Chalcogenide optical fibres based on gallium lanthanum sulphide-Se for passive and active applications

Chalcogenide optical fibres contain mixtures of chalcogen elements (i.e. S, Se and Te) bonded covalently to other metallic elements that facilitate a stable glass formation. Our work in particular focuses on chalcogenide glasses containing a high proportion of lanthanum, that is gallium lanthanum sulphide glasses (GLS). These glasses due to their nature are characterized by a range of desirable properties such as chemical durability, host for rare-earth (RE) ions, low thermal expansion, high laser damage threshold, density and refractive index and a good transparency in the infrared (IR) region. Characteristics that are beneficial for active and passive applications such as sensors or high-energy IR laser power delivery, as examples. To increase the IR transmission window of GLS glasses a new family of chalcogenides have been developed, incremental additions of Se to the GLS glasses have proved their value to improve the transmission spectrum from visible to Long Wavelength Infrared (LWIR) range up to 15μm, depending on the composition. The strong thermal and mechanical characteristics of GLS-Se glasses compared to GLS have also shown that they can suit the production of optical elements, such as optical fibres that require certain thermal and mechanical stability for fibre drawing to avoid crystallization and breakages. [1-5] Theoretical minimum loss predictions in GLS based optical fibres have shown up to 0.5 dB km-1 at 3.5 μm, used in thermal imaging, unfortunately we are still far from that value but big efforts are being made to improve the production of optical fibres as shown in Fig. 1 by obtaining novel processes and more pure raw materials. [6] Chalcogenide RE doped glasses have demonstrated laser action, showing that they are suitable for active applications such as optical amplifiers and lasers [7]. The aim of this research is to join the well-known properties of chalcogenides glasses for the IR region with the development of a novel process to obtain functional passive and active optical fibres and prove the reliability as a host for RE ions, future work will include laser demonstration