Single-Mode Ring Resonator-Based Optomechanical Transducers for Advanced Atomic Force Sensing

Atomic force microscopy (AFM) is a widely used technique for high-resolution imaging and force sensing, yet its performance is fundamentally constrained by the cantilever size, spring constants, and mechanical frequencies. To overcome these limitations, we present a compact and highly efficient single-mode ring resonator-based optomechanical transducer on a silicon-on-insulator (SOI) platform. Unlike conventional designs that rely on whispering gallery modes (WGMs) resonators, our approach ensures mode stability, facilitates straightforward signal interpretation, and enhances measurement reliability by eliminating mode-splitting effects and complex optical responses. Coupled with a picogram-scale cantilever, our system achieves exceptional displacement sensitivity of 6.7 × 10^(-16) m/Hz^(1/2)Hz and force detection down to 5.0 × 10^(-14) N, providing a high performance alternative to existing optomechanical AFM transducers. The tunable mechanical resonance frequency (1.3 MHz to 22.5 MHz) and adjustable stiffness (0.46 N/m to 3.54 N/m) enable precise force sensing across a broad range of applications, from soft matter characterization to high-speed imaging. Importantly, our results exhibit strong agreement with theoretical predictions, ensuring accurate and direct displacement measurements. This is a key advantage over WGM-based approaches that suffer from optical mode instability. Our results establish this single-mode optomechanical transducer as a robust, high-sensitivity platform for next-generation AFM and nanoscale sensing applications, offering a compact, cost-effective, and highly precise alternative to traditional free-space optical detection methods. The combination of high displacement sensitivity, mode stability, and tunable performance establishes this optomechanical transducer as a promising advancement in integrated nanoscale sensing and AFM applications.