Selenium modified GeTe 4 based glasses optical fibers for far-infrared sensing S. Maurugeon a , B. Bureau a,⇑ , C. Boussard-Plédel a , A.J. Faber b , P. Lucas c , X.H. Zhang a , J. Lucas a a Equipe Verres et Céramiques, UMR-CNRS 6226 Sciences chimiques de Rennes, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes, France b TNO Science and Industry, P.O. Box 6235, 6500 HE Eindhoven, The Netherlands c Department of Material Science and Engineering, University of Arizona, Tucson, AZ 85721, USA article info Article history: Received 16 June 2010 Received in revised form 25 November 2010 Accepted 29 November 2010 Available online 23 December 2010 Keywords: Tellurium glasses Optical fiber Infrared sensing Far-infrared abstract This study reports on the synthesis of telluride glasses that have transmission far beyond the second atmospheric window and are stable enough toward crystallisation to be drawn into optical fiber. These glasses are based on the GeTe 4 initial composition which has been stabilized by the introduction of few percents of Se and a modified the Te/Ge ratio. In that domain, Ge 21 Se 3 Te 76 constitute the optimum com- position and some mono index optical fibers have been successfully drawn. It is shown that their optical transparencies extend from 5 to almost 16 lm in the mid-infrared, establishing a record for chalcogenide glass fibers. These fibers have been used to implement Fiber Evanescent Wave Spectroscopy experiments, permitting to detect infrared molecule signatures beyond 12 lm, infrared domain that was unreachable by now. These innovative fibers are also used to detect the broad absorption band of gaseous CO 2 lying from 13 to 16 lm and therefore hold promises in the framework of the Darwin mission of the European Space Agency. Both of these results suggest that these new optical fibers will become essential in the field of infrared remote sensing. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Chalcogenide glasses have been studied for several decades in regards to different applications [1–9]. Sulphide glasses are mainly studied as hosts for rare earth doping and selenide glasses have excellent infrared transmission covering the two atmospheric win- dows at 3–5 and 8–14 lm. Telluride based compositions have been studied mostly as phase change materials for optical or electric storage of numerical data, as these compositions have a strong ten- dency to crystallize [10–12]. Nevertheless, telluride glasses can have transmission up to 25 lm far beyond the second atmospheric window [13–17] but this potential has attracted limited attention due to the lack of applications resulting from the strong atmospheric absorption in that range. More recently the research on these glasses have been intensified thanks to the European Space project Darwin whose objective is to discover extra solar earth-like planets and to analyse their atmosphere in the spectroscopic band of 6–20 lm. The sys- tem will be based in space and the operation band is set to cover the fundamental absorption of H 2 O, O 3 and CO 2 . These molecules are considered as markers for potential life on remote planets [18–21]. Carbon dioxide is also considered to be the most important green house gas responsible for global warming. The decrease of its production and its underground storage are important research subjects nowadays. The CO 2 molecule has a large absorption peak between 13 and 16 lm, much larger than the one in the 4.2 lm re- gion. Tellurium based glass fibers are the only glass fibers having a large enough optical window to cover this large absorption peak, making the underground monitoring of CO 2 possible for example [22,23]. Stable tellurium glass compositions have previously been ob- tained by combining this element with halogens [24], giving glasses in the Te–Cl and Te–Br systems. These glasses are stable against crystallisation, but suffer from low glass transition temper- ature T g and low environmental stability. Tentative has been made to increase the T g by introducing other elements such as As and Ge [25,26] but significant selenium content is, in these cases, also nec- essary to get crystallisation resistant glass compositions. More recently, tellurium based glasses have been studied start- ing from the GeTe 4 which is a bad glass former. Different third ele- ments such as gallium, iodine or selenium have been introduced into this binary composition in order to improve its resistance towards crystallisation. More stable glasses have been obtained [13–15,17] and one of the most promising solutions appears to be the introduction of selenium in order to increase the difference between T g and the crystallisation temperature to values greater than that of 79 °C for the GeTe 4 . But while large selenium content can greatly improve the resistance towards crystallisation; it also induce unacceptable absorption beyond 16 lm [27–31]. Hence, in this study we investigated the Ge–Te–Se glassy system in order 0925-3467/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2010.11.025 ⇑ Corresponding author. Tel.: +33 2 23 23 65 73; fax: +33 2 23 23 56 11. E-mail address: bruno.bureau@univ-rennes1.fr (B. Bureau). Optical Materials 33 (2011) 660–663 Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat