High-gain waveguide amplifiers in Si₃N₄ technology via double-layer monolithic integration

Silicon nitride (Si₃N₄)-on-SiO₂ attracts increasing interest in integrated photonics owing to its low propagation loss and wide transparency window, extending from ∼400 nm to 2350 nm. Scalable integration of active devices such as amplifiers and lasers on the Si₃N₄ platform will enable applications requiring optical gain and a much-needed alternative to hybrid integration, which suffers from high cost and lack of high-volume manufacturability. We demonstrate a high-gain optical amplifier in Al₂O₃:Er³⁺ monolithically integrated on the Si₃N₄ platform using a double photonic layer approach. The device exhibits a net Si₃N₄-to-Si₃N₄ gain of 18.1 ± 0.9 dB at 1532 nm, and a broadband gain operation over 70 nm covering wavelengths in the S-, C- and L-bands. This work shows that rare-earth-ion-doped materials and in particular, rare-earth-ion-doped Al₂O₃, can provide very high net amplification for the Si₃N₄ platform, paving the way to the development of different active devices monolithically integrated in this passive platform.