Abstract
A CMOS single-photon avalanche diode (SPAD) quanta image sensor is used to reconstruct depth and intensity profiles when operating in a range-gated mode used in conjunction with pulsed laser illumination. By designing the CMOS SPAD array to acquire photons within a pre-determined temporal gate, the need for timing circuitry was avoided and it was therefore possible to have an enhanced fill factor (61% in this case) and a frame rate (100,000 frames per second) that is more difficult to achieve in a SPAD array which uses time-correlated single-photon counting. When coupled with appropriate image reconstruction algorithms, millimeter resolution depth profiles were achieved by iterating through a sequence of temporal delay steps in synchronization with laser illumination pulses. For photon data with high signal-to-noise ratios, depth images with millimeter scale depth uncertainty can be estimated using a standard cross-correlation approach. To enhance the estimation of depth and intensity images in the sparse photon regime, we used a bespoke clustering-based image restoration strategy, taking into account the binomial statistics of the photon data and non-local spatial correlations within the scene. For sparse photon data with total exposure times of 75 ms or less, the bespoke algorithm can reconstruct depth images with millimeter scale depth uncertainty at a stand-off distance of approximately 2 meters. We demonstrate a new approach to single-photon depth and intensity profiling using different target scenes, taking full advantage of the high fill-factor, high frame rate and large array format of this range-gated CMOS SPAD array.
Highlights
In recent years, advanced silicon complementary metal-oxide-semiconductor (CMOS) singlephoton avalanche diode (SPAD) arrays have shown excellent potential for high-resolution, high-speed, high-efficiency and low-noise time-resolved imaging [1, 2] as well as low-light level imaging [3,4,5]
At detector and system level, CMOS SPAD image sensors have a significant advantage in cost and read-out noise compared to off-the-shelf single-photon sensitive cameras such as electron-multiplying charge-coupled devices (EMCCDs), intensified CCDs (ICCDs), and scientific CMOS image sensors
Pulsed direct time-of-flight 3D imaging based on SPAD arrays with time-stamping photon counters, e.g. on-chip time-to-digital converters (TDCs) has been achieved [9], most SPAD arrays with the time-correlated singlephoton counting (TCSPC) functionality available today are typically of a 32 × 32 format or similar [10, 11]
Summary
In recent years, advanced silicon complementary metal-oxide-semiconductor (CMOS) singlephoton avalanche diode (SPAD) arrays have shown excellent potential for high-resolution, high-speed, high-efficiency and low-noise time-resolved imaging [1, 2] as well as low-light level imaging [3,4,5]. Pulsed direct time-of-flight 3D imaging based on SPAD arrays with time-stamping photon counters, e.g. on-chip time-to-digital converters (TDCs) has been achieved [9], most SPAD arrays with the time-correlated singlephoton counting (TCSPC) functionality available today are typically of a 32 × 32 format or similar [10, 11] While these arrays provide 2D spatial resolution without the need for a scanning system, their 3D depth profiling performance is limited by their low fill-factor and relatively small format. The binary response of each pixel in a QIS array allows these image sensors to operate at very high frame rates with negligible read-out noise This approach results in a less complex pixel design not requiring picosecond resolution time-stamping, allowing small pixel dimensions and high fill-factor without requiring the use of stacked CMOS configurations. Depth images with millimeter-level depth uncertainty are constructed from these histograms using both a pixel-wise cross-correlation approach and a bespoke clustering-based image restoration algorithm
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