In recent years, a growing interest has settled for optical materials and fibers for the mid infrared (mid-IR) region. This interest originates from societal needs for health and environment for instance, and also from demand for defence applications. Indeed, the mid-IR spectral region contains the atmospheric transparent windows (3-5 μm) and (8-12 μm) where thermal imaging (military and civilian) can take place. The elaboration of chalcogenide microstructured optical fibers (MOFs) permits to combine the mid infrared transmission of chalcogenide glasses up to 18 μm to the unique optical properties of MOFs thanks to the high degree of freedom in the design of their geometrical structure. In this context, additive manufacturing of glass materials appears as an attractive technique to achieve more elaborate designs that can hardly be obtain using more common methods such as the stack-and-draw or molding. Taking advantages of the specific physical properties of chalcogenide glasses such as low Tg and extrusion temperature, we have shown that chalcogenide preforms can be rapidly obtained by fused deposition modeling (FDM) using a customized RepRap-style 3D printed fed with chalcogenide glass rods. Such as-prepared preforms can be drawn into chalcogenide optical fibers. Those early-stage results open a new way for the elaboration of chalcogenide MOFs.
Alternative way of synthesis for high refractive index tellurides based glasses has been experimented, in addition to low temperature Spark Plasma Sintering. The composition tested, Ge25Se10Te65, has been chose in the Ge-Se-Te system and characterized. Its index refractive index of 3.12 and overall optical, thermal and mechanical properties makes it the perfect candidate for IR application. However, due to its relative instability regarding crystallization, formation of GeTe crystals occurs during mechanical alloying using raw elements. Transparency has not been achieved in the sintered samples using this powder, as the crystallization rate is accelerated by the pressure during the process. In parallel, glass samples synthesized by melt-quenching have been used to determine optimal sintering parameters for this composition. The main issue met during those tests has been the carbon contamination, reducing overall transparency of the samples through scatterings. As such, it has been shown that the critical parameter to consider to limiting this pollution is the powder granulometry, needing to be above 100μm for optimal performance. This shows the potential for this method to produce high refractive index IR optics, using even unstable glasses.
Fiber Evanescent Wave Spectroscopy (FEWS) is an efficient way to collect optical spectra in situ, in real time and even, hopefully, in vivo. Thanks to selenide glass fibers, it is possible to get such spectra over the whole mid-infrared range from 2 to 12 μm. This working window gives access to the fundamental vibration band of most of biological molecules. Moreover selenide glasses are stable and easy to handle, and it is possible to shape the fiber and create a tapered sensing head to drastically increase the sensitivity. Within the past decades, numerous multi-disciplinary studies have been conducted in collaboration with the City Hospital of Rennes. Clinical trials have provided very promising results in biology and medicine which have led to the creation in 2011 of the DIAFIR Company dedicated to the commercialization of fiber-based infrared biosensors. In addition, new glasses based on tellurium only have been recently developed, initially in the framework of the Darwin mission led by the European Space Agency (ESA). These glasses transmit light further into the far-infrared and could also be very useful for medical applications in the near future. Indeed, they permit to reach the vibrational bands of biomolecules laying from 12 to 16 μm where selenide glasses do not transmit light anymore. However, while Se is a very good glass former, telluride glasses tend to crystallize easily due to the metallic nature of Te bonds. Hence, further work is under way to stabilize the glass composition for fibers drawing and to lower the optical losses for improving their sensitivity as bio-sensors.
Chalcogenide glasses are a matchless material as far as mid-infrared (IR) applications are concerned. They transmit light typically from 2 to 12 μm and even as far as 20 μm depending on their composition, and numerous glass compositions can be designed for optical fibers. One of the most promising applications of these fibers consists in implementing fiber evanescent wave spectroscopy, which enables detection of the mid-IR signature of most biomolecules. The principles of fiber evanescent wave spectroscopy are recalled together with the benefit of using selenide glass to carry out this spectroscopy. Then, two large-scale studies in recent years in medicine and food safety are exposed. To conclude, the future strategy is presented. It focuses on the development of rare earth-doped fibers used as mid-IR sources on one hand and tellurium-based glasses to shift the limit of detection toward longer wavelength on the other hand.
Chalcogenide glasses are well known materials due to their transparency in the infrared optical range and their ability to
be drawn into optical fibers. Such fibers can transmit light from 1 to 20 μm depending on the composition of the glass
constituting the fiber. Besides, microstructured silica fibers have been successfully used as fiber sensors as the holes can
be filled with liquid or gas to achieve overlap of the mode field (doing the sensing) and the sample. Since gas generally
shows a characteristic optical absorption spectrum in the mid-infrared, it can be detected selectively and quantitatively in
a given environment by analysing mid-IR spectra, in a region where silica fibers can't be used due to their low
transmission. Microstructured optical fibers made of chalcogenide glass will permit to implement this measurement and
detect species such as CO2 through its absorption band near 4.2 μm.
Among the measures to reduce CO2 emissions, capture and geological storage holds out promise for the future in the
fight against climate change. The aim of this project is to develop a remote optical sensor working in the mid-infrared
range which will be able to detect and monitor carbon dioxide gas. Thus, chalcogenide glasses, transmitting light in the
1-6 μm range, are matchless materials. The first of our optical device is based on the use of two GeSe4 chalcogenide
optical fibers, connected to an FTIR spectrometer and where CO2 gas can flow freely through a 4 mm-spacing between
fibers. Such sensor system is fully reversible and the sensitivity threshold is about 0.5 vol.%. Fiber Evanescent Wave
Spectroscopy technology was also studied using a microstructured chalcogenide fiber and first tests led at 4.2 μm have
provided very promising results. Finally, in order to explore the potentiality of integrated optical structures for microsensor,
sulphide or selenide Ge25Sb10S(Se)65 rib waveguide were deposited on Si/SiO2 wafer substrates, using pulsed
laser deposition and RF magnetron sputtering deposition methods. The final aim of this study is to develop a rib
waveguide adapted for middle-IR including an Y-splitter with a reference beam and sensor beam targeting an accurate
CO2 detection.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.