Fig. 1. Photonic bands in an unperturbed ring resonator, plotted in a folded-zone diagram. A solid line corresponds to forward propagating bands, and a dashed line to backward-propagating ones. Each band is labeled with its corresponding band index. The resonances are marked when the bands cross the k=0 line. (a) Constant refractive index. (b) Artificial quadratic normal dispersion (exaggerated for visibility).

Fig. 2. (a) Schematic of a waveguide-based ring having a width modulation with only two different non-zero Fourier coefficients. (b) Scanning electron microscope image of a fabricated silicon nitride ring and its coupling waveguide.

Fig. 3. Experimental transmission spectrum of four different rings with different perturbation amplitudes. The bottom spectrum is that of an unperturbed ring, and the perturbation amplitudes increase going up (corresponding to 0-, 120-, 130-, 140-, and 150-nm width modulation amplitudes). The black lines correspond to the experimental data, and the thin red lines are the Lorentzian dips required to fit each corresponding mode. The traces are offset for visibility.