Study Of Graphene Integrated Waveguide Electro-optic Modulator

Broadband,high-speed and compact integrated optical modulator is the key component of high-speed fiber-optic communication systems.With tunable Fermi level,ultra-high carrier mobility and thermal conductivity,graphene combined with optical waveguides are an ideal solution for modulators,which can satisfy the needs of wide bandwidth,ultra-fast modulation,high integration,low modulation voltage and low power consumption.Compared with silicon waveguides,silicon nitride waveguides have the advantages of low transmission loss,low nonlinear loss,easy fabrication and low cost.In this thesis,a four-layer graphene electro-optic modulator,a graphene TM-Pass polarizer based on double-stripe silicon nitride waveguide and a graphene thermo-optic modulator based on silicon nitride micro-ring resonator were studied.Based on the principle of the graphene electro-optic modulator,a four-layer graphene electro-absorption modulator based on double-stripe silicon nitride waveguide was designed and optimized by finite element method.Benefiting from the co-electrode design between the graphene layers,the device's total resistance is reduced by 50%.The proposed modulator achieves 3dB modulation with an active length of 18.09?m at 1550 nm and the modulation bandwidth is as high as 30.6GHz.The extinction ratio and figure of merit reach 0.1658dB/?m and 9.7,respectively.And the modulation switching voltage range is only ?V=3.8180 V and energy consumption is 780.50fJ/bit.In addition,this four-layer graphene double-stripe silicon nitride waveguide can be used as a broadband and low insertion loss graphene TM-Pass polarizer.When the length of graphene sheet is 200?m,an extinction ratio as high as 38.4dB and a rather small insertion loss of 0.8dB can be achieved at 1550 nm wavelength.Moreover,such a polarizer can also achieve an extinction ratio of higher than 33.8dB and an insertion loss of less than 0.87 dB over 1520 to 1720 nm wavelength range.Finally,a single layer graphene silicon nitride micro-ring thermo-optic modulator was designed.The extinction ratio of the modulator reaches 40 dB and the full width at half maximum(FWHM)is 0.33 nm.The rise and fall response time are 17.8 ?s and 18.3 ?s,respectively.At the same time,two transfer methods of graphene were investigated and characterized,and the device was experimentally fabricated initially.The proposed electro-optic modulator,TM-pass polarizer and thermo-optic modulator may remedy the lack of high speed modulator,broadband polarizer on the passive silicon nitride waveguide platform.