Research On Microparticle Manipulation And Transportation Based On Multi-fiber Thermal Convection

In the field of micromanipulation,the application of optical tweezers technology is mainly divided into two categories.The one is the micromanipulation technology based on the optical force effect,which can achieve the capture and manipulation of high refractive index medium particles.The other is the micromanipulation technology based on the photothermal effect,which can be applied to the capture and manipulation of absorbent particles.At present,both of them have trouble in the complicated structure,difficult operation,low accuracy and small control range in practice.In view of this situation,this thesis combines optical fiber tweezers with thermal convection manipulation technology,and proposes the manipulation and transportation method based on multi-fiber thermal convection.Through reasonably arranging multiple optical fibers,and designing the manipulation and transportation devices from both horizontal and vertical aspects,this work achieved precise manipulation and transportation of microparticles.The introductioin of optical switches,beam splitters,fiber arrays,etc.achieved the circular transportation and continuous transportation over large distances of particles,which provides an insightful idea for the development of micromotors and optical fluid chips.The main research is as follows:Firstly,this thesis reviews and discusses the development and research of microparticles manipulation based on optical force and photothermal effects,and a technical solution for particle manipulation and transportation based on the multi-fiber thermal convection effect is proposed.Combined with the actual manipulation process,the theories and principles involved are analyzed and the related formulas are derived.And it is the basis of simulation calculation and experimental preparation in this thesis.Secondly,the optical trap force involved in the optical fiber thermal convection system was calculated using the finite element numerical method,and the physical process near the fiber port was simulated and analyzed by the finite element software COMSOL Multiphysics 5.3a.When the power of light source is 20mW,the flow rate of thermal convection field is up to 80μm/s in horizontal fiber system.When the power of light source is 30mW,the flow rate of thermal convection field is up to 120μm/s in vertical fiber system.It theoretically proves the feasibility of particle manipulation.with the simulation results,an experimental platform based on multi-fiber thermal convection was established.The temperature difference of the aqueous solution was actually measured by the fluorescence temperature measurement method.And two kinds of particle transport devices based on the thermal convection of horizontal multi fiber and vertical fiber array are designed.Finally,with the help of multi fiber thermal convection devices,the circular transportation and long-distance continuous transportation of SiO₂particles are realized.In the process of circular transportation,the transport path of particles is precisely controlled by adjusting the height of optical fiber.In the process of continuous transportation,when the number of optical fibers is 31,with the cooperation of 1×8optical switch and 1×2 optical splitter,SiO₂particles with a diameter of 100μm are continuously transported in two channels with a maximum distance of 7.5 mm.