Photon-Number-Resolving Detection Laser Ranging

Single-photon detectors can reach the quantum limit with the help of time-correlated single photon counting (TCSPC) technology, which had important applications in long-distance or eye-safe laser ranging and 3D imaging. Due to the small dynamic range, the single-photon-detectors are easy to be saturated in strong background. And we cannot extract the signal from the strong background, when there is not enough time to detect the target and accumulate enough counts for TCSPC. So, we demonstrated photon-counting-resolving detection in laser ranging to improve the dynamic range and measuring speed.We developed a photon-number resolving detector (PNRD) based on multi-pixel photon counter (MPPC). It can distinguish more than ten photons per pulse. PNRDs are not only sensitive to single photon, but also can detect the photon number of the reflecting laser pulse. To set the threshold of the PNRD, it can suppress the background noise effectively. In the experiment, when the detector threshold was set at 5-photon/pulse, the system error count rate dropped one order of magnitude. But because of the dark counts and cross talk of the MPPC were serious, the probability of multiple photon counting in experiment was bigger than that in reality, and this phenomenon weakened the ability of photon-number-resolving system to suppress the background noise.Considering the weakness of the MPPC, we developed a multi-channel coincidence counting laser ranging method to decrease the noise of the detectors. It eliminated the cross talk of the MPPC and improved the capability of suppressing the noise. With the method of two-channel coincidence counting, the signal-to-noise ratio was improved to 8.54 dB when the background noise was 5M/s. It could be applied for detecting fast-moving targets with just one laser shot at fewer photon level.