A Research Of Structure And Properties Of Electro-Optical Modulator Based On Graphene On Silicon Slot Waveguide

Electro-optic modulators are an important part of optical communication and optical interconnection.With the rapid development of communication networks,current electro-optic modulators have the disadvantages of narrow bandwidth,large volume,and high loss.In recent years,because graphene has unique electrical and optical properties,researchers have focused their research on graphene materials.For example,the high optical coupling efficiency,there is no selectivity for light absorption,high carrier mobility at room temperature and compatible with CMOS process.Therefore,the electro-optic modulator based on graphene has become a research hotspot in recent years.The development and trend of optical fiber communication is first introduced and then the working principle of the traditional electro-optic modulator is summarized.The modulators are divided into three categories according to the materials used including LiNbO₃ electro-optic modulator,III-V group semiconductor electro-optic modulator and organic polymer electro-optic modulator and the advantages and disadvantages of electro-optic modulators based on different materials are analyzed.The electrical and optical properties of graphene are introduced,including strong interaction with light,high stability and flexibility,and high carrier mobility.This makes it easy to adjust its chemical potential and carrier concentration by field effect and gate voltage.The variation trend of the conductivity,dielectric constant and refractive index of graphene with the chemical potential of graphene is analyzed.Graphene-based slot waveguide is compared to graphene-based strip waveguide by COMSOL software.The result shows that the center energy of the graphene-based slot waveguide is greatly improved compared with the graphene-based strip waveguide,and the electric field intensity in the slot waveguide is more uniform.The graphene-based SiO₂ slot waveguide is then compared to a graphene-based air slot waveguide.Compared to air-slot waveguide,SiO₂ slot waveguide results in smaller device sizes and power consumption when the total transmission loss is equal.By analyzing the influence of the size of the slot waveguide on the MPA value and modulation depth of the modulator,the variation of the waveguide performance with the size is obtained,which lays a solid foundation for the design of the electro-optic modulator.Based on the above analysis,a graphene waveguide polarization independent electro-optic modulator is proposed.The polarization independence is analyzed,when the chemical potential of graphene is in the range of 0.42¹ eV,the real change of the effective refractive index of TM and TE modes are 0.015 and 0.015,respectively,and the waveguide loss curves of the two modes coincide.TM and TE modes are very consistent with real changes in effective refractive index and unit transmission loss,it can thus be seen that the electro-optic modulator has the same modulation effect for the TM and TE modes.In order to optimize the phase modulation capability of the structure,a graphene-based single-slot waveguide phase modulator is proposed.Through COMSOL software simulation analysis,the real part of the effective refractive index changes up to?Re(N_eff)=0.0259 in the range of 0.43¹ eV,and the imaginary part of the refractive index remains at a low level;When the voltage is in the range of 1.133².206 V,the TE mode produces a?phase transition,which requires a modulation length of 65?m.When the modulation length is set to 150?m and the voltage is changed from 1.133 to 6.1 V,the TE mode can achieve a phase change of 5?.In addition,this phase modulator has a 3 dB modulation bandwidth of up to 108.6 GHz and realizes the power consumption of the?phase as low as0.073pJ/bit.