Tunable microresonators formed at the intersection of straight optical fibers

We experimentally demonstrate the formation of high Q-factor free spectral range (FSR) tunable microresonator formed at the intersection of two straight optical fibers. The FSR of these microresonators can be tuned from 2 pm to 10 pm by precisely varying the intersection angle from 1 mrad to 15 mrad. Importantly, this microresonator permits substantial tuning of its millimeter scale dimensions, which is difficult to achieve in compact monolithic designs of the conventional optical microresonators. This feature is promising for applications, including cavity quantum electrodynamics, optical signal processing and frequency comb generation.