A Highly Sensitive Fibre-Optic Nano-Displacement Sensor Based on Surface Plasmon Resonance

A highly sensitive fibre-optic nano-displacement sensor based on surface plasmon resonance (SPR) is proposed. The displacement sensing head consists of a single-mode fibre (SMF) with a plasmonic facet and a cladding partly removed single-mode fibre (CPR-SMF) with an air gap. The gold film is deposited on the end of the SMF instead of the flat of the CPR-SMF. The simulation results show that the SPR transmission spectrum shifts significantly toward shorter wavelengths with widening displacement. The relationship between SPR transmission wavelength and the displacement is sinusoidal, and the sensitivity of the proposed sensor can be as high as 31.45 nm/nm. The performance of the proposed sensor can be optimized by choosing a favourable combination of the gold film thickness of 40 to 50 nm and a residual cladding thickness of 100 to 150 nm. Because of the high sensitivity and compact configuration, it is feasible to achieve high sensitivity nano or angstrom displacement measurement and control.