Evanescent field trapping and propulsion of Janus particles along optical nanofibers

Small composite objects, known as Janus particles, drive sustained scientific interest primarily targeted at biomedical applications, where such objects act as micro- or nanoscale actuators, carriers, or imaging agents. A major practical challenge is to develop effective methods for the manipulation of Janus particles. The available long-range methods mostly rely on chemical reactions or thermal gradients, therefore having limited precision and strong dependency on the content and properties of the carrier fluid. To tackle these limitations, we propose the manipulation of Janus particles (here, silica microspheres half-coated with gold) by optical forces in the evanescent field of an optical nanofiber. We find that Janus particles exhibit strong transverse localization on the nanofiber and much faster propulsion compared to all-dielectric particles of the same size. These results establish the effectiveness of near-field geometries for optical manipulation of composite particles, where new waveguide-based or plasmonic solutions could be envisaged.journal articl

Ultrathin Optical Fibers : Guided Modes, Angular Momentum, and Applications

Ultrathin optical fibers have emerged as efficient and versatile platforms for studying light-matter interactions. Owing to their geometry, they are characterized by intense evanescent fields extending beyond the fiber surface. These fields can carry both spin and orbital angular momentum of guided light. Complex spatial intensity, phase, and polarization profiles can be generated at the fiber waist by propagating higher order fiber modes. In this paper, we review applications of ultrathin optical fibers, with an emphasis on optical manipulation at the micro-and nanoscale. We also discuss mode content and angular momentum of light guided by ultrathin fibers

Light-induced rotation of dielectric microparticles around an optical nanofiber

Evanescent electromagnetic fields near a waveguide can exert a transverse radiation force on scattering objects. To prove this experimentally, we demonstrate light-induced orbiting of isotropic, dielectric microparticles around an optical nanofiber that guides elliptically polarized, fundamental modes. The orbit frequency is proportional to the helicity of the coupled light. Interestingly, the observed motion is opposite to the energy flow circulation around the fiber. This result verifies the theoretically predicted negative optical torque on a sufficiently large particle in the vicinity of a nanofiber

Evanescent field trapping and propulsion of Janus particles along optical nanofibers

Manipulation of Janus particles is challenging and has limited precision. Here, the authors propose manipulation of Janus particles by optical forces in the evanescent field of an optical nanofiber, and demonstrate that they exhibit strong transverse localization on the nanofiber and much faster propulsion compared to all-dielectric particles of the same size