Enhancing Dynamic Range in Microcavity Sensing via Nonlinear Harmonic of Fano Resonance

The optical resonators with ultrahigh quality (Q) factor are advantageous as highly sensitive sensors, benefiting from the sharp characteristics of their resonance peaks. However, this high sensitivity is usually achieved at the expense of linear range, so the sensing dynamic range is physically limited. In this paper, we propose a nonlinear modulation method based on the generation of an interference phenomenon between two scattering amplitudes. The recursive property of the Bessel function is utilized to construct expressions for the combination of harmonic components in order to improve the dynamic range of microcavity sensing. By utilizing the interference mechanism between discrete and continuous states, we obtain a Fano line shape with a higher slope. Using modulation and demodulation techniques, we achieve a magnetic sensing sensitivity of 20.5 pT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> . Meanwhile, by solving for the higher-order Bessel higher harmonics of the Fano resonance, a linear range of 1.06 μT is achieved, and the final dynamic range is improved by 8.4 dB. The proposed method is expected to become a generic solution for overcoming the limited dynamic range of microcavity sensors.