Floquet optical ring resonators*

This work discusses Floquet optical ring resonators (FORRs) on the silicon nitride photonics platform. A FORR builds upon the principles of a standard ring resonator with the addition of a small, periodic perturbation to the ring’s dielectric material. Similar to a standard photonic crystal, this perturbation results in the formation of multiple photonic band gaps (PBGs) in the ring’s optical spectrum. The size of the PBGs can be related to the degree of coupling between degenerate propagating and counter-propagating resonances of the ring. Through application of Bloch-Floquet theory, it is seen that the degree of spectral splitting between two degenerate modes can be precisely controlled by varying the strength of the l-th order Fourier coefficient of the ring’s dielectric profile. Additionally, multiple Fourier coefficients may be added to the unperturbed ring’s dielectric profile to split resonances across a broad spectrum of the ring. As a result, FORRs provide a new degree of freedom in manipulating the dispersion relation of a ring resonator, providing control over the spectral frequency and group velocity dispersion of a resonance. Potential applications of FORRs include dispersion engineering of optical frequency combs and integrated single photon sources.