Structure Design、Fabrication Process and Property Research of PANDA PMF
|School||Huazhong University of Science and Technology|
|Keywords||PANDA polarization-maintaining fiber birefringence polarization state fiber gyroscrope fiber communication|
With the development of high-bit-rate communication system and the high-precision fiber sensors such as fiber-optic gyroscope, the system control of polarization state becomes very important. Then, the technology related to the polarization-maintaining fibers and their applications is widely investigated and researched. PANDA polarization-maintaining fiber (PMF) is a single mode fiber with two circular stress regions induced symmetrically into its cross section, and obtains characteristically high birefringence properties due to the mode degeneration between LP01x and LP01y.The theoretical research, fabrication processing and optical properties of PMF are presented in this dissertation. The main contents are as follows:(1) The development status and their applications of PMF are synoptically investigated. The PMF principle, birefringence characteristics, fabrication process and applications in devices are respectively introduced in the exordium. Refer to the PMF specifications of oversea products, the development status is reviewed, and the technical bottlenecks restricting domestic field are analyzed for our national development.(2) Because the stress regions are induced into the cross-section of PMF, and special birefringence characteristics are embodied, it is necessary to analyze and design the structure parameters of PMF theoretically, to investigate the measurement principle of birefringence characteristics and to evaluate the mechanical reliability of PMF. In the part of product design, the stress model and Maxwell equation are respectively applied to the design of both the stress structure parameters and the core profiles, then the structure designs and specifications for PANDA PMFs are listed. In this dissertation, the concepts related to the polarization state are introduced, and a feasibility of measuring beat length operating in different wavelengths is analyzed by the method of measuring the group delay difference, then a measurement procedure suitable to industrialized production is opened after comparing with the other classical measurement procedures. Based on the lifetime forecast of conventional fibers, the failure principle and lifetime forecast for PMF are deduced after the residual stress is thought into the PMF structure. Then, the procedures are opened to evaluate the mechanical reliability of PMF.(3) In the part of fabrication process of this dissertation, the core technologies of conventional fibers are reviewed, and the process principle, process control and realization method of Plasma Chemical Vopour Deposition (PCVD) process are introduced mainly, related to domestic bottlenecks. Based on the discussion of features and principles of both PCVD deposition and cone formation in drawing process, the process parameters are investigated, respectively related to core rod and fiber properties. A method of“PCVD Big-preform Assembling Drawing Process”is deeply investigated to realize the long-length and low-loss PMF. The technical route, process step and realization method are respectively introduced in detail. Based on the property discussion of glass highly doped with boron, the material design and fabrication process are also opened in this dissertation. Then, after the process bottlenecks are overcomed such as the fabrication of stress application preforms with bigger size, the drilling process of solid silicon preforms, PANDA PMFs are successfully fabricated, with two classifications including five kinds of products.(4) The optical properties of fibers which are the proofs to judge fibers decide the communication characteristics. The geometrical properties are embodied by the optical properties, and the mechanical reliability of fiber is related to the application lifetime. After reviewing the measurement principles of birefringence and mechanical reliability, the measurement procedures related to geometrical properties, mechanical reliability, birefringence properties, optical properties and environment properties are also introduced. After fabrication process is optimized according to the measurement results, five kinds of products are industrialized finally.The main achievements of this dissertation are as follows:(1) The stress model is proposed to investigate the structure parameters of different stress application polarization-maintaining fibers. It is instructive for the design of stress region to calculate birefringences based on this stress model;(2) Reviewing the design of stress region, the dopant concentration of stress region, the refractive index profile in core and so on, the structure parameters and specifications of two classifications of PANDA PMFs are proposed with five kinds of products;(3) A measurement procedure of beat length with high precision and convenient operation is proposed to match the industrialization of PANDA PMFs;(4) Considering the residual stress into the investigation of failure and lifetime of PANDA PMFs, a method is proposed to evaluate their failure probability and mechanical reliability; (5) A method of“PCVD Big-preform Assembling Drawing Process”is proposed for the industrialized production with good uniformity and universal process, and the industrialization of PANDA PMFs are successfully realized with long-length and low-loss properties;(6) PCVD process is successfully applied to the fabrication of bigger stress application preforms, and the boron preforms are obtained with bigger diameter exceeding 10mm and dopant concentration of about 22mol%;(7) Drilling process with high precision and low roughness is successfully realized.