons collected over 2.5 ms. The precise spacing of comb peaks enables a least-squares fit, resulting in a 10.1 km distance estimation with a standard deviation of 7 mm. Averaging the correlation functions for seven datasets with a mean of 866 detected photons each reduces the standard deviation to 4 mm. The demonstrated precision, fast measurement rate, and low-intensity CW propagation, together with the potential insensitivity to atmospheric turbulence and background noise, make the GFC method well-suited for ranging and target tracking applications.