3D luminescent waveguides micromachining by femtosecond laser inscription in niobium germanate glass

Three-dimensional (3D) microstructures were written by femtosecond (fs) laser aiming to manufacture waveguides inside niobium germanate glasses. The laser-induced damage threshold using 1030 nm fs-laser irradiation was investigated, and the waveguides were written in different fluences. The morphology, structural information and refractive index changes of microstructures were discussed. The waveguide cross-section microscopy data shows an elliptical shape with a diameter varying with the applied pulse energy. The micro-Raman maps demonstrate the occurrence of structural modifications with different microregions along the laser propagation direction. The refractive index profiles point to the formation of at least one microregion containing a positive refractive index change along the laser propagation. Guided light transmission measurements demonstrate the formation of single-mode waveguides inscribed at low pulse energy (up to 132 nJ) and an emitting waveguide in the rare-earth-doped sample. The visible luminescent response of erbium ions in the waveguide output was demonstrated and supports the possibility of using these core waveguides for future 3D multi-functional photonic devices operating in the visible region.