Research On All-optical Logic Devices Based On Two-dimensional Photonic Crystals

With the rapid development of information technology and communication technology,people's requirements for data transmission and processing are constantly increasing.The existing communication network is difficult to meet the demand,so there is an urgent need to develop an all-optical communication network with ultra-large capacity and ultra-high-speed.The development of all-optical communication is inseparable from all-optical signal processing,and all-optical logic devices are an important part of all-optical signal processing,so they have become a current research focus.The photonic crystal is a new type of artificial synthetic material.Because of its unique photonic bandgap and photon local effect,it has become one of the important materials for making photonic devices and has attracted extensive attention from domestic and foreign researchers.In this paper,using the bandgap characteristics of photonic crystals and the principle of linear interference,an all-optical three-input logic ‘AND' gate,and an all-optical 4-2 encoder are proposed and optimized.The specific work is as follows:(1)Based on the waveguide coupling effect of photonic crystals and the principle of linear interference,a three-input all-optical logic ‘AND' gate is proposed.By introducing an idle waveguide and an offset dielectric rod,using the superposition principle of linear interference,the function of the three-input logic AND gate is realized.The normalized output energy,contrast ratio,and response time of the proposed three-input all-optical logic AND gate are studied by the plane wave expansion method and finite difference time domain method.The simulation results show that the working wavelength of the proposed three-input AND gate is 1550?1554nm,the contrast ratio is not less than 3.5d B,the response time reaches the sub-picosecond level and the horizontal offset range of the offset dielectric rod is 0.044?0.083?m.Based on the proposed three-input AND gate,the idle port introduces control light,and the interference between the control light and the signal light is used to cancel the contrast of the proposed AND gate.The simulation results show that the optimized three-input AND gate has a working wavelength of 1528?1573nm,the contrast ratio is not less than 5.6d B,the response time reaches the sub-picosecond level,range that the offset dielectric rod can shift horizontally is 0.359?0.547?m.The relative energy of the control light can be changed from 0.49 to 1.20,and the initial phase of the control light can be changed from 144 to214°.(2)Based on the waveguide coupling effect of photonic crystals,a 4-2 encoder based on two-dimensional photonic crystals is proposed.The logic function of the all-optical 4-2 encoder is realized by introducing beam splitting structure and coupling waveguide structure.The normalized output energy,contrast ratio,and response time of the proposed 4-2 encoder are studied by the plane wave expansion method and finite difference time domain method.The simulation results show that the working wavelength range of the proposed all-optical 4-2 encoder is 1546?1551nm,the contrast ratio is not less than 10 d B,and the response time is not more than 0.34 ps.The coupling waveguide structure and output waveguide structure of the proposed 4-2 encoder is changed to optimize the performance of the 4-2 encoder.The simulation results show that the optimized all-optical 4-2encoder has a working wavelength range of 1538?1666nm,a contrast ratio of not less than 17 d B,a response time of not more than 0.52 ps,and the range of horizontal deviation of the dielectric rod is440?584nm.The proposed all-optical three-input logic AND gate and all-optical 4-2 encoder have the characteristics of simple structure,easy integration,short response time,and wide working bandwidth.They meet the requirements of modern optical communication and optical integrated devices and are used in all-optical signal processing.It has very good application prospects in all-optical signal processing systems and integrated optical circuits.