Study On Optical Fiber Tweezers Based On Laser-Induced Thermal Convection Effect And Its Application

Optical fiber tweezers have the advantages of simple preparation,strong controllability,small volume and low cost,and can capture and control the micro and nano scale particles such as biological cells in the liquid environment without contact,damage and with high precision.They are widely used in the field of biology and medicine.Compared with the traditional lens-based optical tweezers,the core idea of optical fiber tweezers is to integrate complex spatial optical paths into a single optical fiber,so as to achieve the function of system simplification and convenient operation.However,we have to accept the defect of single fiber tweezers when we get this progress.It is a technical problem for optical fiber tweezers to simplify the system of optical fiber tweezers and to control a large number of particles at the same time.In this paper,the laser-induced thermal convection effect and optical fiber tweezers technology are combined to achieve the operations of a large number of particles in the liquid environment,with the advantages of rapid non-contact,non-damage,large-scale capture,regular arrangement and sorting,which lay a technical foundation for the more extensive and practical application of optical fiber tweezers technology.This thesis focuses on the following work of the single fiber optical tweezers based on the laser-induced thermal convection effect:1.Based on the probe of tapered single fiber optical tweezers,this thesis studies the mechanism of laser-induced thermal convection effect,including the selection of laser wavelength,the distribution of optical field,the temperature distribution of laser-induced thermal field,the velocity distribution of thermal effect of the flow field and the velocity field distribution of particles driven by liquid.In addition,the optical trapping force produced by the probe of tapered single fiber optical tweezers is simulated and calculated.2.We proposed a new non adiabatic tapered single fiber optical tweezers based on the laser-induced thermal convection effect to realize the linear aggregation and regular arrangement of a large number of particles in the liquid environment.The so-called non adiabatic taper means that the optical power transmitted in the tapered fiber probe will be output from the side of the tapered fiber,and then the linear heat source will be constructed to realize the linear regular arrangement of a large number of particles in the liquid environment.In order to improve the energy conversion efficiency of laser-induced thermal convection effect,we plated a layer of metal film on the tapered area of optical fiber,and discussed the influence of the thickness of metal film on the conversion efficiency.In addition,the temperature field and velocity field of the nonadiabatic tapered fiber optical tweezers in the liquid environment are simulated and tested,and many factors affecting the particle distribution are analyzed and discussed to obtain the basic parameters of the optimal experimental effect.3.We studied a kind of adiabatic tapered single fiber optical tweezers based on laser-induced thermal convection effect,which realizes the regular arrangement and sorting of a large number of particles in the liquid environment.The so-called adiabatic taper means that when the optical power is transmitted in the tapered fiber probe,the power will not be output from the side of the tapered fiber,but will be emitted from the tip of the fiber,and then the point heat source can be constructed.At the same time,the output light field of the adiabatic tapered fiber probe meets the light field distribution conditions of the particles trapping,and can realize the capture and control of a single particle.Therefore,combined with the wavelength multiplexing technology,we realized the regular arrangement of a large number of particles and the modification of individual arrangement gaps.1480 nm laser light source is selected as the photothermal effect light source to realize the regular arrangement of a large number of particles;980nm laser light source is selected as the capture light source to realize the vacancy modification in the particle arrangement.In addition,using the characteristics of different particle moving different speeds in the flow field,the particles with different size and the same texture can be sorted quickly and efficiently.4.We designed an all fiber filter based on laser-induced thermal convection effect to collect and remove impurities in liquid environment.The laser produced by the tapered fiber probe can induce microbubbles in the liquid environment to excite the thermal convection effect in the liquid environment,so as to realize the rapid aggregation of impurities towards the microbubbles in the liquid environment and complete the collection of impurities in the liquid environment.In addition,we use hollow hanging core fiber to introduce hollow liquid channel,which can achieve impurity collection and export at the same time.That is,the function of impurity collection and removal is integrated into a fiber probe,which adds a fast and effective all optical method for impurity filtration in liquid environment.