Measuring And Utilizing Femto-Newton Optical Force Based On Evanescent Field Coupling

Optical force determines the fundamental process of momentum exchange between light and matter.However,owing to ultra-weak mechanical effect of optical force and relative large stiffness of optomechanical devices,pico-Newton(10^-12N)optical force is required to manipulate micro-/nano-particles and optical response of optical devices.By far,it is still challenging to sense static femto-Newton(10^-15N)optical forces and exploit it to actuate micro-optical devices.On the other hand,micro-/nano-fiber?MNF?has some unique advantages such as strong evanescent field,ultra-low stiffness and small weight.With these advantages,by evanescent field coupling,femto-Newton optical force can be generated on MNF.The accurate measurement of this femto-Newton optical force provides evidence for solving Abraham-Minkowski dilemma.Moreover,the measuring method of femto-Newton optical force provides feasible reference method for sensing ultra-low forces,such as intermolecular and intramolecular interaction forces.Besides,utilizing femto-Newton optical force for all-optical manipulation reduces the power consume in optomechanical devices.Here,using a tapered nanofiber?TNF?with ultra-low stiffness,an ultra-sensitive and cost-effective scheme is demonstrated to generate,sense,and exploit f N optical forces.According to the method we exploited,using equipartition theorem and evanescent field coupling,stiffness of TNF has been measured as 0.54f N/nm,sharing the same order of theoretical prediction.Meanwhile,white light interferometry method for nanometer deformation detection is exploited,for maximum deformation as 400.7nm and minimum as 10.0nm causing by optical forces have been measured,indicating the ultra-weak optical force as 5.4fN can be detected.Moreover,with the extremely low optical force induced by evanescent field coupling as 61.2fN/mW,combining with the ultra-low stiffness of TNF,utilization of femto-Newton optical forces is realizable.As demonstrated below,an all-optical wide spectrum optical power control system using fN optical forces has been achieved.As the strong evanescent field coupling between TNF and glass substrate,pump light generates femto-Newton optical forces ranging from 5.4fN to 216.4f N,resulting a wider range than290nm of probe lights are all-optically tuned with maximum modulation depth of1.42dB/mW.The innovations of this work lie in:1.Presented a method to measure femto-Newton optical force.2.Presented a method to measure the stiffness of micro-/nano-fiber?MNF?.3.Utilizing femto-Newton optical forces for all-optical wide spectrum optical power control.