Spectral Engineering of a Micro-Cavity using Nano-Scale Asymmetry

A nano-scale asymmetrical grating applied to the circumference of a micro-cavity is proposed, creating a simple asymmetric micro-gear structure with unique characteristics. We demonstrate the effect of this asymmetry on mode splitting by correlating its dimensions to the free spectral range. Additionally, mode-dependent emission behavior is observed, selectively radiating whispering gallery modes (WGM) out-of-plane. Due to asymmetry, clockwise and counterclockwise versions of the cavity exist, enhancing the probability of a certain rotational direction of the WGMs. This enables the generation of vertically emitted modes of nonzero orbital angular momentum with specific order and chirality.