Lidar is a key technology used in a wide range of applications including autonomous driving, free-space optical communications, 3D holography, biomedical sensing and virtual reality. It operates much like radar except using laser pulses to acquire 3D information about a scene or object instead of microwaves. Steering the laser beams is a key technology for all lidar systems. However, today’s systems typically use mechanical beam steering systems which are bulky, expensive, sensitive to vibration and limited in speed.
Meanwhile, devices known as chip-based optical phased arrays (or OPAs) can quickly and precisely steer light in a non-mechanical way. But, until now, these devices have had poor beam quality and a field of view typically below 100 degrees. As described recently in the journal Optica, researchers at the University of Denmark have developed a new chip-based OPA which solves many of the problems that have plagued OPAs. They show that the device can eliminate a key optical artifact known as aliasing.
This new chip can achieve beam steering over a large field of view while maintaining high beam quality, a combination that could greatly improve lidar systems. These groundbreaking results lay the groundwork for OPA-based lidar that is low cost and compact. The dramatically lower cost lidar enabled by this breakthrough could be widely used for a variety of applications including high-level advanced driver-assistance systems that can assist in driving and parking and increase safety.
To avoid the aliasing error and achieve a 180° field of view, the emitters need to be close together, but this causes strong crosstalk between adjacent emitters and degrades the beam quality. Thus, 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 by using a “slab grating” to create a single emitter.
This 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 desired optical interference and beam formation 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. This new chip-based OPA shows unprecedented performance and overcomes the long-standing problems with OPAs by simultaneously achieving aliasing-free 2D beam steering over the entire 180° field of view and high beam quality with a low side-lobe level.