Georg Pucker

Terbium(III) doped silica-xerogels: effect of aluminium(III) co-doping

Monolithic silica xerogels doped with diAerent concentrations of Tb 3a and Al 3a (xTbO1:5‐x6AlO1:5‐SiO2, xa 2 · 10 ˇ4 ,4 ·10 ˇ4 ,5 ·10 ˇ3 ) were prepared by a sol‐gel route: Mixtures of tetra-methoxy-silane, Tb(NO3)3 AE 5H2O, Al(NO3)3 AE 9H2O, ethanol, and water were condensed at 60∞C using HNO3 as catalyst. The samples were sintered at 950∞C for 86 h in air. The Raman spectra indicate several structural diAerences among the samples and show that there is a compositional dependence of the gel glass transformation temperature. The sample with xa 5 · 10 ˇ3 is glasslike on the outer part showing onset of crystallisation in the inner part of the sample. The samples with smallest dopant concentrations (xa 2 · 10 ˇ4 ,4 ·10 ˇ4 ) contain pores. All samples luminesce from the 5 D4 and 5 D3 states of Tb 3a with excitation at 355 nm. The 5 D3 luminescence increases with respect to the 5 D4 luminescence with increasing dopant concentration, indicating that the larger Al 3a concentrations are eAective in dispersing Tb 3a ions. This result is also confirmed by the analysis of the decay of the 5 D3 and 5 D4 luminescence. ” 1999 Elsevier Science B.V. All rights reserved.

Optical spectroscopy of Pr3+ ions in sol-gel derived GeO2-SiO2 planar waveguides

A GeO 2 -SiO 2 planar waveguide, activated with 1% mol Pr 3+ , has been prepared using a dip-coating technique. The GeO 2 -SiO 2 film was deposited on a substrate consisting of a silicon wafer with a silica buffer layer. After annealing at 800°C and 900°C the waveguide luminescence and Raman spectra were measured. The Raman spectra show that complete densification is achieved after annealing at 800°C. Analysis of the emission spectra and the decay curves from the 3 P 0 and 1 D 2 states of Pr 3+ indicates that the non-radiative relaxation due to the rare-earth clustering is less important than in massive silica xerogels.

Electroluminescence in MOS structures with Si/SiO2 nanometric multilayers

Abstract Silicon light emitting devices, compatible with the conventional CMOS process, have been fabricated and tested. The structure of the devices is based on a MOS capacitor where nanometer thick silicon/silicon dioxide multilayers have been grown in the dielectric. Room temperature photo- and electroluminescence were measured. While photoluminescence has been recognized as being due to electron–hole recombination in the nanometer thick silicon layers, electroluminescence was mainly related to hot-electron relaxation in the substrate. The measured external quantum efficiency of the electroluminescence is about 5×10 −5 .

Fluorescence line narrowing study of Cr3+ ions in cordierite glass nucleating MgAl2O4 nanocrystals

Abstract The luminescence of Cr 3+ ions in cordierite glass nucleating MgAl 2 O 4 nanocrystallites has been investigated. The time resolved fluorescence line narrowing measurements and the temperature dependence of the homogeneous line width show that most Cr 3+ ions are inside the nanocrystallites. Cr 3+ ions occupy non-equivalent crystal sites, due to the Mg 2+ –Al 3+ inversion effect. The values of the homogeneous line width compare well with those of previous studies in crystals. No surface effect has been observed due to the large size of the crystals.

Raman and luminescence studies of Tb3+ doped monolithic silica xerogels

Abstract Monolithic silica xerogels were doped with Tb3+ concentrations ranging from 200 to 40u2008000 ppm. Structural differences, such as the degree of densification or the different OH-contents were quantified by Raman spectroscopy. The Tb3+ luminescence properties were studied as a function of the temperature of heat-treatment, the time of heat-treatment, and the Tb3+ concentration. Samples densified at 900°C or above and with a Tb3+ content lower than 20u2008000 ppm show emission from both the 5D3 and the 5D4 state. Emission spectra and decay curves indicate that Tb3+ ions have a strong tendency to form clusters also at a very low Tb3+ concentration. This clustering results in a very efficient quenching of the 5D3 emission due to energy transfer processes among Tb3+ ions. Moreover, the luminescence of the 5D3 state is quenched by non-radiative transitions induced by OH vibrations.

Effect of Pr3+ Doping on the OH Content of Silica Xerogels

Pr2O3-SiO2 xerogels doped with different Pr/Si concentrations were annealed at 900°C for 120 h and then investigated by FTIR, NIR absorption, Raman and luminescence spectroscopies. It is observed that the content of surface silanol groups is lower for higher Pr3+ concentrations. Luminescence measurements indicate that the amount of the residual OH plays an important role in the spectroscopic properties of the Pr3+ ion and in particular the quantum yield of the emission from the 3P0,1 and 1D2 states.

