Dispersion engineering and measurement in crystalline microresonators using a fiber ring etalon

Dispersion engineering and measurement are significant for nonlinear photonic applications using whispering gallery mode microresonators.Specifically,the Kerr microresonator frequency comb as an important example has attracted a great amount of interest in research fields due to the potential capability of full integration on a chip.A simple and cost-efficient way for dispersion measurements is thereby in high demand for designing such a microcomb device.Here,we report a dispersion measurement approach using a fiber ring etalon reference.The free spectral range of the etalon is first measured through sideband modulation,and the dispersion of the etalon is inferred by binary function fitting during the dispersion measurement.This method is demonstrated on two MgF_(2) disk resonators.Experimental results show good agreement with numerical simulations using the finite element method.Dispersion engineering on such resonators is also numerically investigated.

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.

Hundredfold increase of stimulated Brillouin-scattering bandwidth in whispering-gallery mode resonators

Backward stimulated Brillouin scattering(SBS)is widely exploited for various applications in optics and optoelectronics.It typically features a narrow gain bandwidth of a few tens of megahertz in fluoride crystals.Here we report a hundredfold increase of SBS bandwidth in whispering-gallery mode resonators.The crystalline orientation results in a large variation of the acoustic phase velocity upon propagation along the periphery,from which a broad Brillouin gain is formed.Over 2.5 GHz wide Brillouin gain profile is theoretically found and experimentally validated.SBS phenomena with Brillouin shift frequencies ranging from 11.73 to 14.47 GHz in ultrahigh Q Z-cut magnesium fluoride cavities pumped at the telecommunication wavelength are demonstrated.Furthermore,the Brillouin-Kerr comb in this device is demonstrated.Over 400 comb lines spanning across a spectral window of 120 nm are observed.Our finding paves a new way for tailoring and harnessing the Brillouin gain in crystals.