Correlation-Assisted Direct Time-of-Flight (CA-dToF) is demonstrated for the first time with a 320×240-pixel SPAD array. SPAD triggers are processed in-pixel, avoiding data communication over the array and/or storage bottlenecks. This is accomplished by sampling two orthogonal triangle waves that are synchronized with short light pulses illuminating the scene. Using small switched-capacitor circuits, exponential-moving-averaging (EMA) is applied to the sampled voltages, delivering two analog voltages (VQ2, VI2). These contain the phase delay, or the time of flight between the light pulse and photon’s time of arrival (ToA). Uncorrelated ambient photons and dark counts are averaged out, leaving only their associated shot noise impacting the phase precision. The QVGA camera allows capturing depth-sense images with sub-cm precision over 6-m range of detection, even with a small PDE of 0.7% at 850-nm wavelength.

Correlation-Assisted Direct Time-of-Flight (CA-dToF) is demonstrated for the first time on a large 320 × 240-pixel SPAD array sensor that includes on-chip high-speed timing support circuitry. SPAD events are processed in-pixel, avoiding data communication over the array and/or storage bottlenecks. This is accomplished by sampling two orthogonal triangle waves that are synchronized with short light pulses illuminating the scene. Using small switched-capacitor circuits, exponential moving averaging (EMA) is applied to the sampled voltages, delivering two analog voltages (VQ2, VI2). These contain the phase delay, or the time of flight between the light pulse and photon’s time of arrival (ToA). Uncorrelated ambient photons and dark counts are averaged out, leaving only their associated shot noise impacting the phase precision. The QVGA camera allows for capturing depth-sense images with sub-cm precision over a 6 m range of detection, even with a small PDE of 0.7% at an 850 nm wavelength.

A video rate fluorescence lifetime (FLT) imaging system is presented featuring in-pixel lifetime calculation based on the center-of-mass of the times-of-arrival (ToA) of photons received by the single-photon avalanche diode (SPAD) of the pixel. The ToAs of photons received during a gating window placed in the decay of the returned fluorescent emission are averaged by a switched-capacitor circuit, implementing the center-of-mass method (CMM) in a compact pixel circuit. Binning of ToAs or complex time-to-digital circuits are avoided, and instead, optimal use of all received photons is achieved on a small pixel area with low communication and computational overhead. The system is validated through analytical modeling, Monte Carlo simulations, and real-world experiments using fluorophores with known lifetimes, demonstrating agreement with the analytical model and achieving accurate FLT estimations across a large range of photon counts. A dedicated QVGA (320 × 240pixel) image sensor that includes all necessary circuitry for the CMM currently reaches 10 frames per second and demonstrates the real-time FLT imaging capability of the system.

Current-Assistance (CA) has emerged as a popular pathway for high-performance time-resolved imaging in the near-infrared spectrum. It demodulates photogenerated charges classically by injecting Ohmic majority currents in a low-resistivity epilayer, obtaining a uniform drift field deep into the photodetection volume. To reduce its power consumption, recent implementations utilize high-resistivity epilayers, which introduce strong nonlinearities in the resulting drift fields. This work provides a physical description of the distribution of drift fields in highresistivity silicon substrates by considering that the injected majority currents are in fact Space-Charge-Limited (SCL). A two-dimensional analytical model for the potential and electric field in the epilayer is derived and validated using TCAD drift-diffusion simulations, introducing the concept of the Virtual Cathode (VC) for CA. The SCL nature of the injected majority current is verified through I-V measurements. These insights establish a physical understanding for the design of future current-assisted photodetectors in high-resistivity epilayers.

Fluorescence-guided surgery is a significant advancement in medical imaging, particularly for distinguishing malignant from healthy tissue during cancer surgery. Recent advancements in endoscopy technology and fluorescence-lifetime (FLT) imaging can provide better insight into identifying abnormal tissues during surgery than white light endoscopy imaging. Current imaging systems used in fluorescence-guided surgery are primarily designed to provide surgeons with a combined view of natural color (RGB) images and fluorescence overlays. These systems typically rely on an RGB camera, incapable of FLT imaging. Our novel approach sequentially illuminates the scene with red, green, and blue light pulses and Near Infrared (NIR) pulses, captured selectively with a single fast time-gated camera. The camera is synchronized to the pulsed illumination and positions its gate windows to capture only one of the illumination pulses; afterwards, it overlays the NIR fluorescence lifetime image on the natural color image. The VUB-ETRO team developed the tauCAMTM camera based on Current-Assisted Photonic Sampler (CAPS) image sensor technology, which intends to offer real-time FLT imaging, particularly in the NIR area. This paper presents an LED-based time-multiplexing RGB + FLT endoscopy imaging with tauCAMTM, designed to enhance visualization in real-time surgical settings. By combining RGB and FLT imaging, surgeons could receive comprehensive insights into tissue characteristics, supporting precise interventions.