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ABSTRACT: Differences in the confinement of electrons and holes in quantum dots are shown to profoundly impact the magnitude of scattering with acoustic phonons. Using an extensive model that includes the non-Markovian nature of the phonon reservoir, we show how the effect may be addressed by photoluminescence excitation spectroscopy of a single quantum dot. We also investigate the implications for cavity QED, i.e., a coupled quantum dot-cavity system, and demonstrate that the phonon scattering may be strongly quenched. The quenching is explained by a balancing between the deformation potential interaction strengths and the carrier confinement and depends on the quantum dot shape. Numerical examples suggest a route towards engineering the phonon scattering.
Physical Review Letters 02/2013; 110(8):087401. · 7.37 Impact Factor
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ABSTRACT: We investigate the influence of the electron-phonon interaction on the decay
dynamics of a quantum dot coupled to an optical microcavity. We show that the
electron-phonon interaction has important consequences on the dynamics,
especially when the quantum dot and cavity are tuned out of resonance, in which
case the phonons may add or remove energy leading to an effective non-resonant
coupling between quantum dot and cavity. The system is investigated using two
different theoretical approaches: (i) a second-order expansion in the bare
phonon coupling constant, and (ii) an expansion in a polaron-photon coupling
constant, arising from the polaron transformation which allows an accurate
description at high temperatures. In the low temperature regime we find
excellent agreement between the two approaches. An extensive study of the
quantum dot decay dynamics is performed, where important parameter dependencies
are covered. We find that in general the electron-phonon interaction gives rise
to a greatly increased bandwidth of the coupling between quantum dot and
cavity. At low temperature an asymmetry in the quantum dot decay rate is
observed, leading to a faster decay when the quantum dot has a larger energy
than to the cavity. We explain this as due to the absence of phonon absorption
processes. Furthermore, we derive approximate analytical expressions for the
quantum dot decay rate, applicable when the cavity can be adiabatically
eliminated. The expressions lead to a clear interpretation of the physics and
emphasizes the important role played by the effective phonon density,
describing the availability of phonons for scattering, in quantum dot decay
dynamics. Based on the analytical expressions we present the parameter regimes
where phonon effects are expected to be important. Also, we include all
technical developments in appendices.
05/2012;
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ABSTRACT: We study the fundamental limit on single-photon indistinguishability imposed
by decoherence due to phonon interactions in semiconductor quantum dot-cavity
QED systems. Employing an exact diagonalization approach we find large
differences compared to standard methods. An important finding is that
short-time non-Markovian effects limit the maximal attainable
indistinguishability. The results are explained using a polariton picture that
yields valuable insight into the phonon-induced dephasing dynamics.
03/2012;
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ABSTRACT: A photonic nanowire single-photon source design incorporating an inverted conical tapering is proposed. The inverted taper allows for easy electrical contacting and a high photon extraction efficiency of 89 %. Unlike cavity-based approaches, the photonic nanowire features broadband spontaneous emission control and an improved tolerance towards fabrication imperfections.
Numerical Simulation of Optoelectronic Devices (NUSOD), 2011 11th International Conference on; 10/2011
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ABSTRACT: In this work we investigate a novel electrically-pumped photonic nanowire SPS design. It features an QD section, a bottom mirror, an inverted taper and a top contact section with an anti reflection coating and a gold annular ring contact. Using a single-mode model based on an elements-splitting approach, we analyze the performance of the various elements as function of geometrical parameters.
Lasers and Electro-Optics Europe (CLEO EUROPE/EQEC), 2011 Conference on and 12th European Quantum Electronics Conference; 06/2011
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ABSTRACT: We provide a comprehensive review of the application of slow and fast light (SFL) techniques to the field of microwave photonics. Basic principles leading to the implementation of phase shifting and true time delay operations which are instrumental in this field are first considered. We then focus on the description of the main results obtained by our groups in the implementation of broadband, full 360 phase shifting using coherent population oscillations in semiconductor waveguides. Next, attention is given to the evaluation of the system impairments implied by these devices when included in analog links. Finally, the main results obtained for several microwave photonic applications such as filtering, arbitrary waveform generation and optoelectronic oscillators (OEOs) are reviewed, and other directions for future research in the field are discussed.
