Ultrafast all-optical switching by cross phase modulation induced wavelength conversion in silicon-on-insulator waveguides and ring resonators

We present new results on ultrafast alloptical wavelength conversion in Silicon-on-Insulator waveguides through cross phase modulation. We demonstrate sub-picosecond all-optical switching with 13dB on/off ratio by combining the nonlinear wavelength conversion in the port waveguide with passive filtering using an integrated SOI microring resonator.\u

Ultrafast all-optical wavelength conversion in silicon-insulator waveguides by means of cross phase modulation using 300 femtosecond pulses

In this paper we report the ultrafast all-optical wavelength conversion in Silicon-on-Insulator (SOI) waveguides. We used a pump-probe setup with 300 femtosecond pulses to demonstrate large temporal phase-shifts, caused by the Kerr effect and free carrier generation. Large wavelength shifts of a 1683nm probe signal have been observed. The wavelength conversion, ranging from 10nm redshifts to 15nm blueshifts, depending on the time delay between the pump and probe pulses, is caused by the pump induced Cross Phase Modulation. Furthermore, an all-optical switching scheme using SOI microring resonators is discussed. These results enable ultrafast all-optical switching using SOI microring resonators

Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics

Femtosecond optical pulses at mid-infrared frequencies have opened up the nonlinear control of lattice vibrations in solids. So far, all applications have relied on second order phonon nonlinearities, which are dominant at field strengths near 1 MVcm-1. In this regime, nonlinear phononics can transiently change the average lattice structure, and with it the functionality of a material. Here, we achieve an order-of-magnitude increase in field strength, and explore higher-order lattice nonlinearities. We drive up to five phonon harmonics of the A1 mode in LiNbO3. Phase-sensitive measurements of atomic trajectories in this regime are used to experimentally reconstruct the interatomic potential and to benchmark ab-initio calculations for this material. Tomography of the Free Energy surface by high-order nonlinear phononics will impact many aspects of materials research, including the study of classical and quantum phase transitions

Ultrafast all-optical wavelength conversion in silicon waveguides using femtosecond pump-probe pulses

Experimental results on ultrafast all-optical wavelength conversion in silicon-on-insulator waveguides are presented. Red and blue shifts of 10nm have been observed in femtosecond pump-probe experiments. Alloptical switching and the importance of waveguide dispersion are discussed

Coherent Modulation of the YBa2Cu3O6+x Atomic Structure by Displacive Stimulated Ionic Raman Scattering

We discuss the mechanism of coherent phonon generation by Stimulated Ionic Raman Scattering, a process different from conventional excitation with near visible optical pulses. Ionic Raman scattering is driven by anharmonic coupling between a directly excited infrared-active phonon mode and other Raman modes. We experimentally study the response of YBa2Cu3O6+x to the resonant excitation of apical oxygen motions at 20 THz by mid-infrared pulses, which has been shown in the past to enhance the interlayer superconducting coupling. We find coherent oscillations of four totally symmetric (Ag) Raman modes and make a critical assessment of the role of these oscillatory motions in the enhancement of superconductivity.Comment: 12 pages, 4 figure

Ab-initio simulations on growth and interface properties of epitaxial oxides on silicon

The replacement of SiO2 by so-called high-k oxides is one of the major challenges for the semiconductor industry to date. Based on electronic structure calculations and ab-initio molecular dynamics simulations, we are able to provide a consistent picture of the growth process of a class of epitaxial oxides around SrO and SrTiO3. The detailed understanding of the interfacial binding principles has also allowed us to propose a way to engineer the band-offsets between the oxide and the silicon substrate.Comment: 6 pages, 6 figures, proceeding for the INFOS2005 conference (http://www.imec.be/infos/

Pump frequency resonances for light-induced incipient superconductivity in YBa2_2Cu3_3O6.5_{6.5}

Optical excitation in the cuprates has been shown to induce transient superconducting correlations above the thermodynamic transition temperature, $T_C$, as evidenced by the terahertz frequency optical properties in the non-equilibrium state. In YBa$_2$Cu$_3$O$_{6+x}$ this phenomenon has so far been associated with the nonlinear excitation of certain lattice modes and the creation of new crystal structures. In other compounds, like La$_{2-x}$Ba$_x$CuO$_4$, similar effects were reported also for excitation at near infrared frequencies, and were interpreted as a signature of the melting of competing orders. However, to date it has not been possible to systematically tune the pump frequency widely in any one compound, to comprehensively compare the frequency dependent photo-susceptibility for this phenomenon. Here, we make use of a newly developed optical parametric amplifier, which generates widely tunable high intensity femtosecond pulses, to excite YBa$_2$Cu$_3$O$_{6.5}$ throughout the entire optical spectrum (3 - 750 THz). In the far-infrared region (3 - 25 THz), signatures of non-equilibrium superconductivity are induced only for excitation of the 16.4 THz and 19.2 THz vibrational modes that drive $c$-axis apical oxygen atomic positions. For higher driving frequencies (25 - 750 THz), a second resonance is observed around the charge transfer band edge at ~350 THz. These observations highlight the importance of coupling to the electronic structure of the CuO$_2$ planes, either mediated by a phonon or by charge transfer.Comment: 47 pages, 21 figures, 2 table