Si-microring resonator with sidewall nanograting structures for high-Q resonance modes.

A nanograting microring resonator is proposed for achieving concentric mode field profiles as the effect of guided-mode resonance. Based on a numerical simulation of the 2D finite-difference time-domain method, we clarified that the microring resonator with a combination of nanograting microring and sidewall blocks could generate two operating modes. The first is the optical whispering gallery mode, by which the light was in resonance inside the microring by total internal reflection and traveled in a circle around the microring. The second mode is guided-mode resonance, by which the light scattering from the grating structures is in resonance to create concentric magnetic-field distributions. The characteristics of resonance modes of the mode numbers, mode distribution, and Q factors are analyzed at the changes of the microring radius and the nanograting structures. A design of a nanograting bus waveguide with the same grating period as the nanograting microring is verified to achieve a high efficiency of the coupling ratio. [ABSTRACT FROM AUTHOR]