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

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 SiO2-TiO2-Er2O3-Yb2O3-Al2O3 and its composition was optimized by measuring the fluorescence lifetime tau of the I-4(13/2) metastable level of Er3+ ions. The Er concentration was chosen as the quenching concentration, which was found to be 1.4 x 10(20) ions/cm(3). The Yb concentration was found to have little influence on tau, whereas a concentration of 1.5 x 10(21) ions/cm(3) of AlO3/2 was found to be enough to maximize tau. 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. (C) 1999 Elsevier Science B.V. All rights reserved.