Ultrahigh-Q crystalline microresonator fabrication with only precision machining

The development of ultrahigh quality factor (Q) microresonators has been driving such technologies as cavity quantum electrodynamics (QED), high-precision sensing, optomechanics, and optical frequency comb generation. Here we report ultrahigh-Q crystalline microresonator fabrication with a Q exceeding $10^8$, for the first time, achieved solely by computer-controlled ultraprecision machining. Our fabrication method readily achieved the dispersion engineering and size control of fabricated devices via programmed machine motion. Moreover, in contrast to the conventional polishing method, our machining fabrication approach avoids the need for subsequent careful polishing, which is generally required to ensure that surface integrity is maintained, and this enabled us to realize an ultrahigh-Q. We carefully addressed the cutting condition and crystal anisotropy to overcome the large surface roughness that has thus far been the primary cause of the low-Q in the machining process. Our result paves the way for future mass-production with a view to various photonic applications utilizing ultrahigh-Q crystalline microresonators.