Design And Performance Study Of Optical Devices Based On PT Symmetric Photonic Crystal

With the in-depth development of photoelectric fusion technology,“Internet of Things”technology and artificial intelligence technology,optical devices with photons as the information carrier will play an important role in the future optical communication,all-optical network construction,optical road integration and other fields.It can be predicted that innovation in optical device design will make it possible to ultra high frequency,large bandwidth and high-speed signal transmission,which will solve the bottleneck problem faced by traditional semiconductor chips.Accordingly,how to design high-performance optical devices through structural design or material selection has become a popular research topic in recent years.In this paper,based on the basic structure of one-dimensional photonic crystal（1D-PC）,by studying the optical properties of parity time（PT）symmetric photonic crystal,high-performance optical modulator,optical sensor and graphene-based light absorber with PT-symmetric configuration are designed respectively,and the related parameters are optimized and analyzed in combination with the working performance of each structure.Compared with the traditional similar optical structure,the designs of this paper not only have simple structure,but also the comprehensive performance index are greatly improved.Firstly,in this paper,hydro-based Mn Fe₂O₄magnetic fluid is selected as the defect layer to construct a PT-symmetric photonic crystal micro-nano structure with defect cavity,and the number of structural periods and the macro Lorentz oscillation intensity are numerically optimized.Through the mag-optic effect of the magnetic fluid,the modulation characteristics of the structure on the optical signal in the range of 1513 nm to1587 nm are analyzed.The calculation results show that the maximum gain of the mag-optical modulator is close to 25 d B,the maximum and the minimum extinction ratio are close to 60 d B and 30 d B,respectively.Simultaneously,the average modulation sensitivity of incident light transmission and wavelength shift can reach the maximum of74.51 d B/unit and 108.2 nm/unit,respectively.Next,using the correspondence between blood plasma concentration and refractive index,the blood sample layer is taken as the defect cavity,and a blood detection structure based on PT-symmetric photonic crystal is proposed.By analyzing the output light wave signal corresponding to the defect mode within the range of blood plasma concentration from 0 g/L to 50 g/L,the average quality factor,sensitivity,average figure of merit,average detection limit and average resolution of the structure can reach 78564,0.4409nm/（g/L）（or 227.05 nm/RIU）,11515 RIU^-1,5.1×10^-6RIU and 0.038 g/L,respectively.Finally,a graphene-based electroadjustable high intensity light absorber is proposed in this paper.The effects of macro-Lorentz oscillation intensity,incident light angle and chemical potential on graphene absorption are investigated,and the electrotunable properties of graphene absorption are further analyzed using the electro-optical effect of Li Nb O₃crystal.The main innovations of this paper are as follows:1.The mag-optical modulation and blood detection structures designed in this paper satisfy the PT-symmetric condition,the structures exhibit special light amplification effects.Compared with electro-optic modulator and acoustooptic modulator in the same field,the optical modulation with high extinction ratio and high sensitivity can be realized in this paper.For the blood detection structure,compared with the previous biomedical sensor structure,the comprehensive performance has been improved,so as to avoid a single index to limit the practical application of the sensor.2.In terms of the research of graphene absorber,through placing the PT-symmetric photonic crystal structure under the graphene,based on the amplification effect,the structure can achieve a high intensity absorption of 31.5 d B for incident light wave at1550 nm.Meanwhile,the electro-optic effect of Li Nb O₃can be utilized to achieve the electrically tunable characteristics of graphene absorption,and the modulation depth and operating speed of the design can reach 100%and 8.171 GHz,respectively.