Ultra-low-loss microresonators at the intersection of optical fibers can be finely tuned by fiber rotation in strongly confining/ enhancing light

https://www.eurekalert.org/news-releases/1088089

"tiny fraction of degree rotation translates to µm-scale fiber displacements, enabling: mm-scale changes in resonator geometry, pm-scale tuning of its spectral/ free spectral range characteristics... van der Waals forces keep fibers in direct contact, contributing to resonator formation over sub-mm regions... micro-electromechanical systems (MEMS) integration, communication, quantum information processors, low-repetition-rate frequency comb generators, tuneable delay lines, nonlocal optofluidic sensors"