Study Of Silicon-based Graphene Optical Waveguide And Its Modulation Characteristics

In optoelectronic integrated circuits,one of the most critical devices is the electro-optic(EO)modulator.The shortage of high-speed and small-footprint EO modulator remains a critical challenge until recent researches on graphene,which has unique optical and electrical properties.In this paper,according to the principles of graphene's Fermi level tunability and surface plasmon resonance,we design two graphene modulators based on silicon.And the performances of the two modulators are analyzed and optimized theoretically.First,the electrical and optical properties of graphene are introduced,including graphene's conductivity,refractive index,dielectric constant,chemical potential and the principle of graphene's Fermi level tunability.Then,the theory of surface plasmon resonance(SPR)is introduced in detail in two categories.One is the surface plasmon polaritons(SPP)and the other one is the localized surface plasmon resonance(LSPR).The properties and advantages of various waveguide structures based on SPP are also introduced,such as MIM waveguide,IMI waveguide,hybrid surface plasmon waveguide,dielectric loaded surface plasmon waveguide and so on.Then,a four-layer graphene modulator based on surface plasmon waveguide was designed and optimized.By using the metal/dielectric/silicon/dielectric/metal(MISiIM)waveguide structure combined with graphene,the modulator achieves a good balance between the modulation depth and insertion loss.The effects of the structure parameters and the dielectric material's refractive index on the modulation depth,insertion loss,modulation bandwidth and power consumption of the device were simulated and analyzed.After optimization,the modulation depth and the propagation loss of the modulator are 0.524dB/?m and 0.05dB/?m respectively.And the figure of merit is 10.9.The obtained modulation bandwidth and power consumption are 150 GHz and 0.607pJ/bit respectively.Finally,we designed a double-layer graphene modulator based on LSPR with a hybrid waveguide consisting of a chain of metal disks on silicon waveguide.By combining the hybrid waveguide with graphene,the length of the modulator can be reduced to less than 1?m.Simultaneously,the effects of the structure paramters on the transmission characteristics of the device were analyzed.With a length of only 740 nm,the extinction ratio of the modulator can reach 5.5dB and the insertion loss of the modulator is 1.9dB.The modulation bandwidth and power consumption of the device are 211 GHz and 4.47fJ/bit respectively.