The breakthrough of coherent two-photon lidar overcomes distance limitations

Schematic diagram of experimental setup
New research has revealed advances in light detection and ranging technology, providing unparalleled sensitivity and accuracy in measuring the distance of distant objects.

This study was published in the Physical Review Letters and was the result of a collaboration between Professor Yoon Ho Kim's team at POSTECH in South Korea and the Center for Quantum Science and Technology at the University of Portsmouth.

Coherent LiDAR has long been the cornerstone of ranging, but its ability is limited by the coherence time of the light source. In a groundbreaking initiative, researchers have introduced two-photon LiDAR to eliminate the range limitation imposed by coherence time, enabling accurate and precise ranging of distant objects with coherence time determined by the spectral bandwidth of far exceeding light sources.

The inspiration for this study comes from the recent work led by Professor Vincenzo Tamma, Director of the Center for Quantum Science and Technology, which utilizes two-photon interference of thermal light, surpassing coherence. Unlike traditional coherent lidar, coherence time is a limiting factor, and the second-order interference fringes in coherent two-photon lidar are not affected by the short coherence time of the light source and are determined by its spectral bandwidth.

The experimentally proven scheme utilizes a simple thermal light source, such as sunlight, interacting with a double slit mask, where two slits A and B are separated by more than the coherence length of the light source, as well as two cameras. The light emitted from two slits either travels along a known optical length path towards the first detector D1 or propagates at an unknown distance towards a distant object, and is detected by the second detector D2 after being reflected by it.

A recent study led by Professor Tamma, in collaboration with Bari University and POSTEC in South Korea, has theoretically demonstrated for the first time that even in the presence of turbulence, the distance of distant objects can be estimated by measuring the spatial correlation of light intensity detected by two detectors.

If either of the two slits is closed, phase dependent interference cannot be observed. The famous Hanbury Brown and Twist experiments were in this situation, paving the way for the development of quantum optics and quantum technology in 1954. In fact, in the standard HBT two-photon interference, due to the contribution of only one slit at that time, interference jitter can be observed by correlated measurements of the light intensity of the two detectors.

However, when both slits are open, one can observe an additional, but this time depends on the interference contribution of the phase, which depends on the unknown distance of the remote object, and is caused by interference between two possible two-photon paths from two different slits to two detectors, as mentioned earlier.

From a fundamental perspective, the generation of this phase dependent contribution is a highly counterintuitive effect and is at the core of this technological influence, which has now been experimentally demonstrated in Professor Yoon Ho Kim's laboratory at POTECH.

This new study indicates that the coherent company's two-photon LiDAR has robustness to turbulence and environmental noise, marking a significant leap in the applicability of LiDAR technology in challenging environments.

"This breakthrough opens up new applications of two-photon correlation in classical light, breaking through the boundaries previously believed to be possible for LiDAR technology," said Professor Tamma, co-author of the study. "Our coherent two-photon lidar technology not only overcomes the range limitations related to coherence time, but also exhibits extraordinary resilience in the face of external interference."

These findings may lead to the development of new sensing technologies based on the use of thermal optical correlation measurements. These products may be used in autonomous vehicle, robots, environmental monitoring and other fields.

The ability to measure distances beyond coherent time with higher accuracy and reliability may reshape industries that rely on precise distance measurement.

The research team envisions collaborating with industry partners and stakeholders to further develop and implement coherent two-photon lidar in the real world.

Source: Laser Net