A photonic integrated circuit–based erbium-doped amplifier

Erbium-doped fiber amplifiers revolutionized long-haul optical communications and laser technology. Erbium ions could provide a basis for efficient optical amplification in photonic integrated circuits but their use remains impractical as a result of insufficient output power. We demonstrate a photonic integrated circuit–based erbium amplifier reaching 145 milliwatts of output power and more than 30 decibels of small-signal gain—on par with commercial fiber amplifiers and surpassing state-of-the-art III-V heterogeneously integrated semiconductor amplifiers. We apply ion implantation to ultralow–loss silicon nitride (Si 3 N 4 ) photonic integrated circuits, which are able to increase the soliton microcomb output power by 100 times, achieving power requirements for low-noise photonic microwave generation and wavelength-division multiplexing optical communications. Endowing Si 3 N 4 photonic integrated circuits with gain enables the miniaturization of various fiber-based devices such as high–pulse-energy femtosecond mode-locked lasers. The success of long-haul optical communications and our information society is largely due to the invention of the erbium-doped fiber amplifier. Because the need for faster chips is expected to see a shift from electronics- to photonics-based technologies, erbium ions could form the basis for amplification in optical integrated circuits. Liu et al . used an ultra-low-loss silicon nitride photonic integrated circuit with a waveguide length up to 0.5 meters and erbium ion implantation to fabricate an erbium-doped waveguide amplifier on a compact photonic chip (see the Perspective by Kim). Operating in the continuous-wave regime and providing large optical gain in the telecommunication bands, the results are promising for device applications. —ISO An erbium-doped optical amplifier is fabricated on a silicon-nitride-based optical platform.