H. El Hamzaoui

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.

Linear and nonlinear optical properties of gold nanoparticle-doped photonic crystal fiber.

The concept of photonic crystal fibers (PCFs) has opened the route to a new family of optical fibers available for a wide range of applications in nonlinear optics. The nonlinear performances are based both on the easy chromatic dispersion management possible with PCFs and on the increased fiber nonlinearity, thanks to the small effective mode areas accessible with these fibers. Hence, even if necessary, the intrinsic nonlinearity of the material used to realize the fiber generally plays a secondary role. This is true for most of the realizations which are based on pure silica glass, a matrix with modest nonlinear coefficients. However, various glass matrices are known to offer larger nonlinear coefficients and could be useful to further improve the performances of systems based on highly nonlinear fibers. Among these, conventional glasses containing dopants presenting nonlinear properties, like gold nanoparticles (Au NPs), appear as promising candidates [1]. However, realization of glasses doped by Au NPs is mainly limited to films and bulk materials and there are only two reports of insertion of such systems in the core of a conventional optical fiber, mainly due to the difficulty induced by the high temperatures commonly used to synthesize optical fibers (typically 1500–2000°C) as compared to the gold melting point [2,3].

Line broadening of confined CO gas: From molecule-wall to molecule-molecule collisions with pressure

The infrared absorption in the fundamental band of CO gas confined in porous silica xerogel has been recorded at room temperature for pressures between about 5 and 920 hPa using a high resolution Fourier transform spectrometer. The widths of individual lines are determined from fits of measured spectra and compared with ab initio predictions obtained from requantized classical molecular dynamics simulations. Good agreement is obtained from the low pressure regime where the line shapes are governed by molecule-wall collisions to high pressures where the influence of molecule-molecule interactions dominates. These results, together with those obtained with a simple analytical model, indicate that both mechanisms contribute in a practically additive way to the observed linewidths. They also confirm that a single collision of a molecule with a wall changes its rotational state. These results are of interest for the determination of some characteristics of the opened porosity of porous materials through optical soundings.

Structure determination of molecular nanocomposites by combining pair distribution function analysis and solid-state NMR

Transparent mesoporous silica monoliths of well-controlled porosity and a narrow pore size distribution around 6 nm have been used to prepare sodium nitroprusside (SNP) nanocomposites. The obtained nanomaterials could be characterised using X-ray total scattering coupled to atomic pair distribution function analysis (PDF) and solid-state NMR spectroscopy. The PDF analysis allows for a structural description of the confined species, as well as for the identification of the various coexisting phases: SNP isolated molecules and SNP crystalline nanoparticles. The model obtained suggests that the nanocrystals have the same molecular structure as the bulk crystalline material and measure about 6 nm in diameter. This result is quite exceptional because the space available inside the pores is only about ten times the size of the molecules. The multi-nuclei solid state NMR investigation confirms the structural model proposed by the PDF analysis and assigns the isolated molecules to the dynamic disorder of a solvated phase. The latter approach additionally provides quantitative information on the relative ratio between the dynamic molecules and the rigid nanocrystals. This result is exploited to study the evolution of the two confined SNP phases with respect to solvating water molecules. We show that the confined SNP nanocrystals can be easily dissolved when storing the nanocomposites at increasing atmospheric relative humidity.

Synthesis and nonlinear optical properties of zirconia-protected gold nanoparticles embedded in sol–gel derived silica glass

A new approach to dope a silica glass with gold nanoparticles (GNPs) is presented. It consisted in embedding zirconia-coated GNPs in a silica sol to form a doped silica gel. Then, the sol-doped nanoporous silica xerogel is densified leading to the formation of a glass monolith. The spectral position and shape of the surface plasmon resonance (SPR) reported around 520 nm remain compatible with small spherical GNPs in a silica matrix. The saturable absorption behavior of this gold/zirconia-doped silica glass has been evidenced by Z-scan technique. A second-order nonlinear absorption coefficient β of about −13.7 cm GW−1 has been obtained at a wavelength near the SPR of the GNPs.

