Unique chip-based light source allows combining scanning lidar with 3D flash lidar — ScienceDaily

Our roads may one day be safer thanks to an entirely new type of system that overcomes some of lidar’s limitations. Lidar, which uses pulsed lasers to map objects and scenes, helps autonomous robots, vehicles and drones navigate their environment. The new system is the first time that the capabilities of conventional beam scanning lidar systems have been combined with a newer 3D approach known as flash lidar.

In OpticsLed by Susumu Noda of Kyoto University, Japan, in the journal Optica Publishing Group, they describe their new non-mechanical 3D lidar system that fits in the palm of a hand. They also show that it can be used to measure the distance to poorly reflective objects and automatically track the movement of those objects.

“With our lidar system, robots and cars will be able to reliably and safely navigate dynamic environments without losing sight of poorly reflective objects such as black metal cars,” Noda said. “Incorporating this technology into cars, for example, will make autonomous driving safer.”

The new system is made possible by a unique light source the researchers developed, called a doubly modulated photonic crystal laser (DM-PCSEL). Because this light source is chip-based, it may eventually enable the development of a chip-based 3D lidar system.

“DM-PCSEL combines non-mechanical, electronically controlled beam scanning with flash illumination used in flash lidar to acquire a complete 3D image with a single flash of light,” Noda said. “This unique source allows us to achieve both flash and scanning illumination without moving parts or large external optical elements such as lenses and diffractive optical elements.”

Combining scanning and flash lighting

Lidar systems map objects in the field of view by illuminating those objects with laser beams, then calculate the distance to those objects by measuring the beam’s time-of-flight (ToF), the time it takes for light to travel to the objects, be reflected, and then back. return to the system. Most lidar systems in use and under development rely on moving parts such as motors to scan the laser beam, making these systems bulky, expensive and unreliable.

One non-mechanical approach, known as flash lidar, simultaneously illuminates and estimates the distances of all objects in the field of view with one broad, diffuse light beam. However, flash lidar systems cannot be used to measure distances to poorly reflective objects, such as black metal cars, because the light reflected from these objects is very small. These systems also tend to be large because of the external lenses and optical elements needed to create the flash beam.

To address these critical limitations, the researchers developed the DM-PCSEL light source. It has both a flash source that can illuminate a wide 30°×30° field of view and a beam scanning source that provides spot illumination with 100 narrow laser beams.

They incorporated the DM-PCSEL into a 3D lidar system that allowed them to measure the distances of multiple objects simultaneously using a wide beam, while selectively illuminating poorly reflective objects with a more focused light beam. The researchers also installed a ToF camera to make distance measurements and developed software to automatically track the movement of poorly reflective objects using beam-scanning illumination.

Measurement of objects with different reflectivity

“Our DM-PCSEL-based 3D lidar system allows us to locate highly reflective and poorly reflective objects simultaneously,” Noda said. “The lasers, ToF camera and all the associated components needed to operate the system were assembled in a compact form, resulting in an overall system footprint that is smaller than a business card.”

The researchers demonstrated the new lidar system by using it to measure distances to poorly reflective objects placed on a table in the laboratory. They also demonstrated that the system can automatically recognize poorly reflective objects and track their movement using selective illumination.

The researchers are now working to demonstrate the system in practical applications, such as the autonomous movement of robots and vehicles. They also want to see if replacing the ToF camera with an optically more sensitive single-photon avalanche photodiode array would allow them to measure objects at even longer distances.

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