However, the presence of lead oxide in the glass composition contributes to the downgrade of both thermal and mechanical properties, i.e., Tg below 400 ☌ and Vickers hardness down to 2.5 GPa 7, while restricting their use in various application fields due to severe worldwide regulations on lead-containing products. To date, minimal germanate losses (200 dB km −1) were obtained in lead-germanate glasses 6.
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Indeed, their Tg can reach 700 ☌, their optical transmission windows can span from 0.28 up to 5.5 μm and their Knoop micro-hardness can extend up to 5.1 GPa 5. Although the fluoride glasses expand over a large choice of glass compositions, including the zirconium fluoride, indium fluoride or aluminum fluoride families, these soft glasses possess a low glass transition temperature (Tg), while their reduced thermal/mechanical/chemical stability compared to other MIR glasses makes their handling more challenging 3, 4.Īmong other MIR glasses, germanate glasses are one of the best alternatives to fluoride glasses in terms of thermal and mechanical properties. The development of fluoride fibers has somehow overcome most of the other MIR glass families, with a wide range of fibers now commercially available. As a result, complementary MIR-transmitting glass families have been discovered and developed, including tellurite, chalcogenide, fluoride and germanate glasses. However, silica fibers do not transmit light above 2.5 μm and thus cannot be employed for applications in the so-called mid-infrared (MIR) domain 3. Accordingly, to the best of our knowledge, we report the lowest losses ever measured in a BGG glass fiber i.e., down to 200 dB km −1 at 1350 nm.įollowing the outstanding development of low-loss silica fibers in the 1970s, the emergence of high-speed long-haul telecommunication systems and high-power fiber lasers have revolutionized our daily lives 1, 2. Each of the three factors is then addressed in setting up a protocol enabling the fabrication of low-loss optical fibers from gallium-rich BGG glass compositions. In this article, we first identify the three most important factors that prevent the fabrication of low-loss BGG fibers i.e., surface quality, volumic striae and glass thermal-darkening. However, over 30 years of fiber fabrication optimization, the final missing step of drawing BGG fibers with acceptable losses for meters-long active and passive optical devices had not yet been reached.
To overcome these issues, the parallel development of heavy-metal oxide optical fiber from the barium-germanium-gallium oxide vitreous system (BGG) has revealed a promising alternative. Although the commercialization of FCGs-based optical devices has rapidly grown during the last decade, their development is rather cumbersome due to either poor crystallization and hygroscopicity resilience or poor mechanical-thermal properties of the FCGs. To date, most mid-infrared glass-based devices are employing fluoride or chalcogenide glasses (FCGs). The development of efficient and compact photonic systems in support of mid-infrared integrated optics is currently facing several challenges.
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