Research On Diffractive Lens At The End Of Optical Fiber

In recent years,more and more optical fiber micro-lens are needed in the field of optical fiber technology.Fiber micro-lens is a fiber optical device that effectively transmits optical signals from one end to another port.It has great research value and application prospects in the fields of optical communication,sensing,laser signal processing and so on.Therefore,micro-lens based on optical fiber has become a research hotspot in the field of optical fiber technology.Fabrication of micro-lens on the end of the fiber is the most effective and low-cost method to promote the modal matching between fiber and laser signal,which can effectively improve the coupling efficiency of the laser signal.By forming a specific lens structure on the end face of the optical fiber,arbitrary light field conversion can be performed on the light emitted from the optical fiber.With the development of fiber micro-lens processing technology,it is easier to realize the optical field transformation at the fiber end.Femtosecond laser technology is one of the better technologies for manufacturing optical fiber micro-lens at present,which greatly enriches the preparation methods of fiber micro-lens.Based on the existing technology of processing optical fiber micro-lens,this paper focuses on the optical fiber end face micro-lens,and uses femtosecond laser processing technology to fabricate a Fresnel lens on the coreless fiber end face.The lens structure is numerically analyzed and verified by experiments.Firstly,the research progress of fiber micro-lens at home and abroad is analyzed,and the research method and content of this paper are put forward.Secondly,the principle and research progress of femtosecond laser processing technology are analyzed.At the same time,the wet etching principle is studied and the inclined cone lens is processed by femtosecond laser micromachining system.Finally,a "sandwich" combined optical fiber tweezers micro-lens structure is designed,and a Fresnel lens is fabricated on the end face of coreless fiber by femtosecond machining system.The numerical simulation of this lens structure is carried out,and the variation curves of horizontal optical trapping force and axial optical trapping force of this structure under different parameters are drawn.From the simulation results,it can be concluded that the transverse optical trapping force and transverse trapping range of particles will increase with the increase of particle radius or refractive index,but the transverse trapping position will remain unchanged.Through simulation,it is also found that the axial gradient force on the particles is small,and the particles cannot be stably captured in the axial direction.Therefore,when we do the experiment,the optical fiber and the sample cell are at a certain angle,so that the horizontal components of the gradient force and scattering force are balanced,and thus the particles can be manipulated in two dimensions.The experiment proves the feasibility of the theory.