Study On Active Control Of PT Symmetry Phase Transition In Terahertz Metasurface

Bender first proposed the Parity-Time(PT)inversion symmetrical quantum theory in 1998 to describe a class of non-Hermitian quantum systems that satisfy the requirements of PT symmetry.Because of the similarity between the paraxial approximation equation and the Schr?dinger equation,PT symmetry theory has also been greatly developed in the field of optics.M.Lawrence et al.achieved the purpose of passively regulating the phase transition by changing the distance between the two resonators.Others have used superconductor niobium nitride or graphene materials to achieve dynamic modulation.In contrast,the optical tuning of silicon has attracted widespread attention due to its ultra-fast modulation speed.In this thesis,we propose a non-Hermitian metasurface system whose unit cell consists of two orthogonal directional split ring resonators(SRRs)with the same resonant frequency but different loss coefficients,a tunable photosensitive silicon was placed in the opening gap of one of the SRRs to investigate PT-symmetry phase transition.By adjusting the conductivity of the photosensitive silicon,the dissipation rate of the SRR is indirectly changed,the system can spontaneously transition from PT symmetry to PT symmetry broken.Through simulation,we prove the phase transition of the system's intrinsic polarization state.The results show that when?_Si=1600 Sm^-1,the two eigentransmission spectra coincide and only a left circular polarized state is obtained,indicating exceptional point appearance.For conductivity below and upon 1600 Sm^-1,PT-symmetry and PT breaking regimes are separately provided.This tunable system avoids the formation of a series of metasurface structures,provides a promising approach for dynamically engineering the phase transition of non-Hermitian quantum symmetric system and may promote the practical application of PT symmetric photonics devices.