Many important molecules show strong characteristic vibrational transitions in the mid-infrared (MIR) part of the electromagnetic spectrum. This leads to applications in spectroscopy, chemical and bio-molecular sensing, security and industry, especially over the mid- and long- wave infrared atmospheric transmission windows of 3-5 μm and 8-13 μm. In this paper, we review some of our more recent experimental and simulation work aimed at developing new light sources based on chalcogenide glass optical fibres that can help us utilize this spectral region for biomedical applications. This includes the development of supercontinuum and bright luminescent sources and our progress towards fibre-based lasers. We place these developments in the context of MIR imaging and spectroscopy in order to show how they bring the promise a new era in healthcare and clinical diagnostics.
Novel chalcogenide glass-based fiber opens up the mid-infrared (MIR) range for real-time monitoring and control in medical diagnostics and chemical processing. Fibers with long wavelength cut-off are of interest here. Sulfide, selenide and telluride based chalcogenide glass are candidates, but there are differences in their glass forming region, thermal stability and in the short and long wavelength cut-off positions. In general sulfide and selenide glasses have greater glass stability, but shorter long-wavelength cut-off edge, compared to telluride glasses; selenide-telluride glasses are a good compromise. Low optical loss selenide-telluride based long wavelength fibers could play a substantial role in improving medical diagnostic systems, chemical sensing, and processing, and in security and agriculture. For biological tissue, the molecular finger print lies between ~3-15 μm wavelengths in the MIR region. Using MIR spectral mapping, information about diseased tissue may be obtained with improved accuracy and in vivo using bright broadband MIR super-continuum generation (SCG) fiber sources and low optical loss fiber for routing. The Ge-As-Se-Te chalcogenide glass system is a potential candidate for both MIR SCG and passive-routing fiber, with good thermal stability, wide intrinsic transparency from ~1.5 to 20 μm and low phonon energy. This paper investigates Ge-As-Se-Te glass system pairs for developing high numerical aperture (NA) small-core, step-index optical fiber for MIR SCG and low NA passive step-index optical fiber for an in vivo fiber probe. Control of fiber geometry of small-core optical fiber and methods of producing the glass material are also included in this paper.
In the 21st century, cancer has become a common and feared illness. Early detection is crucial for delivering the most
effective treatment of patients, yet current diagnostic tests depend upon the skill of a consultant clinician and histologist
for recognition of the cancerous cells. Therefore it is necessary to develop a medical diagnostic system which can
analyze and image tissue instantly, removing the margin of human error and with the additional benefit of being
minimally invasive. The molecular fingerprint of biological tissue lies within the mid-infrared (IR) region of the
electromagnetic spectrum, 3-25μm wavelength. This can be used to determine a tissue spectral map and provide
information about the absence or existence of disease, potentially in real-time and in vivo. However, current mid-IR
broadband sources are not bright enough to achieve this. One alternative is to develop broadband, mid-IR,
supercontinuum generation (SCG). Chalcogenide glass optical fibers have the potential to provide such mid-IR SC light.
A popular chalcogenide glass fiber type is based on Ge-As-Se. For biomedical applications it is prudent to avoid the use
of arsenic, on account of its toxicity. This paper investigates replacing arsenic with antimony, towards Ge-Sb-Se smallcore
optical fibers for SCG. Physical properties of candidate glass pairs are investigated for glass stability via differential
thermal analysis etc. and fiber optical loss measurements of associated fibers are assessed. These results are compared to
analogous arsenic-containing chalcogenide glasses and optical fibers, and conclusions are drawn focusing on whether
there is potential for antimony chalcogenide glass to be used for SCG for mid-infrared medical diagnostics.