Optical gain in silicon nanocrystals

Abstract We report measurements of stimulated emission and single pass light amplification in Si nanocrystals obtained by ion implantation. We argue that population inversion involves Siue605O interface states.

Porous silicon optical devices and Si/SiO2 quantum wells: Recent results

Abstract The recent progress accomplished in our research group is here presented. Firstly porous Si (PS) microcavities were formed on p-type-doped (6-9ωcm) substrates with very narrow bandwidth (6 nm) and a good ratio of the peak to background emission, reaching at the same time a high emission quantum efficiency. Secondly light-emitting diodes (LEDs) based on n-type-doped Si/PS heterojunctions were studied. The improvement in the proposed LED structure with respect to the usual metal/PS LED is demonstrated. Anodic oxidation experiments show further improvements in the LED efficiency. Thirdly, SiO2/ Si/SiO2 quantum wells with room-temperature efficient light emission in the visible range were investigated. We report here the preparation and photoluminescence properties of thin SiO2/Si layers obtained by low-pressure chemical vapour-phase deposition and thermal oxidation processes. The growth technique is fully compatible with standard very-large-scale integration complementary metal-oxide-semiconductor technology.

Are on-chip heralded single photon sources possible by intermodal four wave mixing in silicon waveguides?

On-chip heralded single photon sources are of key importance in the development of chip-scale devices exploiting the quantum properties of light. Single photon states can be produced as single photons heralded from correlated photon pairs generated through spontaneous four wave mixing. On-chip heralded single photon sources based on spontaneous four wave mixing have been already demonstrated. However, the heralded and herald photons are usually generated with wavelengths very close to the pump one, limiting the pump rejection efficiency and the application to the mid infrared. Moreover, the common sources of heralded photons based on spontaneous four wave mixing require spectral post filtering to achieve high purity, limiting the brightness and the integration of these sources. A solution to these problems can be provided by intermodal four wave mixing. In this work, we demonstrate the generation of photon pairs through intermodal four wave mixing in silicon waveguides, measuring the coincidences between the idler at 1.281 μm and the signal at 1.952 μm. We then discuss the application of intermodal four wave mixing to on-chip heralded single photon sources.

Intermodal four wave mixing in silicon waveguides for on-chip wavelength conversion and generation (Conference Presentation)

Silicon photonics is currently moving towards the Mid Infrared (MIR), which attracts plenty of emerging technologies, from integrated spectroscopy to quantum communications. However, the development of MIR-photonics is hindered by the lack of efficient detectors and light sources. A possible solution could be an integrated system able to link the MIR with the near infrared, where detectors and light sources have been already developed for telecommunications. Because of this, the possibility to perform broad and tunable wavelength conversion and generation is of great interest. In particular, the generation and conversion can be accomplished by means of Four Wave Mixing (FWM), a nonlinear optical process in which two input pump photons are converted into signal and idler photons of different frequency. nnCrucial for efficient FWM is the phase matching condition, which determines the spectral position of the maximum efficiency of the process. In order to achieve large spectral translation between signal and idler, we propose to use Intermodal FWM (IMFWM), which exploits the dispersion of the higher order waveguide modes to achieve the phase matching condition. In IMFWM, the pump, signal and idler propagate on different waveguide modes. With respect to common phase matching techniques, IMFWM does not require anomalous GVD, resulting in an easier handling of the phase matching condition. Moreover, due to the sensitivity of the higher order mode dispersion with the waveguide geometry, the spectral position of the intermodal phase matching can be easily tuned by engineering the waveguide cross-section, achieving also large detunings from the pump wavelength. Another advantage is the high tolerance to the fabrication defects, related to the large widths of the multimode waveguides used.nnIn our work, we report the first experimental demonstration of spontaneous and stimulated on-chip IMFWM using Silicon-On-Insulator (SOI) channel multimode waveguides. We used a pulsed pump laser at 1550 nm with 10 MHz repetition rate and 40 ps pulse width. The excitation of the higher order modes is attained by displacing horizontally the input tapered lensed fiber with respect to the center of the waveguide facet. nWe investigated an intermodal combination involving the pump injected on both the first and second order modes, the signal on the second order mode and the idler on the first order mode, with transverse electric polarization.nWe used a 3.8-um-wide waveguide, of 1.5 cm length, to perform a spectral conversion of 140 nm with -21 dB efficiency. With the same waveguide, we measured -85 dB between the pump and the spontaneously generated idler. The coupled peak pump power was about 2 W.nWe then measured the spectral position of the idler as a function of the waveguide width, achieving a maximum wavelength detuning between the idler and the signal wavelengths of 861 nm in a 2-um-wide waveguide, corresponding to the generation of 1231 nm idler and 2092 nm signal. nnIMFWM enables effective and viable wavelength conversion and generation. It also promotes the development of emerging technologies, like mode division multiplexing and modal quantum interference, whose working principle relies on the higher order waveguide modes.