Beam steering is a key technology in lidar systems, but traditional mechanical-based beam steering systems are cumbersome, expensive, sensitive to vibration, and limited in speed, although devices known as chip-based optical phased arrays (OPAs) can Direct light quickly and precisely in a non-mechanical way, but to date these devices have had poor beam quality and fields of view typically below 100 degrees.” Hu and co-author Yong Liu in Optica — the Optica Publishing Group’s high-impact research journal describe their new chip-based OPA that addresses many of the problems that plague OPA. They show that the device can eliminate a key optical artifact known as aliasing and achieve a large field of view while maintaining high beam quality. Beam steering. This combination can greatly improve lidar systems.
This development lays the foundation for OPA-based lidars, which are low-cost and compact, which will enable lidars to be widely used in various applications, such as high-level advanced driver assistance systems that can assist in driving and parking, Improve security. OPA performs beam steering by electronically controlling the phase profile of light to create specific light patterns. Most OPAs use an array of waveguides to launch many beams and then apply interference in the far field (away from the transmitter) to form a pattern. However, the fact that these waveguide emitters are typically far apart from each other and produce multiple beams in the far field creates an optical artifact known as aliasing. To avoid aliasing errors and achieve a 180° field of view, the emitters need to be close together, but this causes strong crosstalk between adjacent emitters and reduces beam quality. So, until now, there has been a trade-off between OPA’s field of view and beam quality.
To overcome this trade-off, the scientists designed a new type of OPA that replaces the multiple emitters of conventional OPAs with a plate-like grating to create a single emitter. This setup eliminates aliasing errors because adjacent channels in a plate grating can be very close to each other. In plate gratings, coupling between adjacent channels is not detrimental, as it enables interference and beam formation in the near field (closer to a single emitter). The light can then be launched into the far field at a desired angle. To reduce background noise and reduce other optical artifacts, such as lateral lobes, the researchers also applied other optical techniques.
To test their new device, the scientists built a special imaging system to measure the average far-field optical power in the horizontal direction within a 180° field of view. They demonstrated alias-free beam steering in this direction, including steering beyond ±70°, although some beam degradation was seen. They then characterized the beam steering in the vertical direction by tuning the wavelength from 1480 nanometers to 1580 nanometers, achieving a tuning range of 13.5°. Finally, they demonstrate the versatility of OPA, using it to form 2D of the letters “D”, “T” and “U” centered at -60°, 0° and 60° by adjusting the wavelength and phase shifter image. The experiments were performed with a beam width of 2.1°, and the researchers are now working to reduce the beam width to achieve beam steering with higher resolution and longer distances.