Research On High Precision Micro-displacement Sensor Based On SPR

Surface plasmon resonance(SPR)is a novel sensing technology based on interactions between light beams and metal layers for detecting environment variables.The first prism structure SPR sensor model was proposed in the late 1970 s.With about five decades of development,now various optical-fiber SPR sensors are becoming a new hotspot,which is due to their high sensitivity.SPR sensor is typically used to detect refractive index and has a wide range of applications such as biomedicine,pharmaceutical industry,petrochemical industry and environmental monitoring.Though optical-fiber SPR sensor has been widely used for refractive index detecting,other physical variables are still needed to be researched.An optical-fiber micro-displacement sensor based on SPR for detecting submicron to micron sized micro displacement is proposed in this thesis.It is significant in the high precision detection equipment.This thesis launched some researches about optical-fiber SPR micro-displacement sensor on following aspects:1.The spectra of SPR can be influenced by both refractive index and incident angle.It is obvious that the function relationship between displacement and refractive index is hard to establish.By contrast,it is easy to establish the function relationship between displacement and incident angle.However,light beams propagate disorderly in optical fiber,which makes it difficult for establishing the function relationship between incident angle and displacement.To solve this problem,the property of beam propagation in graded index multimode fiber is lucubrated in this dissertation.Finally,the function between beam propagation path and incident angle in graded index multimode fiber is established.Hence,the function relationship between displacement and incident angle can be established easily as well.2.Based on the above study,a novel structure is proposed in this thesis.The graded index multimode fiber is welded with plastic cladding step index multimode fiber.The sensing region is a piece of gold firm coated on plastic cladding step index multimode fiber.A section of single mode fiber is placed at input end of graded index multimode fiber for controlling the incident beam which represents the displacement by calculating the distance between axes of single mode fiber and graded index multimode fiber.The displacement can change the incident beam path and thereby change the incident angle.The spectra of SPR can be influenced by the variation of the incident angle,as a result,the displacement sensing is achieved.3.To enhance the sensitivity of the sensor,the structure of the sensor is improved based on the above study.The sensing region is integrated on graded index multimode fiber by grinding the end-surface,which can reduce the beam divergence for increasing sensitivity and improving the spectra quality.Besides,the effects of grinding angle and the medium refractive index on sensitivity are also researched.The results indicate that sensitivity can be improved significantly by increasing the grinding angle or increasing the medium refractive index.The temperature noise is also studied in this thesis.It requires exacting control over temperature during the precise measurement for decreasing deviation.