The ability to detect motion and track a moving object hidden around a corner or behind a wall provides a crucial advantage when physically going around the obstacle is impossible or dangerous. Previous methods have demonstrated that is possible to reconstruct the shape of an object hidden from view. However, these methods do not enable the tracking of movement in real-time. We demonstrate a compact non-line-of-sight laser ranging technology that relies upon the ability to send light around an obstacle using a scattering floor and to detect the return signal from a hidden object with only a few seconds acquisition time. By detecting this signal with a single-photon avalanche diode (SPAD) camera, we follow the movement of an object located a meter away from the camera with centimetre precision. We discuss the possibility of applying this technology to a variety of real-life situations in the 1 near future.Recent years have seen remarkable advances in the field of image processing and data acquisition, allowing for a range of novel applications [1][2][3][4][5][6][7][8]. An exciting new avenue is using optical imaging techniques to observe and track objects that are both in movement and hidden from the direct line-of-sight. The ability to detect motion and track a moving object hidden from view would provide a crucial advantage when physically going around the obstacle is impossible or dangerous, for example to detect a person moving behind a wall or a car approaching from behind a blind corner.Techniques for imaging static objects that are hidden from view have been recently demonstrated relying on, for example, radar technology [9,10], variations of laser illuminated detection and ranging (LIDAR) [3,5,11,12], or speckle-based imaging. The latter approach was first developed for imaging through opaque barriers [13][14][15], and also allows for imaging around corners [16,17]. The work of Velten et al. [5] and, more recently, Buttafava et al. [8] sets out to establish the 3D shape of a static hidden object by collecting the return scattered light with a streak camera or single-photon avalanche diode, respectively. While remarkable 3D reconstruction of objects are achieved with these techniques, Buttafava et al. point out that the requirement for scanning and subsequent long acquisition times mean that their technique is currently unsuitable for imaging moving objects.Notwithstanding these ingenious imaging systems, locating the position of a hidden object in motion and monitoring its movement in real time remains to date a major challenge. We set out to solve the tracking problem and develop a technique based on both hardware and software implementations that are specifically designed for this 2 purpose. Our solution is based on a LIDAR-like approach where a single-photon avalanche diode (SPAD) camera [7,[18][19][20][21][22] is used to image light that is backscattered from beyond the direct line-of-sight (see Methods for camera details). The high temporal resolution of the camera relies on the fact that each indiv...

A 256 x 256 single photon avalanche diode (SPAD) sensor integrated in a 3D-stacked 90nm 1P4M/40nm 1P8M process is reported for flash light detection and ranging (LIDAR) or high speed direct time of flight (ToF) 3D imaging. The sensor bottom tier is composed of a 64x64 matrix of 36.72 m pitch modular photon processing units which operate from shared 4x4 SPADs at 9.18 m pitch and 51% fill-factor. A 16 x 14-bit counter array integrates photon counts or events to compress data to 31.4 Mbps at 30 fps readout over 8 I/O operating at 100 MHz. The pixel-parallel multi-event TDC approach employs a programmable internal or external clock for 0.56 ns to 560 ns time bin resolution. In conjunction with a perpixel correlator, the power is reduced to less than 100 mW in practical daylight ranging scenarios. Examples of ranging and high speed 3D TOF applications are given. Index Terms-3-D imaging, CMOS, direct time of flight (dTOF), histogramming, image sensor, light detection and ranging (LiDAR), single photon avalanche diodes (SPADs), time-to-digital converter (TDC), TDC sharing architecture, TOF.

A remote-sensing system that can determine the position of hidden objects has applications in many critical real-life scenarios, such as search and rescue missions and safe autonomous driving. Previous work has shown the ability to range and image objects hidden from the direct line of sight, employing advanced optical imaging technologies aimed at small objects at short range. In this work we demonstrate a long-range tracking system based on single laser illumination and single-pixel single-photon detection. This enables us to track one or more people hidden from view at a stand-off distance of over 50 m. These results pave the way towards next generation LiDAR systems that will reconstruct not only the direct-view scene but also the main elements hidden behind walls or corners.

Imaging systems with temporal resolution play a vital role in a diverse range of scientific, industrial, and consumer applications, e.g., fluorescent lifetime imaging in microscopy and time-of-flight (ToF) depth sensing in autonomous vehicles. In recent years, single-photon avalanche diode (SPAD) arrays with picosecond timing capabilities have emerged as a key technology driving these systems forward. Here we report a high-speed 3D imaging system enabled by a state-of-the-art SPAD sensor used in a hybrid imaging mode that can perform multi-event histogramming. The hybrid imaging modality alternates between photon counting and timing frames at rates exceeding 1000 frames per second, enabling guided upscaling of depth data from a native resolution of 64 × 32 to 256 × 128 . The combination of hardware and processing allows us to demonstrate high-speed ToF 3D imaging in outdoor conditions and with low latency. The results indicate potential in a range of applications where real-time, high throughput data are necessary. One such example is improving the accuracy and speed of situational awareness in autonomous systems and robotics.

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