Research On Novel Micro-structured Optical Fiber Devices Based On Material Modification

Micro-structured optical fiber（MOF）has broken through the limitations of traditional fiber because of their flexible structure design and the unique characteristics.MOFs bring out a profound revolution to fiber optics,and also provide a new way for the development of fiber technology and their application fields.In recent years,the research of MOFs and their applications has become a hot topic in the world,which provides a new opportunity to break through many bottleneck problems in the fields of optical communication,optical sensors,optical devices,quantum optics,biomedicine,etc.The air holes in the MOFs provide a natural channel for the modification of functional materials.By filling function material into the air hole,the modified MOFs can combine the the excellent optical properties of materials with the flexible structure design of the MOFs together,which provides a new way for further improving the performance of the MOFs,expanding its application scope and developing new optical devices.With the support of the project of National Natural Science Foundation of China and Beijing Jiaotong University doctoral innovation fund project,this dissertation has carried out theoretical and experimental research based on metal modified MOFs,especially,the research of broadband MOF polarization filters,single-mode cylindrical vector beam mode selector and high-performance fiber sensors.The main innovative achievements are as follows:1.A gold-coated micro-structured optical fiber with polarization filtering characteristic is proposed.Considering the tradeoff of enhancing surface plasmon resonance（SPR）and reducing the influence of gold coating on optical fiber loss,a large air hole is designed in the second ring of air holes of the cladding.It is not only convenient to realize the gold coating film but also to break the rotational symmetry of the optical fiber.The two polarization states of the fundamental mode are no longer degenerate.By coating gold film on the inner wall of the large air hole,a polarization state of the fundamental mode couples strongly with the surface plasma wave on the surface of metal,and thus the polarization filtering characteristic is realized successfully.Simulation results show that the loss of y-polarized fundamental mode and x-polarized fundamental mode are 2138.34 d B/cm and 2.03 d B/cm at the wavelength of 1.31 μm,respectively.Thus the loss ratio of y-polarized fundamental mode to x-polarized fundamental mode is 1054.3.When The fiber length of 300 μm is selected as polarization filter.The corresponding bandwidth of polarization extinction ratio of 20 d B is 530 nm covering the wavelength range from 1.15 μm to 1.68 μm.The maximum polarization extinction ratio reaches 525 d B.As a result,a broadband miniaturized polarization filter is successfully realized.2.For the first time,the composite gold nanowire is introduced into the ring-core MOF.The ring-core MOF filled with composite gold nanowire is proposed,which can realize quasi single mode cylindrical vector beam（CVB）transmission.By filling gold-quartz-gold composite nanowires into the air hole in the center of the ring-core MOF,the loss ratio of other modes in the ring-core to TE01 mode is greater than 50 within the wavelength range of from 1.3 μm to 1.39 μm,that is,90 nm bandwidth.The modes in the ring-core MOF can be effectively separated,and the quasi single TE01 mode CVB transmission can be realized by using gold-quartz-gold composite nanowires embeded MOF.Compared with the existing CVB single mode transmission system using optical fiber,the gold-quartz-gold composite nanowires embeded MOF not only has the advantages of simple structure and good stability,but also solves the problem of single mode transmission and high loss of single mode transmission.3.A gold-coated D-shaped MOF for refractive index sensing is proposed.In order to reduce the difficulty of gold coating,a D-shaped MOF is selected.By coating strip gold film on the side plane,the degrees of structural freedom are increased and the refractive index detection range of the sensor is also improved by adjusting the width of gold coating strip.With the optimal structure parameters,the sensor has a very wide refractive index detection range from 1.2 to 1.4 and a maximum sensitivity of 3751.5 nm / RIU.The refractive index resolution of the sensor is better than 1 × 10^-5 RIU.Compared with other MOF refractive index sensors based on metal modification,the designed sensor has the wider range of refractive index detection,which greatly extends the application of the refractive index sensor.4.For the first time,the method of embedded metal wire is applied to hollow core anti-resonant fiber（HC-ARF）.A single-layer elliptical tube HC-ARF modified by gold nanowire with polarization filtering performance is proposed.By embedding a gold nanowire into each of the two elliptical tubes in the horizontal direction,a polarization state of the fundamental mode couples strongly with the surface plasma wave.In the wavelength range of 200 nm bandwidth covering from 1.3 μm to 1.5 μm,the loss ratio of high-order mode and y-polarized fundamental mode to x-polarized fundamental mode are all greater than 100,and thus a good polarization filtering performance is achieved.In order to reduce the difficulty of fabrication,an improved metal modified HC-ARF is proposed by replacing the elliptical tubes with circular tubes.Two aluminum nanowires are embedded into the walls of two large horizontal tubes,and two small tubes are embedded in two horizontal tubes.The single polarization single mode region is effectively extended to 320 nm,covering the wavelength range from 1.26 μm to 1.58 μm.The cost of metal aluminum is much lower than that of metal gold.Therefore,the improved metal modified HC-ARF has the advantages of low preparation difficulty,wide bandwidth of single polarization single mode and low cost.The proposed fiber has a good application prospect in coherent hollow fiber communication system and ultra wide band laser polarization light source.5.A MOF multi-function sensor based on Sagnac interferometer is designed and fabricated by using the homemade MOF with a germanium-doped core.Four physical quantities can be detected separately.Experimental results show that the sensor has good pressure sensing characteristics.In the pressure measurement range from 0.4 MPa to 1.8 MPa,the ultra-high pressure sensitivity of 11.5 nm/MPa is obtained.In addition,the sensor is also sensitive to strain,curvature and temperature.In the axial strain range from 0 με to 4000 με,the strain sensitivity is 8.99 pm/με.The curvature sensitivity is-386.29 pm/m^-1 in the curvature range from 3.5 m^-1 to 6.0 m^-1.The temperature measurement range is from 25 ℃ to 65 °C,and the temperature sensitivity is 466.18 pm/ ℃.The multifunctional sensor has simple structure and stable performance,which can be used in many complex environments.