Research On Optical Trapping Characteristics Of All-Fiber Near-Field Optical Tweezer With Twin Core Fiber

In 1986,American scientist Arthur Ashkin used the mechanical action of light to achieve three-dimensional trapping of particles,which they called optical tweezers.Optical tweezers have received widespread attention from researchers in fields such as biology,physics,and mechanics due to their non-contact and non-mechanical damage characteristics.After years of development,optical trapping technology based on optical tweezers has made great progress in two aspects: optical applications and optical manipulation.In terms of optical applications,researchers have achieved multifunctional applications such as optical driving,optical transmission,and optical measurement.In terms of optical manipulation,researchers have achieved manipulation of various samples,including dielectric particles of different sizes,biological molecules and biological cells.Due to the existence of the optical diffraction limit,the optical gradient force generated by Gaussian beams imposes limitations on the trapping and manipulation of nanoscale particles.In recent years,near-field optical tweezers have achieved a breakthrough in diffraction limit,providing new methods for manipulating nanoparticles.Therefore,near-field optical tweezers have become an effective tool commonly used by researchers in studying the microscopic world.This research purpose of this article is to improve and develop the study of near-field optical trapping in the microscale field,and to achieve a stable and non-destructive way to tarp nanoparticle.This article designs an all-fiber near-field optical tweezer with a double cone structure using twin core fiber as materials.Two laser beams from the twin core optical fiber propagate in the opposite direction on the end face.Interference effect enhances the gradient force used for trapping and manipulating nanoparticles.At the same time,the scattering force is cancelled out,ensuring stable optical trapping and manipulation.This research work of this article is simulating the distribution of the outgoing light field and the magnitude of the optical trap force experienced by particles in the trapping experiment.The gradient force is 2.77 p N when the laser power is 50 m W.At the same time,this study also simulates the distribution of temperature fields during the trapping process.The max temperature rise of an all-fiber optical tweezer is 0.0765 K.This result is much smaller than the temperature rise generated by other near-field optical tweezers.Finally,based on the simulation results and existing experimental instruments,an all-fiber near-field optical tweezer system based on a twin core fiber is proposed.This system is based on a twin core optical fiber as the substrate,and the optical fiber is ground twice at a grinding angle of 18° and 54° to obtain a double cone structure.This structure ensures that the laser is completely reflected at an angle of incidence of 72° on the end face of the optical fiber.Finally,the study achieves stable trapping and manipulation of 100 nm fluorescent particle.In addition,the temperature effect during the experimental process is measured using fluorescence dye measurement.The max temperature rise is 0.091 K.Compared with other near-field optical tweezers,the all-fiber near-field optical tweezer will not generate a significant thermal effect.