Experimental observation of the exceptional point in a nanocylinderloaded silicon microring

Exceptional points (EPs) in whispering-gallery-mode microresonators systems have attracted substantial attention due to their intriguing and anomalous optical characteristics. Recently, EPs have been experimentally observed in silicon microrings with coupling manipulation elements, such as an S-shaped waveguide and notch. In this paper, the observation of EP in a nanocylinder-loaded silicon microring is experimentally demonstrated. The device consists of a 5 mu m microring with two nanocylinders placed close to the outer edge of the microring. By tailoring the size and position of the two nanocylinders, the fully asymmetric coupling between the clockwise- and counterclockwise-propagating modes occurs, leading to the implementation of EP. Experimentally, the spectral response is investigated by single-side excitation from clockwise and counter-clockwise directions. The reciprocal transmission and nonreciprocal reflection spectra are observed, which confirms the proposed device works in the vicinity of EP. The construction of EP in silicon microring paves the way to basic science and applied technology in non-Hermitian physics.