Scientists used high efficiency optical devices and a new noise-suppression technology to realize single-photon 3D imaging over 200 km. This is regarded as a virtually 'heroic' attempt at single-photon lidar imaging at extremely long distances.
This feat was achieved by a team of researchers headed by Professor Jianwei Pan and Professor Feihu Xu from the University of Science and Technology of China.
In the recent past, lidar imaging technology has allowed high precision 3D imaging of a target scene.
Single-photon imaging lidar is a perfect technology to achieve remote optical imaging at picosecond resolution and single-photon level sensitivity.
However, its imaging range is highly restricted by the count of photons that echo back, which tends to decrease quadratically.
Firstly, the researchers optimized the transceiver optics. The lidar system configuration was based on a coaxial scanning design for the transmit and receive optical paths. This setup helps to align the transmitting and receiving spots more accurately, thereby achieving imaging at a higher resolution when compared to the conventional method.
The team differentiated weak echo signal from strong background noise by developing a single-photon avalanche diode detector (SPAD). This detector featured a low dark count rate of 0.1 kHz and a detection efficiency of 19.3%.
Then, the researchers coated telescope to realize high transmission at a wavelength of 1550 nm. All these optimizations helped achieve a higher collection efficiency than earlier.
In addition, the team employed an efficient temporal filtering method for suppressing noise. This method can decrease the total number of noise photon counts to around 0.4 kHz, which is nearly 50 times smaller when compared to what was achieved in earlier studies.
The results of the experiment demonstrated that the system can realize precise 3D imaging at distances of up to 201.5 km with single-photon sensitivity.
This study could offer optimized methods for low-power, single-photon lidar to enable high-resolution active imaging and sensing over longer distances and pave a new path for the use of long-range target recognition and earth observation.
Li, Z.-P., et al. (2021) Single-photon imaging over 200 km. Optica. doi.org/10.1364/OPTICA.408657.