Measurement concept for direct time-of-flight sensors at high ambient light

A fast and reliable three dimensional monitoring of the environment is indispensable for robotics, automation engineering or autonomous driving. For these applications LiDAR is a key sensor technology. Normally a light source in the near infrared range is used, which is invisible to human eyes. High ambient light compared to the laser source intensity is a major problem for these systems. Therefore, a measurement concept to reduce the impact of ambient light is necessary. In this paper we present a measurement concept in which the full distance range is scanned and the probability to detect events from far objects is improved. The general problem is that a photon of the background illumination can be detected instead of the reflected laser signal which stops the measurement. The concept allows us to detect the received laser pulse buried in the superimposed background light easier and improve the measurement quality. This is possible due to the delayed start of the measurement and thus the selection of different measurement windows in which an earlier detection of the laser generated events is accessible. In consequence, the probability for receiving an unwanted ambient photon is reduced. For this technique no prior information about the object conditions or its rough distance is required and it can be applied in all situations of the direct time-of-flight measurement to cope with high ambient light. Hence it allows a reliable distance measurement at various ambient and target conditions.