Design Of Sensor And Logic Gates Based On Two-Dimensional Photonic Crystal Microcavity

Photonic crystal cavity(PCC)is the structure constructed by introducing point defects into the photonic crystal(PC).PCC is widely used in lasers,sensors,add-drop filters and all-optical logic gates owing to the superiorities such as high quality factor,strong light confinement and small modal volume.PCC sensors can help diagnose illnesses,and logic gates based on PCC are basic elements in the future optical communication networks.More recently,many sensors and logic gates based on PCC with various forms of defects are proposed by researchers,which are always with shortcomings such as low sensitivity,low contrast ratio or weak robustness.Th e aim of this thesis is to investigate the design of high sensitivity sensor and robust logic gates based on PCC.The outcomes of the thesis mainly include the following contents:1.The relationships between the frequencies of band gap,including upper gap frequency and lower gap frequency and the radius of air holes,and the relationship between the width of band gap and relative width of band gap,and the radius of air holes of circular photonic crystal(CPC)are calculated by finite-difference time-domain(FDTD)method.The materials of the CPC are Si(silicon),GaAs(gallium arsenide),InP(indium phosphide)and Ge(germanium),which are always used to construct optical devices.The maximum relative width of band gap and the corresponding radius of air holes are obtained.The results show that the widths of band gap of the CPC with different materials have little difference.2.A sensor model with high sensitivity based on PCC is proposed.The relationships between the performance parameters,including resonant wavelength,sensitivity and quality factor(Q-factor),and the structure parameters are obtained by FDTD method.The optimal structure parameters are obtained after trade-off.The performance of the optimal sensor is analyzed.Meanwhile,the H_z field distribution and the resonant wavelength of the sensor with air holes filled with different analytes are obtained.The results show that the proposed sensor shows very high sensitivity.3.The band diagram of the supercell of the waveguide constructed by PC and gyromagnetic photonic crystal(GPC)is calculated by finite element method(FEM)and the band of edge state is obtained.The ratio between forward and backward transmission efficiencies of waveguides constructed by GPC with GPC,and GPC with PC are calculated.The“OR”gate,“XOR”gate and“NOR”gate based on edge state in GPC are designed.The relationships between the transmission efficien cy and the length of perfect electric conductor(PEC)in“OR”gate are obtained,and the results indicate that the proposed“OR”gate shows strong isolation effect for signals from different input channel.The relationships between the performance parameters,including transmission efficiency and contrast ratio,and the structure parameters of“XOR”gate and“NOR”gate are investigated by FEM.The optimal structure parameters are obtained after trade-off.The E_z field distributions of the gates when they normally work are simulated,the results show that the three logic gates have strong robustness.