Microfiber knot resonator with 10⁷ Q-factor record

Despite the realization of ultra-high-quality-factor (UHQ) in various dielectric micro-resonators with extensive applications, UHQ microfiber resonators which are directly compatible with all-fiber framework have not yet been achieved, primarily because of the insufficient research on the mechanical properties of microfibers, and the challenges of coupling regulation. Here, we constructed an UHQ microfiber knot resonator (MKR) fabrication model, addressing the decades-long Q-factor bottleneck and achieving a record Q-factor of 3.9 × 10⁷, which is an improvement of three orders of magnitude compared to conventional levels. By controlling environmental parameters for producing high-quality microfibers with uniform stress and low loss, along with experimental and theoretical investigation in coupling mechanism, optimized conditions are attained, offering experimental guidance for fabricating UHQ-MKR stably and reproducibly. After fabrication and characterization, the UHQ-MKR device is also applied into an all-fiber laser scheme to boost narrow-linewidth single-frequency laser operation, highlighting the potential of the resonator. The research opens an era of UHQ microfiber resonator exceeding 10⁷ level, paving the path for more precision and efficient microfiber guiding-wave photonics.