High-Q-factor tunable microresonators induced by twisting optical fibers

We experimentally demonstrate tunable surface-nanoscale axial photonics (SNAP) microresonators formed by two twisted optical fibers. One end of a pair of slightly separated and almost parallel fibers is fixed while the other is rotated, bringing the fibers into contact at the center to form a mechanically robust, high-Q whispering-gallerymode microresonator. The microresonator free-spectral range tunes from 5 pm to 14 pm with dramatically small sub-degree changes in twist angle while maintaining Q-factors ⁓ 10⁶ limited by uncontrolled lab environment conditions. This simple, robust, and tunable microresonator has potential for compact implementations of integrated optical delay lines, low-repetition-rate frequency-comb generators, cavity quantum electrodynamics experiments, and sensitive, reconfigurable photonic sensors