Optical waveguide writing is demonstrated by means of a diode-pumped cavity-dumped Yb:glass femtosecond laser oscillator with a pulse energy of 270 nJ at a 166-kHz repetition rate. Waveguides realized on an Er:Yb-doped phosphate glass are almost perfectly mode matched to standard single-mode fibers at 1.55 microm and show a 1.2-dB net gain in a standard telecommunications amplifier setup. Waveguide writing with a compact femtosecond laser oscillator is an important step toward introducing this technique into an industrial context.