The combination of fast, high-power pulsed lasers with time-resolved, single-photon imaging has been identified as one of the most promising technologies for autonomous spacecrafts.
Operations include: collision avoidance, rendez-vous, proximity navigation, and landing.
In this context, single-photon technology suffers from the pile-up effect, occurring when the inter-arrival time between clicks is comparable with the detector dead time.
This condition is either caused by strong uncorrelated background light interfering with the laser signal or by radiation damaged devices exhibiting very high dark count rates.
In this work, we present a 3D sensor module based on a 64x64-pixel single-photon CMOS detector for direct time-of-flight measurements.
Each pixel contains an array of single-photon avalanche diodes (SPADs), whose outputs are combined and pre-processed by a smart logic that generates a valid trigger only when photon correlations are observed with a short period of time.
In every pixel, valid triggers are then timestamped by a 16-bit time-to-digital (TDC) converter, while a 4-bit photon counter can be used to provide a reliability measure of the generated timestamp.
Thanks to the smart triggering logic, uncorrelated events are discarded at pixel level, thus reducing the memory requirements and the processing load on the FPGA controlling the module.
The detector can provide 2D maps of timestamps at a maximum rate of 18.5 kfps, thus enabling the generation of depth images at high frame rates.