Recently, a research group led by Prof. YAO Baoli and Dr. XU Xiaohao from Xi'an Institute of Optics and Precision Mechanics (XIOPM) of the Chinese Academy of Sciences, developed artificial potential field (APF)-empowered holographic optical tweezers (HOTs), which solved the problem of inter-particle collisions during dynamic optical micromanipulation of multiple particles, thus enabling fully-parallel assembly and optimal-path control of particle arrays. The study was published in PhotoniX.

HOTs are used to confine and manipulate multiple particles simultaneously through multiple optical traps created with tailored light fields, allowing them to be assembled into specific patterned structures. However, the parallel manipulation capability of HOTs is not fully exploited in practical use. This is because the parallel manipulation is prone to collisions among particles, especially for high-density particle clusters, which could result in agglomeration or loss of particles, and ultimately lead to defects in the assembled structure.

In this study, inspired by unmanned aerial vehicle cluster control and underwater-robot queue manipulation techniques, researchers introduced APF into HOTs. The method applied an additional virtual repulsive field to a particle in an optical trap through an intelligent algorithm where the repulsive force was inversely proportional to the spacing of particles, thus allowing particles to efficiently bypass obstacles through localized displacements when collisions were imminent.

Using APF-empowered HOTs, researchers realized defect-free assembly of the particle arrays with a full parallelism of manipulation, thus maximizing the assembly efficiency. After eliminating the potential collision risk, they achieved efficient transformation between different patterns by using the minimum path optimization scheme obtained from the Hungarian algorithm.

"This work will promote advanced applications of optical tweezers, opening new opportunities for quantum computation, artificial material manufacturing, and real-time display at the microscale level. It may also inspire the development of other assembly techniques such as holographic acoustic tweezers," said Dr. XU.