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 ( \:≈\:200\:nm ) and mechanical sensitivities ( \:SM≈\:100\:nm/g ) within a \:±\:2\:g range, operating across a bandwidth of \:≈\:473\:Hz . Structural stability is verified through pre-stressed analysis, showing negligible warpage ( \:≈\:1\:nm ) and a substantial safety factor ( \:≈\:10⁴ ), while maintaining minimal axis interference with cross-axis coupling \:<0.2% . 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 \:≈\:-6.29\:dB across the visible-to-near-infrared spectrum ( $$\:500-1500\:nm$$ ). 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 \:≈\:0.002\:nm⁻¹ . Systematic noise analysis reveals a NEA of \:≈\:0.78\:μ\:g/√Hz , supporting sub-µg resolution, while the minimum optical resolution for the Y-axis is calculated as \:61.07\:μ\:g . 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.