Self-Sweeping LiDAR Could Dramatically Shrink 3D Mapping Systems

Self-Sweeping LiDAR Could Dramatically Shrink 3D Mapping Systems

A team of UC Berkeley engineers led by Connie Chang-Hasnain, a professor of electrical engineering and computer sciences, used a novel concept to automate the way a light source changes its wavelength as it sweeps the surrounding landscape.

The advance could have implications for imaging technology using LIDAR, or light detection and ranging, and OCT, or optical coherence tomography. A new approach that uses light to move mirrors could usher in a new generation of laser technology for a wide range of applications, including remote sensing, self-driving car navigation and 3D biomedical imaging.

This self-sweeping laser couples an optical field with the mechanical motion of a high-contrast grating (HCG) mirror. The HCG mirror is supported by mechanical springs connected to layers of semiconductor material. The red layer represents the laser’s gain (for light amplification), and the blue layers form the system’s second mirror. The force of the light causes the top mirror to vibrate at high speed. The vibration allows the laser to automatically change color as it scans. (Schematic by Weijian Yang)

This self-sweeping laser couples an optical field with the mechanical motion of a high-contrast grating (HCG) mirror. The HCG mirror is supported by mechanical springs connected to layers of semiconductor material. The red layer represents the laser’s gain (for light amplification), and the blue layers form the system’s second mirror. The force of the light causes the top mirror to vibrate at high speed. The vibration allows the laser to automatically change color as it scans. (Schematic by Weijian Yang)

LIDAR works by shining a beam of light at a target and measuring the amount of time it takes to bounce back. Because the speed of light is constant, this system can then be used to calculate distance. Self-driving vehicles and remote sensing technology use LIDAR for navigation and the creation of 3D maps.

Moving mirrors with light

In both applications, as the laser moves along, it must continuously change its frequency so that it can calculate the difference between the incoming, reflected light and the outgoing light. To change the frequency, at least one of the two mirrors in the laser cavity must move precisely.

The coupling of the laser with an ultra-thin, high-contrast grating (HCG) mirror allowed the researchers to harness the physical force of the light to move the mirror.  In their experiments, the researchers found that this optomechanical interaction of the laser and the mirror can sweep across a wavelength range of more than 23 nanometers in the infrared spectrum without the need for external controls.

Moreover, the period of the sweeping cycle can be as short as a few hundred nanoseconds, enabling several million sweeps per second. This speedy sweeping rate enables 3D image capture for real-time videos and visualization of depth change.

The study authors said the next stage of the research will be to incorporate this new laser design in current LIDAR or OCT systems, and to demonstrate its application in 3D mapping.

A U.S. Department of Defense National Security Science and Engineering Faculty Fellowship helped support this work.

Categories: LiDAR

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