Non-PT-symmetric two-layer cylindrical waveguide for exceptional-point-enhanced optical devices.

We investigate the exceptional points in a two-layer cylindrical waveguide structure consisting of absorbing and non-absorbing dielectrics. We show that, by tuning the core to total radius ratio and the refractive index of the core layer in such a structure, the complex effective indices of two waveguide modes can coalesce so that an exceptional point is formed. We show that the sensitivity of the effective index of the waveguide mode to variations of the refractive index of the material filling the shell layer is enhanced at the exceptional point. In addition, we show that larger sensitivity enhancement is obtained for smaller perturbations. Our results could potentially contribute to the development of a new generation of chip-scale exceptional-point-enhanced optical waveguide devices for modulation, switching, and sensing.