January 17, 2017

Autonomous vehicles see with lasers

					Autonomous vehicles

Lasers will help autonomous driving. LiDAR (light detection and ranging) systems use lasers to measure the distance to obstacles in the vehicle’s surroundings.

Optical technologies are in demand for vehicles, such as laser high beam, with which BMW and Osram were nominated for the 2016 German Future Prize. Blue laser diodes are the core component: The beam is converted into white light and directed onto the road via tiny reflectors. Thanks to the high light density of the laser, drivers can now see 600 meters ahead of them, which is about double the distance possible with the previous LED high beams.

With full beam. lasers compensate for the inferior night vision of the human eye. In a few years, they will completely take over the driving. With the aid of sensors, autonomous vehicles will be able to handle complex traffic situations. LiDAR systems are the key to this development. Research institutes, photonics companies and traditional automotive parts suppliers are currently positioning themselves with new LiDAR technology so that they can play a part in this market of the future.

Laser pulses instead of radar waves

The basic principle of LiDAR is similar to that of radar, but instead of radio waves, laser pulses are sent out. If they encounter objects, the reflected light is received and analyzed. Based on the time the light takes to travel, the systems calculate the distance to obstacles and, using high frequency repeated measurements, also calculate their speed. This creates a continuously updated 3D image of the vehicle’s surroundings. The position and speed of bicycles, pedestrians, vehicles and all conceivable obstacles are recorded accurately. Autonomous vehicles find extensive orientation by comparing camera data and acceleration, speed and GPS data.

The Fraunhofer Institute for Microelectronic Circuits and Systems IMS recently presented a Flash LiDAR. Instead of directing the laser beam onto a rotating mirror for a 360 degrees view, the system emits laser flashes that expose a rectangular measuring field up to 100 meters wide. Highly sensitive single photon avalanche diodes (SPADs) detect reflected light. These are installed on tiny chips along with the evaluation technology. This allows simple integration in the headlamp or behind the windshield. The technology will already be used in serial production in 2018.

The variety of LiDAR processes is growing

At electronica in Munich, Germany in the fall of 2016, Osram Opto Semiconductors presented a LiDAR process for autonomous vehicles, which is based on a four-channel laser. The key component is a laser bar with four very precisely positioned laser diodes with a wavelength of 905 nanometers, which can be controlled individually via an integrated circuit. Ultimately, the bar works like a laser that emits four perfectly parallel beams with up to 85 watts of optical output at 30 amperes. The fact that this system poses no health risks despite the high output is especially due to the extremely short pulse length of less than five nanoseconds. In daylight the system recognizes vehicles at a distance of 200 meters and pedestrians at 70 meters.

U.S. company Princeton Lightwave, Inc. believes Geiger-mode LiDAR is the technology of the future. As with the Fraunhofer system, highly sensitive single photon avalanche diodes are used. This allows the use of weaker laser beam sources. Since, as opposed to linear measurements, pixel by pixel time-of-flight measurements of individual photons are possible in Geiger mode, current diodes with 1024 pixels in the mode with more than 180,000 frames per second enable very fast, high resolution surround sensors. But Princeton Lightwave is not resting on its laurels. The company recently announced a new generation of its Geiger LiDAR module, which will offer a 4.5 times faster scanning rate of about 900 megasamples per second in half the space (4x4x6 cm). It certainly looks as if the car of the future will learn to see with lasers.