Slot-mode cantilever optomechanical system for mass sensing

We present a slot-mode optomechanical platform that integrates a one-dimensional photonic crystal (PhC) cavity with a cantilever (CL) mechanical resonator. This architecture enables a high optomechanical coupling value (G/2<i>π</i> = 0.80 GHz/nm) while maintaining a low effective motional mass (<i>m</i>_eff = 13 fg), essential for high-sensitivity mass sensing. In contrast to typical slot-mode designs based on doubly clamped beams, the use of a cantilever offers reduced mass and enhanced dynamic range. We fabricate devices using silicon-on-insulator substrates and demonstrate coupling between MHz-frequency cantilever modes and localized THz optical modes. Through thermomechanical noise analysis and phase-locked loop frequency tracking, we estimate a mass sensitivity level of ≈30 zg. We also identify potential dominant noise sources, including temperature-driven cavity frequency fluctuations, and propose practical routes toward sub-zeptogram sensitivity through improvements in optomechanical coupling and cavity quality factor.