Eigenfrequency splitting with EPs order tunability in a coupled triple cavity system

Degeneracies of non-Hermitian Hamiltonian i.e., exceptional points (EPs) of parity-time (PT)-symmetric system have received considerable research attention. At EPs, at least two eigenvalues as well as their eigenvector coalesce. Second-order EPs are widely explored, and higher-order EPs are now receiving a surge of research attention due to their various possible applications in realization of better optical devices. Recently, the effect of the eigenfrequency splitting on transfer function near EP is studied for an optical system consisting of two rings, which leads to complex splitting in PT symmetric and real splitting in anti PT symmetric sensors. Here, we propose a simple system of three coupled ring resonators to show real splitting in both PT- and anti-PT-symmetric parameter domains by exploiting higher-order EPs. In present work, we indirectly couple two rings with equal amount of gain and loss respectively via an intermediate neutral ring. This system is then tested for refractive index (RI) sensing by modulating the cladding index. Also, we analyzed that the order of EP can be tuned by slight change in perturbation in cladding. This study may set up wide range of application in non-Hermitian triplet systems.