Authors : C.H. Tan, B.K. Yap and F.R. Mahamd Adikan
Abstract: Fiber optic sensing based on etched Fiber Bragg Grating (FBG) for concentration of ethanol solution is presented in this work. Different concentrations of ethanol solution were analyzed by observing the peak wavelength shift via Optical Spectrum Analyzer (OSA). FBG fiber sensor SMF-28 were chosen in this experiment with fiber cladding diameter 125 μm and fiber core diameter of 8.2 μm. A broadband signal from an Amplified Spontaneous Emission (ASE) light source was injected into the fiber through a 3-port circulator and the reflected spectra from the FBG was observed and monitored via an Optical Spectrum Analyzer (OSA) during the etching process. FBG wavelength was taken at time zero in room temperature environment before the etching experiment start. The fiber cladding was wet-etched by dipping the FBG in an aqueous solution of Hydrofluoric (HF) acid of 49% concentration, to enhance the FBG sensitivity to the surrounding Reflective Index (RI) change. Final FBG fiber thickness was then inspected and measured via Scanning Electron Microscope (SEM). The entire etching duration took about 20 min whereby the FBG thickness was etched from 125-9.7 μm. A total of nine different FBG thicknesses (125, 90, 58.30, 28.20, 12.60, 11.20, 10.90, 10.60 and 9.70 μm) were prepared by immersing in five different concentrations of ethanol (10, 15, 20, 30 and 40%). It is observed that the Bragg wavelength shifted more in higher concentration of ethanol and with thinner FBG. Peak wavelength for FBG with 9.7 μm thickness shifted 0.46 nm in concentration of 40% as compared to in 10% concentration with 0.33 nm shift. The peak wavelength for FBG with 90 μm shifted 0.03 nm in 40% of ethanol concentration compared to 0.01 nm in 10% of concentration. This proved that the FBG is more sensitive when the cladding thickness is reducing while in contact with high chemical concentration.On the other hand, FBG sensitiveness has linear relationship with FBG thickness.
C.H. Tan, B.K. Yap and F.R. Mahamd Adikan, 2016. Etched Fiber Bragg Grating to Detect Ethanol Concentrations. Journal of Engineering and Applied Sciences, 11: 1377-1378.