Er3+-activated tellurite films deposited on a large area by Pulsed Laser Deposition technique

The need to broaden the amplification band for WDM transmission has led to the investigation of other hosts where the 4I13/2?4I15/2 transition of Er3+ ions, exploited for optical amplification, might have broader emission. Tellurite glasses have proved to be good candidates as they combine an 4I13/2?4I15/2 emission bandwidth as broad as 60 nm and extended up to 1630 nm with acceptable features for fiber drawing and planar waveguide fabrication. Thin films of tellurite glass have been deposited by Pulsed Laser Deposition technique (PLD) ablating a tellurite target of nominal composition: 45%TeO2-39%WO3-15%Na2O-1%ErO3. Because of the complex stoichiometry of the starting material, PLD technique is particularly indicated for the deposition. The irradiations were performed with an ArF excimer laser in a dynamic flow of oxygen at a pressure of 5 Pa. The laser fluence was set at 2 J/cm2. The films were deposited on pure silica substrates at three different substrate temperatures (Room Temperature, 100°C and 200°C) under the same experimental conditions. The layers with a thickness greater than one micrometer were deposited on a large area (about 4 cm2) with a consecutive number of 40000 laser pulses, moving the x-y computer assisted substrate holder during the deposition. The thickness uniformity over all the area of the films was determined by using an optical Film Thickness Probe. The optical transmission of the films in the NIR-visible-UV regions (200-3200 nm) was measured by using a double beam spectrophotometer and the optical spectra were analyzed by computer code, to evaluate the dispersion curves of the refractive index n and of the extinction coefficient k along with the film thickness. Optical parameters were evaluated also by modal measurements. The substrate temperature strongly influenced the optical properties of the films. In particular, with an increase in temperature the films became less transparent. This behavior is typical of films with a sub-stoichiometry of oxygen. An explanation of this behavior is discussed.