Nanostructured Antireflection Surface For Micrn-optics In Optical Communication Systems

The surface of the moth eye has a conical protrusion structure arranged periodically.The size of this tiny structure is generally smaller than the wavelength of light,so the surface of the moth eye is a sub-wavelength structure.When light is incident on such a nanostructure,since the light cannot see this subwavelength structure,this subwavelength structure can be regarded as a layer with a corresponding equivalent refractive index coating.An important feature of the sub-wavelength structure is its excellent anti-reflection performance,and its anti-reflection performance is very stable in a wide-angle wide-spectrum range.A nanostructured antireflection design is presented for micro-optics at multi-wavelengths in fiber optical communication systems.The finite-difference time domain(FDTD)method was used to search for a moth-eye nanostructure capable of significantly reducing reflectivity in the wavelengths ranging from 1250 to 1650 nm.A multi-objective optimization algorithm was developed to optimize the wideband reflectance up to an oblique incidence of 30 degrees.The optimization was implemented for a parameter space consisting of nano-pillar geometrical arrangements,radius,height and period.A near zero reflectance of 0.0287%was obtained by simulation at wavelength of 1550 nm.Experimentally a reflectance of 0.157%was measured at 1550 nm for the samples fabricated with the optimal design.Discrepancy between simulated result and experimental measurement was analyzed in view of change in reflective index with wavelength.This thesis also introduces the research background and current status of anti-reflection nanostructures,introduces the principle of moth-eye antireflection technology and its application in optical communication and other fields,describes several mathematical modeling methods for antireflection nanostructures and compares them The advantages and disadvantages of several methods,the principle of traditional anti-reflection coatings are analyzed,the characteristics of nanoimprint technology and the advantages in preparing sub-wavelength structures are introduced.This thesis mainly completed the following six parts:(1)Starting from the moth-eye bionic technology,the design and preparation of anti-reflection sub-wavelength structures are realized through nano-pillar arrays.The combination of simulation and experimental measurement proves that the anti-reflection structure designed in this paper is a practical and effective method to reduce the harm of reflected light to the optical components in the entire optical path in the optical communication system.(2)Explains in detail many different mathematical models that can be used to process and analyze the electromagnetic radiation generated by sub-wavelength anti-reflection structures.These methods include finite-difference time-domain(FDTD)methods,transfer matrix methods(TMM,modeling only thin films),strict coupled-wave analysis(also known as Fourier modal methods RCWA/FMM),and finite element methods(FEM)Etc.,and mainly compared FDTD method and RCWA method,and chose the FDTD method for mathematical modeling in this study.(3)The theory of single-layer ?/4 anti-reflection coating,double-layer ?/4 anti-reflection coating,and multilayer ?/4 anti-reflection coating is theoretically analyzed,and the calculation method of film reflectance is determined.(4)The characteristics of nano-imprint technology are analyzed,the three typical nano-imprint technology processes and their key technologies are introduced,the UV-curing imprint technology process used in this institute is introduced in detail,and the UV-curing imprint technology is used to carry out Preparation of Moth-Eye Antireflection Nanostructures Designed by the Institute.(5)Moth-eye anti-reflection structure was designed and optimized using FDTD Solutions software.The designed anti-reflection structure was prepared by nano-imprint technology.An experimental system was set up to measure the structure of the structure indirectly by measuring the fiber insertion loss.The reflectivity is compared and analyzed with the simulation results.(6)Aiming at the self-cleaning and anti-pollution properties of moth-eye nano-structures,the relevant experimental verification of the anti-reflection structure are designed in this research.