Research On Mode Converters Based On Zero Index Metamaterials

Compared with traditional electric signals transmission,optical signal transmission has the advantages of short response time,no electromagnetic interference and no thermal loss.Integrated photonic devices are widely used in optical sensing,optical computing,and optical communications.As an important component of integrated photonic devices,mode converter plays the role of signal conversion and transmission control in them.The study of small-size mode converters with high mode conversion efficiency and transmission efficiency is of great significance for the development of integrated photonic devices.At the same time,zero index metamaterial(ZIM),as an important component of artificial electromagnetic metamaterials,has been widely concerned because of its special properties in phase modulation.This paper mainly studies the mode converter based on zero index metamaterials,and analyzes the final designed structure and evaluates the result of mode conversion.The details are as follows:Firstly,we analyze the characteristics of ZIM in detail,and an example of its application in the air waveguide with perfect boundary condition to realize the mode conversion effect is given,and analyze the factors affecting the mode conversion effect.We prove the possibility of using these waveguide materials to realize the double zero index metamaterials by calculating the band structures of the photonic crystals of silicon and silicon nitride.Secondly,we design the initial functional area structure of the mode converter with metal boundary based on the existing theories and experience.In order to improve the efficiency of mode conversion,we introduce the structural topology optimization method to optimize the structure of functional area.Finally,the design and optimization of high-quality mode converter in silicon and silicon nitride waveguide are completed.The length of the functional area of the silicon waveguide mode converter is only 1 ?m,and the transmission efficiency at the center wavelength is 0.95,and the mode purity is 0.998,which realizes the high efficiency mode conversion.Finally,in order to design a high-quality mode converter that is easier to manufacture,we also conducted research on non-zero index mode converters.Both of initial structure have obtained high quality mode converter structure,after being optimized.The 2D and quasi-3D finite element models are used to evaluate the effect of mode conversion in multiple dimensions.