Coupling-driven optimization of on-chip optical mode localization sensing

Optical mode localization sensing has been shown to achieve a three-order-of-magnitude sensitivity enhancement compared to frequency-shift-based sensing, demonstrating great potential for ultra-sensitive detection applications. This work further explores the key parameters that limit the performance of such sensors, with the aim of providing critical design guidelines for their optimized implementation. Using on-chip coupled microring resonators with tuned coupling coefficients (K = 0.5527-0.2775) achieved through precise gap and length variations, we characterized the dynamics of split modes under different external perturbations. Experimental results confirm significant sensitivity improvements: at the minimal coupling coefficient, the anti-symmetric (AS) mode shows a 46-fold sensitivity increase (0.06 dB/V to 2.76 dB/V), while the symmetric (S) mode achieves a 7.5-fold enhancement (0.34 dB/V to 2.56 dB/V). Furthermore, we identify an inherent trade-off between sensitivity and measurable range: higher sensitivity accelerates the variation of mode amplitude, causing it to reach the dynamic range boundary more quickly. This, in turn, narrows the measurable perturbation window. Overall, this study systematically establishes the comprehensive relationships between coupling strength, sensitivity, dynamic range limits, and measurable range constraints in optical mode-localized systems. It provides foundational insights for the development of high-precision optical mode localization sensors.