Bidirectional optical transportation and controllable positioning of nanoparticles using an optical nanofiber

This work provides a technique allowing bidirectional optical transportation and controllable positioning of nanoparticles using two counter-propagating laser beams at a wavelength of 980 nm in an optical nanofiber. With the assistance of an evanescent wave at the fiber surface, particles suspended in water were trapped onto the fiber by a gradient force and then transported along the fiber by a scattering force. By changing the difference between the input laser powers coupled into two ends of the fiber with ΔP = -10 to 10 mW, the magnitude and direction of the scattering force that acted on the particles were changed, and thus the transportation direction and velocity of the particles were controlled. According to these properties, the bidirectional optical transportation of the particles along the fiber can be realized by coupling different laser powers into the two ends of the fiber (ΔP≠ 0 mW). At the same time, the transported particles can be controllably positioned on the fiber by coupling the same laser powers into the two ends of the fiber (ΔP = 0 mW). The relationship between the transportation velocity of the particles and the input optical power difference was investigated. Experiments were conducted with a 910 nm diameter fiber and 713 nm diameter polystyrene (PS) particle suspensions to demonstrate the effectiveness of this method. The experimental results were interpreted by numerical simulation and theoretical analysis.