American defence research agency Darpa has developed a lidar system small enough to be integrated on a microchip yet offering better performance than conventional bulky mechanical devices.
A more precise alternative to radar, measuring distances using laser beams instead of radio waves, lidar is essential for many military capabilities including autonomous navigation, chemical-biological sensing, precision targeting and communications.
Until today, lidar devices have required bulky mechanical assemblies to sweep the laser beam around, which are both expensive and sensitive to mechanical shocks and fluctuations of temperature. The use of the technology has therefore so far been limited.
Darpa’s researchers working under the Short-range Wide-field-of-view Extremely agile Electronically steered Photonic EmitteR (SWEEPER) programme have now announced a major breakthrough that could pave the way for more widespread adoption of lidar technology.
“By finding a way to steer lasers without mechanical means, we’ve been able to transform what currently is the largest and most expensive part of laser-scanning systems into something that could be inexpensive, ubiquitous, robust and fabricated using the same manufacturing technology as silicon microchips, said Josh Conway, Darpa programme manager.
“This wide-angle demonstration of optical phased array technology could lead to greatly enhanced capabilities for numerous military and commercial technologies, including autonomous vehicles, robotics, sensors and high-data-rate communications.”
The new device, which can be integrated onto a microchip, is not only small and simple. It also offers significant improvements compared to traditional devices. Its silicon-based laser consisting of billions of light-emitting dots can be swept around more than 10,000 times faster than what is currently possible with mechanical lidar systems – up to 100,000 per second.
Moreover, it can steer the laser precisely across a 51-degree arc, offering the widest field of view of all chip-scale optical scanning systems.
The device relies on the so called phased-array techniques developed in the 1960s for radar technology. Phased arrays use carefully engineered surfaces to control the direction of selected electromagnetic signals by varying the phase across many small antennas.
The technology, revolutionary at its time, enabled using multiple beams and rapid scanning speeds, as well as the ability to shape the arrays into curved surfaces.
However, using the concept with optical technology presented many challenges. As optical wavelengths are thousands of times smaller than those of radio waves used by radar, elements of the array must be placed within only a few microns of each other. The manufacturing requires extreme precision as deviations as small as 100 nanometres can affect performance.