Research On The Basic Optical Properties And OAM Propagation Property Of The Novel Photonic Quasi-crystal Fiber

Photonic quasi-crystal fiber（PQF）is a new kind of micro-structure fiber after the invention of photonic crystal fiber（PCF）.Its lattice structure exhibits rotational symmetry and long-rang order,but no translational symmetry.Compared to the PCF,each of the lattice point affects the guiding mode individually,enabling PQF higher structural degrees of freedom,more methods of optimizing propagation properties and richer defect states.Therefore,PQF presents large advantages for tailoring the properties including chrome dispersion,confinement loss,nonlinear coefficient,et al.it thus is highly expected to apply in optical communication system,optical measurement,high-power laser,et al.In addition,the design of ring-core PQF can realize the robust transmission of orbital angular momentum（OAM）modes with high capacity and efficiency,which offers a well solution for broadening the technique of wavelength division multiplexing system and satisfies the ever-increasing requirement of capacity of transmitting information in the modern communication network.In this thesis,the dependence of optical properties on the structure parameters of silica-based PQF is investigated first and then specific PQFs are designed and analyzed for the optical communication system and high-power laser system.The methods of engineering specific fiber,guiding-mechanism and the propagation features of PQF are studied fundamentally,and the results are promising to provide a theoretical guidance for the research on the physical properties and fabrication technique of PQF.The innovative achievements of the thesis are as the followings.（1）A simulation is conducted to confirm the qualitative relationship between the optical preparties and structural parameters in PQF.The results show that confinement loss appears hopping mechanism as the air-filling fraction of inner cladding is more than 0.65 and the maximum peak of confinement loss presents an exponential function of wavelength.With the air-filling fraction increasing,the dispersion value decreases first,and then increases,approaching to the minimum value as the fraction nears 0.25.For the effective mode area,it enlarges as the ring number of inner cladding increases within a certain range of air-filling fraction.If not,it keeps almost unchanged.In addition,the order of rotational symmetry in PQF functions as the maximum diameter of air holes in uniform-air hole fiber and it strongly affects the propagation properties of PQF such as,propagation constant,distribution of electric field,dispersion,effective mode area and nonlinear coefficient.Therefore,it can be a well parameter for optimizing the propagation properties.Using the current six-fold rotational symmetry,the PQF supports the endlessly single-mode propagation with a high air-filling fraction0.575 that is around 30%higher than that of PCF.（2）A dual-cladding PQF with broad band,flattened and near-zero dispersion,low confinement loss and large effective mode area is proposed theoretically.The fiber can achieve a flattened dispersion of 0.014±0.293 ps/nm/km in wavelength range λ∈[1.27μm,1.67μm]with around 400 nm operation band covering all telecommunication windows.At wavelength 1.55μm,the confinement loss is less than 1.8×10^-4 d B/km and the effective mode area is higher than 25.7μm².It is also demonstrated that the fiber can almost maintain the well optical peripeties with a 3%structural deviation for the possible imperfect preparation and thus presents a well tolerability.To increase the resistance to bending degree,a low bending loss and large mode area PQF is proposed based on a gradient radical diameter with an endlessly single-mode propagation.It exhibits a low bending loss of 8.04×10^-3d B/km and a mode area of 1105μm² at communication wavelength with bending radius R=15 cm.The result confirms the fact that the design of gradient diameter structure can effectively imped the occurrence of deviation of fundamental mode from the fiber core and facilitate single-mode propagation when the fiber is bent strongly.（3）A novel design of OAM-supported Stampfli-type PQF with dual-cladding and ring-core is proposed.The fiber can realize a robust propagation for 6 OAM modes（or8 information-bearing states）in wide band of>200 nm.Optimizing the structure parameter of the ring-core,the effective index separation of constituent vortex modes in LP mode family can achieve a high order of 10^-2 to avoid the crosstalk between the OAM modes.The study shows that most of OAM modes exhibit a flattened dispersion and low confinement loss and can keep the well propagation properties within±3%deviation of diameter of all air holes.However,the higher order OAM modes suffers from larger dispersion.To compensating the accumulated dispersion,a dual-core PQF is proposed for dispersion compensation for controllable OAM mode with an achievement of large negative dispersion of-3039.45 ps/nm/km and high effective index separation of 2.15×10^-3for HE₃₁ mode at communication wavelength 1.55μm.Tuning fiber parameters can change the OAM mode for dispersion compensation.