Recently, researchers from the Danish University of technology have developed a chip based beam steering device, which can help reduce the size and cost of high-performance laser radar. The device can be used in automatic driving, free space optical communication, 3D holography, biomedical sensing, virtual reality and other fields.
Hao Hu, the head of the research group, pointed out that the traditional mechanical beam steering system in the lidar system is large, expensive, sensitive to vibration and limited in speed. Although chip based optical phased array (OPAs) can guide light quickly and accurately, such devices are often affected by poor beam quality and limited field of vision.
Specifically, the team demonstrated an optical phased array, replacing multiple transmitters of the traditional OPA with a flat grating to form a new type of OPA with a single emission source. This design can obtain a wide field of vision without sacrificing the beam quality, so as to achieve a small, cost-effective and high-performance lidar system. The study was published in the journal optics.
OPA turns the light beam by electronically controlling the phase profile of the light to form a specific pattern. Most use waveguide arrays to transmit multiple beams and apply interference to form patterns in the far field. However, since the distance between waveguides is usually far and the interference occurs in the far field, it is easy to introduce and dope aliasing. In the past, in order to achieve a 180 ° field of view, the emitters had to be placed together. However, this tightness will introduce crosstalk, which will reduce the beam quality.
In this demonstration, instead of using multiple emitters, researchers used a flat grating to create a single emitter. The results show that aliasing is eliminated - because adjacent channels can be arranged more closely, one by one. In addition, the coupling between adjacent channels will not have a negative impact in the flat grating, because it makes near-field interference and beam formation possible. The light can then be emitted in the far field at the desired angle. The team also adopted additional optical technologies to reduce background and other optical artifacts, such as side lobes.
In order to test the equipment, the team established an imaging system to measure the average far-field optical power along the horizontal direction in the 180 ° field of view. Although the researchers observed some signs of beam degradation and attenuation, it proved that there was no aliasing beam steering in this direction, including steering more than ± 70 °.
Then, by adjusting the wavelength between 1480nm and 1580nm, the researchers achieved a tuning range of 13.5 ° and characterized the steering of the beam in the vertical direction. Finally, they demonstrated the versatility of OPA by adjusting the wavelength and phase shifter to form a 2D image of three letters centered at - 60 °, 0 ° and 60 °. Finally, they successfully achieved optical tuning with a beam width of 2.1 °. At present, researchers are trying to reduce this width to achieve higher resolution and wider beam steering.
Source: OFweek laser network
