Study On Electro-optic Logic Devices Using Mach-Zehnder Switches Based On Graphene-silicon Waveguides

With the increase in integration for integrated circuits,fabrication process parameters are gradually approaching the physical limits.Compared with traditional electrical interconnects,optical interconnects has the advantage of low power consumption,low lantency,and high bandwidth.Optical logic devices are one of the key components for optical interconnects.And how to achieve an intergrated optical logic device with high speed,high extinction ratio,low power consumption has become a key issue.In this thesis,three different electro-optic logic devices using 2×2 Mach-Zehnder switches based on graphene-silicon hybrid waveguides and multimode interference couplers are studied.The main contents of this thesis are stated as follows:1.An electro-optical half-adder using Mach-Zehnder switches based on graphene-silicon waveguides is presented.The device is composed of three cascaded Mach-Zehnder switches using the graphene-Hf O2-graphene-Si structure.By changing graphene’s chemical potential,the switching function of the Mach-Zehnder switch is achieved at high speed and thus the proposed electro-optical half-adder is realized.The designed switch has a crosstalk less than-21.57 d B and an insertion loss lower than 0.109 d B within a bandwidth from 1520 nm to 1600 nm.The worst extinction ratio of the designed electro-optical half-adder is 41.05 d B.2.An electro-optical majority voting circuit using Mach-Zehnder switches based on graphene-silicon waveguides is presented.The device consists of cascaded Mach-Zehnder switches using the graphene-Si O2-graphene-Si structure and 2×1 multimode interference couplers.By applying the voltage to tune graphene’s chemical potential,the modal effective index of the phase shifter using the graphene-Si O2-graphene-Si structure is changed to achieve the switching function at high speed and thus the proposed electro-optical majority voting circuit is realized.The designed electro-optical majority voting circuit has a 3-d B bandwidth of 30.6 GHz,an energy consumption of 10.29 p J/bit,and the worst extinction ratio of 26.1d B.3.An electro-optical Toffoli gate using Mach-Zehnder switches based on graphene-silicon waveguides is presented.The device comprises cascaded Mach-Zehnder switches using the graphene-Si3N4-graphene-Si structure,2×1 multimode interference couplers and 1×2 multimode interference couplers.By tuning graphene’s chemical potential,the switching state of the Mach-Zehnder switch can be controlled,and then a high-speed electro-optical Toffoli gate is realized.The 3-d B bandwidth,the power consumption and the worst extinction ratio of the designed electro-optical Toffoli gate are 13.92 GHz,6.6p J/bit,and 15.6d B respectively.