Non-Hermitian scattering characteristics in a PT-symmetric bilayer structure with parabolic gain–loss profile

In the present work, we demonstrate scattering properties of parity-time (PT) symmetric one-dimensional bilayer structure with spatially distributed gain and loss in the dielectric layers. We report the effect of parabolic modulation of loss and gain on the non-Hermitian characteristics of the PT-symmetric system such as exceptional points (EPs), lasing points (LPs), and coherent perfect absorption (CPA) for normal and oblique illuminations for TE & TM polarizations. We observe a significant enhancement in CPA-LP, which also shows a red shift with parabolic modulation in the spatially distributed imaginary part of the dielectric permittivity for the normal incident waves. On the other hand, under oblique incidence, the spatial parabolic modulation in gain–loss tunes all the scattering properties of PT-symmetric systems such as CPA-LP and EPs. In addition, we have also investigated the effect of the introduction of a silicon layer with varying thickness between the bilayer exhibiting gain and loss on EPs and CPAs. The optical properties of the PT-symmetric structure under consideration are studied by employing the scattering and transfer matrix method and all these results are further corroborated with COMSOL® Multiphysics simulations. The proposed PT-symmetric system exhibits promising applications to achieve CPA, exotic lasing, phase modulators, and optical isolators due to the non-reciprocal behaviour of the bilayer system.