Single-Photon Detection Apparatus Using Time-Gated Avalanche Photodiode

The detection process is segmented into multiple independent detection cycles with gate signals that open and close the detection window. By dividing continuous detection into discrete time-gated segments, dark counts occurring outside the gate window are excluded, and after-pulse noise from previous cycles is prevented from affecting current detection. This temporal segmentation resolves the contradiction by maintaining detection efficiency while eliminating noise contributions.

The gate signal applies periodic voltage pulses to the avalanche photodiode, creating periodic detection windows at optimized intervals. This periodic action allows the system to reset between detection events, preventing charge carrier accumulation that causes after-pulse noise, while maintaining high detection efficiency during active gate windows. The periodic gating resolves the noise-efficiency contradiction by establishing rhythmic detection cycles.

The gate signal applies a preliminary voltage boost to the avalanche photodiode immediately before photon arrival, temporarily raising the bias voltage close to the breakdown voltage only during the critical detection window. This preliminary action maintains low dark counts during most of the cycle while ensuring high detection sensitivity when needed, resolving the contradiction between noise reduction and detection sensitivity.

The bias voltage is made dynamic rather than static, continuously adjusting between a low baseline voltage (reducing dark counts) and a high peak voltage during gate windows (enhancing detection sensitivity). This dynamic voltage control allows the system to adapt its operating point in real-time, simultaneously achieving low dark count rates and high sensitivity to low breakdown currents.