Impact of Nd3+ doping and Au-core separation on plasmon assisted optical gain in TeO2–ZnO pedestal waveguides

Abstract

This work extends a previous investigation on plasmon enhanced optical gain in Nd³⁺ doped TeO₂-ZnO (TZ) pedestal waveguides incorporating gold nanoparticles (Au NPs) for applications at 1064 nm. The influence of Nd³⁺ concentration and the role of a SiO₂ spacer layer on the plasmon assisted optical gain of Nd³⁺ doped TZ were investigated. Thin films were deposited by RF magnetron sputtering, with the Nd³⁺ concentration controlled by varying the number of Nd₂O₃ pellets (1, 2, and 3). Pedestal waveguides with heights of ∼3.6 μm and widths ranging from 4 to 40 μm were characterized. Optical gain measurements at 1064 nm under 808 nm excitation showed that the lowest Nd₂O₃ concentration achieved the highest relative gain (G_R) with enhancement of up to ∼80% due to Au NPs. Although higher Nd³⁺ concentrations led to smaller improvements, attributed to self-absorption and non-radiative losses, the positive role of Au-NPs was observed. The introduction of SiO₂ spacer layers (25 or 100 nm) between the active core and Au NPs completely suppressed the plasmonic enhancement, confirming the importance of adequate distances between the rare-earth ions and the metallic NPs. These findings highlights the critical roles of dopant concentration and nanoscale Au NPs-core separation in maximizing plasmon assisted G_R in Nd³⁺ doped TZ based waveguides, providing guidance for the design of compact and efficient on-chip optical amplifiers.