Mohamed Bouazaoui

Up-conversion fluorescence spectroscopy in Er3+: TiO2 planar waveguides prepared by a sol-gel process

The up-conversion of infrared radiation into blue, green and red fluorescences has been investigated for erbium-doped titanium dioxide (TiO2) optical planar waveguides. These waveguides have been prepared by a sol-gel process and a dip-coating technique. The lifetime measurements of the 4S32 level (green fluorescence) were performed using a pulsed excimer-pumped dye laser operating at 650 nm. They were found to depend strongly on the Er3+ ion concentration.

Fluorescence of Er3+ ions in TiO2 planar waveguides prepared by a sol-gel process

Abstract Erbium-doped optical planar waveguides are prepared by a sol-gel process and a dip-coating technique. The guides are optically pumped at room temperature using a Ti: sapphire laser with λ=800 nm; the observed fluorescence of Er3+ ions at 1.53 μm is investigated. It is shown that the shape of the 4 I 13 2 → 4 I 15 2 transition depends on the concentration of Er3 + ions in TiO2 thin films (thickness=80nm), indicating that Er3+ ions modify the structure of TiO2 gel network. This effect is confirmed by waveguide Raman spectroscopy. The dependence on heat treatment of Er3+ fluorescence spectra is also investigated. Furthermore, it is worthy of note that titanium oxide (TiO2) has lower phonon energies (

Tailoring CW supercontinuum generation in microstructured fibers with two-zero dispersion wavelengths

We theoretically study broadband supercontinuum generation in photonic crystal fibers exhibiting two zero dispersion wavelengths and under continuous-wave pumping. We show that when the pump wavelength is located in between the zero-dispersion wavelengths, a wide and uniform spectral broadening is achieved through modulation instability, generation of both blue-shifted and red-shifted dispersive waves and subsequently through soliton self-frequency shift. This supercontinuum is therefore bounded by these two dispersive waves which allow the control of its bandwidth by a suitable tuning of the fiber dispersion. As a relevant example, we predict that broadband (1050-1600 nm) continuous-wave light can be generated in short lengths of microstructured fibers pumped by use of a 10-W Ytterbium fiber laser.

Structural characterisation of Er3+ doped sol–gel TiO2 planar optical waveguides

Abstract We report on the fabrication and the structural study of TiO2/Er3+ planar optical waveguides. The effects of erbium concentration and annealing temperature were first studied using the waveguide Raman spectroscopy technique. The later showed an important modification of the TiO2 host matrix induced by the presence of the Er3+ ions. Depending on their concentration, these ions seem to stabilize the TiO2 amorphous phase or limit the crystallization process. This result is confirmed by transmission electron microscopy (TEM) and X-ray diffraction.

Fluorescence properties of sol-gel derived Er3+:SiO2GeO2 planar waveguides

Fluorescence of Er3+ ions embedded in sol-gel germanosilicates planar waveguides has been characterised. Green and infrared bands, centred at 0.551 and 1.534 μm for the 4S32 → 4I0152 and 4I132 → 4I152 Er3+ transitions, respectively, have been observed. The lifetime measurements of the 4I132 excited state (λ = 1.534 μm) were performed for different annealing temperatures, Er3+ ion concentration and compositions of SiO2GeO2 samples. For a 0.25-at%Er3+: SiO2GeO2 sample with a molar ratio SiGe = 1, the lifetime ranges from 1 to 5.2 ms when the annealing temperature varies from 500 to 1200°C. However, for the same erbium doping (0.25-at%Er3+) incorporated in a sample with a low germanium content, SiGe = 9, the lifetime reaches 6.5 ms for an annealing temperature of 1200°C. These lifetime variations are related to the presence of hydroxyl groups (OH−) which is found to be more important for samples containing a large amount of germanium.

