09 Aug 2022
TU Denmark-developed device cuts aliasing, achieving sharp beam steering over large field of view.
“Optical beam steering is a key technology for lidar systems, but conventional mechanical-based beam steering systems are bulky, expensive, sensitive to vibration and limited in speed,” commented Hao Hu, research team leader at the Technical University of Denmark.
“Although devices known as chip-based optical phased arrays (OPAs) can quickly and precisely steer light in a non-mechanical way, so far, these devices have had poor beam quality and a field of view; typically below 100 degrees,” he added.
Hu and co-author Yong Liu describe how their new chip-based OPA that solves many of the problems that have plagued OPAs in a paper in Optica. They show that the device can eliminate a key optical artifact known as aliasing, achieving beam steering over a large field of view while maintaining high beam quality.
Hu said, “This development lays the groundwork for OPA-based lidar that is low cost and compact, which would allow lidar to be widely used for a variety of applications such as high-level advanced driver-assistance systems for driving and parking and increased safety.”
OPAs perform beam steering by electronically controlling light’s phase profile to form specific light patterns. Most OPAs use an array of waveguides to emit many beams of light and then interference is applied in far field (away from the emitter) to form the pattern.
However, the fact that these waveguide emitters are typically spaced far apart from each other and generate multiple beams in the far field creates an optical artifact known as aliasing.
To avoid the aliasing error and achieve a 180 degrees field of view, the emitters need to be close together, but this causes strong crosstalk between adjacent emitters and degrades the beam quality.
Until now, there has been a trade-off between OPA field of view and beam quality. To overcome this trade-off, the researchers designed a new type of OPA that replaces the multiple emitters of traditional OPAs with a slab grating to create a single emitter.
The TU Denmark setup eliminates the aliasing error because the adjacent channels in the slab grating can be very close to each other. The coupling between the adjacent channels is not detrimental in the slab grating because it enables the interference and beam formation in the near field, close to the single emitter. The light can then be emitted to the far field with the desired angle.
The researchers also applied additional optical techniques to lower the background noise and reduce other optical artifacts such as side lobes.