Spatially structured light for optical micromanipulation

Optical micromanipulation enables the noncontact trapping and motion control of micro- and nanoscale objects through linear and angular momentum exchange between light and matter. Conventional Gaussian optical tweezers provide limited control over spatial field structure, restricting their capabilities in parallel multiparticle manipulation, complex-trajectory transport, and multidimensional motion control. By tailoring amplitude, phase, and polarization, spatially structured light can reshape intensity gradients, local energy flow, and momentum and angular momentum distributions, enabling the on-demand design of optical forces, torques, and trapping potentials. This review introduces the orbital–spin decomposition of optical momentum and discusses how its real and imaginary components relate to the electromagnetic responses of particles. Representative scalar and vector structured-light modes are then surveyed, together with advances in field generation from two-dimensional complex-amplitude modulation to three-dimensional scalar and fully vectorial field synthesis. Recent developments in multiparticle trapping, complex-trajectory transport, dark-trap manipulation, particle rotation and orientation, three-dimensional control, and light-driven micro- and nanorobots are reviewed, with emphasis on emerging mechanisms associated with polarization gradients, spin-related momentum, and imaginary momentum. Future directions include spatiotemporal and ultrafast structured light, dynamically reconfigurable devices, diverse structured waves, and the manipulation of quantum and biological objects. By clarifying the connections among spatial field structure, electromagnetic momentum transfer, and particle motion, this review provides a basis for developing high-dimensional, dynamic, and integrated optical micromanipulation systems.