[TuD4] Photo Detection Technologies

5:15 PM - 5:30 PM JST(8:15 AM - 8:30 AM UTC)

[TuD4-03] Low-Photon SWIR Detection at 200 MHz Count Rates Using Linear-Mode AlGaAsSb APDs

〇Benjamin Sheridan^1,2, Xiao Collins², Benjamin White², Chee Hing Tan¹ (1. The Univ. of Sheffield (UK), 2. Phlux Technology Ltd. (UK))

We report a room-temperature short-wave infrared (SWIR) optical receiver capable of detecting very weak optical pulses at count rates up to 200 MHz using linear-mode AlGaAsSb avalanche photodiodes (APDs). The receiver targets applications such as LiDAR and free-space optical communications at 1–1.65 µm, where high sensitivity must be maintained at fast count rates. The front end combines an uncooled InGaAs/AlGaAsSb APD exhibiting ultra-low excess noise with a low-noise transimpedance amplifier and high-speed FPGA-based readout. At room temperature, the system achieves high avalanche gains (M > 200) while preserving linearity and avoiding afterpulsing. Under 1550 nm pulsed illumination, the free-running receiver demonstrates near-unity detection efficiency at photon levels as low as 100 photons per pulse and supports count rates up to the laser-limited 200 MHz. Unlike Geiger-mode SPADs, the linear-mode operation enables high count rates and the preservation of amplitude information without dead time. Dark current presently limits performance at even lower photon levels, but strong improvements are expected with modest cooling, highlighting the potential of AlGaAsSb APDs for high-speed, photon-starved SWIR detection.