  Erbium-doped fiber amplifiers have revolutionized long-haul optical
communications and laser technology. Erbium ions could equally provide a basis
for efficient optical amplification in photonic integrated circuits. However,
this approach has thus far remained impractical due to insufficient output
power. Here, we demonstrate a photonic integrated circuit based erbium
amplifier reaching 145 mW output power and more than 30 dB small-signal gain --
on par with commercial fiber amplifiers and beyond state-of-the-art III-V
heterogeneously integrated semiconductor amplifiers. We achieve this by
applying ion implantation to recently emerged ultralow-loss Si3N4 photonic
integrated circuits with meter-scale-length waveguides. We utilize the device
to increase by 100-fold the output power of soliton microcombs, required for
low-noise photonic microwave generation or as a source for wavelength-division
multiplexed optical communications. Endowing Si3N4 photonic integrated circuits
with gain enables the miniaturization of a wide range of fiber-based devices
such as high-pulse-energy femtosecond mode-locked lasers.
