Optical materials capable of advanced functionality in the infrared will enable optical designs that can offer lightweight or small footprint solutions in both planar and bulk optical systems. The University of Central Florida’s Glass Processing and Characterization Laboratory, together with our collaborators, have been evaluating compositional design and processing protocols for both bulk and film strategies employing multicomponent chalcogenide glasses (ChGs). These materials can be processed with broad compositional flexibility that allows tailoring of their transmission window, physical and optical properties, which allows them to be engineered for compatibility with other homogeneous amorphous or crystalline optical components. We review progress in forming ChG-based gradient refractive index (GRIN) materials from diverse processing methodologies, including solution-derived ChG layers, poled ChGs with gradient compositional and surface reactivity behavior, nanocomposite bulk ChGs and glass ceramics, and metalens structures realized through multiphoton lithography. We discussed current design and metrology tools that lend critical information to material design efforts to realize next-generation IR GRIN media for bulk or film applications.
Rare-earth (RE) doped optical fibers are extensively used in lasers and optical amplifier devices. These key applications rely on the qualities of silica glass: mechanical and chemical stability, high optical damage threshold, low cost, etc. However, silica glass has certain characteristics which may make it less efficient compared to other types of glass, particularly in some potential applications using RE ions: high phonon energy, low solubility of RE ions, etc. To overcome these limitations, one recent strategy consists of developing a fabrication method which triggers RE encapsulation in phase-separated nanoparticles. The development of this family of optical fibers was driven by this requirement: the particles must be as small as possible to avoid light scattering. However, recent studies discussed in this article tend to disapprove this doxa. First, we present the fabrication process of such fibers, emphasizing the drawing step as a process to control the shape and size of the nanoparticles. Then, we discuss on the characterization of the composition of these nanoparticles at the nm-scale. To reach this goal, we took advantage of a recent technology: Atom Probe Tomography. These results will be compared with molecular dynamics simulations. We demonstrate that the phase-separated nanoparticle composition and therefore the chemical environment of the encapsulated RE ions is nanoparticles size dependent. As a consequence, the smallest nanoparticles, promoted by the doxa, would offer limited alteration of the luminescent properties. Finally, light scattering is not only an issue but is also an opportunity to develop new temperature, strain, refractive index multiplexed optical fiber sensors.
The study of amorphous phase-separated Dielectric Nano-Particles (DNPs) smaller than 10 nm is a great challenge for the materials community. In conjunction with Transmission Electron Microscopy (TEM) and Electron-Probe Micro-Analysis (EPMA), we took advantage of a recent technology, Tri-Dimensional (3D) Atom Probe Tomography (APT) to investigate the variations of the chemical composition in sub-20-nm oxide nanoparticles, grown in silicate glass through heat treatments, at their early stages of nucleation. More precisely, we are investigating the core of an optical fiber drawn from a preform prepared according to the Modified Chemical Vapor Deposition (MCVD) process. We provide here a comprehensive set of experimental data obtained from direct measurements of the concentration for P, Mg, Ge and Er within amorphous dielectric nanoparticles (DNP) of radii ranging from 1 nm to 10 nm. We report on an increase of the concentration of Mg and P with the size of the DNPs. Most importantly, we also demonstrate that erbium ions are partitioned in these small DNPs and their environment changes with the size of the nanoparticles. Molecular dynamics simulations were also implemented to discuss the structural modifications of the Er environment. This presentation highlights the trade off on the size of the DNPs: smaller to reduce light scattering vs bigger to modify luminescence properties.