A Compact Upconversion Single-Photon Imager for Full-Range and Accurate 3-D Imaging

The rapid development of single-photon detection technology offers the possibility for an imaging system to go beyond traditional limits. Recently, single-photon imagers based on the upconversion technique have achieved unprecedentedly high resolution and noise tolerance in 3-D imaging. Nevertheless, the limited imaging range, complicated optical path, and long data acquisition time impose remaining challenges to practical applications. In this work, we build an upconversion single-photon imager for full-range and accurate 3-D imaging. A compact all-fiber design allows our system to work robustly in an open environment. Compared to the previous imagers, the imaging speed is increased by three orders of magnitude due to the high upconversion efficiency and photon-efficient algorithm. With the application of a high-repetition laser and a nanosecond optical delay line (ODL), we achieve full-range imaging under the upconversion scheme against high solar background noise. For close-up scenes, our imager achieves ultrahigh axial resolution up to
$20 \mu \text{m}$
, which is not affected by the time jitter or pileup effect of the single-photon detector. Our proposal can stimulate practical applications in sophisticated scenarios.