Abstract
An original method able to fully characterize high-Q resonators in an add-drop configuration has been implemented. The method is based on the study of two cavity ringdown (CRD) signals, which are produced at the transmission and drop ports by wavelength sweeping a resonance in a time interval comparable with the photon cavity lifetime. All the resonator parameters can be assessed with a single set of simultaneous measurements. We first developed a model describing the two CRD output signals and a fitting program able to deduce the key parameters from the measured profiles. We successfully validated the model with an experiment based on a fiber ring resonator of known characteristics. Finally, we characterized a high-Q, home-made, MgF2 whispering gallery mode disk resonator in the add-drop configuration, assessing its intrinsic and coupling parameters.
Highlights
Whispering gallery mode (WGM) resonators are a family of resonators with curved dielectric interfaces with cylindrical symmetry that allow guiding light in two directions by total internal reflection on a quasi-circular path
We have studied a ring resonator in the add-drop configuration, which is a common configuration in applied optics as well as in some fundamental studies involving highQ WGM resonators
The standard analysis method, which is based on the data fitting of stationary profiles, proved to be not sufficient for this purpose, and we investigated a different approach, studying the cavity ringdown (CRD) regime, which allowed us to fully characterise the system
Summary
Whispering gallery mode (WGM) resonators are a family of resonators with curved dielectric interfaces with cylindrical symmetry that allow guiding light in two directions by total internal reflection on a quasi-circular path. The add-drop configuration is very important for a number of studies based on ultra-high-Q WGM microresonators that have recently gained great interest, including, for instance, the implementation of innovative compact Kerr frequency combs [2,3,4,5], the generation of non linear parametric [6, 7] and non-parametric [8, 9] oscillations, the stabilization of semiconductor lasers operating in the resonators transparent wavelength range [10,11,12], or the modelocking of fast pulsed lasers [13]. We do not make any assumptions on the specific features of the resonator or the waveguide, so that the model can be general and can describe any type of waveguideresonator combination
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