Dual-mode optical sensing: three-dimensional imaging and seeing around a corner

Abstract. The application of nonline-of-sight (NLoS) vision and seeing around a corner has been demonstrated in the recent past on a laboratory level with round trip path lengths on the scale of 1 m as well as 10 m. This method uses a computational imaging approach to analyze the scattered information of objects which are hidden from the sensor’s direct field of view. A detailed knowledge about the scattering surfaces is necessary for the analysis. The authors evaluate the realization of dual-mode concepts with the aim of collecting all necessary information to enable both the direct three-dimensional imaging of a scene as well as the indirect sensing on hidden objects. Two different sensing approaches, laser gated viewing (LGV) and time-correlated single-photon counting, are investigated operating at laser wavelengths of 532 and 1545 nm, respectively. While LGV sensors have high spatial resolution, their application for NLoS sensing suffers from a low temporal resolution, i.e., a minimal gate width of 2 ns. On the other hand, Geiger-mode single-photon counting devices have high temporal resolution (250 ps), but the array size is limited to some thousand sensor elements. The authors present detailed theoretical and experimental evaluations of both sensing approaches.