Exceptional points (EPs) are the topological singularities in open quantum/ wave systems where at least two coupled states coalesce [1-3]. A dynamically encircled EP with time (or length) dependent parametric distribution and associated adiabatic breakdown in the modal dynamics offers a unique light manipulation tool in the context of asymmetric mode conversion [1-3]. Here depending on the chirality of the device and owing to the associated nonadiabatic corrections around EP, light is converted to a specific dominating mode, irrespective of the choice of input mode [1-3]. In this paper, we report a gain-loss assisted dual-mode optical waveguide that hosts a parameter space to encircle an EP dynamically. With the onset of saturable nonlinearity in the spatial index distribution of the waveguide, we investigate the nonreciprocal light dynamics below the isolation limit and study an interplay between the conversion efficiencies during EP- aided asymmetric-mode-conversions and the amount of optical nonlinearity in the optical medium.

© 2019 Japan Society of Applied Physics, The Optical Society (OSA)

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