We use a two-dimensional deformable mirror to shape the spatial profile of an ultrafast laser beam that is then used to inscribe structures in a soda-lime silica glass slide. By doing so we demonstrate that it is possible to control the asymmetry of the cross section of ultrafast laser inscribed optical waveguides via the curvature of the deformable mirror. When tested using 1.55 um light, the optimum waveguide exhibited coupling losses of ˜ 0.2 dB/facet to Corning SMF-28 single mode fiber and propagation losses of ˜ 1.5 dB-cm -1. This technique promises the possibility of combining rapid processing speeds with the ability to vary the waveguide cross section along its length. © 2008 Optical Society of America.