In recent years, many applications have been proposed that require detection of light signals in the near-infrared (NIR) range with single-photon sensitivity and time resolution below 100 ps; notably laser ranging, biomedical imaging, quantum key distribution (QKD) and quantum information and communication experiments. The current state of the art in terms of timing resolution in the NIR range is a jitter below 20 ps achieved by superconducting nanowire single-photon detector (SNSPD). A more practical and compact alternative that does not require cryogenic cooling is represented by InGaAs/InP single-photon avalanche diodes (SPADs). Indeed, gated-mode SPADs can achieve a timing resolution below 50 ps at relatively high excess biases (above 7 V). However, despite their good performance in terms of photon detection efficiency, dark count rate and timing resolution, standard InGaAs/InP SPADs are limited by their afterpulsing noise to gated-mode operation, thus precluding their use in many applications.
Negative-feedback avalanche diodes (NFADs) are a special structure of InGaAs/InP SPADs where a monolitically-integrated quenching resistor is used to reduce the afterpulsing noise contribution hence allowing free-running operation. Here, we present our recent results on the characterization of the timing response of different NFAD detectors for temperatures down to 143 K that demonstrate how NFADs can achieve timing jitter down to 50 ps in an extended range of operating conditions.
In recent years, many applications have been proposed that require detection of light signals in the near-infrared range with single-photon sensitivity and time resolution down to few hundreds of picoseconds. InGaAs/InP singlephoton avalanche diodes (SPADs) are a viable choice for these tasks thanks to their compactness and ease-of-use. Unfortunately, their performance is traditionally limited by high dark count rates (DCRs) and afterpulsing effects. However, a recent demonstration of negative feedback avalanche diodes (NFADs), operating in the free-running regime, achieved a DCR down to 1 cps at 10 % photon detection efficiency (PDE) at telecom wavelengths. Here we present our recent results on the characterization of NFAD detectors for temperatures down to approximately 150 K. A FPGA controlled test-bench facilitates the acquisition of all the parameters of interest like PDE, DCR, afterpulsing probability etc. We also demonstrate the performance of the detector in different applications: In particular, with low-temperature NFADs, we achieved high secret key rates with quantum key distribution over fiber links between 100-300 km. But low noise InGaAs/InP SPADs will certainly find applications in yet unexplored fields like photodynamic therapy, near infrared diffuse optical spectroscopy and many more. For example with a large area detector, we made time-resolved measurements of singlet-oxygen luminescence from a standard Rose Bengal dye in aqueous solution.
Single-photon detectors are the best option for applications where low noise measurements and/or high timing
resolution are required. At wavelengths between 900 nm and 1700 nm, however, low noise detectors have typically
been based on cryogenic superconducting technology, precluding their extended use in industrial or clinical
applications. Here we present a practical (i.e. compact, reliable and affordable) detector, based on a negative
feedback InGaAs/InP avalanche photodiode and exhibiting dark counts < 1 count-per-second at 10% efficiency, and
with efficiencies of up to 27%. We show how this detector enables novel applications such as singlet-oxygen
luminescence detection for Photo Dynamic Therapy (PDT) but can be an enabling technology also for a diverse set
of applications in both quantum communication (e.g. long-distance quantum key distribution) and biomedical
imaging.
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