Fabrication of an ultra-high quality MgF₂ micro-resonator for a single soliton comb generation

Crystalline micro-resonators are attractive for a wide range of applications due to their extremely high quality (Q) factor. In this paper, we develop a semi-automatic method for fabricating ultra-high Q-factor MgF₂ crystalline micro-resonators. By utilizing a force feedback sensor and corresponding control, we made a semi-automatic precision grind-and-polishing machine, and successfully fabricated trapezoid MgF₂ resonators with diameter of 9.5 mm and a root mean square surface roughness of 0.26 nm. The maximum difference of peaks and valleys is about 1.5 nm. The Q-factor was characterized to be 9.24 × 10⁹at 1550 nm by the cavity ring-down spectroscopy. A single soliton optical frequency comb was generated by pumping the microcavity with 150 mW optical power.