Multi-parameter sensing based on surface plasma resonance with tungsten disulfide sheets coated.

A tungsten disulfide (WS) coated surface plasmon resonance (SPR) sensor based on gradient pitch Mach-Zehnder interferometer (GP-MZI) for measuring ethanol vapor concentration is proposed and verified by experiments. Under continuous CO laser heating, a MZI based on GP helix structure is fabricated by twisting single mode fiber (SMF), which can excites multi-order cladding modes. A gold film is deposited on the surface of the GP helix structure by a magnetic sputtering coating machine. WS film is coated on the gold film of the GP helix structure, which increases the evanescent field strength of the twisted structure surface and enhances the interaction between SPR wave and ethanol molecules. Since the absorption of ethanol molecules by WS sheets will cause the change of effective refractive index (RI) of WS film, the intensity of transmission signal can be adjusted accordingly. For multi-order cladding modes, the effective RI and the effective thermo-optic coefficient vary with the modal order, so the RI and temperature sensitivity of different modal orders are also different. So, the ethanol vapor concentration, relative humidity (RH), and temperature can be simultaneously measured by monitoring the intensity of those dips with the resolution of ± 0.030 mg/L, ±0.035%RH, and ± 0.010 ℃, respectively. This sensor structure provides a promising platform for multi-parameter sensing applications.