Studies And Experiments Of A Surface Plasmon Resonance-based Hydrogen Sensor Using A Tapered Fiber

A surface plasmon resonance (SPR) hydrogen sensor using a tapered fiber requires an interdisciplinary study. It comprises the study of the thin film for the hydrogen sensing, an SPR sensor, analysis of the field distribution around the tapered fiber, the deposition technique, the measurement approach and the data processing. The designed SPR hydrogen sensor using a tapered fiber is a novel approach as compared with the conventional electrochemical or resistance hydrogen sensor.The design and implementation of an SPR hydrogen sensor using a tapered fiber is introduced in this thesis. The research work mainly includes the hydrogen sensing principle of the Pd₉0Ag₁0 film, technology and simulation of the SPR sensor, fabrication of the tapered fiber, deposition of the Pd₉0Ag₁0 thin film, the experimental results (including the design of the set-up) and the discussions.A SPR hydrogen sensor coated with a palladium (Pd) film on the prism side is presented. A program in Fortran is made to numerically simulate and obtain the thickness of the Pd film and analyze the sensitivity of the hydrogen sensing system. The simulation results show that the sensitivity of the sensor is influenced significantly by the thickness of the Pd film. A highly sensitive system can be achieved when the thickness of the Pd film is in the range of 10-30nm and the hydrogen concentration is in 1%-10%. A novel sensor structure consisting of a combined Pd and gold (Au) thin film is investigated for the optical sensing of hydrogen. Composited Au/Pd hydrogen structure is optimized by a genetic algorithm. It indicates that the optimal layer configuration should be Au(2nm)/Pd(27nm) for achieving the best performance. Compared with the traditional pure palladium thin film hydrogen sensor, the sensitivity of the proposed structure is three times higher. A hydrogen sensor based on the integrated optical waveguide structure is promising and can give much better performance than prism sensors. The sensitive region of the waveguide is covered with a thin Pd layer whose optical constants are influenced by the concentration of the hydrogen in the surrounding medium. A finite difference method (FDM) is used to calculate the field distribution of the structure. The relationship between the waveguide property and the optical constants of the palladium layer is analyzed. The output power of the structure is calculatedby the beam propagation method (BPM) and an optimal thickness is obtained to achieve the maximal sensitivity. A novel measurement approach using two light beams is presented, which can be used in situ. The phase modulation technology is also introduced. The structure and the working principle of the tapered single-mode fiber for hydrogen sensing are designed, fabricated and studied. The techniques for fabricating the tapered fiber sensor are also presented. The transmission and reflection of the original guided light in the interaction section (where fundamental mode LP01 accounts for 95%) are approximately analyzed by considering the case of the transmission and reflection, respectively, of monochromatic plane waves.A new technique for the deposition of high-quality homogeneous Pd₉0Ag₁0 thin film on an optical fiber is reported. A special clamp for depositing Pd₉0Ag₁0 film on the fiber is designed. The film deposition is processed and the parameters are obtained by the experiment. The experimental set-up for hydrogen sensing includes the light source, gas cell, mass flow controller, stainless steel helical tubing and the detector, etc. The experimental results are also discussed.