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    Wyświetlanie 1-12 z 12
    Tytuł:
    Convolutive Blind Signal Separation Spatial Effectiveness in Speech Intelligibility Improvement
    Autorzy:
    Kociński, J.
    Sęk, A.
    Libiszewski, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/1504381.pdf
    Data publikacji:
    2011-06
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    43.72.-p
    43.60.-c
    43.60.+d
    Opis:
    Blind signal separation is one of the latest methods to improve the signal to noise ratio. The main objective of blind source separation is the transformation of mixtures of recorded signals to obtain each source signal at the output of the procedure, assuming that they are statistically independent. For acoustic signals it can be concluded that the correct separation is possible only if the source signals are spatially separated. That finding suggests analogies with the classical spatial filtering (beamforming). In this study we analyzed an effect of the angular separation of two source signals (i.e. speech and babble noise) to improve speech intelligibility. For this purpose, we chose the blind source separation algorithm based on the convolutive separation, based on second order statistics only. As a system of sensors a dummy head was used (one microphone inside each ear canal), which simulated two hearing aids of a hearing impaired person. The speech reception threshold, before and after the blind source separation was determined. The results have shown significant improvement in speech intelligibility after applying blind source separation (speach reception threshold fell even more than a dozen dB) in cases where the source signals were angularly separated. However, in cases where the source signals were coming from the same directions, the improvement was not observed. Moreover, the effectiveness of the blind source separation, to a large extent, depended on the relative positions of signal sources in space.
    Źródło:
    Acta Physica Polonica A; 2011, 119, 6A; 996-999
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Hole Subband Mixing and Polarization of Luminescence from Quantum Dashes: A Simple Model
    Autorzy:
    Kaczmarkiewicz, P.
    Musiał, A.
    Sęk, G.
    Podemski, P.
    Machnikowski, P.
    Misiewicz, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/2048063.pdf
    Data publikacji:
    2011-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.67.Hc
    73.22.-f
    Opis:
    In this paper, we address the problem of luminescence polarization in the case of nanostructures characterized by an in-plane shape asymmetry. We develop a simple semi-qualitative model revealing the mechanism that accounts for the selective polarization properties of such structures. It shows that they are not a straightforward consequence of the geometry but are related to it via valence subband mixing. Our model allows us to predict the degree of polarization dependence on the in-plane dimensions of investigated structures assuming a predominantly heavy hole character of the valence band states, simplifying the shape of confining potential and neglecting the influence of the out-of-plane dimension. The energy dependence modeling reveals the importance of different excited states in subsequent spectral ranges leading to non-monotonic character of the degree of polarization. The modeling results show good agreement with the experimental data for an ensemble of InAs/InP quantum dashes for a set of realistic parameters with the heavy-light hole states separation being the only adjustable one. All characteristic features are reproduced in the framework of the proposed model and their origin can be well explained and understood. We also make some further predictions about the influence of both the internal characteristics of the nanostructures (e.g. height) and the external conditions (excitation power, temperature) on the overall degree of polarization.
    Źródło:
    Acta Physica Polonica A; 2011, 119, 5; 633-636
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Phonon-Assisted Radiative Recombination of Excitons Confined in InAs Quantum Dashes
    Autorzy:
    Dusanowski, Ł.
    Musiał, A.
    Sęk, G.
    Machnikowski, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/1399092.pdf
    Data publikacji:
    2013-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.67.Hc
    63.20.kk
    Opis:
    In this report we have investigated theoretically the phonon-assisted recombination process of excitons confined in strongly elongated semiconductor nanostructures, called quantum dashes. Interaction with phonon bath leads to the occurrence of phonon-assisted recombination, which in the case of acoustic phonons is manifested in the optical spectra as a deviation of the homogeneously broadened emission line shape from expected Lorentzian profile via occurrence of the so-called phonon sidebands. Hereby, we have modeled the influence of the quantum dash geometry on this spectral feature proving pronounced suppression of phonon-induced decoherence for strongly elongated nanostructures. Furthermore, the importance of different phonon coupling mechanisms has been evaluated and the spectral diffusion effects, unavoidable in the time-integrated photoluminescence experiments, have been accounted for.
    Źródło:
    Acta Physica Polonica A; 2013, 124, 5; 813-816
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electronic Structure of Elongated $In_{0.3}Ga_{0.7}As//GaAs$ Quantum Dots
    Autorzy:
    Pieczarka, M.
    Musiał, A.
    Podemski, P.
    Sęk, G.
