Ultrafast laser produces permanent optical waveguides in bulk glass
Researchers at the Hirao Active Glass Project (Kyoto, Japan) fabricated permanent waveguides in various bulk glasses by focusing 120-fs pulses from a regeneratively amplified Ti:sapphire laser system through a microscope objective and translating the glass sample parallel to the axis of the laser beam. The laser pulse photoinduced a refractive-index change in the glass. The laser wavelength was 800 nm, peak power was 109 W, and the glass sample was translated at a rate of 20 µm/s. The refractive-index changes were induced along the path traversed by the focal point, and the waveguides were written inside glasses such as fused and synthetic silica, germanium-doped silica, fluoride glasses, and others. The researchers also found that control of the refractive-index difference and core diameter was possible by adjustment of the writing conditions, such as the average power of the writing laser. Single-mode propagation was seen for small core diameters, while higher-order modes were observed with an increase of the core diameter. The work suggests new possibilities in integrated optics and three-dimensional optical circuits, especially in the area of compact, all-solid-state lasers, amplifiers, and switches.