Marc-André Dupertuis

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We have measured phase modulation in the first chemical beam epitaxy grown InGaAsP/InP barrier, reservoir, and quantum well electron transfer structures. We obtain a negative refractive index change, DELTAn, similar to that found in the InGaAs/InAlAs system. Using new designs to reduce the leakage current in this material system, we obtain a leakage current

We have studied systems of asymmetric coupled GaAs V-groove quantum wires p-i-n diodes, in which the electrons and holes are injected into different wires. Despite the use of a 7 nm thick AlGaAs tunnel barrier, and although we demonstrate that holes tunnel more slowly than electrons, we observe a very efficient and fast tunneling between the quantum wires (QWR's). We attribute this to the achievement of a resonance between hole levels in the two QWR's. Photoluminescence excitation experiments are compared w

We investigated the optical properties of excitons in quasi-one-dimensional semiconductor quantum structures by photoluminescence and photoluminescence excitation: High-quality GaAs/AlxGa1-xAs heterostructures were grown using low-pressure organometallic chemical vapour deposition (OMCVD) on non-planar substrates. The experimentally observed subband separations are in good agreement with a theoretical calculation of the quantum-confined eigenstates, which includes the mapping of the crescent-shaped wire obt

A fully two-dimensional study of the electronic sub-bands in crescent-shaped quantum wires is presented. The confinement energies and the wave functions are compared by means of an aspect ratio to those produced by the adiabatic approximation. Guidelines for applying the adiabatic model are provided and the adiabatic quantum number classification scheme is discussed. "Non-adiabatic" states are determined among the first few sub-bands and a built-in dipole is identified. The energy spectrum is explored as a

The spatial and time-reversal symmetries of excitons in quantum wires are discussed, including possible use in numerical computation. Particular attention is paid to the important case of a single symmetry plane (group C-s). Even in such a low symmetry case group theory proves very useful. For instance we can explain the appearance of new transitions recently observed and find interesting excitonic optical selection rules describing in a new way the polarization anisotropy coming from valence band-mixing.

We present a novel theory of polaritons which contains the crucial tools to securely tackle the many-body physics of polaritons. Microcavitly polaritons are central to exciting Bose-Einstein condensation and parametric scattering experiments in semiconductors. Besides Coulomb and Pauli scattering (dressed by the relevant exciton-Hopfield coefficients), it beautifully unravels a novel fundamental scattering between two polaritons which can be physically associated with a photon-assisted exchange process, wit

A dynamical theory of multiphoton transitions in semiconductors is developed using a density matrix approach. It is shown that, in dipole approximation, these transitions require a mixed parity of the basis stales and that band-diagonal coupling's of the electromagnetic field to Bloch electrons have to be included. The general theory is outlined using the simple, but solvable model of a diatomic tight-binding chain. Possible extensions and applications of the approach are discussed.

Pump and Probe measurements with femtosecond pulses are performed on a Gain-Clamped Semiconductor Optical Amplifier (a special laser structure). The relaxation oscillations of the carriers density are observed directly in the time domain, Reasonable values of the differential gain and the nonlinear gain factors are extracted from the current dependence of the oscillations.

The optical speed-up at transparency principle has been successfully applied to a gain-clamped semiconductor optical amplifier yielding a remarkable acceleration in the gain recovery of the device as well as to the disappearance of the typical relaxation oscillations stemming from the coupling between the internal lasing mode and the carrier density. A record gain recovery time of 13 ps has been measured with an available gain of still 16 dB. A small-signal analysis of the semiconductor laser amplifier rate

We analyze the electronic properties of quantum wires with a Z-like profile within four-band models for the valence band of a semiconductor of diamond and zinc blende type. Group-theoretical considerations show that the valence-band structure is doubly degenerate only when the linear k-terms (coming e.g. from the bulk crystal inversion asymmetry) are neglected. The considerations apply to the more general case of a profile containing a 2D center of inversion.

The paper describes gain measurements in InGaAs/InGaAsP multiquantum-well lasers at 1.55-mu-m derived from the spontaneous emission under current injection. The gain spectrum in a broad-area laser device is determined from the spontaneous emission spectrum on using the measured differential quantum efficiency and the loss conditions at the lasing wavelength at threshold. Spectral measurements from 1.0 to 1.7-mu-m with intensity resolution over four orders of magnitude clearly exhibit contributions from the

We propose a new configuration for semiconductor optical amplifiers (SOAs), called optical speed-up at transparency (OSAT), which allows to speed up the gain recovery of SOAs and their saturation power without sacrificing the gain, nor increasing the applied current, The proposed configuration is particularly well-suited for high-speed WDM or OTDM applications, It consists of an optical cw-signal injected at the transparency point of the SOA, This setup is potentially integrable on a single chip, and still

