
Laser scanners deliver high-quality, high-resolution images of the surroundings of a car. Therefore, they are widely regarded as an indispensable ingredient to automated driving. The downside: They are very expensive; some carry a price tag one would expect at a compact car. This however could change: A team of researchers of the UC Berkeley led by professor Connie Chang-Hasnain has found a way to reduce power consumption, weight, size and cost of LIDAR system; likewise optical coherence tomography (OCT) systems could benefit from the development.
In automotive LIDAR applications, a laser beam is shining at a target; the amount of time it takes to come back is used to measure the distance to this target. The laser beam is then moved across a certain angular range or even by 360 degrees, much like a radar system for air traffic control purposes. Thus, the LIDAR system or laser scanner generates a rather detailed image, at a quality that is clearly superior to radar images due to the shorter wavelength of laser. As the laser moves along, it must continuously change its wavelength to enable the processing circuitry to differentiate between the reflected and the outgoing light. This requires a precise movement of mirrors within the laser cavity. The mechanisms controlling this movement are the reason why today’s LIDAR systems are so bulky and expensive, says Weijan Yang, one of the members of the Berkeley research team.
To avoid this problem, the researchers have integrated the semiconductor laser with the mirror. This leads to a drastic reduction of the size – the laser source can be shrunk to a few hundred square micrometres. At the same time, power consumption drops so far that the device can be powered by an AA battery, the authors say. The coupling of the laser with an ultra-thing, high-contrast grating mirror allowed the researchers to harness the physical force of the light to move the mirror. The mirror consists of rows of tiny ridges and has been developed in Chang-Hasnain’s lab. Though the force generated is just in the nano-newton range it is enough to cause the mirror to vibrate, resulting in a wavelength sweep of some 23 nanometres in the infrared spectrum. This is enough to provide the resolution required to scan a vehicle’s environments – and it is done without any external controls. The study authors, who published their findings “Scientific Reports” on September 3, said the next stage of the research will be incorporating their design into current LIDAR systems.
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