The Fabrication And Characterization Of Chalcogenide Refractive Index Guiding Photonic Crystal Fibers

Photonic-crystal fiber(PCF) is a new class of optical fiber based on the properties of photonic crystals. Because of its ability to guild light with flexible confinement characteristics not possible in conventional optical fiber with core/cladding structure, PCF is now finding applications in fiber-optic communications, fiber sensors, fiber lasers, nonlinear optical devices, and many other emerging research areas. Refractive index-guiding PCF is a kind of fibers auxiliary regulated by air holes which realize the full inner reflection guiding by adjusting the number and distribution of holes in the cladding to decrease the refractive index of cladding compared with the fiber core. Refractive Index Guiding PCF may be considered a subgroup of a more general class of micro-structured optical fibers, where light is appropriately guided by flexible structural modifications, and not only by refractive index differences. Chalcogenides glasses(Ch Gs)are based on chalcogen elements(Sulphur, Selenium and Tellurium) and other additive elements such as Arsenic, Germanium, Antimony, or Gallium. Compared to silica glass their transmission window extends far in the infrared spectral region over the spectral range 0.5-1 μm to 12-18 μm,so it is the very ideal materials for preparation of infrared optical fibers and the researches about chalcogenide fibers have attracted much attentions.In this thesis, we study the fabrication and characterization of chalcogenide PCF and the main content includes the following:(1) The more mature Se based Ch Gs were improved and a systematic series of Ge20Sb5Se75-xIx(x = 0, 5, 10, 15, 20 at%) infrared(IR) chalcohalide glasses were prepared to decrease the weak absorption tail(WAT) and improve the mid-IR transparency. The structural evolutions of these glasses were revealed by Raman spectroscopy. The mechanisms of the halogen I affecting the physical, thermal, and optical properties were also deeply analyzed. On the basis of glass composition optimization, the optimal glass composition was determined as Ge20Sb5Se55I20. Because iodine is easy to be combined with water, it is very hard to purify the Ge-Sb-Se-I glasses. A feasible method to purify the glass through distillation was put forward, and the intensity of the impurity absorption peaks caused by Ge-O, H2 O, and Se-H was reduced or absent in the purified glasses.(2) The thermal drawing process of chalcogenide optical fiber preform is the essential step to ensure the successful preparation of chalcogenide PCF. The Ge20Sb5Se55I20 was selected for the preparation of the IR fiber based on the optimization of compositions. Then, Ge20Sb5Se55I20 chalcogenide glass fiber for mid-infrared transmission was fabricated using high-purity materials. The transmission loss of the Ge20Sb5Se55I20 fiber was greatly reduced compared with that of the Ge20Sb5Se75 glass fiber. The lowest losses obtained were 3.5 d B/m at 3.3 μm for Ge20Sb5Se75I20 fiber, which was remarkably improved compared with the 48 d B/m of the Ge20Sb5Se75 fiber.(3) The difficulties of chalcogenide PCF preparation lie in the preparation of PCF prforms. The advanced isolated stacked extrusion method was proposed to prepare chalcogenide glass fiber preforms and this method laid the foundation for preparation of chalcogenide glass tubes. Ge-Sb-Se/Ge-Sb-S fiber preforms with optimal stability of core/cladding ratio throughout the 160 mm length were prepared using the developed extrusion method. Typical fiber structure defects between the core/cladding interface, such as bubbles, cracks, and core diameter variation, were effectively eliminated. The transmission loss, fiber bending loss, and other optical characters of the fibers were characterized.(4) The stacking-extrusion method by fully combing the advantage of the stacking-capillary method and thermal-extrusion method was presented. Based on the optimal designed results of the PCF structure using multi-pole method, the As2S3 PCF with three layers of air holes was prepared and the dispersion characteristics, the zero dispersion wavelength, and the nonlinear coefficient was calculated using the multi-pole method. The 1550 nm fiber laser propagation effects and the laser spot energy distribution were measured. These results certificated the PCF light energy confinement ability in the infrared wavelength region.