Abstract

Erbium-doped fiber lasers (EDFLs) [1] have become indispensable sources of highly coherent laser light for numerous applications, owing to the all-fiber-based cavities, slow gain relaxation of Erbium ions at optical communications wavelengths, and lower spontaneous emission than short semiconductor-based lasers. Erbium ions can provide a basis for compact photonic integrated circuit-based lasers—miniaturized fiber lasers on photonic chips—with reduced footprint, susceptibility to environment variations, and amenability to wafer-scale fabrication. Prior attempts have been made to implement Erbium-doped waveguide lasers (EDWLs) [3] using Erbium-doped materials such as Al₂O₃ and LiNbO₃, but their laser linewidth remains at MHz level that is far below the Hz-level linewidth achieved in fiber lasers due to the low round-trip gain and the high cavity loss rate. This long-standing challenge has remained unsolved until the recently demonstrated Erbium-implanted silicon nitride (Er:Si₃N₄) photonic integrated circuits [3] that provide > 30 dB optical gain and >140 mW output powers.

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