The fabrication and characterization of infra-red optical fibre, ultra-thin fibre and large diameter chalcogenide glass

Abstract

The development of speciality infra-red glasses has produced a number of alternative compositions which have become well established for many applications, both for industrial use and academic research. Among them, gallium lanthanum sulphide glass (GLS) is a particularly suitable competitor. This glass possesses a tunable and uniquely located transmission window among chalcogenides, ranging from 500 nm to 15 µm in bulk glass. In addition to its mechanical strength and high transition temperatures, the combination of visible and infra-red transmission makes this glass an exceptional candidate for a variety of applications, such as thermal imaging and chemical sensing. The thermal properties of GLS make shaping it to conform to a particular application delicate and challenging work. In particular, its crystallization temperature lies near its softening temperature, making any process involving softened or molten glass highly time constrained. In this work, previously established techniques have been revisited and improved upon, and a set of novel methods have been developed and employed, in order to enable gallium lanthanum sulphide to fulfil new applications. In particular, oxygen-free GLS fibre has been fabricated, significantly increasing the breadth of its transmission window in fibre form. Optimization through design of experiments (DOE) has allowed to fabricate crucible-drawn GLS fibre for the first time. Further refinements of GLS processing developed herein include the fabrication of ultra-thin fibre (less than 10 µm in diameter), casting and cutting into fibre drawing preforms and the fabrication of large diameter (>90mm) windows. Its glass formation range has also been expanded by increasing the quenching rate, new characterization methods have been implemented, and in-house polishing techniques for cylindrical sections of glass have been developed. Overall, this work has advanced the use of chalcogenides based on GLS for a number of applications which include infra-red optical fibre fabrication, multi spectral windows, chemical sensing and imaging fibre bundles.

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ORCID for Daniel Hewak: orcid.org/0000-0002-2093-5773

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