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

Abstract

Abstract 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 ( $$\:\approx\:200\:nm$$ ) and mechanical sensitivities ( $$\:{S}_{M}\approx\:100\:nm/g$$ ) within a $$\:\pm\:2\:g$$ range, operating across a bandwidth of $$\:\approx\:473\:Hz$$ . Structural stability is verified through pre-stressed analysis, showing negligible warpage ( $$\:\approx\:1\:nm$$ ) and a substantial safety factor ( $$\:\approx\:{10}^{4}$$ ), while maintaining minimal axis interference with cross-axis coupling $$\:<0.2\text{\%}$$ . 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 $$\:\approx\:-6.29\:dB$$ 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 $$\:\approx\:0.002\:{nm}^{-1}$$ . Systematic noise analysis reveals a NEA of $$\:\approx\:0.78\:\mu\:g/\sqrt{Hz}$$ , supporting sub-µg resolution, while the minimum optical resolution for the Y-axis is calculated as $$\:61.07\:\mu\:g$$ . 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.