IEEE Transactions on Microwave Theory and Techniques 12/2010; · 1.85 Impact Factor
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ABSTRACT: A tunable delay of ultrashort laser pulses in semiconductor waveguide structures are demonstrated in cascaded amplifying and absorbing semiconductor waveguides and compared with a single sectioned waveguide. The single sectioned waveguide shows a low transmission at the maximum delay. This is effectively avoided with the cascaded waveguide configuration, where it is demonstrated viable achieving a net pulse delay while maintaining a transmission of unity. For both types of devices, a pulse advancement is observed, at large pulse energies, that existing models are unable to account for.
IEEE Photonics Technology Letters 04/2010; · 2.19 Impact Factor
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ABSTRACT: Using multiband k*p theory we study the size and geometry dependence on the slow light properties of conical semiconductor quantum dots. We find the V-type scheme for electromagnetically induced transparency (EIT) to be most favorable, and identify an optimal height and size for efficient EIT operation. In case of the ladder scheme, the existence of additional dipole allowed intraband transitions along with an almost equidistant energy level spacing adds additional decay pathways, which significantly impairs the EIT effect. We further study the influence of strain and band mixing comparing four different k*p band structure models. In addition to the separation of the heavy and light holes due to the biaxial strain component, we observe a general reduction in the transition strengths due to energy crossings in the valence bands caused by strain and band mixing effects. We furthermore find a non-trivial quantum dot size dependence of the dipole moments directly related to the biaxial strain component. Due to the separation of the heavy and light holes the optical transition strengths between the lower conduction and upper most valence-band states computed using one-band model and eight-band model show general qualitative agreement, with exceptions relevant for EIT operation. Comment: 9 pages, 12 figures
02/2010;
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ABSTRACT: We present a theoretical method for calculating small-signal modulation responses and noise spectra of active Fabry-Perot semiconductor waveguides with external light injection. Small-signal responses due to either a modulation of the pump current or due to an optical amplitude or phase modulation of the input field can be calculated. Both responses and noise spectra are given through semianalytical expressions taking into account the longitudinal extent and finite end-facet reflectivities of the active device. Different examples of responses and spectra are presented for semiconductor optical amplifiers and an injection-locked laser. We also demonstrate the applicability of the method to analyze slow and fast light effects in semiconductor waveguides. Finite reflectivities of the facets are found to influence the phase changes of the injected microwave-modulated light.
IEEE Journal of Quantum Electronics 09/2009; · 1.88 Impact Factor
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ABSTRACT: We review the theory of slow and fast light effect in semiconductor waveguides and potential applications of these effects in microwave photonic systems as RF phase shifters. Recent applications as microwave photonic filters is presented. Also, in the presentation more applications like optoelectronic oscillators and arbitrary waveform generators will be described. Some work related to the noise and distortion will also be discussed.
Transparent Optical Networks, 2009. ICTON '09. 11th International Conference on; 08/2009
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ABSTRACT: We investigate the impact of many-body interactions on group-velocity slowdown achieved via electromagnetically induced transparency in quantum dots using three different coupling-probe schemes (ladder, V, and Lambda, respectively). We find that for all schemes many-body interactions have an important impact on the slow light properties. In the case of the Lambda and V schemes, the minimum required coupling power to achieve slow light is significantly reduced by many-body interactions. V type schemes are found to be generally preferable due to a favorable redistribution of carriers in energy space.
05/2009;
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ABSTRACT: A continuously tunable microwave photonic notch filter at around 30 GHz is experimentally demonstrated and 100% fractional tuning over 360deg range is achieved without changing the shape of the spectral response. The tuning mechanism is based on the use of slow and fast light effects in semiconductor optical amplifiers assisted by optical filtering.
IEEE Photonics Technology Letters 03/2009; · 2.19 Impact Factor
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ABSTRACT: We give an overview of recent results on slow and fast light in active semiconductor waveguides. The cases of coherent population oscillations as well as electromagnetically induced transparency are covered, emphasizing the physics and fundamental limitations.