Optical properties of Bismuth-doped silica core photonic crystal fiber

Optical properties of a Bismuth-doped pure silica sol-gel core photonic crystal fiber (PCF) were investigated. We report on the absorption, CW luminescence and time resolved luminescence spectra at different excitation wavelengths at room temperature. Complex structure of the energy levels of Bismuth-connected centers in pure silica glass is put in evidence.

Sol-gel derived ionic copper-doped microstructured optical fiber: a potential selective ultraviolet radiation dosimeter

We report the fabrication and characterization of a photonic crystal fiber (PCF) having a sol-gel core doped with ionic copper. Optical measurements demonstrate that the ionic copper is preserved in the silica glass all along the preparation steps up to fiber drawing. The photoluminescence results clearly show that such an ionic copper-doped fiber constitutes a potential candidate for UV-C (200-280 nm) radiation dosimetry. Indeed, the Cu⁺-related visible photoluminescence of the fiber shows a linear response to 244 nm light excitation measured for an irradiation power up to 2.7 mW at least on the Cu-doped PCF core. Moreover, this response was found to be fully reversible within the measurement accuracy of this study ( ± 1%), underlying the remarkable stability of copper in the Cu⁺ oxidation state within the pure silica core prepared by a sol-gel route. This reversibility offers possibilities for the achievement of reusable real-time optical fiber UV-C dosimeters.

From molecular precursors in solution to microstructured optical fiber: a Sol-gel polymeric route

Solid-core photonic crystal fibers with the core derived from non-doped or Erbium-doped sol-gel silica rods are fabricated. The results demonstrate that the direct polymeric sol-gel route constitutes a promising method to prepare large high quality glass pieces that can be integrated into microstructured optical fibers suitable for passive and active optical fiber applications.

IR luminescence decays and radiative lifetime of the 4Isol132 level in Er3+ doped sol-gel TiO2 planar waveguides

Abstract The lifetime of the 4 I 13 2 level has been analyzed in erbium doped TiO2 sol-gel planar waveguides as a function of the Er3+ concentration and thermal treatments in the way of testing their potentially for optical amplification at 1.53 μm. Luminescence decay measurements were recorded by prism coupling of the 800 nm excitation laser beam into the waveguides and by detecting luminescence at 1.53 μm perpendicularly to the propagation plane. The observed increase of the lifetime with the annealing temperature has been related to the reduction in the hydroxyl group concentration evidenced by FTIR transmission spectra. Moreover, hydroxyl groups seem to play an important role in the strong shortening of decays by increasing Er3+ concentration. The radiative lifetime of the 4 I 13 2 level has been estimated for erbium doped TiO2 gel using the Judd-Ofelt framework. It compares well with the lifetimes of the lowest doped films annealed up to 650°C. This suggests that the 4 I 13 2 level radiative lifetime would almost be attained by means of annealing treatments in low doped waveguides.

Development of a metal-chelated plasmonic interface for the linking of His-peptides with a droplet-based surface plasmon resonance read-off scheme.

Monolayers of metal complexes were covalently attached to the surface of lamellar SPR interfaces (Ti/Ag/a-Si(0.63)C(0.37)) for binding histidine-tagged peptides with a controlled molecular orientation. The method is based on the activation of surface acid groups with N-hydroxysuccinimide (NHS), followed by an amidation reaction with (S)-N-(5-amino-1-carboxypentyl)iminodiacetic acid (NTA). FTIR and X-ray photoelectron spectroscopy (XPS) were used to characterize each surface modification step. The NTA modified SPR interface effectively chelated Cu(2+) ions. Once loaded with metal ions, the modified SPR interface was able to bind specifically to histidine-tagged peptides. The binding process was followed by surface plasmon resonance (SPR) in a droplet based configuration. The Cu(2+)-NTA modified interface showed protein loading comparable to commercially available NTA chips based on dextran chemistry and can thus be regarded as an interesting alternative. The sensor interface can be reused several times due to the easy regeneration step using ethylenediaminetetraacetic acid (EDTA) treatment.