Manipulation On Multiple Parity-time Symmetry And Asymmetric Optical Scattering In A Heterojunction Cavity

The reality of eigenvalues of a Hamiltonian is of special significance.In 1998,Bender and others found that the non-Hermitian Hamiltonian with symmetry can also have real spectrum,in which symmetry means that the system remains unchanged under both a parity operator and a time operator.The symmetry theory promotes the development of many subjects,such as quantum field theory,mathematical physics and nuclear physics.Due to the isomorphism between the paraxial wave propagation equation and the Schr?dinger equation,studies on symmetry have been successfully extended to optics,which lead to many novel phenomena,such as energy oscillation,localization of light and non-reciprocal wave propagation.As a result,-symmetric optics becomes a very popular research direction.Simple heterojunction(SH)is one of the simplest-symmetric scatting structure,which is widely used in practical device.Although the structure is easy to build,it is very inconvenient for dynamic manipulation.To overcome this shortcoming,we consider a sandwich structure by adding a vacuum gap between the two labs of an SH to build a heterojunction cavity.The length of the vacuum layer can be changed to adjust its properties.By adopting the transfer matrix and scattering matrix methods,we found that the heterojunction cavity has a multiple symmetry,as a result of the presence vacuum layer.We find the high order symmetric phases can always be found around the vanishing of right reflection of the vacuum layer in the parameter space.As a consequence of the multiple symmetry,the scattering behaviors of the heterojunction cavity also show different features.At last,we discuss some potential applications of this structure.Because of tremendous sensitivity of the incidental wave vector and maximal transmittance in high order symmetric phases,heterojunction cavity can be used as a wave filter with amplification.Due to the ability of switching of the direction of unidirectional reflectionlessness,it can act as a router in all-optics networks.For several modes of light,it can realize both coherent perfect absorption and laser,which is a uniqueness of-symmetric scatter.