We report on efficient, narrow linewidth exciton recombination in GaAs/AlGaAs V-groove quantum wire light-emitting diodes at room temperature. The high efficiency is due to a selective carrier injection mechanism resulting in an estimated internal quantum efficiency of similar to 20% with an electroluminescence (EL) linewidth as narrow as 15 meV. The thermal broadening contribution to the linewidth is 6 meV due to exciton scattering with optical phonons. An analysis of the EL peak shift in a magnetic field

A bistable etalon, consisting of an optically nonlinear semiconductor spacer layer sandwiched between two Bragg mirrors, has been optimized for use in reflection, using a numerical model for a self-consistent carrier density based on published experimental data for the nonlinear absorption alpha(I,lambda) and refraction DELTA-n(I,lambda). The saturation behavior of the refractive index and the absorption in bulk GaAs has been investigated at different wavelengths. High saturation values of DELTA-n(s) almost

We have directly measured, under operating conditions, the distributions of carrier densities and temperatures in a gain-clamped semiconductor optical amplifier designed for operation at 1.55 mum. As expected, longitudinal spatial hole burning is much smaller than in conventional semiconductor optical amplifiers and the effects of gain clamping are clearly evidenced. The amplifier nevertheless shows a sizeable temperature increase for both the lattice and the carriers at high currents, which are attributed

The influence of coherent optical pumping in semiconductor lasers is investigated theoretically. In particular the mathematical conditions under which an optically pumped system behaves like an electrically (incoherently) pumped system are derived. We show that it is practically impossible to reach the interesting regime where coherent effects are important because of the inherent constraints to absorb photons at the pump frequency and to reach threshold gain at the lasing frequency. The effects of changing

We have studied the effect of disorder on the radiative properties of semiconductor quantum wires by time-resolved photoluminescence spectroscopy. The dependence of the radiative lifetimes is measured over a temperature range extending from 8 to 150 K. At low temperatures we find that the measured dependence does not conform to the theoretical prediction for recombination of free excitons in a quasi-one-dimensional system due to the major influence of disorder. An extension of the theory is developed in ord

Numerical simulations and experimental results are reported on bistable switching in a semiconductor nonlinear vertical Bragg reflector. An improved structure with an additional linear rear mirror and a phase-adjusting layer was predicted to have lower threshold for bistability than a Fabry-Perot type device. The experimental observation of bistable switching in a nonlinear Bragg reflector is reported. Achieved threshold was comparable with a nonlinear Fabry-Perot device; the simpler structure of a nonlinea

We present femtosecond gain measurements in microcavity-embedded quantum wells. When the excitonic transition is saturated by an intense pump field, the spectrum measured with a weak probe pulse is strongly modulated by pump-probe wave mixing processes. A giant probe amplification occurs within the bandwidth of the empty-cavity mode. The optical feedback provided by the microcavity is responsible for a net gain of the broadband probe pulse. [S0163-1829(99)50424-4].

We have studied the effect of valence band mixing on the optical properties of semiconductor quantum wires by analyzing the luminescence polarization. Large polarization anisotropy is observed and directly compared to the effects predicted by a k . p model calculation of the valence band structure.

Marc-André Dupertuis

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Phase Modulation in Ingaasp Barrier, Reservoir, and Quantum-Well Electron-Transfer Structures, Grown by Chemical Beam Epitaxy

Electroluminescence and photoluminescence excitation study of asymmetric coupled GaAs/AlxGa1-xAs V-groove quantum wires

Optical spectroscopy of semiconductor quantum wires

Electronic states in hyperbolic-boundary crescent-shaped quantum wires

The symmetry of excitons in quantum wires

Novel exact approach to polariton-polariton interactions and scattering rates: the limits of bosonization

Dynamical density matrix theory of multiphoton transitions in semiconductors

Direct observation in the temporal domain of relaxation oscillations in a semiconductor laser

Acceleration of a gain-clamped semiconductor optical amplifier by the optical speed-up at transparency scheme

The band structure of Z-like quantum wires

Gain Measurements in InGaAs/InGaAsP Multiquantum-Well Broad-Area Lasers

Extremely fast high-gain and low-current SOA by optical speed-up at transparency

Efficient, narrow linewidth excitonic emission at room temperature from GaAs/AlGaAs V-groove quantum wire light-emitting diodes

Design and Investigation of a Nonlinear Fabry-Perot Device with Gaas Spacer Layer

Density clamping and longitudinal spatial hole burning in a gain-clamped semiconductor optical amplifier

Coherent Optical-Pumping of Semiconductor-Lasers

Effect of disorder on the temperature dependence of radiative lifetimes in V-groove quantum wires

Bistable Switching in a Nonlinear Bragg Reflector

Strong coherent gain from semiconductor microcavities in the regime of excitonic saturation

Polarization anisotropy and valence band mixing in semiconductor quantum wires