Fabrication And Sensing Properties Of Surface Microstructured Micro-Nano Gratings

With the rapid development of microfiber technology and good application prospects,the outstanding strong evanescent field and high light confinement of microfiber not only provide feasibility for its integration with photoelectric functional materials,but also introduce fiber grating formed by periodic changes of refractive index along its axial direction to form significant modulation effect on conducted light.In addition to periodic modulation of the refractive index of the microfiber in the axial direction,the cross section of the fiber is processed into a specific shape before the taper is fused,and the mode refractive index and mode field distribution are achieved by changing the waveguide structure in the radial direction Adjusting the parameters to obtain micro fibers with special optical properties greatly increases the flexibility of fiber photonic device design,effectively expands its application range,and further enriches the physical connotation of microfibers.The research work of this thesis is to prepare a new structural modulated ultralong period microfiber grating(SULPMG)by combining electric arc discharge and flame-heating drawing technology.The transmission characteristics of SULPMG are analyzed by using local coupled mode theory,and the two-parameter sensing characteristics of its refractive index and temperature and micro-displacement and temperature are theoretically analyzed and experimentally verified.At the same time,a dual-directional weak magnetic field sensor is developed in combination with the core offset section.The research work of this thesis mainly includes:1.A SULPMG was prepared by combining electric arc discharge and flame-heating drawing technology.Microfiber gratings with different waist diameters and periods can be prepared by means of parameters such as discharge time and intensity of fusion splicer,and step distance and speed of high-precision translation stage of flame-heating drawing equipment.The local coupled mode theory is used to analyze the changes of the mode field distribution,refractive index distribution and coupling coefficient distribution of the core fundamental mode and cladding mode with the geometric structure and the finally formed transmission spectrum characteristics.2.The dual-parameter sensing characteristics based on SULPMG are studied.By obtaining the sensitivity of refractive index,temperature and microdisplacement,the dual-parameter sensing matrix is designed to realize the dual-parameter sensing of refractive index and temperature and the simultaneous measurement of microdisplacement and temperature.The theoretical analysis and light field simulation respectively verify that the sensing sensitivity of grating increases greatly with the decrease of waist diameter.The experimental results agree with the theoretical analysis.3.A dual-directional weak magnetic field sensor based on SULPMG and core offset section is proposed.Based on the tunable refractive index of magnetic fluid,when magnetic fields which perpendicular or parallel to the light propagation direction is applied to the sensing device,the refractive index of magnetic fluid decreases or increases correspondingly,thus realizing high sensitivity detection of dual-directional weak magnetic field.The distribution characteristics of light field before and after filling into magnetic fluid are simulated and the change of resonance wavelength with the intensity of applied magnetic field is analyzed in detail.