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.
For several years, chalcogenide glasses have been studied as good candidates for numerous applications in the midinfrared region. Indeed, these glasses are transparent from 1 to 20 μm (depending on the composition), a mid- IR windows well-suited for sensing molecules whose optical signatures are located in the 2-16 μm range. In addition, thanks to appropriate thermal properties, chalcogenide glasses can be drawn into fibers, including microstructured optical fibers. In this work, a new method based on 3D-printing process is investigated to produce hollow chalcogenide glass preforms, which are then drawn into hollow-core fibers. The transmission of the “printed” hollow-core fiber has been measured and compared to the initial glass. A significant, but still manageable, increase by a factor of 2.5 is observed. This works opens a promising way for the fabrication of chalcogenide MOFs, more particularly for the elaboration of hollow core fibers.
The last twenty years have seen a dramatic improvement in the performance of infrared detectors, especially those with uncooled microbolometer arrays. These make new commercial applications possible, from the Internet of things to drones for crop monitoring. Such emerging markets are constantly pushing the requirements on the existing technology to improve cost, performance, weight and size. In this context, gradient index (GRIN) lenses can offer a new degree of freedom compared to their homogeneous counterparts. For example, recent papers have shown how GRIN lenses could help reduce the number of elements in a system, by helping correct lens chromatism and athermalization. While the interest in using GRIN is obvious, mastering their fabrication with infrared materials remains highly challenging. Encouraging progress has been made in that direction, for instance by stacking different materials or by laser writing. Very recently, it has been demonstrated that partial crystallization of chalcogenide glass allows for tuning the refractive index. In this paper, we introduce a new technique based on the controlled formation of nano-crystallites in chalcogenide glass to fabricate the first macroscopic radial GRIN in the infrared. We also propose a simple way to test the index gradient value by interferometry and demonstrate GRIN with index contrast of ▵n ~ 3⋅10-2 between the center and the edge of the disk. The process is easily repeated and opens the possibility for a rapid transfer to the industry.
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, we have shown that chalcogenide preforms can be obtained by an original additive manufacturing process We have also shown that these preforms can be drawn into chalcogenide optical fibers. Those early-stage results open a new way for the elaboration of chalcogenide MOFs with more elaborate designs.
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