*Tahere Hemati, Binbin Weng, University of Oklahoma, Norman, OK
The hidden symmetry of physical systems can manifest in degenerate states. Introducing a perturbation breaks this symmetry and leads to the splitting of eigenvalues. This procedure can be used to identify the introduced perturbation. Compared to the Hermitian system, the non-Hermitian Parity-Time (PT)-symmetric system shows a more intense splitting, leading to an easier and more accurate detection. Traditionally, to achieve high sensitivity, the perturbation is introduced at singular points named Exceptional Points (EPs). However, in this research, we aim to study the sensitivity of Coherent Perfect Absorber (CPA) points to the introduced perturbation for the first time. CPAs are direct products of the non-trivial properties of the scattering matrix in a PT-symmetric system. Once the system is located at these points, a significant enhancement in diffraction efficiency is observed. Therefore, introducing a small perturbation drifts the system from CPAs, leading to a significant peak intensity reduction for the diffracted mode. Herein, introducing methane to the active sub-wavelength grating, showing CPAs, interrupts the system, leading to the diffracted mode's attenuation. The gas concentration directly depends on the peak attenuation. This new approach promises super-sensitive on-chip gas sensors with applications in environmental monitoring, disease diagnosis, and national security surveillance.