光纤光阱力计算的近似条件及误差分析

Analysis of Approximate Conditions and Error of Trapping Forces in a Fiber Optical Trap

光纤光镊技术利用光纤出射的光束捕获和操控粒子,其飞速发展对光阱力的理论研究提出了更高的要求。采用射线光学模型对光纤光阱中的米氏微球所受到的光阱力进行数值模拟,讨论了光阱力计算中可采用的近似条件及其应用范围,比较了在近似条件下与直接计算情况下结果的差异,分析了微球与光纤端面之间的距离对近似计算的影响。理论分析和模拟计算表明,当微球与光纤端面之间的距离大于临界值时,可对计算模型中光束在微球表面的入射角、入射点的方位角等角度参量作近似处理,该结论为简化光纤光阱力计算提供了理论依据。

Fiber optical tweezers capture and control particles with fiber output beam. The fast development of fiber optical tweezers puts forward higher requirements to the theoretical study of trapping forces. Numerical simulation of trapping forces of Mie particle whose diameter is larger than the free-space wavelength is done, the approximate conditions in trapping forces calculating and its applied range are discussed, the result of direct calculating and the result calculated under the approximate conditions are obtained and compared. Influence on approximate calculating caused by the distance between particle and fiber end is analyzed. The numerical results show that when the distance between particle and fiber end is larger than a certain value d, which is related to radius of waist beam, some angle parameters such as the incidence angle and the azimuthal angle can be approximated, and the conclusion provides theoretical reason for simplified fiber optical trapping force calculating.