Research Of Optical Force Through Evanescent Field Coupling Of Micro/Nano Fiber Based On White Light Interferometry

Micro-/nano-fiber(MNF) has some special advantages such as strong evanescent field, small weight and excellent flexibility. With these advantages, MNF has been used as basic optical components in building optical devices. It has been found that MNF can be used in investigating physical fundamental problems,such as Abraham-Minkowski dilemma, and in the application of optical force. However, in those researches,the light-driven displacement of nanofiber was phenomenally observed by microscopy and cannot be measured accurately and quantitatively, which impedes the further investigation with the MNF. Therefore, it is significant to measure the transverse displacement of micro-/nano-fiber induced by optical forces.In this paper, a method based on white light interferometry is proposed to measure the nanometric displacement of MNF. Under the illumination of white light source, the color interference pattern is observed on the surface of MNF when the gap between the MNF and glass substrate is smaller than the coherence length of the white light source. There is a linear relationship between the displacement of MNF and the shift of the interference pattern. After calibrating their linear relationship, the displacement of MNF can be measured by measuring the pattern shift. Then this method is used to measure the light-driven displacement of MNF. The results show that this technique has high linearity, sensitivity and resolution.What’s more, the system can archive a very high optomechanical efficiency.The mechanism of light-driven effect is studied in this paper, mostly about optical effect and thermal expansion effect in the experiments. Compared to FDTD simulation of optical force effect at different gaps,the experiment results show that optical effect exists in the experiment. And then the thermal expansion effect is measured and analyzed. Note that thermal expansion effect contribute little in the light-driven effect. This research is the basis of deeper research of optical momentum theory.The innovations of this work lie in:1. The light-driven effect induced by the coupling between the evanescent field of MNF and glass substrate could be observed in experiments.2. A method is proposed to measure the nanometric light-driven displacement of MNF and the sensitivity,resolution, stability and repeatability of the method is studied.3. A method to estimate weak optical force is proposed.4. Through experiment results, the optical force effect is proved.