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Vehicles equipped with autonomous driving capabilities could be made safer with a new version of lidar, known as flash lidar, which combines conventional beam-scanning techniques with a newer, 3D approach.
Autonomous vehicles typically come equipped with lidar systems that use pulsed lasers to map objects and scenes in order to allow autonomous robots, vehicles and drones to navigate their environment.
Kyoto University researchers have developed a non-mechanical 3D lidar system, which fits in the palm of the hand, that can be used to measure the distance of poorly reflective objects and automatically track the motion of these objects.
“With our lidar system, robots and vehicles will be able to reliably and safely navigate dynamic environments without losing sight of poorly reflective objects such as black metallic cars,” said lead researcher Susumu Noda. “Incorporating this technology into cars, for example, would make autonomous driving safer.”
The new system is possible thanks to a unique light source the researchers developed called a dually modulated photonic-crystal laser (DM-PCSEL). Because this light source is chip-based it could eventually enable the development of an on-chip all-solid-state 3D lidar system.
“The DM-PCSEL integrates non-mechanical, electronically controlled beam scanning with flash illumination used in flash lidar to acquire a full 3D image with a single flash of light,” said Noda.
“This unique source allows us to achieve both flash and scanning illumination without any moving parts or bulky external optical elements, such as lenses and diffractive optical elements.”
Lidar systems map objects within view by illuminating those objects with laser beams and then calculating the distance of those objects by measuring the beams’ time of flight (ToF) — the time it takes for the light to travel to objects, be reflected and then 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 evaluates the distances of all objects in the field of view with a single broad, diffuse beam of light.
However, flash lidar systems can’t be used to measure the distances of poorly reflective objects like black metallic cars due to the very small amount of light reflected from these objects. These systems also tend to be large because of the external lenses and optical elements needed to create the flash beam.
The DM-PCSEL light source 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.
The researchers incorporated the DM-PCSEL into a 3D lidar system, which allowed them to measure the distances of many objects simultaneously using wide flash illumination while also selectively illuminating poorly reflective objects with a more concentrated beam of light. They also installed a ToF camera to perform distance measurements and developed software that enables automatic tracking of the motion of poorly reflective objects using beam-scanning illumination.
“Our DM-PCSEL-based 3D lidar system lets us range highly reflective and poorly reflective objects simultaneously,” said Noda. “The lasers, ToF camera and all associated components required to operate the system were assembled in a compact manner, resulting in a total system footprint that is smaller than a business card.”
The researchers demonstrated the new lidar system by using it to measure the distances of poorly reflective objects placed on a table in a lab. They also showed that the system can automatically recognise poorly reflective objects and track their movement using selective illumination.
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