Demonstration of optical microfiber knot resonators

We demonstrate optical resonance from microfiber knots obtained by manipulating freestanding silica microfibers. Q factors as high as 57 000 with finesse of 22 are observed in knots with sizes less than 1 mm. The free spectral range of the resonator can be easily tuned by tightening the knot structure in air. The knot resonators are highly stable in water with Q factors up to 31 000 and finesse of 13. The possibility of supporting the knot resonator with a solid MgF2 substrate is also demonstrated.