All-precision-machining fabrication of ultrahigh-Q crystalline optical microresonators

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 10⁸, for the first time to our knowledge, achieved solely by computer-controlled ultraprecision machining. Our machining fabrication method readily achieves the dispersion engineering and size control of manufactured devices via programmed machine motion, both of which were not possible with the conventional manual polishing method. We can achieve an ultrahigh Q without the need for subsequent careful polishing that is generally required to ensure that surface integrity is maintained. 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 a reliable fabrication with a view to various photonic applications utilizing ultrahigh-Q crystalline microresonators.