Nucleation and growth behavior of tellurite-based glasses suitable for mid-infrared applications.

摘要

Optical fibers transmitting in the 2-5 mum mid-infrared (MIR) spectral region are highly desirable for a variety of military and civilian applications including supercontinuum generation, infrared countermeasures (IRCM), and MIR laser sources. These new applications in the mid-infrared require novel optical materials that transmit in this window and can be fabricated into fiber. As tellurite glasses are known to have good transparency in the (NIR) region, tellurite-based glasses are the material of choice for this study due to their high linear and nonlinear refractive index, their low glass transition temperature and the ability to form them into optical fiber.;This dissertation summarizes findings on tellurite-based glasses with the composition (90-x)TeO2-10Bi2O3-xZnO with x = 15, 17.5, 20 and 25 that were processed and characterized for their potential application as novel optical fibers. Different techniques were deployed for characterization purposes, which include primarily linear refractive index measurements, structural characterization using Raman spectroscopy, and nucleation and growth behaviors, among others. The viscosity of the glasses was measured using a beam bending and parallel plate viscometers. The kinetics of crystallization of the bulk glasses and fiber with x =20 were studied using a differential scanning analyzer (DTA), a hot stage XRD and an optical microscope.;The influence of compositional variation on the physical, thermal and optical properties of the glasses in the TeO2-Bi2O 3-ZnO family was established. The parameters such as the thermal properties, activation energy for crystallization, Johnson-Mehl-Avrami exponent, or nucleation and growth domains and rates were determined and were found to depend on the glass composition. We correlated the composition-dependent variation of these parameters to the structure of the glasses via Raman spectroscopy. Key physical, thermal, structural and optical differences were observed and quantified between bulk glasses and their corresponding core and core-clad fibers. Also reported are the processing and characterization of modified tellurite-based glass in the TeO2-Bi2O3-ZnO glass family and efforts to reduce their absorption loss due to residual hydroxyl (OH) content. We discuss the impact of this OH reduction in the tellurite network on the physical, thermal and structural properties as well as nucleation and growth behavior of bulk glass and fiber.