A tri-axis optomechanical accelerometer with plasmonic MIM waveguide and structural direction-dependent optical signatures.

This paper presents a proposed tri-axis optomechanical accelerometer integrating a monolithic single-proof-mass MEMS suspension with an engineered metal-insulator-metal (MIM) plasmonic platform. The device utilizes a modified frog-arm spring system, optimized via finite element simulations to provide near-identical peak displacements ([Formula: see text]) and mechanical sensitivities ([Formula: see text]) within a [Formula: see text] range, operating across a bandwidth of [Formula: see text]. Structural stability is verified through pre-stressed analysis, showing negligible warpage ([Formula: see text]) and a substantial safety factor ([Formula: see text]), while maintaining minimal axis interference with cross-axis coupling [Formula: see text]. The optical transduction, analyzed through finite-difference time-domain (FDTD) methods, employs a Hybrid Plasmonic Waveguide (HPW) configuration to induce a pronounced Fano-type resonance with an insertion loss of [Formula: see text] across the visible-to-near-infrared spectrum ([Formula: see text]). By adopting an asymmetric structural architecture, the sensor generates direction-sensitive signatures characterized through a Bidirectional Optical Sensitivity Matrix, which maps nanoscale displacements to simultaneous wavelength and intensity modulation. This framework facilitates the discrimination of acceleration polarities (± X, ±Y, ±Z) and yields a balanced tri-axis Full Scale Normalized Optical Sensitivity (FS-NOS) of [Formula: see text]. Systematic noise analysis reveals a NEA of [Formula: see text], supporting sub-µg resolution, while the minimum optical resolution for the Y-axis is calculated as [Formula: see text]. Furthermore, a sequential hierarchical decoupling approach is proposed to reconstruct 3D acceleration vectors from superimposed optical outputs. This work establishes a versatile framework for developing high-resolution, all-optical, EMI-immune plasmonic MOEMS tailored for precision inertial sensing.