Improved direct binary search-based algorithm for generating holograms for the application of holographic optical tweezers

This paper presents an improved direct binary search (DBS)-based algorithm for generating holograms to holographic optical tweezers. The simulations show that the improved algorithm greatly enhances computation speed while maintaining high hologram efficiency and high-intensity homogeneous target spots. The improved algorithm was applied to generate holographic optical tweezers in several experiments. The experiments demonstrate that real-time trap and manipulation can be realized with the improved algorithm if the number of trapped microparticles is small. 1 Introduction Holographic optical tweezers could flexibly trap and manipulate particles, which play an important role in many fields such as physics, chemistry, life sciences, micro-and nanoma-nufacturing, and microfluidics. 1–5 The key to a holographic optical tweezers system is the hologram's design. So far, Gerchberg-Saxton (GS), DBS (Direct Binary Search), and other algorithms have been developed. 6–9 These algorithms need to be optically efficient and fast enough for real-time manipulation. DBS has excellent performance in terms of flexibility and output efficiency, but requires a great deal of computation time. The output plane phase optimize (OPPO) algorithm proposed by Georgiou et al., 10 is an alternative to DBS and very suitable for designing spot-generating holograms for the use in holographic optical tweezers. To create S-target spots on the output plane, the OPPO algorithm chooses randomly 4 − 5 S pixels from the hologram plane, and flip operations are only performed on the selected pixels in order to design a temporary hologram and form the target output plane (DBS is used in this step). Then, the phase of the output spots is measured, and the inverse DFT can be computed in order to obtain the full-resolution hologram. However, the computing speed of OPPO is still a drawback. Based on this research, we improved this algorithm to reduce its run time. The experiments on the improved OPPO were also performed on the holographic optical tweezers platform.