Study Of Fundamental Mode Bessel Optical Fields In Trench-assisted Optical Fibers

Bessel beams have important applications in the field of biomedical optical imaging.Most current methods for generating Bessel beams have spatial optical paths.Due to the high stability of fiber optic systems,this paper investigates the method of generating Bessel beams based on fiber optics.The fiber cross section not only regulates the characteristic parameters such as dispersion,nonlinear coefficient and mode field area of the fiber,but also has a strong ability to modulate the optical field transmitted in it.In this thesis,we focus on the generation of fundamental mode Bessel optical fields based on trench-assisted optical fibers.First,the research background and significance of this topic are introduced,the mathematical mechanism of Bessel beam generation is studied theoretically,the method of Bessel beam generation is introduced,the calculation principle and building process of the full vector finite element software are described,and the optical field distribution in optical fibers is studied based on the theory of mode analysis in fluctuating optics.Secondly,a single-core trench-assisted fiber formed by nesting rings with different refractive indices to each other will be designed based on the mode analysis theory,and the HE₁₁ mode field characteristics of the fiber will be investigated using the finite element method to explore the generation bands of different forms of Bessel beams.The effect of wavelength and fiber cross-sectional structure parameters on the HE₁₁ mode Bessel light field generated by this fiber is further investigated using fiber optical field modulation method,which lays the foundation for discussing the effect of toroidal Bessel beam on the resolution of oblique right-angle imaging system for the application of Bessel beam in practice.Finally,this thesis will propose 4,9 and 16 core trench-assisted fibers in a rectangular arrangement based on single core trench-assisted fibers,and discuss and analyze three types of multi-core trench-assisted fibers.Based on the finite element method and mode coupling theory,the effects of wavelength and different structural parameters on the optical field distribution of the fiber to generate Bessel beams are investigated to obtain the parameter range that can generate Bessel beams.