Asymmetrically coupled bus with tunable ring resonators for multiple functionalities: Fano resonance, asymmetrical transmission, and wavelength shifting

Abstract

Transmission properties of bus waveguides coupled with two nested ring resonators are investigated using the finite difference in time domain (FDTD) method. Both the symmetrical and asymmetrical nested coupling structures are considered and different functionalities are realized in the single structure. Fano resonant transmission spectrums are obtained, of which the parameters can be tuned precisely by changing the position of the inner ring resonator. More importantly, near the Fano resonant wavelength, sharply asymmetrical field localizations in the two ring resonators are obtained when the same signals are incident from different ports. These properties are used to realize optical diodes with an ultra high contrast ratio larger than 2000. We also find that the frequencies of the resonant signals localized in the rings may be shifted due to the dynamic modulation of the coupling coefficients. These structures and properties presented here may find potential applications in nano-photonic systems. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).