Fig. 2: Characterization of the microring resonator.
From: Efficient excitation and control of integrated photonic circuits with virtual critical coupling
a Microscope image of the SiN integrated microresonator coupled to the bus waveguide. b Schematic of the cross-section for the 1500 nm wide × 730 nm high SiN microresonator covered with SiO2, overlaid with the FDTD-simulated mode shape of the fundamental TE optical mode in the waveguide structure. c Cavity ring-down measurement, where the measured data (green line) is fitted (dashed line) to determine the lifetime of the cavity. d Measured transmission spectrum at real frequencies of the SiN resonator. The intensity transmission dip at zero detuning \((\varDelta=0)\) is 0.58. The estimated intrinsic loss and external coupling rates are \({\kappa }_{i}/2\pi=0.16\,{{{{{\rm{GHz}}}}}}\) and \({\kappa }_{ex}/2\pi=1.18\,{{{{{\rm{GHz}}}}}}\); therefore, the resonator is strongly overcoupled to the bus waveguide. e Density plot of \(|1/T(f)|\) in the complex frequency plane. The pole (brightest spot), which is marked by the blue circle, provides the condition for virtual critical coupling.
