Reviewed by Lexie CornerFeb 7 2025
A multi-institutional research team from the USA and the UK has developed a single-photon time-of-flight LiDAR system capable of producing high-resolution 3D images of objects or scenes at distances of up to one kilometer. The study was published in Optica.
Researchers have designed a single-photon time-of-flight LiDAR system that can produce high-resolution 3D images of objects and faces that are some distance away. The top images show 3D-printed pillars imaged from 45 meters away in broad daylight. The lower images depict a recognizable human face from a person 325 meters away. Image Credit: Aongus McCarthy, Heriot-Watt University
The system enables detailed imaging in challenging environmental conditions and can detect objects obscured by foliage or camouflage netting. It has potential applications in security, surveillance, and remote sensing.
Our system uses a single-photon detector approximately twice as efficient as detectors deployed in similar LiDAR systems reported by other research groups and has a system timing resolution at least 10 times better. These improvements allow the imaging system to collect more scattered photons from the target and achieve a much higher spatial resolution.
Aongus McCarthy, Research Team Member and Research Fellow, Heriot-Watt University
The researchers demonstrated that the system could generate a 3D image of a human face from a distance of 325 meters. The team includes researchers from Gerald Buller's group at Heriot-Watt University, Robert Hadfield's group at the University of Glasgow, Matthew Shaw’s group at the NASA Jet Propulsion Laboratory, and Karl Berggren's group at MIT.
“This type of measurement system could lead to improved security and monitoring systems that could, for example, acquire detailed depth images through smoke or fog and of cluttered scenes. It could also enable the remote identification of objects in various environments and monitoring of movement of buildings or rock faces to assess subsidence or other potential hazards,” McCarthy added.
Light-Based Range Finding
The single-photon time-of-flight depth imaging system determines object distances by measuring the time a laser pulse takes to travel to the object and return. These time-of-flight measurements are repeated across multiple points to generate 3D data.
The system incorporates a superconducting nanowire single-photon detector (SNSPD), developed by researchers at MIT and JPL. The SNSPD detects individual photons, enabling precise measurements using low-power, eye-safe lasers over long distances. To minimize noise, the detector was cooled to just below 1 Kelvin using a compact cryocooler designed by the University of Glasgow team.
The cooled SNSPD was integrated with a proprietary single-pixel scanning transceiver, developed by McCarthy at Heriot-Watt University, which operates at a wavelength of 1550 nm. The system also features high-precision timing equipment capable of measuring time intervals with picosecond accuracy. For reference, light travels approximately 300 millimeters (one foot) in 1,000 picoseconds. This level of precision allowed the system to distinguish surfaces with depth separations of approximately 1 mm from a distance of 325 meters.
McCarthy added, “These factors all provide improved flexibility in the trade-off between standoff distance, laser power levels, data acquisition time, and depth resolution. Also, since SNSPD detectors can operate at wavelengths longer than 1550 nm, this design opens the door to developing a mid-infrared single-photon LiDAR system, which could further enhance imaging through fog and smoke and other obscurants.”
3D Measurements of Distant Objects
The researchers conducted field tests of their LiDAR system on the Heriot-Watt University campus, measuring objects at distances of 45 meters, 325 meters, and 1 kilometer.
To evaluate spatial and depth resolution, they scanned a custom 3D-printed target with varying pillar sizes and heights. The system resolved details as fine as 1 mm in daylight at 45 and 325 meters, nearly ten times higher than their previous depth resolution. Additionally, they generated a 3D image of a human face at these distances using a 1 ms per-pixel acquisition time, an eye-safe 3.5 mW laser, and minimal data processing.
“The excellent depth resolution of the system means that it would be particularly well suited for imaging objects behind clutter, such as foliage or camouflage netting, a scenario that would be difficult for a digital camera. For example, it could distinguish an object located a few centimeters behind a camouflage netting while systems with poorer resolution would not be able to make out the object,” McCarthy stated.
While initial field trials were conducted at a maximum distance of one kilometer, the researchers plan to extend testing to distances of up to ten kilometers and evaluate performance in environments with atmospheric obscurants such as smoke and fog. Future work will also focus on applying advanced computational techniques to accelerate data analysis and improve imaging capabilities at greater distances.
Journal Reference:
McCarthy, A. et. al. (2025) High-resolution long-distance depth imaging LiDAR with ultra-low timing jitter superconducting nanowire single-photon detectors. Optica. doi.org/10.1364/OPTICA.544877