  An original optical tweezers using one or two chemically etched fiber
nano-tips is developed. We demonstrate optical trapping of 1 micrometer
polystyrene spheres at optical powers down to 2 mW. Harmonic trap potentials
were found in the case of dual fiber tweezers by analyzing the trapped particle
position fluctuations. The trap stiffness was deduced using three different
models. Consistent values of up to 1 fN/nm were found. The stiffness linearly
decreases with decreasing light intensity and increasing fiber tip-to-tip
distance.
