Al₂O₃ as a multifunctional platform for rare-earth ion doped integrated waveguide amplifiers (Invited Paper)

Aluminum oxide (Al₂O₃) is a versatile integrated photonics platform due to its low optical loss and broad transparency from the ultraviolet to the infrared, enabling the integration of both active and passive photonic components. In this work, we present an overview of rare-earth ion doped Al₂O₃ integrated waveguide amplifiers developed using reactive co-sputtering. The platform supports efficient incorporation of multiple rare-earth dopants, including erbium (Er), thulium (Tm), and neodymium (Nd), enabling on-chip amplification across different wavelength regimes. Both single-layer and heterogeneously integrated device architectures are reviewed. The demonstrated results highlight broadband gain, high output power, and scalable fabrication, illustrating the potential of Al₂O₃ as a multifunctional and CMOS-compatible platform for integrated photonic systems.