Multiple particle trapping and self-organization in the evanescent fields of optical micro- and nanofibres

Abstract

Evanescent fields in optical micro- and nanofibres (MNF) have been proposed as efficient means for multiple microparticle trapping and prolusion [1, 2]. Here, we demonstrate the propulsion of 3 µm polystyrene particle chains in the evanescent fields of the fundamental and first higher order modes in an MNF system. The power at the waist was estimated to be 25mW in both cases Self-assembly and speed variation of particle chains was observed. This observation implies that strong optical interactions between trapped particles within a particle chain occur along the fibre waist region The effect is associated with the long-range, one dimensional optical binding. The numerical finite element and analytical scattering-matrix approaches were used to investigate the field dynamics surrounding the trapped particles. The optical forces and velocities of bound particle chains were calculated using these particle-field dynamics. Both the analytical and numerical analyses show good agreements with the experimental data The observation reveal that higher order modes in a microfibre offer stable multiple particle trapping faster particle propulsion speeds, and allow for the capability to better control each individual trapped object in particle ensembles near the microfibre surface compare to the fundamental mode [3].