C.E. Chryssou

Luminescence from erbium-doped silicon nanocrystals in silica: Excitation mechanisms

We develop a model for the excitation of erbium ions in erbium-doped silicon nanocrystals via coupling from confined excitons generated within the silicon nanoclusters. The model provides a phenomenological picture of the exchange mechanism and allows us to evaluate an effective absorption cross section for erbium of up to 7.3×10−17 cm2: four orders of magnitude higher than in stoichiometric silica. We address the origin of the 1.6 eV emission band associated with the silicon nanoclusters and determine absorption cross sections and excitonic lifetimes for nanoclusters in silica which are of the order of 1.02×10−16 cm2 and 20–100 μs, respectively.

Evidence of energy coupling between Si nanocrystals and Er3+ in ion-implanted silica thin films

Silica thin films containing Si nanocrystals and Er3+ were prepared by ion implantation. Excess Si concentrations ranged from 5% to 15%; Er3+ concentration for all samples was 0.5%. Samples exhibited photoluminescence at 742 nm (attributed to Si nanocrystals), 654 nm (defects due to Er3+ implantation), and at 1.53 μm (intra-4f transitions). Photoluminescence intensity at 1.53 μm increased ten times by incorporating Si nanocrystals. Strong, broad photoluminescence at 1.53 μm was observed for λPump away from Er3+ absorption peaks, implying energy transfer from Si nanocrystals. Erbium fluorescence lifetime decreased from 4 ms to 1 ms when excess Si increased from 5% to 15%, suggesting that at high Si content Er3+ ions are primarily situated inside Si nanocrystals.

Theoretical analysis of tapering fused silica optical fibers using a carbon dioxide laser

Tapering of fused silica optical fiber using a carbon dioxide (CO2) laser as the heating source is analyzed taking into account a Gaussian profile for the laser power distribution. The differential thermal equation is solved numerically using an implicit Crank-Nicolson finite difference method. The interaction of the CO2 laser electromagnetic (EM) radiation with the optical fiber is treated using Mie theory following the approach of plane-wave light scattering from thin rods. The fiber surface temperature is studied as a function of fiber diameter and laser power. The effect of different EM polarizations (parallel and perpendicular to the fiber axis) on the fiber temperature is also investigated. The final taper diameter values predicted by the present model are compared with experimentally acquired data. The analysis shows that to achieve final taper diameters of the order of 20 mm laser powers in excess of 25 W are required.

Investigation of energy exchange between silicon nanocrystals and Er3+ in silica

We present a photoluminescence study of 1.53 μm emission from erbium in silicon-rich silica that demonstrates efficient energy exchange between silicon nanocrystals and optically active erbium ions. We develop a rate-equation model of the interaction. Using this, we determine the effective erbium absorption cross-section, which appears to be several orders of magnitude higher than that in stoichiometric silica. This cross-section enhancement suggests the possibility of producing very efficient silicon-based broadband pumped optical devices for integrated optoelectronics, which exploit the nanocrystal, rare-earth coupling mechanism.

Indirect excitation of 1.5 μm emission from Er3+ in silicon-rich silica

We report the observation of near-IR emission from erbium in silicon-rich silica, excited using a filtered white-light source. The characteristic 4I13/2–4I15/2 intra-4f transition at 1535 nm is observed even when excitation wavelengths corresponding to the principal erbium optical absorption bands are removed using selective filtering. We ascribe this effect to an efficient transfer mechanism between silicon nanoclusters present in the silicon-rich silica films and the rare-earth ions. This is in good agreement with our previous work in this area and suggests the possibility of obtaining flashlamp-pumped erbium optoelectronic devices.

Broad-band and flashlamp pumping of 1.53 μm emission from erbium-doped silicon nanocrystals

We report recent results showing broad-band excitation of erbium ions implanted into thin films of silica containing silicon nanocrystals. Evidence for the existence of nanocrystals is presented in the form of HR-TEM images of crystalline regions of the thin films. Indirect excitation of the rare-earth ions is mediated by the nanocrystals, which are either grown in during plasma enhanced CVD of the films, or are formed by implantation of thermally grown SiO 2 layers with Si + ions. We demonstrate efficient flashlamp pumping of the erbium 1.535 μm PL band and discuss the device implications of this material.

Broadband Sensitization of 1.53 mu m Er[sup 3+] Luminescence in Erbium-Implanted Alumina

Experimental evidence of an efficient broadband sensitization mechanism in erbium-implanted alumina is presented. Alumina thin films were deposited by plasma-enhanced chemical vapor deposition using trimethyl-amine alane and nitrous oxide. The as-grown films, together with sapphire crystals, were implanted with erbium. Photoluminescence excitation spectra showed that erbium-implanted sapphire crystals exhibit characteristic Er3+ luminescence at 1.53μm only when pumped resonantly. In contrast, erbium-implanted alumina thin films exhibit 1.53μm luminescence even when pumped at wavelengths outside Er3+ absorption bands. We postulate that the sensitizing species is either small nanoclusters of aluminum or pairs of aluminum ions.

Lossless stripe waveguide optical beam splitter: modeling of the Y-structure

We present a theoretical model of a loss-compensated symmetric Y-junction acting as an optical beam splitter. We consider silica (SiO/sub 2/) channel waveguides which are assumed to be highly doped with Er/sup 3+/. The model was developed using the beam propagation method (BPM) and a fast-Fourier-transform (FFT)-based algorithm. The analysis showed that considerable gain levels, about 4.2 dB/cm at each port of the Y-junction, can be achieved for erbium concentration 2.5/spl times/10/sup 20/ ions/cm/sup 3/, signal power 1 /spl mu/W and pump power 250 mW.

Photoluminescence characterization of Er3+ -implanted silica thin films containing Si nanocrystals

Si nanocrystals (nc-Si) embedded in silica have recently attracted a lot of attention as a potential optoelectronic material due to their light emission at approximately 1.7 eV. Er3+ is attractive because its 1.53 micrometers emission coincides with the low attenuation region of silica optical fibers. In this paper, we report the experimental investigation of energy transfer between nc-Si and Er3+ in ion implanted material which may relax requirements on the Er3+ pump source and lead to broad-band pumped optical devices.