Microengineering of Optical Properties of GeO₂ Glass by Ultrafast Laser Nanostructuring

Abstract Nanostructuring in glass by ultrafast laser paves the way for integrated optics. In this paper, form birefringence induced by ultrafast laser direct writing in GeO₂ glass is systematically investigated. It is shown that the pulse energy for maximum retardance in GeO₂ glass is ≈65% lower than in fused silica. The induced retardance by laser scanning is two times higher than that by stationary irradiation under the same processing conditions. The optimum pulse duration for maximum retardance in GeO₂ glass lies within sub‐picosecond region, i.e., typically around 500 fs, while in fused silica it is in the picosecond regime at around 1–2 ps. A reversed polarization dependence of retardance at low pulse densities and low pulse repetition rates is observed in GeO₂ glass. As a result, two optical applications including a radial polarization vortex converter and a computer‐generated hologram are demonstrated in GeO₂ glass by spatial manipulation of the optical axis of the locally induced form birefringence. The microengineering of optical properties of GeO₂ glass by ultrafast laser direct writing may lead to new applications in near‐/mid‐infrared optics.