Design And Implementation Of Special Single Optical Fiber Tweezers

The optical tweezers technic uses laser beams to trap and manipulate micro particles in a non-invasive way,thus it won't injure the cells and influent the environment around the cells.The biological cell itself has a good penetrability to light,making the optical technic especially suitable to be used in the manipulation of biological cells.Thus the studying of optical tweezers helps to promote the development of biochemistry and biophysics,which needs to study the single molecule independently.The optical fiber tweezers has the advantages of small size,flexible manipulation and low cost,it has unparalleled advantages to promote the development of biomedical,biophysical and other fields.At present,the existing optical fiber tweezers are still in the stage of laboratory exploration and research.In order to make it applied in the real life solving the problems we faced,the completeness of function still needs researchers to continue to explore.To develop more flexible and convenient optical tweezers which can meet the practical needs,this paper combines optical tweezers and special optical fibers to realize some control functions that conventional optical fiber tweezers are difficult to realize,and continue to improve the function of optical fiber tweezers,broaden its application areas.First,the origin and development of optical fiber tweezers are briefly reviewed in this paper.According to the existing optical fiber tweezers,the optical fiber tweezers are classified according to the grinding method,the heating and drawing method,the chemical etching method and the high-precision micromachining method respectively,and the application fields of the optical fiber tweezers are listed.Second,the mechanism of fiber optic tweezers is analyzed,from the fiber mode theory,light trap force calculation and other aspects.Firstly,the principle of optical tweezers is analyzed,and the reason why the optical tweezers can capture the particles is the balance between the gradient force and the scattering force.What is linear polarization mode,the characteristics of linear polarization mode and LPmn mode and the relationship between LPmn mode and vector mode are introduced.From the general to the special,the LP₁₁ mode is analyzed separately,and the optical potential well characteristics of LP₁₁ mode are analyzed.Finally,the electromagnetic force model and the third kind of particle model are introduced to analyze the force of the particles at different scales,and the FDTD algorithm is introduced to realize the optical trap force simulation and calculation.Third,in this paper,the optical characteristic of the elliptical core is studied.The LP₁₁ mode is simulated by the optical simulation software,and the distribution of the LP₁₁ mode in the elliptical core is verified by experiments.It is found that the LP₁₁ mode can stays stably in the long axis of the optical axis of the elliptical fiber,and rotates with the fiber almost simultaneously.Based on this characteristic,this paper presents a single-fiber optical tweezers based on elliptical core fiber.A wedge-shaped fiber probe is fabricated by grinding method.The LP₁₁ mode is used to trap and rotate the yeast particles in the front of the fiber probe,the yeast particles can be synchronized rotates with the optical fiber.Fourth,this paper proposes a novel single-fiber optical tweezers to capture and move a single droplet.On the one hand,the annular core is polished to a truncated cone shape as a fiber optic tweezers probe,the beam focus point and fiber optic tweezers probe face is separated,thus it can achieve long-range trap,and the space reserved can be used to manipulate a single micro droplet.The annular core in the annular core fiber is equivalent to the stack of many symmetrical distributed double cores,so that the optical trap formed by the focused optical field emitted by the annular core optical tweezers has a stronger capture force.The superposition of these two advantages,so that we can successfully trap liquid microspheres and move it in 3 dimensions in the experiment,which have diameters ranging from a few to several tens of microns.