Design And Research Of High Performance Silicon-based Electro-optic Modulator

The transmission capacity of optical communication systems rapidly grows in recent years,which has demanded electro-optic modulators to possess a large modulation bandwidth and high modulation efficiency to transmit and process signals at high bit rates.As the core device of optical communication systems,the electro-optic modulator plays the role of modulating electrical signals onto optical carriers for optical domain transmission or processing.The carrier-depletion-type Mach-Zehnder electro-optic modulator based on silicon phase shifter exhibits high performances and has become a research hotspot in both academia and industry.However,due to the inherent limitation of the weak plasma dispersion effect of silicon material,it is difficult for the modulator to simultaneously improve the modulation efficiency and modulation bandwidth,and reduce insertion loss.Therefore,the design and research of the silicon-based electro-optic modulator is of great significance.Based on this background,this thesis proposes two new silicon-based electro-optic modulators.The phase shifting efficiency and insertion loss of phase shifters are researched.The bandwidths of traveling wave electrodes(TWEs)are analyzed.The specific research contents and results in this thesis are summarized as follows:1.This thesis studies high efficiency silicon phase shifter.Firstly,silicon phase shifter models are established to simulate the carrier distribution and optical mode in rib waveguides.On this basis,the effects of doping concentration and PN junction placement location in the rib waveguide on phase shifting efficiency and insertion loss of silicon phase shifters are analyzed.Finally,the key structural parameters of the doping region are optimized.The results show that when the range of doping concentrations between 3×1017 cm-3 to 5×1017 cm-3 is chosen and the PN junction shifts towards the N-doped region in the rib waveguide,the phase shifting efficiency and insertion loss of silicon phase shifters are obviously improved.2.This thesis proposes a wide bandwidth electro-optic modulator based on silicon phase shifter.Firstly,the effects of material and structure of silicon substrate on microwave signal transmission are studied.Then,the equivalent circuit model of the proposed modulator TWE is established.On this basis,calculation formulas of key circuit components are given.This thesis deduces expressions to calculate the characteristic impedance,the microwave transmission loss and the microwave effective refractive index of the proposed modulator TWE.Based on these researches,the size parameters of transmission line are appropriately optimized.Finally,corresponding TWE models are established and simulated.The transmission coefficients of TWEs with different doping concentrations,PN junction placement locations and silicon substrates are analyzed,and their bandwidths are calculated.Calculation results show that the transmission loss of microwave signal can be reduced and the bandwidth of TWE can be improved by introducing air in silicon substrate.The bandwidth of TWE with modified silicon substrate mostly improves 7.8 GHz.3.This thesis proposes a high efficiency,wide bandwidth and low insertion loss electro-optic modulator based on InP/Si phase shifter.Firstly,the modulation performance of Si phase shifter and InP phase shifter is compared.A novel InP/Si phase shifter is proposed by combining the advantages of two phase shifters.The change of effective refractive index of InP phase shifter is higher than Si phase shifter,but insertion loss of Si phase shifter is lower.On this basis,the effects of thickness of N-InP layer and overlap width between N-InP and N-Si on the modulation efficiency and insertion loss are analyzed.Next,the equivalent model of InP/Si phase shifter is firstly studied,and the calculation formulas of series capacitance and resistance are deduced.Finally,the TWE models with InP/Si phase shifter are established and simulated.The transmission coefficients of TWEs with different thickness of N-InP layer and silicon substrates are analyzed,and their bandwidths are calculated.Calculation results show that the electro-optic modulator based on InP/Si phase shifter simultaneously improves the modulation efficiency and modulation bandwidth,and reduces insertion loss.The research above provides novel ideas for design and research of the high efficiency,wide bandwidth and low insertion loss silicon-based electro-optic modulator.