IEEE/LEOS Winter Topicals Meeting Series, 2009; 02/2009
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ABSTRACT: A new vertical-cavity surface-emitting laser (VCSEL) structure based on a subwavelength grating mirror and a thin oxide gap is suggested and numerically investigated. The structure is shown to exhibit similar threshold gain, suppression of higher order transverse modes, and polarization stability as a grating-mirror VCSEL reported in the literature based on a thick air gap. The thin oxide gap structure has a number of advantages including easier fabrication, better mechanical stability, and very strong single-mode properties.
IEEE Photonics Technology Letters 02/2008; · 2.19 Impact Factor
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ABSTRACT: A broadband microwave photonic phase shifter is presented based on the polarisation properties of a Mach-Zehnder intensity modulator and nonlinear polarisation rotation in a semiconductor optical amplifier. The system can realise about 150deg phase shift in the frequency range from 50 MHz to 19 GHz.
Electronics Letters 02/2008; · 0.96 Impact Factor
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ABSTRACT: We have developed a second-order small-signal model for describing the nonlinear redistribution of noise in a saturated semiconductor optical amplifier. In this paper, the details of the model are presented. A numerical example is used to compare the model to statistical simulations. We show that the proper inclusion of second-order noise terms is required for describing the change in the skewness (third-order moment) of the noise distributions. The calculated probability density functions are described far out in the tails and can hence describe signals with very low bit error rate (BER). The work is relevant for describing the noise distribution and BER in, for example, optical regeneration.
IEEE Journal of Quantum Electronics 01/2008; · 1.88 Impact Factor
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ABSTRACT: All optical 2R-regeneration based on the integration of semiconductor optical amplifiers and electroabsorbers in a single waveguide is experimentally demonstrated. Static transfer functions of concatenated structures show strong improvements of the nonlinearity. An extinction ratio improvement > 4.5 dB has been obtained under dynamics operation. For optical signal- to-noise ratio values above 17 dB, improvement in BER is observed. A receiver sensitivity improvement > 2 dB at BER of 10<sup>-9</sup> was found for 10 Gb/s operation.
Lasers and Electro-Optics Society, 2007. LEOS 2007. The 20th Annual Meeting of the IEEE; 11/2007
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ABSTRACT: We present a novel scheme for the control of microwave signals in the optical domain. We propose the use of alternating amplifying and absorbing sections to implement phase control by using fast and slow light effects in semiconductors. The potential benefits from the proposed semiconductor optical amplifier and electroabsorber structures are the high tuning speed, the continuous scan of the phase delay that brings antenna angular continuing scanning, the small size, the capability of integration, the low insertion losses, and the low bias voltage. We have obtained phase changes of almost 60deg around 10 GHz using commercially available components that were not optimized for this purpose. These results indicate a potential for several microwave photonic applications including the change of the direction of the radiation pattern of photonic phase-array antennas or the implementation of fast tunable microwave photonic filters.
IEEE Photonics Technology Letters 11/2007; · 2.19 Impact Factor
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ABSTRACT: We have investigated the slow and fast light properties of a semiconductor waveguide device employing concatenated gain and absorber sections. This letter presents the experimental results as well as theoretical modeling. A large phase shift of 110deg and a true-time delay of more than 150 ps are demonstrated. The combination of amplitude and phase control of the modulated signal shows great promise for applications within microwave photonics.
IEEE Photonics Technology Letters 09/2007; · 2.19 Impact Factor
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ABSTRACT: For high-speed optical communication systems, timing jitter is a crucial parameter for switching operations between the data and control signal. This is especially the case for the demultiplexer. The effect of timing jitter becomes very important as the bit rate of the data signal increases beyond 100 Gb/s and it is, therefore, essential to quantify its effect. In this letter, the impact of gating timing jitter on a 160-Gb/s demultiplexer is investigated by using two pulse sources with different timing jitter properties. We also investigate the interplay between the control signal pulsewidth and timing jitter. The experiment shows that it is essential to minimize jitter in the 20-kHz to 10-MHz range. Furthermore, we show that the impact of timing jitter can be reduced if the control signal pulses are broader than data signal pulses.
IEEE Photonics Technology Letters 08/2007; · 2.19 Impact Factor