Influence of Al/Ge ratio on radiation-induced attenuation in nanostructured erbium-doped fibers preforms

We have compared the radiation resistance of various Er3+-doped fiber preforms manufactured with different technologies: Si and Al nanoparticles doped fibers, and standard MCVD fibers. All of them have been irradiated with a total gamma dose of 5.9 kGy and then studied using absorption and EPR spectroscopies.

Combination of porous silica monolith and gold thin films for electrode material of supercapacitor

An all-solid electrical double layer supercapacitor was prepared, starting from a porous silica matrix coated with a gold thin-film. The metallization of the silica xerogel was performed by an original wet chemical process, based on the controlled growth of gold nanoparticles on two opposite faces of the silica monolith as a seed layer, followed by an electroless deposition of a continuous gold thin film. The thickness of the metallic thin film was assessed to be 700 nm. The silica plays two major roles: (1) it is used as a porous matrix for the gold electrode, creating a large specific surface area, and (2) it acts as a separator (non-metallized part of the silica). The silica monolith was soaked in a polyvinyl alcohol and phosphoric acid mixture which is used as polymer electrolyte. Capacitance effect was demonstrated by cyclic voltammetry experiments. The specific capacitance was found to be equal to 0.95 mF cm− 2 (9.5 F g−1). No major degradation occurs within more than 3000 cycles.

Very large mode area Solid-Core Photonic BandGap fiber laser with hetero-structured cladding and Yb-doped Sol-Gel core

Single-Mode Large Mode Area (SM-LMA) fibers are highly demanded for high power laser applications, due to the quality of the beam they deliver together with reduced impairments caused by non-linear effects. Even though LMA fibers demonstrated large progress during the last decade, the need for flexible, active or passive LMA fibers still persists. Besides this, fiber-integrated functionalities, like spectral filtering or chromatic dispersion control can be needed. In this context, Solid-Core Photonic BandGap (SC-PBG) fibers appear as good candidates for the realization of LMA structures. Recently, based on the concept introduced by Murao et al. in 2009 [1], we experimentally demonstrated that High Order Modes (HOM) can be removed by hetero-structuring the cladding in SC-PBG fibers. Thus, by introducing 6 outer cores around the central one, it has been possible to fabricate passive LMA fiber with a mode field diameter (MFD) of 44 μm when working in the 4th PBG and a MFD of 33 μm when working in the 3rd PBG [2]. In the present work, this concept is extended to double-clad active fiber.

Linear and nonlinear optical properties of gold nanoparticle-doped photonic crystal fiber

The concept of photonic crystal fibers (PCFs) has opened the route to a new family of optical fibers available for a wide range of applications in nonlinear optics. The nonlinear performances are based both on the easy chromatic dispersion management possible with PCFs and on the increased fiber nonlinearity, thanks to the small effective mode areas accessible with these fibers. Hence, even if necessary, the intrinsic nonlinearity of the material used to realize the fiber generally plays a secondary role. This is true for most of the realizations which are based on pure silica glass, a matrix with modest nonlinear coefficients. However, various glass matrices are known to offer larger nonlinear coefficients and could be useful to further improve the performances of systems based on highly nonlinear fibers. Among these, conventional glasses containing dopants presenting nonlinear properties, like gold nanoparticles (Au NPs), appear as promising candidates [1]. However, realization of glasses doped by Au NPs is mainly limited to films and bulk materials and there are only two reports of insertion of such systems in the core of a conventional optical fiber, mainly due to the difficulty induced by the high temperatures commonly used to synthesize optical fibers (typically 1500–2000°C) as compared to the gold melting point [2,3].

Nano-engineered Bismuth-doped silica glasses and origin of near infrared photoluminescence

Since the first demonstration of a broadband near infrared (NIR) photoluminescence in Bi-doped silica glasses [1], a great number of hypotheses on its origin were proposed. Nevertheless, up to now the nature of luminescent centres in various glasses remains unclear. Recently, using sol-gel nano-porous pure silica glasses as a host material, we have shown [2,3] that even in so simple glass composition the absorption and PL spectra were still complex and multiple centres connected to bismuth doping should exist.