Rare Earth-Activated Glass Confined Structures for Photonics: Planar Waveguides and 1-D Photonic Crystals

We report some recent results in dielectric photonic systems, where light confinement induces an enhancement of optical and/or spectroscopic properties. In particular, the following topics are presented: (i) SiO2 - TiO2: Er3+/Yb3+ planar waveguides fabricated by rf sputtering technique; (ii) sol gel-derived SiO2 - HfO2: Er3+ planar waveguides; (iii) rare earth-activated 1-D photonic crystals prepared by sol gel route. SiO2-HfO2 planar waveguides, activated by different Er3+ concentrations, were prepared by sol-gel method using dip-coating technique. The waveguide deposited on silica-on-silicon substrates shows a single mode at 1500 nm, with a confinement coefficient of 0.81 and attenuation coefficient of 0.8 dB/cm at 632.8nm. Emission in the C-telecommunication band was observed at room temperature for all the samples upon continuous-wave excitation at 980 nm or 514.5 nm. A radiative quantum efficiency of about 85% is estimated for the 4I13/2 level in all the samples doped with 0.3 mol% of erbium. SiO2 - TiO2: Er3+/Yb3+ waveguides were prepared by rf-sputtering technique on silica-on-silicon and v-SiO2 substrates. The preparation parameters were chosen in order to optimize the waveguides for operation in the NIR region with particular attention to the minimization of losses. The losses, for the TE0 mode, were evaluated at 632.8 and 1300 nm: a value equal or lower than 0.2 dB/cm was measured at both wavelengths. The structural properties were investigated with Energy Dispersive Spectroscopy and Raman Spectroscopy. All waveguides were single-mode at 1550 nm. The emission of 4I13/2 - 4I15/2 of Er3+ ion transition with a 40 nm bandwidth was observed upon excitation in the TE0 mode at 981 and 514.5 nm. Back energy transfer from Er3+ to Yb3+ was demonstrated. Photoluminescence excitation spectroscopy was used to obtain information about the effective excitation efficiency of Er3+ ions by co-doping with Yb3+ ions. Starting from both sol-gel and rf-sputtered slab waveguides, rib waveguides were obtained by etching the active film by dry and wet etching process, respectively. 1-D Photonic crystals were fabricated by sol-gel route and dip coating technique. The cavities were constituted by Bragg mirrors fabricated by stacking alternately undoped TiO2 and SiO2 sol-gel thin films. The defects consisted in a layer activated either by Eu3+ or Er3+/Yb3+ ions. Transmission measurements and luminescence spectroscopy at different angles of the incident and observed light were employed to characterize the spectroscopic feature in the visible region of the sample. Authors acknowledge the financial support of MIUR-FIRB "Miniaturized systems for electronics and photonics", PAT 2004-2006 FAPVU "Fabrication of ultratransparent glass ceramics-based planar optical amplifiers", MIUR-COFIN 2002 "Preparation of hybrid organic-inorganic materials by assembling of nanostructured molecular units", and MIUR-COFIN 2002 "Nanostructured materials for integrated optics".