Femtosecond laser-based writing (FSLW) as a micro fabrication technique is employed to fabricate 3D microstructures such as waveguides and waveguide based devices inside the bulk material of interest. This paper describes the direct fabrication of buried channel optical waveguides inside hybrid sol-gel films by femtosecond laser. Particularly, we focus on the effects of writing parameters such as total exposure energy, and writing speed on the fabrication of buried channel waveguides. Additionally, the obtained refractive indices of the fabricated waveguides and their dependences on above parameters are provided. It was observed that at a given writing speed. the refractive index (RI) increases with the increase of total exposure energy. Furthermore, wider waveguides were obtained at lower writing speed while keeping the total exposure energy fixed. (c) 2005 Elsevier B.V All rights reserved.