    Misiewicz, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1399091.pdf
    Data publikacji:
    2013-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.67.Hc
    73.21.La
    73.22.-f
    Opis:
    In this contribution the electronic structure of large $In_{0.3}Ga_{0.7}As//GaAs$ quantum dots is studied theoretically by means of 8 band k · p modeling. These quantum dots constitute unique physical system due to the low strain limit of the Stranski-Krastanow growth mode resulting in relatively large physical volume and elongation of the quantum dots in [1-10] direction. As a result of these critical growth conditions the electronic structure is expected to be very sensitive to the nanostructure size, shape, and composition of the quantum dot as well as the accompanying wetting layer. Another peculiarity of investigated system is the confining potential which is rather shallow and weakened in comparison to standard quantum dots. It makes them very interesting in view of both fundamental study and potential applications. To reveal physical mechanisms determining the optical properties of the investigated system, the electronic structure, mainly the number of confined states, and the wave function extension as a function of both quantum dot size and geometry have been simulated numerically and the importance of electron-hole Coulomb interactions has been evaluated.
    Źródło:
    Acta Physica Polonica A; 2013, 124, 5; 809-812
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Energy Transfer Processes in InAs/GaAs Quantum Dot Bilayer Structure
    Autorzy:
    Pieczarka, M.
    Maryński, A.
    Podemski, P.
    Misiewicz, J.
    Spencer, P.
    Murray, R.
    Sęk, G.
    Powiązania:
    https://bibliotekanauki.pl/articles/1185237.pdf
    Data publikacji:
    2016-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.67.Hc
    71.35.-y
    78.55.-m
    Opis:
    We investigate double layer InAs/GaAs quantum dots grown in the Stransky-Krastanov mode by molecular beam epitaxy. The sample consists of two layers of InAs quantum dots separated by 10 nm thick GaAs layer, where the top quantum dot layer of an improved homogeneity is covered by an InGaAs cap. This configuration has allowed for the extension of the dots' emission to longer wavelengths. We probed the carrier transfer between the states confined in a double quantum well composed of InGaAs cap and the quantum dots wetting layer to the states in the quantum dots by means of photoluminescence excitation and photoreflectance spectroscopies. Efficient emission from quantum dots excited at the double quantum well ground state energy was observed. There is also presented a discussion on the carrier injection efficiency from the capping layer to the quantum dots.
    Źródło:
    Acta Physica Polonica A; 2016, 129, 1a; A-59-A-61
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    InAs on InP Quantum Dashes as Single Photon Emitters at the Second Telecommunication Window: Optical, Kinetic, and Excitonic Properties
    Autorzy:
    Mrowiński, P.
    Dusanowski, Ł.
    Somers, A.
    Höfling, S.
    Reithmaier, J.
    Misiewicz, J.
    Sęk, G.
    Powiązania:
    https://bibliotekanauki.pl/articles/1033861.pdf
    Data publikacji:
    2017-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    photoluminescence
    quantum dash
    excitonic complexes
    antibunching
    autocorrelation
    single photon source
    telecommunication
    time-resolved
    Opis:
    In this work, InAs/InGaAlAs/InP quantum dashes have been investigated in terms of their optical, kinetic, and excitonic properties with respect to their application within the 1300± 40 nm spectral range, i.e. the O-band of the telecommunication technologies. We focused on the basic excitonic complexes such as neutral exciton, biexciton, and charged exciton, which have been identified by means of photoluminescence measurements. Emission and carriers' dynamics have been analyzed using rate equation model and fitting the experimental data obtained for both continuous-wave and pulsed excitation regimes. There has been found a significant impact of the charge carrier imbalance in the system and electron capturing rate on the dynamics of the optical and electronic transitions, which results in a high occupation of the negatively charged trion state. Autocorrelation measurements show clear antibunching of trion emission for non-resonant excitation which indicates a potential of such kind of emitters as single photon sources for short-range quantum communication schemes.
    Źródło:
    Acta Physica Polonica A; 2017, 132, 2; 382-386
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Effect of Confinement Anisotropy on Excitonic Properties in InAs/InP Quantum Dashes
    Autorzy:
    Mrowiński, P.
    Musiał, A.
    Sęk, G.
    Misiewicz, J.
    Höfling, S.
    Somers, A.
    Hein, S.
    Forchel, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1399087.pdf
    Data publikacji:
    2013-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.35.-y
    71.70.Gm
    78.67.Hc
    73.21.-b
    81.07.Ta
    Opis:
    The influence of confinement potential anisotropy on emission properties of strongly elongated single InAs/InGaAlAs/InP quantum dashes has been investigated by polarization-resolved microphotoluminescence spectroscopy at around 1.5 μm. There have been determined the exciton fine structure splitting, degree of linear polarization of surface emission and biexciton binding energy. The investigated dashes exhibited usually: the exciton anisotropy splitting larger than 100 μeV, the corresponding biexciton binding energy of about 3 meV, and the degree of linear polarization values in the range from 24% to 55%. Here, we presented a correlation of these parameters for several quantum dashes, which can be attributed either to a change in lateral aspect ratio within the ensemble, or the carrier localization on random fluctuations of the dash confinement potential.
