Technology could benefit lidar applications, from autonomous driving to virtual reality

Researchers have staged a new chip-based beam steering technology that offers a promising route to small lidar (or light detection and ranging) systems. light) profitable and efficient. Lidar, which uses laser pulses to acquire 3D information about a scene or object, is used in a wide range of applications such as autonomous driving, free-space optical communications, 3D holography, biomedical sensing and virtual reality.

“Optical beam racing is a key technology for lidar systems, but conventional beam racing systems based on mechanics are bulky, expensive, sensitive to vibrations and limited in speed,” said research team leader Hao Hu from the University of Denmark. “Although devices known as chip-based optical phased arrays (OPAs) can quickly and accurately steer light non-mechanically, until now these devices have had poor beam quality and generally less field of view. less than 100 degrees.”

In Optica, the Optica Publishing Team’s journal for high-powered research effect, Hu and co-author Yong Liu describe their new chip-based AOP that solves many of the problems that have plagued OPAs. They show that the device can eliminate a key optical artifact known as aliasing, achieving beam travel over a wide field of vision while maintaining high beam quality, a combination that could greatly improve lidar systems.

“We believe our results are groundbreaking in the field of optical beam pathing,” Hu said. “This development lays the foundation for an OPA-based lidar that is inexpensive and compact, which would allow lidar to be widely used for a variety of applications such as advanced high-level driver assistance systems which can help driving and parking and increase safety.”

A new OPA design

OPAs effect beam travel by electronically controlling the sectional profile of the light to form specific light patterns. Most AOPs use an array of waveguides to emit many beams of light, then interference is applied in the far field (far from the emitter) to precede the pattern. However, the fact that these waveguide emitters are usually spaced far apart and generate multiple beams in the far field creates an optical artifact known as aliasing. To avoid the aliasing error and obtain a 100° field of view, the emitters must be close to each other, but this causes strong crosstalk between the adjacent transmitters and degrades beam quality. Thus, until now, there has been a trade-off between the OPA eyesight field and the beam quality.

To overcome this trade-off, the researchers designed a new form of d ‘OPA which replaces the multiple transmitters of traditional OPAs with a network of tiles to create a single transmitter. This configuration eliminates aliasing error because adjacent channels in the slab array can be very close to each other. Coupling between adjacent channels is not detrimental in the slab array as it allows interference and beamforming in the near field (close to the distinctive transmitter). Light can then be emitted to the far field at the desired angle. Researchers also applied additional optical techniques to reduce background noise and reduce other optical artifacts such as sidelobes.

High quality and wide field eyesight

To test their new device, the researchers built a special imaging system to measure the average far-field optical power in the horizontal path over a field of view of 100°. They demonstrated alias-free beam steering in this path, including path beyond ±70°, although some beam degradation was observed.

They then characterized the orientation of the beam in the vertical route by adjusting the wavelength from 1480nm to 1580nm, achieving an adjustment range of 13,5°. Finally. “T” and “U” centered at angles of -60°, 0° and 60° by adjusting both the wavelength and the phase shifters. The experiments were performed with a beamwidth of 2.1°, which researchers are now working to narrow to achieve beam steering with higher resolution and longer range.

“Our new chip-based OPA delivers unprecedented performance and overcomes long-standing problems with OPAs by simultaneously realizing an alias-free 2D beam route across the entire field of eyesight at 180° and high beam quality with low side lobe level,” said Hu.

This work is funded by VILLUM FONDEN and Innovationsfonden Denmark.

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