Optical trapping of microparticles with cascaded tapered waveguides

Recently, near-field optical tweezers integrated on a chip based on silicon on insulator (SOI) have attracted more attention and are promising for biological and chemical analyses. Here we propose a low-loss tapered Si waveguide with a high-intensity gradient in the electric field to trap microparticles whose diameters vary from 1 mu m to 5 mu m. The high transmittance allows for cascading the traps along the direction of light propagation. Optical forces in all three dimensions are analyzed around a high-stiffness potential well obtained.