Study Of Graphene-Based Hybrid Plasmonic Modulator

Recent years,traditional optical modulators are difficult to keep up with the development of optical fiber communication.Optical modulators with high-speed,boardband,compact footprint are urgently required.Graphene,two-dimension material with a honeycomb lattice structure,possesses out-standing electrical,thermal and optical properties.This thesis tends to design the Mach-Zehnder thermo-optic polymer modulator with graphene-thermode and the graphene-based hybrid plasmonic electro-optic modulator,focusing on modulation mechanism,structure simulation and performance analysis of the device.Metal,such as aluminum,is often used as the heating electrode for polymer thermo-optic modulator.In these cases,thick upper cladding layers are necessary in order to avoid the light absorption of the metal.This will result in longer response time,higher power consumption of the device and also directly reduce the extinction ratio.To solve this problem,this paper designs a Mach-Zehnder thermo-optic polymer modulator with graphene-thermode based on the theory of optical waveguide and thermo-optic effect.Due to the weak light absorption of graphene,the heating electrode can directly contact the core layer.With superior thermal conductivity of graphene,this structure improves the thermal efficiency and time response of the device.The simulation results show that for modulator with only 50 ?m-long graphene heating electrode,power comsumption is 2.1 mW,heating efficiency is 50 K/mW,and response time is only 290 ?s.For incident light wavelength of 1550 nm,the extinction ratio is as high as 51.7 dB.Experimentally,this paper improves the process of wet transferring graphene and also characterizes the graphene transferred by the new method using optical microscopy,Raman spectroscopy and scanning electron microscope.Draw from the results,the tape-assisted method can reduce the breakage of transferred graphene.Combined with the traditional microfabrication technology,this paper carries out experiments of the fabrication for the graphenebased polymer thermo-optic modulator,and the device is fabricated finally.In order to further improve the extinction ratio,modulation bandwidth and footprint of the modulator,this paper continues to research graphene-base electro-optic modulator.Combined with high-index dielectric waveguides/resonators,graphene-based modulators have already been realized.However,as optical modes are limited in high-index dielectric region and far away from the interface of graphene/dielectric waveguide,the interaction between light and graphene in modulator is inherently weakened.In this paper,combining the ultra-compact mode size of surface plasmonic polaritions waveguide and the ultra-fast modulation speed of graphene,a graphene-based hybrid plasmonic electro-optic modulator is proposed.Due to a hybrid plasmonic waveguide including buried silicon waveguide and silver waveguides,the fundamental mode is mainly confined in the double layer graphene,and the electric field vector is parallel to the double-layer graphene ensuring the high efficient light absorption of graphene.The specific hybrid structure makes it easy to transfer for the graphene,in which non-coplanar structure of silicon waveguide and silver waveguides also provides simplified fabrication process and more fabrication tolerance.The simulation results demonstrate that board modulation bandwidth of 346 GHz is obtained,and the 3 dB modulation length is only 10 ?m.Also,3 dB modulation depth can be reached for the whole S to U Band.In addition,competitively low propagation loss of 0.85 dB was realized of the hybrid modulator.The modulator holds a great potential as a reliable on-chip device for optical communications and links.