Optically Induced Sieve Effect for Nanoparticles near a Nanofiber Taper

We demonstrate size-selective optical trapping and transport for nanoparticles near an optical nanofiber taper. Using a two-wavelength counterpropagating mode configuration, we show that 100-nm-diameter and 150-nm-diameter gold nanospheres (GNSs) are trapped by the evanescent field in the taper region at different optical powers. Conversely, when one nanoparticle species is trapped the other may be transported, leading to a sievelike effect. Our results show that sophisticated optical manipulation can be achieved in a passive configuration by taking advantage of mode behavior in nanophotonic devices.