Design Of Waveguide Mode Converter Based On Digital Metamaterials

The mode converter can realize the free conversion of different modes in optical waveguides and excite or shield specific modes.Waveguide mode converter is the key component to realize the mode division multiplexing(MDM)system and plays an important role in integrated photonic circuits.Digital metamaterials use elemental materials with different dielectric constants to synthesize electromagnetic materials with required parameters.Specifically,digital metamaterials abstract each design unit into two states of‘0'and‘1'.‘0'and‘1'correspond to different materials,and by changing the 01 arrangement of each design unit,different material structures can be obtained,thus realizing special functions and applications.The introduction of digital metamaterials in the design of waveguide mode converters can simplify the design idea,improve the design freedom and reduce the design difficulty.The work completed in this paper is as follows:1.In the research background,the basic concepts and functions of waveguide mode converters are introduced firstly,and then the definition of digital metamaterials is described.Finally,the research status of mode converters and digital metamaterials at home and abroad is introduced.2.The theoretical basis of design of waveguide mode converter based on digital metamaterials is introduced,including mode transmission characteristics of planar optical waveguide,design theory of digital metamaterials,topology optimization theory,moving asymptote method,finite element theory,etc.3.The design process of the mode converter is discussed,including the design of the planar optical waveguide that can transmit four TE modes,the design of the digital metamaterial functional area on the waveguide,the creation of the optimization objective function,and the adjustment of the parameter Settings in the numerical optimization process.4.Analyze the design results and divide the designed six mode converters into two types according to the mode conversion characteristics.The first type is the conversion from fundamental mode(TE0)to higher order mode(TE1,TE2,TE3),and the second type is the conversion from higher order mode to higher order mode(TE1-TE2,TE1-TE3,TE2-TE3).The structure distribution,internal magnetic field,power flux distribution and transmission efficiency of the two types of mode converters are discussed.The digital metamaterial functional area composed of silicon and air designed in this paper realizes six different mode conversions through different combinations of silicon and air in a small area(1550nm×1000nm),and has high transmission efficiency,compact structure and large working bandwidth.