The activity is focused on the development of single-photon avalanche diodes (SPADs) and associated electronic instrumentation and systems for low-light-level detection, with special attention to applications in life-science, such as micro- and nano-analytical techniques for biomedical and genetic diagnostics, and high-sensitivity and high frame-rate imaging, like 2D spectroscopy and 3D time-of-flight ranging. A driving force is the widespread interest to rapid and efficient detection of fluorescent emission from extremely small biological samples down to single molecules of DNA and proteins. Main goal is the development of new miniaturized detection systems that overcome drawbacks and limitations of existing systems, which rely on bulky and costly equipment and discrete sensors. High attention and remarkable efforts are devoted to imaging with ultrafast time-resolved capability at single-photon level with array detectors in linear and 2D geometries.

• Monolithic SPAD array detectors with wide pixel size
  The first monolithic arrays of SPAD detectors with large (50µm diameter) pixel, high photon detection efficiency (50% @ 550nm) and on-chip timing electronics were developed. A compact 6x8 array system with multiplexed readout was implemented for protein microarray analysis. A 60-element array system with fully parallel output and capability of operation at 20kframes/s was developed for adaptive optics in astrophysics. A 8x1 array was experimented in high-throughput FCS measurements for single-molecule spectroscopy in collaboration with UCLA.

• Resonant-cavity-enhanced (RCE) SPAD detectors
  We developed the first RCE SPAD detectors on a reflecting silicon-on-insulator (SOI) substrate. The substrate incorporates a two-period distributed Bragg reflector, developed in collaboration with Boston University. The RCE SPAD detectors have peak photon detection efficiency (PDE) ranging from 42% at 780 nm to 34% at 850 nm and time resolution of 35-ps full-width at half-maximum. These detectors are suitable for demanding photon-counting applications, where both high PDE and picosecond time resolution are required.

• Fully-programmable 1.55µm photon-counting module for InGaAs/InP SPADs
  We conceived, designed, fully characterized and validated in actual experiments a state-of-the-art near-infrared photon-counting module. The module exploits at best the performance of InGaAs/InP SPADs for detection of very fast and faint optical signals in the near-infrared range up to 1.7 μm; it is flexible and suitable for various advanced applications thanks to a user-friendly interface and a user-adjustable setting of all parameters. We validated the actual electronics and detector performance in nanosecond-gated operation up to 133 MHz gate repetition frequency, verifying excellent photon-timing performance (time jitter better than 100 ps) and detector operation at controlled low temperature.

• CMOS SPAD imagers for 2D single photon counting
  We developed cost-effective fully-CMOS compatible SPAD arrays in a 0.35µm CMOS technology. The array has smart-pixels composed by a SPAD detector, analog sensing and avalanche quenching electronics, in-pixel digital processing for counting the incoming photons and in-pixel memory and buffer stages for global-shutter readout with no dead-time. A 64x32 SPAD imager can acquire 2D images and 2D videos up to 100,000 frames/s with 8bit photon-counting dynamics. A 32x32 SPAD + TDC (Time-to-Digital Converter) imager can acquire 3D images and 3D videos up to 100,000 frames/s with 320 ps photon-timing resolution, corresponding to 5cm in Time-of-Flight 3D ranging. A 32x1 array provides 50ps resolution in photon-timing. The advanced performances have already enabled new scientific results, like sub-Reyleigh imaging via N-photon detection and advanced in Fluorescence Lifetime Imaging and Diffuse Optical Tomography applications.