Fig. 1. (a) Series-coupled double-ring resonator, (b) directional coupler, and (c) uncoupled half-ring.

Fig. 2. (a) Spectral responses of series-coupled double-ring resonator. (b),(c) Influence of coupling coefficients on the resonant passband within the zoom-in area of (a). (b) Internal coupling coefficients K1=0.1 (solid), 0.2 (dotted), and 0.3 (dashed) when K0=K2=0.1. (c) External coupling coefficients K0=K2=0.1 (solid), 0.2 (dotted), 0.3 (dashed), and 0.426 (red) when K1=0.1.

Fig. 3. (a) Input pulse train of 10 GHz. (b) Optical spectra of input pulse train (black line) and series-coupled double-ring resonator (red line). (c) Optical spectrum of output pulse train. (d) Output pulse train with multiplication factor 2. (e) Single pulse with different resonator radii deviation.

Fig. 4. Output pulse trains with multiplication factors 3 (black), 4 (blue), and 5 (red).

Fig. 5. Comparison of power nonuniformity. Inset: output pulse trains by single-ring and double-ring resonator with factor 10.