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- μm 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.
Silicon photonics optical phased arrays have been studied intensively in recent years. As the divergence angle of the light beam is inversely proportional to the size of optical antennas, developing long grating emitters is crucial to the implementation of large aperture optical phased arrays. However, because of the high refractive index contrast between silicon and cladding materials on silicon-on-insulator (SOI) platform and fabrication limitation, the grating strength of a conventional grating is so strong that the light can only propagate a short distance within the grating. Because of the capability to engineer the macro optical properties of materials, subwavelength structures have become important building blocks in integrated photonics. In this paper, we propose subwavelength silicon segments as a promising approach to form long grating emitters. Subwavelength segments are placed a distanced away from a conventional waveguide to assure that they only interact with the evanescent wave of the guided mode. The grating strength can be tailored to any values of interest by optimizing the dimensions and positions of subwavelength segments. As a proof-ofconcept, a millimeter-long, through-etched grating and an apodized grating are designed and fabricated, which shows a divergence angle of 0.081 ° and 0.079°.
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