ZBLAN in Space: Comparing Phase Transitions in Microgravity versus Earth’s Gravity

A. De
United States

Keywords: fiber-optics, ZBLAN, space, ISS, photonics, material science, phase transitions, glass


Apsidal sent its \emph{Universal Intelligent Glass Optics Manufacturing Module (UNIGLO)} payload to the ISS as a part of NASA's In-Space-Manufacturing (InSpa) program. The module was launched on NG-17's Cygnus Capsule as a part of Expedition-66. UNIGLO was a science and technology demonstrator whose ISS mission had four primary scientific objectives: mapping thermal profiles in microgravity, measuring phase transitions in extic glasses, drawing ZBLAN fibers under microgravity conditions, and employing a novel custom laser-interferometer and an AI-feedback control system to improve spooled fiber quality in-situ.For this talk we will discuss glass- and crystallization-transition test results from the International Space Station (ISS) which essentially pave the way for advancing the production of high-valued exotic-glass optical fibers in low-Earth orbit. The comparative behavior of ZBLAN glass undergoing phase transitions in both microgravity and Earth’s gravitational environments was investigated and we find the bulk-glass to be more resistant to crystallization in space. However, the surface continues to be vulnerable under ambient conditions. We conducted a set of 10 differential-calorimetry tests in the Microgravity Science Glovebox, including 2 sets of controls. A similar number of control tests were performed on earth. We subjected our samples to very high temperatures exceeding 430 C and studied and identified various types of crystal formation. We identified several crystals that do manage to form in space that can be orders of magnitude larger and very well faceted. However the fluoride glass also seems to harden in microgravity and becomes more resistant to crystal growth in the bulk. This manner of data collection and metrology is vital to inform future mitigation strategies for manufacturing advanced exotic-glass optical fibers in space.