Thin-ridge SOI disk and ring resonators with "magic radius" and "magic width" phenomena

A number of key sensor and active silicon-on-insulator (SOI) component designs benefit dramatically from TM mode operation due to strong evanescent field. Ultra-tight vertical confinement, shallow ridge waveguides [1] can provide such evanescent behaviour, but TM modes exhibit inherent severe lateral radiation leakage losses [2].We have recently shown that these inherent losses can be effectively mitigated by precision control of the waveguide widths to 'magic widths' where radiation loss components cancel coherently [3]. However, for these waveguides to be incorporated into practical functional integrated devices, they must be configured into fundamental building blocks. Disk or ring resonators are essential for compact and efficient integrated optics. In order to realize high-Q resonators, low propagation losses are required. In this paper, through the mode matching simulation technique, we show that the propagation losses of disk and ring resonators based on thin-ridge SOI structures operating in TM-polarisation depend strongly on the disk or ring radius and the waveguide width, much as their straight waveguide counterparts [3].