Transmission matrix (TM) allows light control through complex media, such as multimode fibers (MMFs), gaining great attention in areas, such as biophotonics, over the past decade. Efforts have been taken to retrieve a complex-valued TM directly from intensity measurements with several representative phase-retrieval algorithms, which still see limitations of slow or suboptimum recovery, especially under noisy environments. Here, we propose a modified nonconvex optimization approach. Through numerical evaluations, it shows that the optimum focusing efficiency is approached with less running time or sampling ratio. The comparative tests under different signal-to-noise levels further indicate its improved robustness. Experimentally, the superior focusing performance of our algorithm is collectively validated by single- and multispot focusing; especially with a sampling ratio of 8, it achieves a 93.6% efficiency of the gold-standard holography method. Based on the recovered TM, image transmission through an MMF is realized with high fidelity. Due to parallel operation and GPU acceleration, our nonconvex approach retrieves a 8685 × 1024 TM (sampling ratio is 8) with 42.3 s on average on a regular computer. The proposed method provides optimum efficiency and fast execution for TM retrieval that avoids the need for an external reference beam, which will facilitate applications of deep-tissue optical imaging, manipulation, and treatment.
Manipulating single cell with optical tweezers in vitro or in vivo plays an important role in biological research, whereas the manipulation of individual cells might be affected by the neighbor cells especially in the crowd environment. To overcome this problem, an annular beam formed by the far-field Bessel beam is introduced to serve as an optical shield to protect the target cells from being disturbed. We demonstrate that an individual cell can be trapped and manipulated through the crowd cells. What’s more, the interaction between two cells can be investigated by using a dual-trap optical tweezers in the crowd environment with the help of the optical shield.
Shaping complex fields with a digital micromirror device (DMD) has attracted much attention recently due to its potential application in optical communication and microscopy. In this paper, we present an optimized Lee method to achieve dynamic shaping of orbital-angular-momentum (OAM) beams using a binary DMD. An error diffusion algorithm is introduced to enhance the accuracy for binary-amplitude hologram design, making it possible to achieve high fidelity wavefront shaping while retaining a high resolution. As a proof of concept, we apply this method to create different classes of OAM beams and experimentally demonstrate the dynamic shaping of different OAM beams including pure modes and mixed modes with a switching rate of up to 17.8 kHz.
Coherent measurement of orbital angular momentum (OAM) spectrum of light fields plays a key role in many important applications, such as OAM-based multiplexing in optical communications. The existing methods for measuring the OAM spectrum by spatially separating OAM components or interferometric technique suffer from poor efficiency and interferometric stability requirements. Here, we propose a novel technique to measure the OAM spectrum of light fields in a single shot manner by exploiting a scattering optical element. Our technique enables to directly extract the OAM spectrum from a recorded single-shot speckle pattern using algorithms based on the speckle-correlation scattering matrix and spatial mode decomposition method. As a proof of concept, we built a robust measurement system based on a fast digital micromirror device to demonstrate the feasibility of the proposed technique.
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