We report on the deposition of high quality optical thin films by a plasma enhanced chemical vapor deposition (PECVD) method. Especially in telecom applications, drag-and-drop filters for dense wavelength division multiplexing (DWDM) systems require 'high-quality' films with performance close to the technical limits, particularly regarding absorption and scattering. Schott has developed a pulsed microwave-induced plasma CVD-technology (PICVD) for the deposition of such films. In this study, optical properties of niobia and tantala films are compared. Refractive indices at 1550 nm reach 2.27 for niobia and 2.10 for tantala. Furthermore, physical properties of Nb2O5/SiO2 multilayer coatings are discussed. The films are synthesized from metal-organic and halide precursors like hexamethyldisiloxane and tantalum chloride or niobium chloride, respectively. The optical performance of narrow bandpass filters made by the PICVD process complies with conventional DWDM requirements. (C) 2003 Elsevier B.V. All rights reserved.