Sabina Ronchin

Er-doped silica-based waveguides prepared by different techniques: RF-sputtering, sol-gel and ion-exchange

Erbium-activated silica-based planar waveguides were prepared by three different technological routes: RF-sputtering, sol–gel and ion exchange. Various parameters of preparation were varied in order to optimize the waveguides for operation in the NIR region. Particular attention was devoted to the minimization of the losses and the increase of the luminescence efficiency of the metastable 4I13/2 state of the Er3+ ion. Waveguide properties were determined by m-line spectroscopy and loss measurements. Waveguide Raman and luminescence spectroscopy were used to obtain information about the structure of␣the prepared films and about the dynamical processes related to the luminescence of the Er3+ ions.

Erbium-Activated Silica-Titania Planar Waveguides

Abstract(100 − x)SiO2-(x)TiO2-ErO3/2 planar waveguides, with 7 ≤ x ≤ 20 have been prepared by sol-gel route using the dip-coating technique. The thickness of the films was optimized to support a single propagating mode at 1550 nm, with a confinement coefficient higher than 0.75. The process of densification of the gel and the devitrification with the growth of TiO2 nanocrystals were studied by Raman scattering. Devitrification is important only for x ≥ 15, but it was not possible to obtain full densification of the samples, even at the lowest TiO2 content, without the appearance of nanocrystals.Emission in the C telecom band was observed; the spectral width of the 4I13/2 → 4I15/2 transition of Er3+ slightly increases with the titania content. For x ≤ 12 most of Er3+ ions (about 65%) decay exponentially with a lifetime of about 8 ms.

Rare-earth-activated fluoride and tellurite glasses: optical and spectroscopic properties

In this work we report on spectroscopic properties of Er3+-doped aluminum fluorophosphate glasses of molar composition 29.8AlF3:3.5 MgF2: 19.8 CaF2: 10.9 SrF2: 12.8 BaF2: 8.4 YF3:9.8 ZrF4:4 NaPO3:1 ErF3 and 30 AlF3:3.5 MgF2:20 CaF2: 11 SrF2: 13 BaF2: 8.4 YF3: 10 ZrF4: 4 NaPO3: 0.1 ErF3, and Er3+-doped tellurite glasses of molar composition 75 TeO2: 12 ZnO: 10 Na2O: 2 PbO: 1 Er2O3 and 75 TeO2: 12 ZnO: 10 Na2O: 2 GeO2: 1 Er2O3. Absorption and Stokes luminescence upon visible excitation were measured. Emission in the third telecom window was observed upon excitation at 514.5 nm and the lifetime of the 4I13/2 level was measured. IR-to-visible up conversion emission under continuous-wave laser excitation at 976 nm was observed. The up conversion results in a strong green emission and a weaker red emission, whose intensity shows a quadratic dependence on the excitation power, indicating that two photons are involved in the process. Lifetime measurements were performed in order to study the dynamical behavior of the up conversion emission and to clarify the contributions of excited state absorption and energy transfer to the up conversion process.

Erbium-activated silica–titania planar waveguides on silica-on-silicon substrates prepared by rf sputtering

Abstract Erbium-activated silica–titania planar waveguides were prepared by radio-frequency (rf) sputtering technique. Silica-on-silicon substrates obtained by plasma-enhanced chemical vapor deposition (PECVD) and rf sputtering (RFS) were employed. The refractive indices, the thickness and the propagation losses of the waveguides were measured. The refractive index and the roughness of the silica substrates produced by RFS appear to be dependent on the thickness. Thermal annealing, which is a necessary condition to obtain light propagation, induces a decrease of the refractive index in the silica substrates. The waveguide deposited on PECVD substrate exhibits several propagating modes with an attenuation coefficient 1.7 dB/cm compared with 12.2 dB/cm measured for the waveguide deposited on silica substrate produced by RFS technique. Emission of the 4 I 13/2 → 4 I 15/2 transition with a 53 nm bandwidth was observed.

Yellow-to-blue frequency upconversion in Pr3+-doped aluminium fluoride glasses

Abstract Rare-earth-doped fluoride glasses are attractive materials for photonics, since they combine a transmission region from ultraviolet to infrared and low vibrational cut-off energy. We report on the spectroscopic properties of aluminium fluorophosphate glasses doped with 0.1, 0.6, 1, 3 and 10 mol% Pr 3+ . Yellow-to-blue upconversion was observed upon pulsed and continuous-wave (CW) excitation at 575 nm. The temporal evolution of the upconverted fluorescence is characterised by rise and decay times depending on Pr 3+ concentration. The upconversion intensity has a quadratic dependence on incident pump power, indicating a two-step process. The upconversion emission is described in the framework of a two-ion energy transfer mechanism. Emission in the second telecom window ( 1.3 μm ) was measured upon excitation at 976 nm.

