Localized in-line precipitation of metallic nanostructures in hybrid optical fibers

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Functional glass fiber has been the key component in a broad variety of optical devices, ranging from passive waveguiding in, e.g., telecommunication and data transfer, to active functionality in fiber light sources, optical amplifiers, sensors, filters and switches. However, for decades, the technological platform has been limited to a relatively small number of principal fiber architectures and, in particular, chemical compositions, where silica and silica-based glasses are still the most prominent fiber material. This has largely been due to fabrication limits and limits of material compatibility, which prevented exploitation of exotic glass properties such as, e.g., the extreme optical nonlinearity of chalcogenides or metal-doped glasses, with the processing stability and optical performance of silica. These so-called hybrid glass fibers today represent one of the major challenges for materials development and processing, as they enable pushing the limits of physical property engineering to beyond what is presently known. For example, they would enable extreme values of numerical aperture or, subject of the present proposal, extreme combinations of functional and passive material architectures for tailored profiles of physical properties. Filling glass-forming liquids (assisted through pressure or surface tension) into the micro- or nanobores of silica-based photonic crystal fiber or capillary devices has recently been introduced as a highly promising platform for fabricating the next generation of hybrid glass fiber devices. A standing issue in this emerging approach to dedicated optical glass fiber processing is, however, the tailoring of local materials properties. Such in line structuring, for example, the generation of dielectric gradients, optical gratings, grids or specific plasmonic activity, on the other side, is the prerequisite for the next step towards solving future device needs. Here, the present key is to obtain a dedicated understanding of such in line processing, its underlying thermokinetic and photochemical principles, and its physical limits. The present proposal therefore targets a fundamental understanding of the local precipitation of metallic nanostructures in hybrid optical fibers through external fields. We intend to explore the basic materials aspects which control particle precipitation inside an optical fiber device, providing mechanistic information on limits of reaction kinetics, lateral resolution, photostability and, most importantly, optical activity of such glass fiber. This shall need to a new generation of active fiber devices which combine the optical properties of silica with the plasmonic activity of photosensitive, metal-doped low-melting glasses.