Research On Graphene Modulators By Employing Enhancement Effect Of Surface Piasmon Polaritons

In optical fiber communication and on-chip integrated systems,electro-optic modulator that determines the bandwidth of optical signals is the core component of optoelectronic systems.Therefore,it's is important to improve performance of modulator for the development of modern optical communication systems.In recent years,graphene-based optical modulators has attracted much attention.This is due to the fact that graphene not only has excellent tunable optical characteristics,but also is compatible with CMOS technology,so the graphene modulator has gradually been considered as a potential candidate of electro-optic modulator.However,due to the diffraction limit,there is a serious scale-mismatching between the optical field of silicon waveguide and the monoatomic thickness of graphene.The scale-mismatching leads to the light can't couple to graphene and interaction between graphene and optical mode is weak,which results in low modulation efficiency and large device footprint.To overcome the issues,we will utilize the sub-wavelength confinement and enhancement mechanism of surface plasmons to improve performance of modulators.The main works are as follows:1.To overcome the problem of diffraction limit of the dielectric waveguide mode,we theoretically research the dispersion relation and field local characteristics of surface plasmon polaritons(SPP),It was found that the surface plasmons can confined well to the metal surface,break the diffraction limit,and achieve subwavelength confinement.On the other hand,a dispersion model and a voltage control method for the graphene permittivity are established.These provide theoretical basis for graphene modulator design with plasmonic waveguides.2.To overcome the problem of low modulation efficiency of graphene silicon modulators,a graphene modulator with a diagonal surface plasmon is proposed in this paper.The diagonal plasmon mode has a subwavelength limitation both in the horizontal and vertical directions,which greatly enhances the "light-graphene" interaction.The modulation efficiency of the modulator is 1.58 dB/?m and the insertion loss is 0.2 dB/?m.And the modulation efficiency is over one order of magnitude larger than traditional graphene-on-silicon modulator.3.To overcome the problem of large loss of plasmonic modulators,utilizing hybrid surface plasmon polariton(HSPP),we proposed double-slot graphene modulator with "Insulator-Metal-Insulator(IMI)" and "Metal-Insulator-Metal(MIM)" structure.The designed HSPP graphene modulator can effectively reduce the loss while having a high modulation efficiency.The modulation efficiency of MIM-HSPP is 0.81 dB/?m,and the insertion loss per length is 0.08 dB/?m,which is far less than the loss(?0.4dB/?m)of the previous plasmonic graphene modulators.