Research On Graphene-based Polarization-insensitive Electro-optic Modulator

An optical modulator is a device that converts other signals into optical signals,such as electro-optic modulator,thermo-optic modulator and acousto-optic modulator.Optical modulator is the key component of integrated photonic circuit,such as optical cross-connect systems and the optical add-drop multiplexer systems.In addition,it has also great application prospects in chip-level optical interconnection and optical computing technology.In recent years,two-dimensional material such as graphene has been widely studied due to its wide spectral absorption,high carrier mobility and CMOS compatibility.However,the graphene-based modulator is polarization-sensitive.To realize the commercial application of the graphene-based modulator,the problem of polarization sensitivity should be overcomed.Therefore some polarization-insensitive structures are desired to realize the goal.In this thesis,the performances of the graphene-based modulators with different structures,including ring resonant modulator,Mach-Zehnder modulator and absorption modulator,are analyzed with silicon waveguide.The polarization characteristics of the graphene absorption modulator based on a rectangular waveguide or an optical fiber are analyzed respectively.Then,a feasible structure of the polarization-insensitive modulator is proposed.The feasibility of the structure is also verified by simulation and experiment.The main contents of this thesis are as follows:1.Several common graphene modulator structures are simulated.The modulation performances of the modulators such as operating spectrum,3dB bandwidth and insertion loss are analyzed.The advantages and disadvantages of various modulators are compared.2.The waveguide mode theory is elaborated.Based on the theories of waveguide mode coupling and mode conversion,a graphene polarization-insensitive electro-optic modulator is proposed.The modulation performance of the modulator is analyzed by simulation.Based on the theory of mode conversion three polarization-insensitive electro-optic modulators with different structures are proposed and studied.They are double-arm graphene embedded modulator,single-arm graphene embedded modulator and double-arm graphene surface-covered modulator respectively.Finally,the advantages and disadvantages of three structures are summarized.3.To realize graphene-based and polarization-insensitive modulation in experiment,the structure of D fiber is used.The polarization characteristics of the D fiber graphene modulator are simulated and analyzed.Two segments D fiber structure is proposed to realize polarization-insensitive modulation.Firstly,the feasibility of two segments D fiber structure is analyzed theoretically by simulation software,and the polarization sensitivity of the modulator is further verified experimentally.