Single-Photon Detection Techniques in Imaging Systems

Single-photon detection techniques have transformed imaging by extending sensitivity to the ultimate limit of light measurement. By registering individual photons, these methods facilitate applications ranging from three-dimensional mapping and autonomous navigation to high-resolution microscopy and quantum information processing. Central to most imaging systems are solid-state detectors such as single-photon avalanche diodes (SPADs), which amplify weak optical signals via an avalanche multiplication process, and superconducting nanowire single-photon detectors (SNSPDs), which leverage superconducting materials to achieve low noise and high timing precision. Advances in semiconductor fabrication, time-to-digital conversion and on-chip signal processing have driven improvements in photon detection efficiency, timing resolution and pixel density. Time-gated and time-correlated single-photon counting techniques enable precise depth measurements in time-of-flight (TOF) applications and fluorescence lifetime imaging, while innovations in pixel architecture and three-dimensional stacking have reduced dark count rates, minimised crosstalk and enhanced dynamic range. Emerging platforms based on germanium-on-silicon and InGaAs/InP alloys extend operation into the short-wave infrared, supporting eye-safe LiDAR and quantum communications. Collectively, these innovations underline the global significance of single-photon imaging in fields as diverse as environmental monitoring, biomedical diagnostics and secure data transmission.

Research from Nature Portfolio

Recent studies have demonstrated an efficient carrier extraction structure in InGaAs/InP SPAD arrays that electrically guides photogenerated carriers away from non-pixel regions, reducing optical–electrical crosstalk by over 90% between adjacent elements. This architecture preserves pixel integrity without etching damage and promises high-pixel-density arrays suited for high-resolution three-dimensional imaging and quantum sensing.

Another work on planar germanium-on-silicon SPAD detectors has introduced a large-area, planar geometry that operates in the short-wave infrared with a single-photon detection efficiency of 38% at 1,310 nm and 125 K. The design delivers a fiftyfold improvement in noise equivalent power compared with traditional mesa structures and mitigates afterpulsing, paving the way for cost-effective, high-data-rate arrays for eye-safe automotive LiDAR and quantum technologies.

Research from all publishers

A comprehensive review of SPAD imagers in biophotonics has charted fifteen years of development in standard CMOS platforms, emphasising on-chip time-stamping, pixel-level processing and architectures that enable fluorescence lifetime imaging, super-resolution microscopy and time-resolved spectroscopy. It highlights the challenge of balancing fill factor, timing precision and noise performance to meet the demands of endoscopic and in vivo applications.

In parallel, a one-megapixel time-gated SPAD sensor realised in 180 nm CMOS technology has showcased 3.8 ns gating windows and 24 kfps frame rates. With a fill factor enhanced by microlenses and dual-exposure dynamic range controls, the imager achieves millimetre-scale depth precision over two metres and supports overlapped multi-object detection in time-of-flight experiments.

Studies of silicon SPAD and silicon photomultiplier (SiPM) arrays for long-range high-speed LiDAR have surveyed various ranging modalities and illumination schemes, detailing how 3D stacking and advanced pixel designs address background light rejection, angular resolution and eye-safety. These efforts guide the next generation of solid-state TOF sensors for autonomous vehicles and robotics.

Single-Photon Detection Techniques in Imaging Systems publication trend

The graph below shows the total number of articles in single-photon detection techniques in imaging systems across all publications each year (not limited to Nature Index journals).

Technical terms

Single-photon avalanche diode (SPAD): A semiconductor detector that triggers an avalanche current upon absorbing a single photon, enabling photon-counting with high timing resolution.

Superconducting nanowire single-photon detector (SNSPD): A thin superconducting wire biased below its critical current that momentarily transitions to a resistive state upon photon absorption, producing a detectable electrical pulse with low dark counts.

Photon detection efficiency (PDE): The probability that an incident photon generates a detectable electrical signal, encompassing absorption, avalanche initiation and readout efficiency.

Time gating: A technique that restricts photon detection to narrow temporal windows, reducing background noise and enabling depth-resolved imaging in time-of-flight systems.

Crosstalk: Unwanted coupling between adjacent pixels, where an avalanche event in one element induces spurious signals in neighbouring detectors, degrading spatial fidelity.

Time-of-flight (TOF): A ranging method that measures the travel time of photon pulses between a source and target to reconstruct depth information with high precision.

References

1. High crosstalk suppression in InGaAs/InP single-photon avalanche diode arrays by carrier extraction structure. Nature Communications (2024).
2. High performance planar germanium-on-silicon single-photon avalanche diode detectors. Nature Communications (2019).
3. Single-photon avalanche diode imagers in biophotonics: review and outlook. Light: Science & Applications (2019).
4. Megapixel time-gated SPAD image sensor for 2D and 3D imaging applications. Optica (2020).
5. SPADs and SiPMs Arrays for Long-Range High-Speed Light Detection and Ranging (LiDAR). Sensors (2021).