Research On Flexible Sensor Based On D-Shaped Optical Fiber

With the emergence and iteration of modern fiber optic technology,fiber optic sensing technology has gradually entered the daily life of human beings.D-shaped optical fiber,as the name implies,is an optical fiber with a cross-section in the style of the letter"D".As an emerging optical fiber sensing substrate,it has become a hot research topic in recent years because of its strong swift field,simple fabrication process,controllable insertion loss,and easy combination with functional materials.Although great progress has been made in sensing research on D-shaped optical fiber,its inherent problems such as easy fracture of sensing structure,cross-sensitivity,and difficulty in controlling the angle between the polished surface and the horizontal surface are difficult to solve.In this thesis,a new type of fiber optic flexible sensor is proposed by combining D-shaped optical fiber with flexible material PDMS in order to improve the flexibility of D-shaped optical fiber.Based on the above condition,this thesis investigates the D-shaped optical fiber multiparameter sensor based on PDMS film,flexible sensing based on D-shaped optical fiber and multiparameter sensor based on dual-core-D-shaped optical fiber,respectively.The main research contents are as follows:A D-shaped fiber multiparameter sensor based on PDMS thin film is proposed.First,a single-mode fiber is processed into a modified D-shaped fiber using a fiber polishing system to excite multimode interference.Then,the modified D-shaped fiber is encapsulated into a micron-thick PDMS film by a lifting-coating method to provide protection and a stable refractive index environment.Due to the asymmetric structure of the D-shaped fiber,the sensor can discriminate between two bending directions with high sensitivity,including curvature sensitivity(2.66 d B/m^-1),temperature sensitivity（0.344 nm/℃）,and stress sensitivity（0.26 pm/με）.Then,based on this sensor,a flexible sensor based on D-shaped optical fiber is proposed for real-time monitoring of dynamic bending and has potential for velocity sensing and displacement sensing.In addition,bending tests are conducted on this sensor to confirm its stability and repeatability,and it is applied to human finger and wrist bending to enable detection of finger and wrist bending amplitude and discriminate the bending direction of the wrist.The aim of this study is to investigate the dual-core-D-shaped fiber-based multiparameter sensor.In the experiment,an interference valley with an extinction ratio of about 15 d B can be observed by fusing the ends of a section of dual-core fiber to a single-mode fiber,using the Mach-Zender interference effect.Then the dual-core fiber is partially polished using a fiber polishing system so that the polishing surface destroys one core,and the optical range difference between the two cores is manipulated by changing the effective refractive index of the external environment for sensing purposes.The experimental results show that the maximum refractive index response of the structure is 188.06 nm/RIU when the refractive index varies from 1.344 to 1.375,and the maximum curvature sensitivity reaches 0.221 d B/m^-1 when the curvature varies from 0～2.56 m^-1.In addition,the sensor also exhibits extremely low temperature sensitivity.In the future,it can be applied to flexible sensing,shape sensing and other fields.