High Sensitivity Mode-Localized Ring Resonator with Tunable Sensitivity

In this paper, we propose a resonator for a mode-localization sensor that offers high and adjustable sensitivity. Two oscillation modes of a fully symmetrical ring resonator are utilized as the dual oscillators for mode-localization sensing. In the proposed resonator, the coupling stiffness, represented as kc, is determined by both the stiffness mismatch, k2-k1, and the angle of the principal axis, θ. This stiffness is inversely proportional to the sensitivity. By leveraging electrostatic forces, these parameters can be adjusted, enabling control of the coupling stiffness, which can even approach zero, yielding infinite sensitivity. Experimental results demonstrate that kc can be adjusted from positive to negative values. The modal shape, represented by the amplitude ratio between the two coordinates, aligns well with mode-localization theory. Furthermore, sensitivity is adjusted using electrostatic tuning. Notably, the sensitivity can be modulated across at least two orders of magnitude.