Ultrawide tuning of photonic microcavities via evanescent field perturbation

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Evanescent field perturbation of an integrated microring resonator is examined as a means of achieving high-fidelity reversible tuning of photonic microcavities over large wavelength ranges. A 1.7% wavelength tuning is achieved through the use of a novel silica fiber probe that provides access to the evanescent field of an air-clad high-index-contrast ring resonator. As the microring is perturbed, the probe-ring distance is found through simultaneous nanometric distance calibration and force measurements. Experimental results agree well with theoretical tuning. Possible microelectromechanical systems implementation of this effect is discussed, as well as avenues for improvement of the tuning range.