Refractive-Index-Based Sorting of Colloidal Particles Using a Subwavelength Optical Fiber in a Static Fluid

An optical-fiber-based technique is presented for refractive-index-based sorting of colloidal particles in a static fluid. The method employs the different optical scattering forces exerted by a subwavelength optical fiber on colloidal particles with different refractive indices. By launching two counterpropagating laser beams at wavelengths of 808 and 1047 nm into a fiber of 800 nm diameter, the resultant scattering forces acting on polystyrene and SiO2 particles can be in opposite directions, which leads to a countertransport of the particles along the fiber. Experiments are performed using the fiber to sort the particles of 650 nm size.