On-chip gain in neodymium-doped aluminium oxide waveguide amplifiers

Aluminium oxide (Al₂O₃) has emerged as a promising platform for the development of photonic integrated circuits. The material has attracted significant attention due to its notable high rare-earth ion solubility. The substantial high rare-earth ion solubility of Al₂O₃ enables the fabrication of waveguide structures embedded with optically active rare earth ions, resulting in high gain waveguide amplifiers. Prior work involving cosputtering of doped-Al₂O₃ layers has resulted in polycrystalline ridge waveguides doped with erbium, ytterbium and thulium ions. However, neodymium-doped aluminium oxide
(Al₂O₃:Nd³⁺) waveguides have not yet been fabricated with this method. The choice of Al₂O₃:Nd³⁺ as material composite is interesting due to its distinct lightmatter interactions. Contrary to Er³⁺, Yb³⁺, and Tm³⁺ ions, the Nd³⁺ ions form a fourlevel system. The four-level characteristics prevent reabsorption of signal photons by the gain medium. Total on-chip gain of 17 dB at a wavelength of 1064 nm has been observed.