Modulation And Nonlinear Effects Of Optical Structures Under PT Symmetric Pole Conditions

The PT(Parity Time)symmetric structure was initially born in the field of quantum mechanics,but with the development of materials science,optics,acoustics and other application fields,PT symmetry has gradually become a new research direction.In materials science,PT symmetry is widely used to design new optical,electronic,phonon and other materials.In the field of optics,PT symmetry can be used to design optical devices,such as controllable filters,modulators,lasers,etc.In the field of acoustics,some new phonon devices can be designed using PT symmetry.In addition,studying PT symmetry also helps to develop new physics theories and methods,promoting progress in physics and even the entire scientific field.This thesis combines the(Parity-Time)PT symmetric structure with one-dimensional photonic crystals.Through the study of coupled micro-cavities,the PT symmetric pole effect is discovered,and phase control and amplification of weak signals are achieved.Based on this,we combine the PT symmetric pole effect with the Faraday transmission matrix,and through the adjustment of different parameters,we achieve control of polarization.Finally,combining the PT symmetric exceptional point effect with nonlinear materials,efficient nonlinear harmonics are realized.Firstly,this thesis designs a structure model of a PT-symmetric coupled microcavity based on the semiconductor magnetic material In Sb.By optimizing the structural parameters,a pole effect with PT symmetry and strong magnetic field coupling is generated.Near the pole frequency,the size of the magnetic induction intensity applied to the magnetic material can be changed by the input current signal to achieve amplified output of the signal in the pole state.This amplification can be in-phase or out-of-phase,and the result realizes a model of a special optical triode.Afterwards,based on the PT symmetric pole effect,we introduced the Faraday transmission matrix to study the transmission and reflection characteristics of the structure.We found that circular polarization can be achieved under pole conditions.For semiconductor magnetic materials,the pole is jointly controlled by factors such as gain-loss coefficient,frequency,and input magnetic field size,therefore,control of the polarization state can be achieved by changing different structural parameters.Finally,this thesis applies nonlinear materials to PT symmetric structures.Firstly,a prism coupled microcavity was constructed,and its gain loss coefficient was changed to excite nonlinear second harmonic under pole conditions.By changing the external electric field,the efficiency of the second harmonic was improved.Next,a new type of photonic crystal model is constructed based on Bragg reflection conditions to study nonlinear third-order harmonics.Under pole conditions,the amplification of nonlinear harmonics is achieved by increasing the input electric field to generate nonlinear third-order harmonics greater than the fundamental field strength.This thesis achieves modulation and nonlinear effects of optical structures through PT symmetric pole effect.Under the condition of PT symmetric poles,optical transistors can control strong signals with weak signals,and electromagnetic wave polarization control can also be achieved,which brings significant significance to the future research of optical components.The implementation of efficient third harmonic generation through PT symmetric pole effect has greatly promoted the development of optical information technology,laser technology,material analysis,and nanophoton technology.