Characteristics Analysis And Theoretical Study Of The Photonic Crystal Fiber

In recent years, Photonic crystal fiber has become a popular topic in the field ofoptics because of its unique light transmitting properties. PCF is a two-dimension defectphotonic crystal structure, that is, along the axial extension, the micro-pore structuredistribute periodically in the transverse surface, which makes PCF can achieve newtransmission characteristics that traditional fibers can not achieve, such as highbirefringence, flexible dispersion characteristic and nonlinear characteristic.The primary works is:In order to fully investigate the basic propagation characteristics of photonic crystalfiber, multi-pole method and full vectorial finite element method are employed. TheCUDOS MOF Utilities software and finite element software-COMSOL Multiphysics areused to establish the models of photonic crystal fiber and give the specific steps. Based onthese models, the model field distribution, birefringence, dispersion and nonlinearcharacteristics are researched.(1) Three kinds of hybrid cladding photonic crystal fibers with different fiber coresare proposed, at the same time the properties of PCFs are compared and the PCF whichhas the better properties are chose. Then the influence of the air-hole diameter on thepropagation properties of the fiber is considered. The numerical simulation demonstratesthat different claddings of the PCF has the different influence on propagation properties:the birefringence is sensitive to the air-hole diameter of the innermost cladding; thechromatic dispersion is sensitive to the air-hole diameter of inner cladding but notsensitive to the air-hole diameter of innermost cladding and outer claddings; theconfinement loss is sensitive to the air-hole diameter of outer claddings and the number ofair hole rings. According to the regularity of the above, we propose a PCF structure inwhich highly birefringence with chromatic dispersion compensation and low confinementloss is obtained.(2) A highly nonlinear photonic crystal fiber is established by finite element method.In order to achieve ultrahigh birefringence, the first cladding is rectangular structure and the hole to hole spacings along the x-direction and y-direction are different. The othercladdings are octagonal structure. The highly birefringence and highly nonlinear can beeasily controlled by varying the air hole diameter. The theory proves that the birefringenceof the fiber is increase due to the increase of air-hole diameter. This could be explained bythe fact that as the air-hole diameter increase, the unsymmetry of the core area becomesbetter, which makes the birefringence increase. The nonlinear of the fiber is sensitive tosmall core area and highly duty cycles. In this paper, in order to achieve ultrahighnonlinear, we increase the air-hole diameter of the cladding surrounding the core todecrease the core area and increase the duty cycles, at the same time, this PCF also hasdispersion compensation function.