Surface Plasmon Resonance-Based Fiber Optic Chlorine Gas Sensor Utilizing Indium-Oxide-Doped Tin Oxide Film

Fabrication and characterization of a surface plasmon resonance (SPR)-based fiber optic chlorine gas sensor are carried out. The fiber optic probe is fabricated by depositing a thin layer of indium-oxide-doped tin oxide over a silver-coated unclad core of the fiber. The SPR spectra of the chlorine gas for its different concentrations are obtained. It is observed that the resonance wavelength increases as the concentration of the chlorine gas increases and appears to saturate for higher concentrations of the gas. The sensitivity of the sensor depends on the thickness and the doping concentration of the indium-oxide-doped tin oxide film. The optimum thickness and the atomic weight percent doping concentration of the film are found to be 12 nm and 6 at. wt.%, respectively. To compare the performance, experiments are also carried out on probes coated with indium oxide and tin oxide layers over silver coated unclad core of the fiber. The performance of both the probes is found to be inferior to the one coated with indium-oxide-doped tin oxide layer. Further, the indium oxide doped tin oxide layer based probe is highly sensitive to chlorine gas for low concentrations. The sensor has low response time and is reversible. The proposed probe has advantages of online monitoring and remote sensing.