Sol–gel silica/titania-on-silicon Er/Yb-doped waveguides for optical amplification at 1.5 μm

Abstract

By combining the sol–gel method and the spin-coating technique, silica-on-silicon Er-doped glass optical planar waveguides were fabricated. The active guiding layer consisted of SiO 2–TiO 2–Er 2O 3–Yb 2O 3–Al 2O 3 and its composition was optimized by measuring the fluorescence lifetime τ of the 4I 13/2 metastable level of Er 3+ ions. The Er concentration was chosen as the quenching concentration, which was found to be 1.4 × 10 20 ions/cm 3. The Yb concentration was found to have little influence on τ, whereas a concentration of 1.5 × 10 21 ions/cm 3 of AlO 3/2 was found to be enough to maximize τ. The 71aluminum concentration barely influenced the flatness of the amplified spontaneous emission spectrum. Strip-loaded waveguides were designed by reactive ion etching of the cladding layer and their performance as candidates for integrated optical amplifiers was assessed. Propagation losses of 0.7 dB/cm and loss reduction of 2.7 dB (for a 5.7 cm long waveguide) were measured.