Design Of Polarization-maintaining Photonic Crystal Fiber For Optical Fiber Sensing Implementations

Photonic crystal fiber,also known as microstructured fiber,is a new type of fiber with structures and characteristics varied from traditional fibers.The photonic crystal fiber has flexible and adjustable structural parameters,with single-mode transmission without cut-off wavelength,adjustable zero-dispersion wavelength,high birefringence,large mode field area,and high nonlinearity.Its implementations in fiber sensing,high-power lasers and nonlinear optics are of great research value.To meet the demand of optical fiber sensing,this thesis proposes and designs two types of polarization-maintaining photonic crystal fibers with novel structures of.The research work is conducted as follows:(1)Based on fundamental principles and classification of photonic crystal fibers,the light guiding mechanism in photonic crystal fibers and the research status domestic and abroad are described,and various design and research methods of photonic crystal fibers are introduced.This work mainly analyzes and studies the fiber modeling and simulation method using the finite element analysis method(FEM).(2)A polarization-maintaining photonic crystal fiber with a solid core and shaped hole structure based on the total internal reflection is proposed and designed.The cladding hole structure with designed combination of elliptical holes and square holes is used to improve the birefringence characteristics of the optical fiber and also to achieve the single-mode single-polarization transmission effect.The software kit was used to analyze and simulate the light guiding characteristics of the designed fiber,and the effects of different cross-section structural parameters on the birefringence and confinement loss were compared and analyzed,which verified its potential in the field of polarization maintaining fiber sensing.(3)A hollow-core polarization-maintaining photonic crystal fiber with a concave-convex refractive index profile based on the photonic bandgap light-guiding mechanism is proposed and designed.The cross section of the optical fiber adopts a hollow-core photon bandgap structure,and the peripheral honeycomb cladding presents a high-low-high varied refractive index distribution along the radial direction.This refractive index profile in the cladding effectively reduces bending loss and improves dispersion flatness.This concave-convex structure photonic crystal fiber is modeled and compared with the traditional photonic crystalfiber.The unique features and optical characteristics including birefringence,dispersion and loss of this designed fiber are studied.In general,two types of polarization-maintaining photonic crystal fibers are designed and analyzed in this thesis and verified in detail using theoretical analysis and simulation methods.This work provides verified modelling and simulation,as well as design guidance,for the practical utilization in polarization maintaining optical fiber sensing applications in future.