Design Of Photonic Crystal Fiber With High Birefringence And Low Confinement Loss

In recent years,Photonic Crystal Fibers（PCF）come out with their excellent characteristics different from traditional fibers,and the design of photonic crystal fibers has developed rapidly.The highly adjustable flexibility of the structure of photonic crystal fibers has unparalleled advantages in achieving characteristics such as birefringence,single-mode transmission,dispersion compensation,and nonlinear optics,the photonic crystal fiber has become a hot topic in the international optoelectronics industry..（1）This paper starts from the research background of photonic crystal fiber and describes the research status of high birefringence and low limiting loss photonic crystal fiber at home and abroad in detail.Then,based on Maxwell’s equations,including effective refractive index method,plane wave expansion method,beam propagation method,full-vector plane wave method,time-domain finite difference method,and finite element method.Finally,the general steps for designing PCFs based on the finite element method were explained,and the selection of boundary conditions during the PCF design process was provided.（2）A novel elliptical air-hole PCF was designed,the effects of changing the minor axis b of the elliptical core and the vertical distance d between circular air holes on the transmission characteristics of PCF1 were studied,leading to the identification of an optimal structure.Under this optimal structure,PCF1 exhibited a high birefringence of5.13×10^-2and a low confinement loss of 4.89×10^-6d B/m at a wavelength of 1.55μm,which represents a significant improvement in birefringence compared to existing elliptical PCFs.Additionally,the confinement loss,dispersion,and nonlinearity of the proposed PCF all exhibited excellent characteristics.（3）To address the issue of slightly high confinement loss,structural adjustments were made to the photonic crystal fiber core array,resulting in the design of PCF2,which effectively reduces confinement loss while achieving high birefringence.Additionally,two circular test air holes were added to the PCF2 core,and germanium and ethanol,which have higher and lower refractive indices than the substrate,respectively,were filled in the test holes.Simulation results found that filling the test holes with both germanium and ethanol increased the birefringence and reduced the confinement loss of PCF2.Finally,a summary of the research content was provided,and further explanations were given regarding the urgent issues and development prospects.