Enhanced Raman-Kerr frequency combs in Zr-doped silica coated hybrid microresonators (Conference Presentation)

Abstract

Ultrahigh quality factor microresonators have extremely long photon lifetimes, enabling high circulating power. As a result of the amplification of the input optical power, these devices are able to excite various nonlinear optical phenomena, such as four-wave mixing (FWM) and stimulated Raman scattering (SRS). Previously, FWM and their cascaded peaks enabled frequency comb generation in silica toroidal resonators. However, high input power (> 60 mW) is required to generate broad frequency combs (>500 nm span) due to the intrinsic material properties of silica. In this present work, we modify the material properties of silica by coating a silica toroidal cavity with a thin film of Zirconium (Zr) doped solgel. This thin layer substantially improves the performance of Raman-Kerr frequency comb generation in hybrid microcavities. A series of concentrations of Zr-doped solgel are synthesized, and the effects of the Zr dopants are characterized with both theoretical calculations and experimental measurements. Doping Zr into the silica matrix enables the Zr-doped devices to have a lower dispersion than a bare silica device, enabling the frequency comb span to increase. Additionally, Zr dopants increase the efficiency of the SRS process. As Zr concentrations increase, Stokes as well as anti-Stokes Raman scattering and their cascaded FWM peaks start contributing to the formation of the frequency comb, generating Raman-Kerr frequency combs. Consequently, Zr doping enables large frequency comb spans with significantly reduced input power.