A comparative study of the gain achievement is performed in a waveguide optical amplifier whose active layer is constituted by a silica matrix containing silicon nanograins acting as sensitizer of either neodymium ions (Nd3+) or erbium ions (Er3+). Due to the large difference between population levels characteristic times (ms) and finite-difference time step (10−17s), the conventional auxiliary differential equation and finite-difference time-domain (ADE-FDTD) method is not appropriate to treat such systems. Consequently, a new two loops algorithm based on ADE-FDTD method is presented in order to model this waveguide optical amplifier. We investigate the steady states regime of both rare earth ions and silicon nanograins levels populations as well as the electromagnetic field for different pumping powers ranging from 1 to 104 mW/mm2 . Furthermore, the three dimensional distribution of achievable gain per unit length has been estimated in this pumping range. The Nd3+ doped waveguide shows a higher gross gain per unit length at 1064 nm (up to 30 dB/cm-1) than the one with Er3+ doped active layer at 1532 nm (up to 2 dB/cm-1). Considering the experimental background losses found on those waveguides we demonstrate that a significant positive net gain can only be achieved with the Nd3+ doped waveguide. The developed algorithm is stable and applicable to optical gain materials with emitters having a wide range of characteristic lifetimes.
The series of Nd3+-doped Si-rich SiO2 thin films with different excess Si content were deposited by magnetron co-sputtering of three different (SiO2, Si and Nd2O3) targets under a plasma of pure argon at 500 °C. The Si excess content in the samples was monitored via a power applied on Si cathode. The films were submitted to the rapid thermal annealing (RTA) at 900, 1000 and 1100 °C, respectively. It was observed a phase separation and a formation of Si nanoclusters embedded in oxide host. The Si excess, remaining after a RTA-1100 °C annealing, was found to be negligible, confirmed nearly complete phase separation. The Nd3+ photoluminescence (PL) property was explored as a function of Si excess and/or annealing temperature. The most efficient Nd3+ PL emission was found for the samples with about 4.7% of Si excess. These optimal samples, submitted to RTA-900 °C-1 min treatment and conventional annealing at 900°C for 1 h in nitrogen flow, demonstrated comparable Nd3+ PL intensities. This offers future application of RTA treatment to achieve an efficient emission from the materials doped with rare-earth ions.
We present a study on erbium (Er)-doped silicon (Si)-rich silicon oxide thin films grown by the magnetron cosputtering of three confocal cathodes according to the deposition temperature and the annealing treatment. It is shown that, through a careful tuning of both deposition and annealing temperatures, it is possible to engineer the fraction of agglomerated Si that may play the role of sensitizer toward Er ions. To investigate the different emitting centers present within the films according to the fraction of agglomerated Si, a cathodoluminescence experiment was made. We observe in all samples contributions from point-defect centers due to some oxygen vacancies and generally known as silicon-oxygen deficient centers (SiODC), at around 450-500 nm. The behavior of such contributions suggests the possible occurrence of an energy transfer from the SiODCs toward Er3+ ions. Photoluminescence experiments were carried out to characterize the energy transfer from Si nanoclusters toward Er3+ ions with a nonresonant wavelength (476 nm) that is unable to excite SiODCs and then exclude any role of these centers in the energy transfer process for the PL experiments. Accordingly, it is shown that structural differences have some effects on the optical properties that lead to better performance for high-temperature deposited material. This aspect is illustrated by the Er-PL efficiency that is found higher for 500°C-deposited, when compared to that for RT-deposited sample. Finally, it is shown that the Er-PL efficiency is gradually increasing as a function of the fraction of agglomerated silicon.
We present a study on erbium-doped silicon rich silicon oxide (SRSO:Er) thin films grown by the magnetron cosputtering
of a three confocal cathodes according to the deposition temperature and the annealing treatment. It is shown
that several parameters such as the stoichiometry SiOx, the Erbium content and the fraction of agglomerated Silicon are
strongly influenced by the deposition temperature. Especially, an increase of the fraction of agglomerated-Si concomitant
to a reduction of the erbium content is observed when the deposition temperature is raised. These structural differences
have some repercussions on the optical properties that lead to better performances for high-temperature deposited
material. It is illustrated by the Er-PL efficiency that is higher for 500°C-deposited than for RT-deposited sample at all
annealing temperatures. Finally an investigation of the different emitting centres within the films is performed with a
cathodoluminescence technique to highlight the emission of optically-active defect centers in the matrix. It is shown that
some oxygen vacancies, namely Silicon-Oxygen Deficient Centers, have a strong contribution around 450-500 nm and
are suspected to contribute to the energy transfer towards Er3+ ions.
V. Boucher, J. Cardin, Dominique Leduc, R. Seveno, R. Le Ny, H. Gundel, C. Boisrobert, S. Legoupy, F. Legros, V. Montembault, F. Odobel, C. Monnereau, E. Blart, D. Bosc, A. Goullet, J. Mevellec
A difunctional NLO Azo-Dye chromophore has been synthesized and polymerization has been performed with a comonomer bearing a side-chain epoxy group. Deposition of the polymer on glass substrates was performed by spin-coating, resulting in uniform films up to 2 μm thickness. The orientation of the chromophore was performed under a "pin-to-plane" positive corona discharge followed by a heat- treatment in order to obtain reticulation of the films. Molecular orientation has been investigated using UV-Vis. and Raman spectroscopy. Poling of the films results in a decay of absorbance as well as in a blue shift of the spectrum. At the same time, the 1600 cm-1 band disappears from the Raman spectra, indicating orientation of the chromophores. Cross-linking has been studied by FTIR and all-optical poling and showed an improved stability of the electro-optic thin films.
Ferroelectric PbxZryTi1-yO3 (PZT) has been prepared by chemical solution deposition (CSD) and spin-coating technique, using acetate and alkoxide precursors. Rapid thermal annealing has been employed in order to obtain crystallization in the perovskite phase. Aiming to study the optical properties of the films, PZT was deposited on different glass substrates. Structural characterization of the films was done by X-ray diffraction, morphology was investigated by SEM micrography. Using standard photography analysis, the films were qualified in terms of crack density, their appearance strongly depending on the type of substrate. Using a visible to the near infrared spectrophotometer, the transmittance normal to the surface of the films was studied. Coupling of laser light into the films by the M-lines technique allowed the determination of the refractive index and the thickness of the ferroelectric layer. A waveguiding interferometer structure of Mach-Zehnder type was realized by photolithography and wet chemical etching.
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