Researchers at Harbin Engineering University and the University of New South Wales demonstrated the additive manufacture of silica optical fiber preforms. According to the research team, additive manufacturing, also known as 3D printing, could transform the way specialty optical fibers are fabricated. Using digital light processing (DLP) 3D-printing technology, the researchers extended small-scale glass “bulk or slice” printing of optical fiber preforms beyond a few millimeters to the centimeter scale. They constructed single- and multimode optical fibers by controlling the printing parameters during the fiber draw process. The capability to 3D-print complex geometries such as multicore fibers could help advance the development of Internet of Things (IoT) technologies. (a) Images of the 3D-printed preforms and subsequently filled cores; (b) optical fiber drawing tower used in this experiment; (c) temperature change of the fiber drawing process; (d) loss spectrum of the 3D-printed single-core and loss of seven-core fibers at 632.8 nm; (e) emission spectra of a single-core fiber excited by the 830 and 980 nm lasers. Courtesy of Y. Chu, X. Fu, Y. Luo, J. Canning, J. Wang, J. Ren, J. Zhang, and G.D. Peng. The fabrication of the 3D-printed preforms involved five steps. First, the researchers prepared ultraviolet (UV)-sensitive resin embedded with amorphous silica nanoparticles. They printed the preform using a commercial DLP 3D printer; then they filled the prepared resin into the holes of the printed cladding preform. This step was followed by thermal polymerization. The fourth step was a de-binding and pre-sintering process, driven by annealing, to remove moisture. Finally, the researchers performed high-temperature sintering to remove any additional impurities and fuse silica nanoparticles into glass during fiber drawing. By introducing several active dopants into the additive manufacturing process, the researchers showed that a diversity of materials can be used for 3D printing of optical fiber preforms. Germanium, titanium, and aluminum were used to form waveguides and enhance the core glass network structure of the optical fiber preform, making it conducive to luminescence. As the researchers increased the number of cores, they adjusted the drawing conditions to allow for lower melting points in the preform. The researchers used bismuth and erbium ions to create additively manufactured bismuth-and-erbium co-doped optical fiber (BEDF). The bismuth and erbium ions were co-doped into single-core and seven-core fibers drawn from 3D-printed preforms. The team fabricated multicomponent fibers and structured fibers. The BEDFs exhibited an ultrabroadband, near-infrared (NIR) luminescence covering all telecommunications O-L bands with 830-nm pump excitation. The researchers believe that BEDFs could become an active medium in fiber amplifiers for the next generation of fiber communication systems. Additionally, the researchers found that the fiber loss in the single-core fiber was substantially diminished when moisture was reduced through the additional annealing and sintering treatment included in the five-step printing process. Improving the symmetry of the fiber by increasing the roundness of the core and cladding also reduced the moisture in the optical fiber, effectively reducing fiber loss. Current optical fiber manufacturing, based on chemical vapor deposition (CVD) technologies and the stack-and-draw approaches used for structured optical fibers, faces numerous challenges in the fabrication of multimaterial composite fibers and multicore fibers, which could drive evolving technologies such as IoT. The researchers believe that optical fibers are moving away from being a single-function transmission technology to being able to perform multiple functions. As such, the researchers said, there will be a growing need for custom-designed, application-specific optical fibers. The researchers see additive manufacturing as a potential disrupter in the optical fiber fabrication space, expanding the functionality of specialty optical fibers and enabling applications such as multicore fiber fan-in/fan-out and ideal mode coupling in space division multiplexing without the need for optical fiber splicing. The research was published in Light: Advanced Manufacturing (www.doi.org/10.37188/lam.2022.021).