Event-driven SPAD camera with 60 ps IRF and up to 1.6·10^8 photon time-tagging measurements per second

We present a compact camera module based on an array of 16 × 16 single-photon avalanche diodes (SPADs) with fastgating capabilities and hosting 16 shared time-to-digital converters (TDCs) with a least significant bit (LSB) of 6 ps. SPADs are gated with a rising-edge of less than 500 ps and show an average instrument response function (IRF) of 60 ps FWHM, including the TDCs, with less than 4 ps time-dispersion across a 30 ns gate window. Differential non-linearity (DNL) and integral non-linearity (INL) are as good as 0.04 LSB and 3.6 LSB, respectively. An event-driven readout protocol optimizes data transfer from the SPAD chip to the FPGA, handling the time-of-flight (TOF) pre-processing in order to minimize the dead-time of the TDCs, thus sustaining up to 1.6 · 10⁸ conversions per second. TOF data can be transferred towards a PC via USB-C with a maximum throughput of about 6 Gbit/s. Our camera meets the requirements of an optimized multi-pixel solution for non-line-of-sight (NLOS) imaging, as it combines fast-gating with narrow IRF: the sub-nanosecond activation of the SPADs is exploited to reject spurious light pulses, like the first bounce one from the relay wall, and properly acquire multiply-scattered photons arriving from the hidden target, while its narrow IRF allows for centimeter-accurate NLOS reconstructions. Furthermore, while the high throughput paves the way towards real-time NLOS acquisitions at video-rates, the compact form