Surface plasmon resonance humidity sensor based on twisted long period fiber grating coated with tungsten disulfide film

A novel surface plasmon resonance (SPR) sensor based on tungsten disulfide (WS2) for relative humidity (RH) sensing is proposed. A spiral twisted long period fiber grating (ST-LPFG) is fabricated by twisting the single-mode fiber (SMF) by hydrogen oxygen flame heating. A layer of gold film is deposited on the surface of the ST-LPFG, and then a layer of WS2 film is deposited on the surface of gold film by natural evaporation. The results showed that the strength of the evanescent field on the surface is enhanced by the WS2 film, which enhances the interaction between the SPR wave and the external matters. These features significantly improve the sensitivity of the proposed humidity sensor. The experimental results show that the sensitivity of the humidity sensor based on WS2 film coated ST-LPFG is up to 37.3 pm/% RH. At the same time, the humidity sensor based on WS2 nanomaterials has good response characteristics. The sensing scheme proposed in this paper provides a promising platform for humidity application.