Functional Optical Fibers with Tailored Side Emission from Modified Rod‐in‐Tube Preforms

Glass optical fibers with well‐defined light‐diffusing properties are an emerging class of light sources for functional and ambient illumination, from photodynamic therapy, agriculture, and photochemistry to architecture and interior design, whenever light with specific spectral characteristics needs to be delivered to difficult locations. This article presents a rod‐in‐tube method as a platform technology to fabricate light guides with tailored light diffusion and elastic and inelastic scattering properties. The approach is based on redrawing a preform made from chemically identical base glasses, whereby the stack interface is modified to include optically active or passive scattering centers. This technique enables the accurate radial placement of a longitudinal scattering layer within an otherwise homogeneous fiber, leading to superior robustness and mechanical performance in practical application. Soft borosilicate with an extended optical transmission window and a drawing temperature below 1100 serves as the base glass for stack manufacture, providing access to a wide variety of active and passive scattering species to be placed into the scattering layer. A slurry‐based approach and sol–gel technique for interface functionalization demonstrate the incorporation of iinescent lanthanide ions and noble metal nanoparticles to obtain side‐emitting light guides with tailored luminescent diffusion, localized surface plasmon resonance, and plasmon‐enhanced photoluminescence, respectively.