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WASHINGTON — Researchers have developed a new chip-based beam guiding technology that offers a promising route to small, cost-effective, high-performance lidar (or light detection and range) systems. Lidar, which uses laser pulses to obtain 3D information about a scene or object, is used in a wide range of applications such as autonomous driving, free space optical communications, 3D imaging, biomedical sensing, and virtual reality.

“Optical beam guiding is a core technology for lidar systems, but conventional mechanical beam guiding systems are bulky, expensive, vibration sensitive and speed limited,” said lead researcher Hau Hu of the Technical University of Denmark. “Although devices known as chip-based optical phase arrays (OPAs) can quickly and accurately direct light in a non-mechanical manner, so far these devices have poor beam quality and a field of view of less than 100 degrees.”

In Optica, the Optica Publishing Group’s journal of high-impact research, Hu and co-author Yong Liu describe a new chip-based OPA that solves many of the problems that have plagued OPA. They show that the device can eliminate a key optical tool known as aliasing, and achieve beam routing over a large field of view while still maintaining high beam quality, a combination that could dramatically improve lidar systems.

“We believe our results are pioneering in the field of optical beam guiding,” Hu said. “This development lays the foundation for low-cost, compact OPA-based lidar, which will allow lidar to be widely used for a variety of applications such as high-level advanced driver assistance systems that can aid in driving and parking and increase safety.”

New OPA design

OPA directs the beam by electronically controlling the light profile to form specific light patterns. Most OPAs use a set of waveguides to emit many beams of light and then far-field (away from the emitter) interference is applied to form the pattern. However, the fact that these waveguide emitters are usually far apart and generate multiple far-field beams creates an optical artifact known as aliasing. To avoid aliasing error and achieve a 180° field of view, the emitters must be close together, but this causes strong interference between adjacent emitters and reduces the quality of the beam. Thus, until now, there has been a trade-off between OPA’s field of view and beam quality.

To overcome this trade-off, the researchers designed a new type of OPA that replaces multiple emitters of conventional OPA with a slab grating to create a single emitter. This setting eliminates the alias error because adjacent channels in the grating of the board can be too close to each other. Adjacent channel coupling is not harmful in a plate grating as it allows interference and beam formation in the near field (near the single emitter). The light can then be emitted into the far field at the desired angle. The researchers also applied additional optical techniques to reduce background noise and reduce other visual effects such as side lobes.

High quality and wide field of view

To test their new device, the researchers built a special imaging system to measure the average far-field optical power along the horizontal direction over a 180-degree field of view. They demonstrated aliasing-free radial steering in this direction, including steering beyond ±70°, although some beam degradation was seen.

Then they characterized the beam orientation in the vertical direction by adjusting the wavelength from 1480 nm to 1580 nm, achieving a tuning range of 13.5 degrees. Finally, they demonstrated the versatility of OPA by using it to generate 2D images of the letters “D”, “T” and “U” centered at angles of -60°, 0° and 60° by tuning both wavelength and phase transformers. The experiments were carried out with a beam width of 2.1 degrees, and the researchers are now working on reducing it to achieve beam guidance with higher accuracy and longer range.

“The new chip-based OPA demonstrates unprecedented performance and overcomes the long-standing problems of OPA by achieving simultaneous 2D aliasing-free beam guidance over the entire 180-degree field of view and high beam quality with a low side-lobe level,” Huh said.

This work was funded by VILLUM FONDEN and Innovationsfonden Denmark.

Paper: Y. Liu, H. Hu, “Silicon optical phase array with 180° field of view for 2D optical beam orientation” Optica, 9,8 (2022).

DOI: 10.1364 / OPTICA.458642.

About Optica

/General release. This material from the original organization/author(s) may be of a point in time nature, and is edited for clarity, style and length. The opinions and opinions expressed are those of the author(s), view them in full here.

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