Quantum LIDAR prototype acquires images while underwater

The LIDAR system uses a green pulsed laser source to illuminate the scene of interest. An array of single-photon detectors detect the reflected pulsed illumination, allowing ultrafast low-light detection and greatly reducing measurement time in photon-starved environments such as highly attenuating water. By taking time-of-flight measurements with picosecond timing resolution, the researchers can routinely resolve millimeter details of the targets in the scene. 

The approach also allows the researchers to distinguish the photons reflected by the target from those reflected by particles in the water, making it particularly suitable for performing 3D imaging in highly turbid waters where optical scattering can ruin image contrast and resolution.

The fact that this approach requires thousands of single-photon detectors, all producing many hundreds of events per second, makes it extremely challenging to retrieve and process the data necessary to reconstruct the 3D image in a short time, especially for real-time applications. However, the team developed algorithms specifically for imaging in highly scattering conditions and applied them in conjunction with widely available graphics processing unit (GPU) hardware.

Aurora Maccarone, a Royal Academy of Engineering research fellow from Heriot-Watt University, explained the potential applications of this technology in a release provided by Optica: "This technology could be useful for a wide range of applications. For example, it could be used to inspect underwater installations, such as underwater wind farm cables and the submerged structure of the turbines. Underwater LIDAR can also be used for monitoring or surveying submerged archaeology sites and for security and defense applications."

The applications of this discovery

Maccarone further stated, "This work aims to make quantum detection technologies available for underwater applications, which means that we will be able to image the scene of interest in very low-light conditions. This will impact the use of offshore cable and energy installations, which are used by everyone. This technology could also allow monitoring without the presence of humans, which would mean less pollution and a less invasive presence in the marine environment."

The team's new technique builds on some important technological advances. "Heriot-Watt University has a long track record in single‑photon detection techniques and image processing of single-photon data, which allowed us to demonstrate advanced single‑photon imaging in extremely challenging conditions," said Maccarone. "The University of Edinburgh has achieved fundamental advances in the design and fabrication of single-photon avalanche diode detector arrays, which allowed us to build compact and robust imaging systems based on quantum detection technologies."

The LIDAR system using quantum detection technology has shown great promise in underwater imaging, which has many potential applications. The team's work provides a new technique for capturing real-time 3D images underwater and opens up many possibilities for the future.