Field distribution of optical fiber probe for trapping particle

摘要

The technique of optical fiber trapping has been successfully used to manipulate small particles, while near field optical tweezers based on the sub-wavelength size fiber tip has been proposed to trap nanometric particles. With some similar physical mechanism and properties they are investigated and analyzed respectively in this paper. Firstly the optical field distributions of uncoated fiber probe with different radii of tip, from several microns down to zero, are calculated and analyzed by 3D finite-difference time-domain (FDTD) method. Then the metal-coated fiber probe is also discussed in the same way. In conclusion, the light from the fiber probe with the radius larger than wavelength is converged at a cometic spot, whatever with or without metal coating. When the radius of metal-coated tip is smaller than half of wavelength, the evanescent field occurs and decays rapidly. The local field enhancement dominates in the metal-coated probe if the radius is smaller.