Reliable Low-Cost Fabrication of Low-Loss $\hbox{Al}_{2}\hbox{O} _{3}{:}\hbox{Er}^{3+}$ Waveguides with 5.4-dB Optical Gain

A reliable and reproducible deposition process for the fabrication of $\hbox{Al}_{2}\hbox{O}_{3}$ waveguides with losses as low as 0.1 dB/cm has been developed. The thin films are grown at ${\sim 5} \hbox{nm}/\min$ deposition rate and exhibit excellent thickness uniformity within 1% over 50×50 $\hbox{mm}^{2}$ area and no detectable $\hbox{OH}^{-}$ incorporation. For applications of the $\hbox{Al}_{2}\hbox{O}_{3}$ films in compact, integrated optical devices, a high-quality channel waveguide fabrication process is utilized. Planar and channel propagation losses as low as 0.1 and 0.2 dB/cm, respectively, are demonstrated. For the development of active integrated optical functions, the implementation of rare-earth-ion doping is investigated by cosputtering of erbium during the $\hbox{Al}_{2}\hbox{O}_{3}$ layer growth. Dopant levels between 0.2–5$\,\times{10} ^{20} \hbox{cm}^{-3}$ are studied. At $\hbox{Er}^{3+}$ concentrations of interest for optical amplification, a lifetime of the ${4}\hbox{I} _{13/2}$ level as long as 7 ms is measured. Gain measurements over 6.4-cm propagation length in a 700-nm-thick $\hbox{Al}_{2}\hbox{O}_{3}{:}\hbox{Er}^{3+}$ channel waveguide result in net optical gain over a 41-nm-wide wavelength range between 1526–1567 nm with a maximum of 5.4 dB at 1533 nm.