# Microfiber knot resonator with 107 Q-factor record

## TL;DR

Researchers created a high-quality microfiber knot resonator with a record Q-factor of 3.9 × 10^7, advancing fiber-based photonics and laser technology.

## Contribution

The study introduces a fabrication model for ultra-high Q-factor microfiber knot resonators, achieving a three-orders-of-magnitude improvement.

## Key findings

- A Q-factor of 3.9 × 10^7 was achieved in a microfiber knot resonator.
- Environmental parameters were optimized to produce high-quality microfibers with uniform stress and low loss.
- The resonator was successfully applied in an all-fiber laser for narrow-linewidth single-frequency operation.

## Abstract

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.

We constructed a silica microfiber knot resonator fabrication model and achieved a record high Q-factor of 3.9 × 107 for this intriguing all-fiber soft resonator scheme, paving the path for more precision and efficient microfiber guiding-wave photonics.