Novel Chemical Routes to Crystalline ZnSe Fiber Optics and Fiber Lasers

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Author:
Aro, Stephen Christopher
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
May 25, 2017
Committee Members:
  • John V Badding, Dissertation Advisor
  • John V Badding, Committee Chair
  • Raymond Edward Schaak, Committee Member
  • Benjamin James Lear, Committee Member
  • Venkatraman Gopalan, Outside Member
Keywords:
  • Cr:ZnSe
  • Zinc Selenide
  • Transition-metal doped
  • HPCVD
  • High Pressure
  • HPCVT
Abstract:
The global fiber optic network is the workhorse of the digital age; without it, the implementation of internet-enabled technologies on the current scale would be impossible. In addition to telecommunications, fiber optics play important roles in fields such as optical sensing, medical surgery, and manufacturing. Despite this success, there are limits to the amorphous glass fiber optic technology in use today. Specifically, when compared to crystalline materials, glasses exhibit higher fundamental loss limits and lower damage thresholds. Additionally, the lanthanide doped glass fiber lasers that have seen great commercial success to date are not continuously tunable over large wavelength ranges, limiting their applicability. However, despite the potential benefits of crystalline fiber optics and fiber lasers, their synthesis has proven challenging, due to their general incompatibility with traditional fiber optic fabrication methods, limiting the advancement of this promising field. This dissertation presents novel chemical, analytical and materials processing methodologies to create crystalline fiber optics and fiber lasers. Specifically, both ZnSe waveguides and the world’s first continuous wave Cr:ZnSe fiber lasers are presented. Intrinsic and doped crystalline ZnSe fiber optics with centimeter lengths and axial dimensions of microns have been created using high pressure chemical vapor deposition (HPCVD), in which MPa pressure gradients drive gas-phase precursors into ultra-high aspect ratio templates, such as silica microcapillaries. In order to decrease the optical loss in these structures due to impurities, gas-phase mass spectroscopy of precursor mixtures and ultra-high vacuum precursor preparation have been integrated into the HPCVD methodology. To decrease loss owing to the scattering of light from grain boundaries, microscale chemical vapor transport and in-fiber laser annealing have been developed. These techniques have been shown to impart improvements in material crystallinity as measured by Raman spectroscopy and x-ray diffraction, while decreasing thermal requirements by hundreds of degrees. Additionally, by establishing an analytical feedback loop using photoluminescence and micro-FTIR spectroscopies to inform modifications to microbubbler technology, dopant concentration in fabricated Cr:ZnSe structures has been increased, increasing optical gain. In addition, the optical losses stemming from several mechanisms in the fiber optics have been improved. Together, this has led to the Cr:ZnSe fibers displaying continuous wave laser emission from an end-pumped geometry, an important indicator of practical applicability. In summary, novel synthetic solid state chemical methods have been developed, leading to crystalline fiber optics and fiber lasers and overcoming the limitations of previous approaches.