Massive photothermal trapping and migration of particles by a tapered optical fiber

A simple but highly efficient method for particles or bacteria trapping and removal from water is of great importance for local water purification, particularly, for sanitation. Here, we report a massive photothermal trapping and migration of dielectric particles (SiO2, 2.08-mu m diameter) in water by using a tapered optical fiber (3.1-mu m diameter for taper). With a laser beam of 1.55 mu m (170 mW) injected into the fiber, particles moved towards the position, which is about 380 mu m away from the tip of the fiber, and assembled at a 290 mu m x 100 mu m spindle-shaped region. The highest assembly speed of particles is 22.1 ind./s and the highest moving velocity is 20.5 mu m/s, which were induced by both negative photophoresis and temperature gradient. The number of assembled particles can reach 10,150 in 15 minutes. With a move of the fiber, the assembled particles will also migrate. We found that, when the fiber was moved 172 mu m away from its original location, almost all of the assembled 10,150 particles were migrated to a new location in 140 s with a distance of 172 mu m from their original location. (C) 2011 Optical Society of America