Single-photon detection and applications
Single-photon detectors are the key components in diverse applications related to ultra-weak optical detection, such as quantum cryptography, optical time-domain reflectometry, imaging, metrology, etc. We are now working on several different approaches including avalanche photodiodes (APD), superconducting nanowire detectors and hybrid devices like up-conversion detectors for various wavelength demands to suit different applications. Here we list our present projects on single-photon detection.
InGaAs/InP APDs working in the Geiger mode are the most important techniques for practical applications requiring single-photon detection in the near-infrared. In the Geiger mode, due to the impact ionization mechanism even a single photon-excited carrier can probably produce a macroscopic avalanche signal. However, the afterpulsing effect severely limits the APD performance. The origins of afterpulses are that some carriers trapped by the defects during the previous avalanches can be subsequently released and create undesired avalanches. Therefore, developing high-performance quenching electronics, particularly to suppress the afterpulsing, is critical to optimize APD performance. In this research direction, our current and future projects include:
These hybrid detectors combine the nonlinear process of sum-frequency generation and high detection efficiency Si APDs. Compared to other single-photon detection techniques, the main advantages of these detectors include low dark counts, high count rate, and low timing resolution, which is well suited for QKD applications.