An optical waveguide amplifier fabricated on erbium-ytterbium-doped phosphate glass by direct femtosecond laser writing is demonstrated. The waveguides are manufactured using 1040-nm radiation from a diode-pumped cavity-dumped Yb:KYW oscillator, operating at a 885 kHz repetition rate, with a 350 fs pulse duration. Peak internal gain of 9.2 dB is obtained at 1535 nm, with a minimum internal gain of 5.2 dB at 1565 nm. Relatively low insertion losses of 1.9 dB enable for the first time an appreciable net gain in the full C-band of optical communications.
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