Mode crossing induced soliton frequency comb generation in high-Q yttria-stabilized zirconia crystalline optical microresonators

We demonstrate for the first time,to the best of our knowledge,the fabrication of high-Q crystalline optical microresonators from cubic yttria-stabilized zirconia(YSZ).Intrinsic Q factors up to 80 million are obtained,indicating an upper bound absorption coefficient of 0.001cm^(−1) for YSZ crystals at the telecom wavelength.Through laser-scanned spectroscopy on a few-mode YSZ microresonator with a radius of 300μm,we find that the mode crossing effect in the case of weak coupling can induce a repelling disruption of free spectral range values between transverse mode families.Generation of soliton and soliton crystals in such a YSZ microcomb platform operated in the normal dispersion regime is observed.A breathing comb behavior is also reported.Our finding has enriched comb generation platforms with potential multidisciplinary capabilities linked to properties of YSZ crystals in superconducting films and sensors.