Fabrication and packaging of whispering gallery mode rod resonators with adjustable coupling

Optical Whispering Gallery Mode (WGM) resonators are an ideal platform for high sensitivity sensors. They exhibit extremely high Q factors - on the order of 10⁶–10⁹ – providing a sensing platform with low detection limit. For some sensing applications, the micrometric diameters of microresonators may be undesirable, and resonators of large diameters are required. Here we present the fabrication and packaging of a cm-scale silica rod resonator with a Q factor of ∼ 7.5·10⁸. The demonstrated packaging provides – for the first time to the best of our knowledge – the ability to tune and adjust the coupling efficiency on demand. The coupling adjustment makes it possible to modulate the transmission power of the tapered fiber used to couple light into the rod resonator, as well as to modulate the loaded Q factor of the resonator.