Dominated mode switching and nanoparticle detection at exceptional points

Abstract

We present a theoretical investigation of dominated mode switching and nanoparticle detection at a wavelength of 2 µm that uses coupled whispering gallery mode (WGM) resonators operating at exceptional points (EPs). The simulations show that with assisted gain and loss the system can be steered to operate at EPs by adjusting the nanoparticle-introduced backscattering. The unbalanced contributions of the clockwise and counterclockwise modes can be observed when the system approaches the EPs, and the dominated mode is switchable by transiting the system from one EP to another. Owing to the square root topology of EPs, the enhanced frequency splitting can be obtained when the system is subjected to a perturbation, which results in a more than five times sensitivity enhancement compared to a traditional sensor. Furthermore, a simulation also reveals that an increased gain–loss contrast in the resonators contributes to an enhanced frequency splitting, and thus a higher sensitivity enhancement factor. Our investigations validate the feasibility of a WGM resonator operating at EPs for unidirectional laser emitting and nanoparticle sensing.