Wavelength-scale directional microdisk lasers based on asymmetric backscattering from rayleigh sacatterers

Abstract

A unique property of micro-disk/ring resonators is that they can support traveling waves due to their chiral symmetry structure. However, microdisk lasers with perfectly symmetric geometries and gain distributions provide standing wave modes because they support both the clockwise and counterclockwise propagating wave of the equal amplitude at the same time. In order to overcome this limitation and achieve the directional emission from the microdisk lasers, we propose partially directional wavelengthscale microdisk semiconductor lasers based on asymmetric backscattering of whispering gallery modes from two Rayleigh scatterers. The mode-splitting characteristics showed that the resonance spectrum even becomes almost one peak depending on the relative locations of two scatterers, which indicates the eigenmodes are close to an exceptional point. From the field distribution simulations, we found that the eigenmodes close to an exceptional point exhibit relatively high chiralities. Partially directional microdisk lasers were also demonstrated experimentally. To visualize the chirality, a waveguide was fabricated such that the coupled light from a microdisk is scattered at the ends of the waveguide and captured by a CCD camera. The general trend of the experiment result was similar to that of the simulation result. We believe that the proposed partially directional microdisk design provide various potential applications including optical signal processing and integrated photonics.