Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore

Ultrafast Multi-focus Optical Tweezer based on a Digital Micromirror Device

Yintao Wang1, Bingxu Chen1 and Shih-Chi Chen1,2,a

1Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong, N.T., Hong Kong SAR, China

2Oxford-CityU Centre for Cerebro-Cardiovascular Health Engineering (CoCHE), Hong Kong Science Park, N.T., Hong Kong SAR, China


Conventional optical tweezers are mostly based on acousto-optic deflectors (AODs) or spatial light modulators (SLMs), which suffer from low spatial or temporal resolution. Accordingly, this limits their use in advanced applications, such as quantitative force measurement, fast particle sorting, and complex 3D micro- or nano-assembly. To address the problem, we present a new optical tweezer system based on binary holography and digital micromirror device (DMD). The DMD-based optical tweezer can operate at 1 kHz in closed-loop mode and 22.7 kHz in open-loop mode, while maintaining the focus resolution and minimal step size close to diffraction limit (i.e., 100s nm). Comparing with conventional systems, the DMD-system has two distinctive advantages: (1) up to 30 laser foci can be simultaneously generated and individually controlled based on binary holography to perform random-access parallel scanning and optical manipulation, where laser scanning is realized via sequentially displaying the synthesize holograms on the DMD. The scanning rate is equivalent to the DMD pattern rate, i.e., 22.7 kHz in our setup; and (2) the binary holograms are synthesized automatically in a highly parallel fashion through custom-developed algorithm in a GPU card, achieving a rate of 8,000 fps, i.e., a 10 to 100 times improvement over CPU-based algorithms. This algorithm enables high-speed closed-loop control of the scanning laser foci at 1 kHz, which may bring opportunities in scientific studies that use optical tweezers. Preliminarily, we have experimentally studied the acceleration, deceleration, dynamic assembling of particles via the DMD system. These results show great potential that DMD-based optical tweezers can bring high-precision, high-speed applications into play.

Keywords: Optical tweezer, Ultra-fast wavefront shaping, Digital micromirror device

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