Propagation through silicon-on-insulator (SOI) waveguide structures of 1.53 μm, 100 fs laser pulses with peak powers up to 400 W is studied experimentally and theoretically. The dominant nonlinear effects are two-photon absorption and self-phase modulation. The two-photon absorption coefficient and the nonlinear refractive index of Si obtained in this work are β2=0.9 cm/GW and n2=0.7×10−13 cm2/W, respectively. At high intensities, free carriers generated by two-photon absorption are demonstrated to have a significant influence on pulse spectra and transmitted power. The figure of merit for all-optical switching obtained in this work (T=1.8) indicates that a switch based on a SOI waveguide structure might be possible at 1.55 μm.
We present a numerical method for studying electron dynamics in semiconductor crystals interacting with electromagnetic fields. The approach employs the length gauge and is consequently free of the unphysical divergences that arise in the velocity gauge as → 0. The topology of the electronic structure of the Brillouin zone is taken into account by the discretization employed, and the computational method is invariant under local gauge symmetry of the Bloch functions. Arbitrary electronic structures and any temporal dependence of the fields can be handled within this approach. We give some illustrative calculations to compare and contrast numerical results of velocity and length gauges for subgap excitations of semiconductors.within the dipole approximation, where H 0 is the full Hamiltonian of the crystal and E͑t͒ is the electric field. When ex-PHYSICAL REVIEW B 76, 035213 ͑2007͒
We propose an experimental scheme to probe the Berry curvature of solids. Our method is sensitive to arbitrary regions of the Brillouin zone and employs only basic optical and terahertz techniques to yield a background-free signal. Using semiconductor quantum wells as a prototypical system, we discuss how to inject Berry curvature macroscopically and probe it in a way that provides information about the underlying microscopic Berry curvature.
Polarization effects are included exactly in a model for a quantum dot in close proximity to a planar interface. Efficient incorporation of this potential into the Schrödinger equation is utilized to map out the influence of the image potential effects on carrier tunneling in such heterostructures. In particular, the interplay between carrier mass and the dielectric constants of a quantum dot, its surrounding matrix, and the electrode is studied. We find that the polarizability of the planar electrode structure can significantly increase the tunneling rates for heavier carriers, potentially resulting in a qualitative change in the dependence of tunneling rate on mass. Our method for treating polarization can be generalized to the screening of two particle interactions, and can thus be applied to calculations such as exciton dissociation and the Coulomb blockade. In contrast to tunneling via intermediate surface localized states of the quantum dot, our work identifies the parameter space over which volume states undergo significant modification in their tunneling characteristics.2
We study the dynamics of impurity-bound electrons interacting with a bath of conduction band electrons in a semiconductor. Only the exchange interaction is considered. We derive master equations for the density matrices of single-and two-qubit systems under the usual Born and Markov approximations. The bath mediated Ruderman-Kittel-Kasuya-Yoshida interaction in the two-qubit case arises naturally. It leads to an energy shift significant only when the ratio ͑R T ͒ of the interqubit distance to the thermal de Broglie wavelength of the bath electrons is small. This bath mediated interaction also has a profound impact on the decoherence times; the effect decreases monotonically with R T .
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