Photon Number Resolving Systems and Instrumentation

Abstract

Time correlated single photon counting (TCSPC) is a technique used in many applications such as light detection and ranging, quantum key distribution, medical imaging and more. One inherent problem of this technique is the 10% limit on the detector count rate to avoid distortion in measurements caused by the pile up effect. Essentially, when a conventional single photon avalanche photodiode (SPAD) detects a photon, it is unable to see another photon until its deadtime completes, which gives rise to early photons having a higher probability of detection if the probability of detecting a photon is too high. Photon number resolving detectors offer an alternative to SPAD and be thought of as a two dimensional array of passively quenched SPADs with the outputs summed together. Such detectors offer photon number resolving capabilities (the output pulse amplitude is proportional to the number of incident photons) as each photon will land in a different place in the two-dimensional array. This comes at the expense of increased noise, as the dark count of all detectors will be present on the output in addition to other problems such as optical cross talk. This might preclude such detectors from quantum experiments, but such detectors could offer significant advantages in LiDAR systems, where extended dynamic range and photon number resolving capabilities could increase the acquisition rate by collecting more light and by allowing such systems to operate at higher mean photon levels. In this work silicon photomultipliers are characterised for their number resolving capabilities and used in photon counting. The SiPMs are shown to have capable single photon sensitivity and can resolve the photon number. Subsequently, a novel real-time instrument has been developed to acquire data. Finally, a comparison has been made between SiPM and SPAD LiDAR, showing that SiPMs can retrieve more photons per excitation pulse and offer greater dynamic range.