Surface modification of optical materials with hydrogen plasma for fabrication of Bragg gratings

We investigate the hydrogen plasma process as a route for creating Bragg gratings (BGs) on optoelectronic materials such as undoped lithium niobate (LiNbO(3)), proton-exchanged LiNbO(3), and soda-lime glass. Photopatterns (periodic modulations, Λ=323-2000  nm) were created on those substrates and the hydrogen plasma process was investigated for its ability to transfer the microstructures and the underlying mechanisms involved in this process. The diffraction efficiency and surface topology of the BG were characterized, as well as the optical properties of corresponding bulk materials undergoing the same plasma treatment. It is shown that the hydrogen plasma treatment changes the complex refractive index and modifies the surface topology with a volume expansion in the near-surface region, and both features are connected to the appearance of structural defects in the materials. The hydrogen plasma offers unique flexibility and advantages that can be explored for the fabrication of integrated photonic components.