Study of a dual mode SWIR active imaging system for direct imaging and non-line-of-sight vision

Abstract

The application of non-line of sight vision and see around a corner has been demonstrated in the recent past on 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 direct sensors field of view. Recent demonstrator systems were driven at laser wavelengths (800 nm and 532 nm) which are far from the eye-safe shortwave infrared (SWIR) wavelength band i.e. between 1.4 μm and 2 μm. Therefore, the application in public or inhabited areas is difficult with respect to international laser safety conventions. In the present work, the authors evaluate the application of recent eye safe laser sources and sensor devices for non-line of sight sensing and give predictions on range and resolution. Further, the realization of a dual mode concept is studied enabling both, the direct view on a scene and the indirect view on a hidden scene. While recent laser gated viewing sensors have high spatial resolution, their application in non-line of sight imaging suffer from a too low temporal resolution due to minimal sensor gate width of around 150 ns. On the other hand, Geiger-mode single photon counting devices have high temporal resolution, but their spatial resolution is (until now) limited to array sizes of some thousand sensor elements. In this publication the authors present detailed theoretical and experimental evaluations.