High resolution flash three-dimensional LIDAR systems based on polarization modulation

Research on Polarization Modulation of Electro-Optical Crystals for 3D Imaging Reconstruction

A method for enhancing the resolution of 3D imaging reconstruction by employing the polarization modulation of electro-optical crystals is proposed. This technique utilizes two polarizers oriented perpendicular to each other along with an electro-optical modulation crystal to achieve high repetition frequency and narrow pulse width gating. By varying the modulation time series of the electro-optical crystal, three-dimensional gray images of the laser at different distances are acquired, and the three-dimensional information of the target is reconstructed using the range energy recovery algorithm. This 3D imaging system can be implemented with large area detectors, independent of the an Intensified Charge-Coupled Device (ICCD) manufacturing process, resulting in improved lateral resolution. Experimental results demonstrate that when imaging a target at the distance of 20 m, the lateral resolution within the region of interest is 2560 × 2160, with a root mean square error of 3.2 cm.

Remote visualization of underwater oil using a flash Raman lidar system

We propose and experimentally demonstrate a new, to the best of our knowledge, underwater monitoring system that incorporates Raman spectroscopy based on a flash lidar. We have visualized underwater oil at a 5 m distance by illuminating the area of around 15 cm diameter with an expanding laser beam at 532 nm and detecting the oil and water Raman images. By calibrating the oil Raman image with the water Raman image, the detection limit of liquid oil thickness has been estimated to be about 0.27 mm. Thus, the proposed technique provides the capability of effectively detecting oil leaks in underwater sea areas.

Metasurface-enhanced light detection and ranging technology

Deploying advanced imaging solutions to robotic and autonomous systems by mimicking human vision requires simultaneous acquisition of multiple fields of views, named the peripheral and fovea regions. Among 3D computer vision techniques, LiDAR is currently considered at the industrial level for robotic vision. Notwithstanding the efforts on LiDAR integration and optimization, commercially available devices have slow frame rate and low resolution, notably limited by the performance of mechanical or solid-state deflection systems. Metasurfaces are versatile optical components that can distribute the optical power in desired regions of space. Here, we report on an advanced LiDAR technology that leverages from ultrafast low FoV deflectors cascaded with large area metasurfaces to achieve large FoV (150°) and high framerate (kHz) which can provide simultaneous peripheral and central imaging zones. The use of our disruptive LiDAR technology with advanced learning algorithms offers perspectives to improve perception and decision-making process of ADAS and robotic systems.

Optical OCDMA coding and 3D imaging technique for non-scanning full-waveform LiDAR system

Full-waveform LiDAR systems have been developed owing to their superiority in terms of high precision and resolution. However, further improving the imaging speed and resolution continues to be a problem. In this study, we propose an optical orthogonal code division multiple access (OCDMA) coding and 3D imaging technique, and a non-scanning full-waveform LiDAR system is first demonstrated. Encoding, multiplexing, and decoding are the essential modules of the OCDMA LiDAR system, which use M detectors and N-bits code to achieve high-accuracy decomposition for ${\rm M} \times {\rm N}$M×N pixels. In this paper, a complete 3D imaging LiDAR system is introduced, and the implementation of encoding and decoding is also illustrated. To prove that the technology is scientific and effective, an imaging experiment is carried out. The experimental result indicates that a system with only four avalanche photodiodes (APDs) can achieve 256 pixels. Moreover, the vertical resolution is about 1.8 cm and the range resolution is 15 cm at the distance of 40 m.

Electro-optic imaging enables efficient wide-field fluorescence lifetime microscopy

Nanosecond temporal resolution enables new methods for wide-field imaging like time-of-flight, gated detection, and fluorescence lifetime. The optical efficiency of existing approaches, however, presents challenges for low-light applications common to fluorescence microscopy and single-molecule imaging. We demonstrate the use of Pockels cells for wide-field image gating with nanosecond temporal resolution and high photon collection efficiency. Two temporal frames are obtained by combining a Pockels cell with a pair of polarizing beam-splitters. We show multi-label fluorescence lifetime imaging microscopy (FLIM), single-molecule lifetime spectroscopy, and fast single-frame FLIM at the camera frame rate with 103-105 times higher throughput than single photon counting. Finally, we demonstrate a space-to-time image multiplexer using a re-imaging optical cavity with a tilted mirror to extend the Pockels cell technique to multiple temporal frames. These methods enable nanosecond imaging with standard optical systems and sensors, opening a new temporal dimension for wide-field low-light microscopy.