Evanescent Field Optical Fiber Hydrogen Sensor Research And Experiment

A hydrogen sensor using evanescent field fiber requires an interdisciplinary study. It comprises the study of the thin film for the hydrogen sensing and the deposition technique, a surface plasmon resonance, the field distribution around the optical fiber, analysis of the power of evanescent field, the measurement approach and the data processing etc. The hydrogen sensors using evanescent field fiber is of complex technics and high sensitive.The design and implementation of hydrogen sensors using evanescent field fiber is introduced in this thesis. The research work mainly includes the hydrogen sensing principle of Pd film, the principle of surface plasmon resonance, study of highly steady laser light, fabrication of the tapered fiber and etched fiber, the deposition of Pd film, the encapsulation of sensor and the experimental results (including the design of the set-up) and the discussions.A structure of a hydrogen sensor using evanescent field fiber is presented. 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 of10-30nm and the hydrogen concentration is in 0~4%. Study the spread characteristic of the ray in the fiber. Analyse the geometry transmit characteristic of ray in the tapered fiber. Analyse the relation of evancent fild and optics constant of Pd film. To make sure the output result is exact, reference light is inducted. Establish the technics of eroding and encapsulating a single optical fiber. Study the flow of RF magnetron sputter.A special clamp for etching optical fiber and depositing Pd film on the fiber is designed. Designed a encapsulation set of the characteristics that is dampproof, shake and eroding resisted. 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.