Near-Field Optical Trapping Used For Micro/Nano-Particles

Since invented in the 1980 s,optical tweezers have been applied in life science,chemical and quantum technology.The development of nano-fabrication promotes the occurrence of near-field optical tweezers on a chip which are highly compact and able to trap smaller particles compared with traditional optical tweezers,and a lot of functions,such as trapping,filtering,and sorting,can be achieved by designing certain structures.In this work,different optical waveguides are investigated to solve problems related to life science and quantum technology.The main contents and innovations are as follows.1.A physical model is established which is used to simulate the trajectories of particles.All of forces exerted on the particle,such as the optical force,the drag force,the gravity,the buoyancy,are all taken into consideration in this model,and the solutions of motion equations of particles in the system are given.2.A low-loss tapered and cascaded waveguide is proposed based on guided-wave optics in order to trap several cells simultaneously on a chip.The optical gradient force,which is created by the electric field gradient,offsets the optical scattering force in the waveguide,and optical potential wells occur.According to the simulation,cells whose diameters range from 1 to 5 μm are trapped in the waveguide,and for 2.5-μm-diameter cells,lateral stiffness and longitudinal stiffness are 616 p N/(W·μm)and 120 p N/(W·μm)respectively.Besides,the transmission of the waveguide is 96%.Combined with microfluidic devices,a cascaded waveguide is able to trap tens of cells at the same time,thus providing a practical tool for studying the properties of cells.3.Two different optical tweezers are proposed to trap quantum dots,and the spontaneous emission rate and the coupling efficiency of a quantum dot increase.These optical tweezers can integrate steps including positioning,excitement,and coupling of quantum dots.Two plausible optical tweezers used to trap nanodiamonds are introduced in this thesis.After the optimization of optical waveguides and nanodiamonds’ shapes,the Purcell factor is 1.4 and the coupling efficiency is 64%.