Active wavefront shaping for multimode fiber optical tweezers with structured light

Optical fiber tweezers have proven highly effective in precisely manipulating and trapping microscopic particles. Most existing demonstrations use single-mode fibers, which require tapered ends and are limited to single-particle control. Although multimode fibers (MMFs) can generate arbitrary structured light fields by transmitting multiple spatial modes simultaneously, inherent mode crosstalk renders the transmitted light field uncontrollable. In this study, we demonstrate MMF optical tweezers capable of manipulating and trapping multiple microspheres by projecting structured light, achieving performance comparable to that of holographic optical tweezers. By employing neural networks to guide active wavefront shaping and mitigate mode crosstalk, we achieved precise projection of structured light fields. Our experimental setup, which includes a green laser and a digital micromirror device, enabled the generation of focused and structured light through the MMF. We successfully manipulated single microspheres along a defined path and trapped multiple microspheres simultaneously using ring-shaped structured light. These results highlight the versatility and potential of MMF optical tweezers for advanced optical manipulation applications.