Theoretical Analysis Of Optical Force Density Distributions At Subwavelength-Diameter Optical Fiber Endfaces

Optical force effects have been extensively studied and applied in optical tweezers,optomechanical systems,and integrated optical waveguides.In particular,subwavelength-diameter optical fiber is an ideal platform for studying optical force due to its unique optical waveguide characteristics(low optical loss,strong evanescent field,tight optical confinement),small mass and freely movable one-dimensional structure.With the application o f the optical force effect o f subwavelength-diameter optical fiber and the publication o f the experimental results o f the momentum exchange,the optical force of subwavelength-diameter optical fiber has received extensive attention.A deep understanding o f near-field forces and motion trends in subwavelength-diameter optical fibers will be of great significance for the further development o f subwavelength-diameter optical fiber optic devices.Since the specific optical density distribution inside subwavelength-diameter optical fiber is still unknown,in order to understand the optical density distribution and its deformation trend inside subwavelength-diameter optical fiber more intuitively and deeply,to overcome the inapplicability o f the analytical method,the optical density distribution in subwavelength-diameter optical fiber is studied in depth by using the numerical calculation method o f three-dimensional finite difference time domain.In this paper,the Maxwell's equations are solved by using three-dimensional finite difference time domain method.The Einstein-Laub formula is used to obtain the internal optical density distribution o f the fiber with flat end face and inclined end face under the action o f x-polarization and y-polarization fundamental mode.The following conclusions:1 ? Under the action of HE11 fundamental mode,the lateral force inside subwavelength-diameter optical fiber with flat end face is the compressive force,and the edge o f it is the tensile force.There is no net lateral force due to the axial symmetry o f the cross section.The internal optical force density o f subwavelength-diameter optical fiber has a significant periodic distribution in the longitudinal direction,the direction o f f z alternates along the positive z-axis or the negative z-axis,and the amplitude near the end face is the largest,and the resultant force is the tensile force along the positive z-axis.2 ? Under the action of HE11 fundamental mode,due to subwavelength-diameter optical fiber with the 20 degrees inclined end surface loses the axial symmetry o f the cross-section along the x-direction,the end o f optical fiber is subjected to lateral optical force,which is along the positive x-axis.Under the action o f the x-polarization fundamental mode,the optical force density does not have a significant periodic distribution in the longitudinal direction,the internal lateral force is the pressing force,and the lateral force o f the edge has a large tensile force along the x-direction;The longitudinal force is mainly thrust along the negative z-axis.Under the action o f the y-polarization fundamental mode,the optical density has a periodic distribution parallel to the inclined end faces near the end faces,while generating a lateral force along the x direction that is larger than the x polarization.It is revealed for the first time that the lateral shift of the fiber is the result of the synergistic effect o f the lateral optical force and the axial optical force,which help us to understand the reasons for the force o f the inclined end subwavelength-diameter optical fiber.Our results will help to analyze the distribution o f optical force density in subwavelength-diameter optical fiber and other complex structures,and predict the deformation trend after its optical force action.It will have important reference significance for improving and optimizing the performance o f photonic devices based on subwavelength-diameter optical fiber photodynamic effect.