Enhanced metasurface scanning lidar technology with wide field of view

July 21, 2023

(Nanowerk News) Pulsed laser scanning lidar is a core technology for autonomous locomotion and robotic mobility. Here, the directional light pulse is scattered backwards by the reflective object and the time elapsed between the emission and detection of the pulse is used to calculate depth. Direct time-of-flight (d-ToF) measurement of these returning light pulses enables three-dimensional imaging of complex scenes.

Currently, lidar technology requires many developments, including increasing the field of view of observation (FoV) with high-angle resolution, increasing the imaging frame rate, expanding the ambiguity range by reducing the signal-to-noise ratio (SNR), and reducing fabrication costs and component sizes, for large-scale industrial applications in the global market.

Patrice Genevet’s group at the Université Côte d’Azur in France have proposed an innovative solution to overcome some of the limitations of lidar technology and meet the demanding requirements of automotive lidar. Their work is available in the journal Gold Open Access Advanced Photonics (“Overcomes the limitations of 3D sensors with a wide field of view enhanced by lidar metasurface scanning”). Ultra fast high FoV metasurface lidar architecture. (a) Emission and lidar scanning module. (b) SEM image of the metasurface sample; (c) concept of metasurface functionality; and (d) lidar imaging scheme. (Image: Marinov et al.)

The researchers presented an experimental prototype of an ultrafast FoV pulsed metasurface scanning lidar. It uses a laser diode modulated by an acousto-optical deflector (AOD) and cascades it with a meta surface, increasing the FoV by up to 150° in both the horizontal and vertical directions. Also, the optical properties of the metasurface are continuously varied to extend the narrow deflector FoV. Finally, the detection portion of the system uses a highly sensitive photodetector which is digitized by an analog to digital converter.

Pulse-scanning lidars, although working on simple physical principles, usually suffer from low SNR and poor accuracy for objects located far within the ambiguity range, i.e. the maximum distance that can be measured. Also, there is a trade-off between the range of ambiguity and the inherent speed of d-ToF imaging. Recognizing this problem, the researchers proposed a new imaging technique that softens the trade-offs mentioned above in lidar pulse scanning.

Inspired by the code division multiple access (CDMA) pulse coding method—a multiplexed illumination technique traditionally used in telecommunications theory—the imaging process takes advantage of the high scanning speed of AOD without sacrificing range ambiguity or architectural simplicity. This technique allows imaging in low SNR environments. Experimental results show that the CDMA block technique extends the range of lidar ambiguity by up to 35 times—to the kilometer distance—compared to traditional single-pulse lidar. This also increases the SNR of the lidar image, enabling better performance in noisy environments or at longer distances.

The researchers highlight that the new scanning lidar system, leveraging the capabilities of metasurfaces, nearly meets the requirements for automotive lidar and is promising for new applications. It is compact and has the potential to be scaled down to chip-scale dimensions. This miniaturization will open up new possibilities and exciting prospects for the autonomous vehicle and robotics industries.

This research provides a solid framework for the next generation of high-speed lidar, offers insight into new capabilities and opens the door to newer cutting-edge technologies. Scientific advances raise the prospect of smoother adaptive autonomous and robotic driving.

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