Study On Birefringence And Sensing Properties Of Photonic Crystal Fibers

Photonic crystal fibers（PCFs）are composed of a periodic array or randomly arranged micro air holes acting as dielectric medium.Owing to its flexibility and variable structure in the cross section,PCF can achieve light guiding characteristics that cannot be achieved by traditional fibers,such as endlessly single mode transmission,high birefringence,high nonlinearity,and ultra-flat dispersion,etc.These special and excellent optical properties have revolutionized modern communication systems in the field of communications and sensing applications.This thesis focuses on the birefringence of PCF and its sensing characteristics.The main research contents are as follows:（1）A new type of V-shape photonic crystal fiber with full elliptical air-holes is proposed,which can realize high birefringence and nonlinearity simultaneously at the wavelength of 1550 nm.In this thesis,we use the full vector finite element method to investigate its characteristics,including the birefringence,the nonlinearity and the dispersion.The results show that the PCF can obtain very high birefringence of 2.89×10^-2 and very high nonlinear coefficient of 102.69 W^-1·km^-1.In particular,the PCF has two zero-dispersion wavelengths（ZDWs）.One of the ZDWs emerges in the visible region（X:640-720 nm and Y:730-760 nm）,which has important application value for the generation of high-power supercontinuum.The other one is located in the near-infrared region（X:1050-1606 nm and Y:850-1500 nm）,which has a strong inhibitory effect on the red shift of solitons.The combination of high birefringence,high nonlinearity and zero dispersion wavelength enables the PCF to maintain the polarization state and to generate a broadband supercontinuum,which play an important role in nonlinear optics.（2）We also design a high-sensitivity photonic crystal fiber whose core and cladding are microstructured structures,which is suitable for liquid analyte sensing application.We use a low refractive index chemical—ethanol,which has industrial value,to infiltrate the fiber core.Relative sensitivity and the confinement loss are investigated and optimized by changing the parameters of the structure at a wide wavelength range from1.0?m to 1.8?m within IR region.The results reveal that the PCF can obtain higher sensitivity of 68.51%for ethanol and the confinement loss of 7.55×10^-7 dB/m at a wavelength of 1330nm.The proposed PCF may have a potential impact on future applications in chemical and biological sensing.The designed photonic crystal fiber with different structures and characteristics can provide a certain reference value for the research of PCF based functional devices.It has great significance and potential applications in nonlinear optics and liquid sensing area.