Research On Tunable Circular Polarization Devices Based On Helical Microstructured Optical Fibe

As a device for selecting circularly polarized light,circular polarizer is widely used in biomolecular detection,circularly polarized microscope and other fields.The traditional circular polarizer has some limitations,such as narrow working bandwidth and no support for wavelength tuning,which limits the development of circular polarizer to a certain extent.As a new generation of optical fiber sensor,microstructure optical fiber(MOF)has attracted the attention of many scholars because of its non-stop single-mode characteristics,controllable dispersion and rich optical nonlinear characteristics.The research and improvement of its characteristics have broad prospects and great scientific research value in the field of circular polarization devices.A tunable circular polarization device based on helical MOF is proposed in this paper.The fiber structure is designed by finite element method,and the characteristics of fiber size,helical torsion index and filling refractive index are analyzed.The research shows that the proposed circular polarization device realizes the characteristics of single circular polarization,that is,it can only transmit a single circular polarization state in the fiber core,and adjust the resonant wavelength position by changing the filling refractive index and torsion,so that the device has wavelength tunability.The scheme to realize tunability is proposed,and the experiment is preliminarily explored.The specific work contents are as follows:(1)Based on the principle of mode coupling,a single circular polarization helical MOF is designed.Based on the basic theory of optical fiber,the finite element method is used for model calculation.Combined with the orbital angular momentum theory and the coupled mode theory of optical fiber,the modeling method of helical MOF is proposed.Based on this,the structure of single circular polarization helical MOF is designed.The effects of fiber size,torsion index and refractive index filling on the characteristics of single circular polarization are analyzed.When hole diameter d =3.3μm.Hole spacing (?)=5.5μm.Torsion ratio α=8.9rad/mm,single circular polarization will occur when the filling refractive index n=1.42807,and the resonant wavelength will also change with the change of parameters,indicating that the helical MOF has wavelength tunability.(2)The wavelength tunable characteristics of helical MOF circular polarizer are analyzed by changing the filling refractive index and torsional index.When the filling refractive index changes between 1.42805～1.42811,the tuning sensitivity is150μm/rad/mm;When the torsion ratio varies from 8.86 to 8.94rad/mm,the tuning sensitivity is 0.635μm/rad/mm.Through the analysis of the single circular polarization bandwidth,it is concluded that when the resonant wavelength changes,the bandwidth basically remains unchanged,indicating that the helical MOF circular polarizer has more sensitive wavelength tunability.(3)Explore the fabrication and tuning experimental scheme of helical MOF circular polarizer.This paper analyzes and summarizes the construction and fabrication process of the experimental platform,discusses the fabrication method of spiral MOF circular polarization device,and puts forward the selective filling scheme and experimental tuning method of spiral MOF device.