Selective excitation of microring resonances using a pulley-coupling structure

We explore the selective excitation of resonances in microring resonators with a pulley-coupling structure. Due to the wavelength dispersion of coupling coefficient, only the resonances near critical coupling exhibit pronounced sharp notches in the transmission spectrum. Experimental results show that the resonance extinction ratio is a strong function of wavelength. Theoretical analysis further predicts that it is possible to highly suppress the neighboring resonances to effectively enlarge the free spectral range (FSR). With a proper design, the FSR can be increased by more than 1 order for a 10 μm radius microring resonator using the pulley-coupling structure.