适用于星载激光雷达的单光子探测原理与技术研究

Single-photon detection is an effective technique to realize the high-resolution topographic Lidar. However, the single-photon detectors currently used in spaceborne Lidar have two major technical obstacles: 1) there is strong reflection and backscattering of sunlight from the Earth's surface and the cloud, which causes large background counts on the single-photon detector. And there is only one shot of the laser pulse on the same location, as the flight speed of satellite is very fast. As a result, we cannot remove the wrong counts of the Lidar by time-correlated photon counting; 2) the laser will be multiple reflected when measuring the vegetation structure, but the single-photon detector cannot measure it due to its big deadtime. This proposal wants to focus on the practical problems of the single-photon detectors in spaceborne Lidar. We plan to invent several novel methods and techniques to realize small deadtime and high-performance photon-number-resolving detection (PNRD), such as passive quenching & fast reset technique for Si MPPC, and GHz gated mode Si GAPD single-photon detection. So we can distinguish between the background counts and the signal by resolving the photon number to remove the wrong counts of the Lidar, and reduce the minimum measuring interval from the current 7.5m to 1.5m, so as to promote the development of spaceborne Lidar.

单光子探测技术为星载高分辨地形测绘激光雷达提供了有效的技术途径。但是，目前在星载激光雷达上使用的单光子探测器存在两大技术障碍：1）地表和云层等对日光有很强的反射和散射，使单光子探测器发生误计数。由于卫星飞行速度非常快，同一位置通常只有一次激光照射，不能通过光子符合计数方法消除激光雷达的误报；2）在测量植被覆盖等情况时，激光会发生多次反射，单光子探测器较大的死时间不能满足需求。本项目围绕单光子探测器在星载激光雷达中遇到的实际问题，提出发展Si MPPC被动抑制与快速恢复相结合的驱动技术、GHz门模式Si GAPD探测技术，实现低死时间和高性能的光子数可分辨探测技术和方法。通过光子数区分背景计数和信号，消除激光雷达的误报，并且使最短测量间距由目前的7.5m缩短至1.5m，从而促进星载激光雷达的发展。

单光子探测技术为星载高分辨地形测绘激光雷达提供了有效的技术途径。本项目围绕单光子探测器在星载激光雷达中遇到的实际问题，提出发展低死时间和高性能的光子数分辨探测技术和方法。通过光子数区分背景计数和信号，消除激光雷达的误报，从而促进星载激光雷达的发展。通过本项目研究，我们发展了多通道单光子符合探测方法，死时间压缩至10纳秒以内，532nm波段探测效率大于50%，暗计数小于1kcps；发展高次谐波GHz单光子探测技术，有效提高了探测效率；发展双模式探测技术，是APD工作在线性/盖格两个模式，可探测光子数动态范围超高6个数量级；发展温度稳定技术，使单光子探测器在-40℃至50℃范围内保持稳定的探测性能；发展温度时间补偿技术，时间漂移温度系数减小至0.67ps/K,探测器时间抖动减少至30ps。基于高性能单光子探测技术基础，我们提出并实现了光子数分辨探测激光测距方法，克服高背景光干扰，实现快速光子计数激光测距；提出多重频光子计数激光测距方法，实现32km外场实验；发展多光束光子计数激光成像技术，实现100光束25km自然目标激光成像实验。这些工作解决了单光子探测激光雷达领域的背景噪声、探测速率、远距离大幅宽成像等难点。