Femtosecond laser micromachining optical waveguides on transparent silica xerogels

Femtosecond laser micromachining stands out as an efficient and flexible tool for fabricating optical waveguides, which are key elements in photonics for their ability to confine and direct light propagation. Different materials, from optical glasses to polymers, as well as geometries, have been studied for the fabrication of three-dimensionally inscribed waveguides. This work demonstrates, for the first time, the fabrication of Type II (double-line) waveguides by fs-laser micromachining in a transparent silica xerogel bulk synthesized by the sol-gel process. Specifically, double-line waveguides were fabricated by the multiscan approach at approximately 200 μm below the surface, with a distance between tracks of 20 μm. It was observed fundamental, first and second-order modes of the waveguides at 632.8 nm, which were corroborated by finite elements simulation. Finally, guiding losses of about 2.9 dB/cm were observed for the fundamental mode at 632.8 nm, which is similar to results obtained for Type II waveguides for other materials. Therefore, the intrinsic features of silica xerogel (e.g. low thermal conductivity, non-toxicity, lightness, and high optical transparency) combined to its light guiding ability indicate the potential of micromachined bulk silica xerogels for photonics devices applications.