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 1mm. 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.