Erbium-activated aluminum fluoride glasses: optical and spectroscopic properties

Abstract Absorption and luminescence measurements have been performed on aluminum fluorophosphate glasses in the system AlF3–MgF2–CaF2–SrF2–BaF2–YF3–ZrF4–NaPO3, doped with 0.1 and 1 mol% Er3+. A green-to-blue upconversion fluorescence has been observed upon continuous-wave excitation at 514.5 nm. The upconversion intensity has a quadratic dependence on the incident pump power, indicating that two photons are responsible for the frequency upconversion process. The main mechanisms that produce the upconversion are excited state absorption and energy transfer among erbium ions. Emission in the third telecom window ( 1.5 μ m) has been measured upon excitation at 514.5 nm.

Erbium-activated monolithic silica xerogels and silica-titania planar waveguides: optical and spectroscopic characterization

Recent results obtained for Er2O3-SiO2 monolithic xerogels and erbium activated SiO2-TiO2 planar waveguides are presented. Monolithic erbium-activated silica xerogels with erbium content ranging from 0 up to 40000 ppm were prepared by the sol-gel technique. Samples were densified by thermal treatment in air at 950 degrees C for 120 hours. The densification degree and the relative content of hydroxyl groups were studied by NIR absorption and Raman spectroscopies. Emission at 1.5 micrometers , characteristic of the 4I13/2 yields 4I15/2 transition of Er3+ ions, was observed at room temperature for all monolithic samples upon continuous wave excitation at 980 nm. For the 5000 Er/Si ppm doped xerogel, an intense photoluminescence was observed with a lifetime of 8 ms for the metastable 4I13/2 level. Passive and erbium-activated SiO2-TiO2 planar waveguides, monomode at 632.8 nm, were prepared by a dip-coating technique. Some parameters such as H2O content, intermediate and final thermal treatments, and the molar ratio TiO2/SiO2 were modified during the preparation of the solution in order to minimize the final content of residual hydroxyl groups and the phase separation between silica and titania. Raman spectroscopy was used to check the structural properties of the waveguides. A lifetime of 7 ms was measured for the metastable 4I13/2 level in a 93SiO2-7TiO2 planar waveguide activated by 10000 ppm Er/(Si + Ti). The best value of the attenuation coefficient was of 0.5 dB/cm at 632.8 nm.

Waveguide luminescence and Raman spectroscopy: Characterization of an inhomogeneous film at different depths

In graded-index planar optical waveguides, different guided modes propagate in layers with different thickness. By comparison of spectra (Raman, luminescence) taken by waveguide excitation in different modes, it is possible to characterize the guide at different depths. The method has been applied to waveguides obtained by ion exchange of silver in a soda-lime substrate. Luminescence from silver ions and Raman scattering from the optical vibrations of the glass and from the acoustic vibrations of silver nanoclusters depend on the silver concentration, providing different spectra for excitation in different modes of the guide.

Erbium-activated silica-titania planar waveguides prepared by rf-sputtering

Erbium-activated silica-titania planar waveguides were prepared by rf-sputtering technique. The films were deposited both on v-SiO2 and silica-on-silica substrates obtained by plasma-enhanced chemical vapor deposition. The refractive index, the thickness and the total attenuation coefficient of the waveguides were measured by prism coupling technique. Scanning electron microscopy was used to analyze the morphology of both substrates and waveguiding film. Energy Dispersive Spectroscopy was performed in order to obtain a compositional analysis. Roughness measurements were carried out by means of a stylus profilometer. After thermal annealing at 600 degrees C for 6 hours the waveguides exhibited several well confined TE and TM propagating modes at 633 nm and one mode at 1550 nm. The attenuation coefficient at 1550 nm was 0.9 and 0.7 dB/cm for the films deposited on silica-on-silicon waveguide Raman spectroscopy. Waveguide luminescence spectroscopy was used to study the 4I13/2 yields 4I15/2 transition of Er3+ ion. The emission at 1530 nm was observed at room temperature upon continuous wave excitation at 514.2 nm. A lifetime of 3.7 ms for the metastable 4I13/2 level was measured.

Structural properties of erbium-activated silica-titania glasses: modeling by molecular dynamics method

Here, we use molecular dynamics simulation to reconstruct a silica-titania glass with a Ti/Si atomic ratio of 8.5% activated by 0.7 at% of erbium. These quantities are chosen because they give both refractive index and optically ions concentration suitable for applications. We use a modified Born-Mayer-Huggins potential taking into account a three- body interaction. The distribution of TiO4 and SiO4 units as well as the bridging to non-bridging oxygen ratios are evaluated. The local environment of rare-earth ions is also analyzed. In particular, the clustering of erbium is discussed. From the simulated structure, the crystal-field strength is computed and discussed according to the Er3+ local environment. Finally, results are compared with information obtained by Raman and photoluminescence spectra.