Scientists achieve high-resolution non-line-of-sight imaging with vectorial digitelligent optics

In a novel breakthrough, researchers have developed a novel technique called vectorial digitelligent optics (VDO) for high-resolution non-line-of-sight (NLOS) imaging, as reported in Engineering. This innovation holds great promise for applications in robotic vision, remote sensing, autonomous driving, and more.

Traditional NLOS imaging techniques face challenges such as the need for ultrafast time-resolved imagers and high computational demands. The echo signal often suffers from intensity and shape deterioration, limiting resolution and image contrast. The new VDO approach aims to overcome these limitations.

The VDO-empowered NLOS imaging system digitally controls the polarization state, phase, and amplitude of the light beam. By using digital optical elements like active metasurfaces or spatial light modulators (SLMs) in conjunction with deep learning algorithms, the system can project an engineered vector wavefront. This counteracts the spatially varying polarization and phase shift induced by the relay wall.

In the experiment, a 532 nm picosecond fiber laser was used as the light source. An SLM was employed to modulate the light beam. For single-object NLOS imaging, reflective tape on cardboard was the object. The results showed that the focal spot size on the object had a full width at half maximum (FWHM) of 0.42 mm, close to the theoretical diffraction-limited spot size of about 0.36 mm. The peak signal-to-noise ratio (PSNR) improved significantly after VDO optimization, with an average improvement of 6.9-fold.

In multi-object NLOS imaging, two objects were placed at different locations. By analyzing the time of flight (TOF) of photons, the axial information was obtained. The relative error in calculating the axial distance between the two objects was about 16.8%.

In polarization-selected NLOS imaging, the researchers found that selecting the appropriate polarization state of the incident light increased the echo signal’s signal-to-noise ratio by 11.38%. The imaging results also showed enhanced contrast and better restoration of object details.

Although there are still some technical challenges, such as real-time signal reading from single-photon avalanche diodes (SPADs), the researchers are exploring solutions like using photomultiplier tubes and combining different optical elements. The combination of metasurface technology with NLOS imaging and other advanced technologies is expected to further enhance imaging speed and quality in future research. This research opens up new avenues for active imaging, communication, and laser wireless power transfer.

The paper “Vectorial Digitelligent Optics for High-Resolution Non-Line-of-Sight Imaging,” authored by Yinghui Guo, Yunsong Lei, Mingbo Pu, Fei Zhang, Qi Zhang, Xiaoyin Li, Runzhe Zhang, Zhibin Zhao, Rui Zhou, Yulong Fan, Xiangang Luo. Full text of the open access paper: https://doi.org/10.1016/j.eng.2024.11.013. For more information about the Engineering, follow us on X (https://twitter.com/EngineeringJrnl) & like us on Facebook (https://www.facebook.com/EngineeringJrnl).