    Źródło:
    Acta Physica Polonica A; 2013, 124, 5; 801-804
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Effect of dielectric medium anisotropy on the polarization degree of emission from a single quantum dash
    Autorzy:
    Mrowiński, P.
    Tarnowski, K.
    Olszewski, J.
    Somers, A.
    Kamp, M.
    Höfling, S.
    Reithmaier, J.
    Urbańczyk, W.
    Misiewicz, J.
    Machnikowski, P.
    Sęk, G.
    Powiązania:
    https://bibliotekanauki.pl/articles/1159588.pdf
    Data publikacji:
    2016-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.67.Hc
    71.35.-y
    78.55.-m
    Opis:
    Excitonic emission from single InAs/InGaAlAs/InP quantum dashes has been investigated in the context of degree of linear polarization by post-growth modification of its surrounding dielectric medium. We present optical spectroscopy measurements on a symmetric squared pedestal structures (mesas), and asymmetric rectangular ones oriented parallel or perpendicular to the main in-plane axis of the dashes [1-10]. Polarization resolved microphotoluminescence shows a significant quantitative modification of the degree of linear polarization value from -20% up to 70%. These results have been confronted with calculations of the coupling between the exciton transition dipole moment and electromagnetic field distributed in the vicinity of a quantum dash inside a processed mesa.
    Źródło:
    Acta Physica Polonica A; 2016, 129, 1a; A-48-A-52
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Optimizing the InGaAs/GaAs quantum dots for 1.3 μm emission
    Autorzy:
    Maryński, A.
    Mrowiński, P.
    Ryczko, K.
    Podemski, P.
    Gawarecki, K.
    Musiał, A.
    Misiewicz, J.
    Quandt, D.
    Strittmatter, A.
    Rodt, S.
    Reitzenstein, S.
    Sęk, G.
    Powiązania:
    https://bibliotekanauki.pl/articles/1055140.pdf
    Data publikacji:
    2017-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.30.Fs
    78.67.-n
    78.67.Hc
    73.22.-f
    Opis:
    Hereby we present comprehensive experimental and theoretical study on fundamental optical properties and electronic structure of GaAs-based quantum dots grown using metalorganic chemical vapor deposition technique. The substantial redshift of emission, to the second telecommunication window of 1.3 μm, in comparison to standard InGaAs/GaAs quantum dots is obtained via strain engineering utilizing additional capping layer of In_{0.2}Ga_{0.8}As in this context referred to as strain reducing layer. It ensures lowering of the energy of the ground state transition to more application relevant spectral range. Optical properties of the quantum dot structure has been experimentally characterized by means of photoreflectance spectroscopy and power-dependent photoluminescence revealing 3 transitions originating from hybrid states confined in an asymmetric double quantum well formed of the wetting layer and strain reducing layer, as well as higher states of the quantum dots themselves with the first excited state transition separated by 67 meV from the ground state transition. Origin of the observed transitions was confirmed in theoretical modelling using 1-band single-particle approach for the quantum well part, and excitonic quantum dot spectrum obtained within 8 band k·p formalism followed by configuration interaction calculations, respectively. Additionally, photoluminescence excitation spectroscopy measurements allowed to identify a spectral range for efficient quasi-resonant excitation of the investigated quantum dots into the 2D density of states to be in the range of 835-905 nm.
    Źródło:
    Acta Physica Polonica A; 2017, 132, 2; 386-390
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Investigation of the Non-Square InGaAsP/InP Quantum Wells in the Electric Field by Photoreflectance
    Autorzy:
    Kudrawiec, R.
    Sęk, G.
    Rudno-Rudziński, W.
    Misiewicz, J.
    Wojcik, J.
    Robinson, B. J.
    Thompson, D. A.
    Mascher, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/2035600.pdf
    Data publikacji:
    2002
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    73.63.Hs
    78.67.-n
    66.10.Cb
    Opis:
    Non-square quantum wells in electric field have been investigated by photoreflectance and photoluminescence spectroscopies. The structures have been obtained by a post-growth modification (rapid thermal annealing) of standard 1.55μm InGaAsP-based laser structures that were grown by gas source molecular beam epitaxy. During rapid thermal annealing a migration of semiconductor atoms across quantum well interfaces changes the quantum well profile from a square well to a rounded well. The modification of the profile changes energy levels in the quantum well and in consequence a blue shift of the quantum well emission peak is observed in photoluminescence. In this paper the blue shift of the ground state transition of post-growth modified quantum well structures has been investigated by both photoluminescence and photoreflectance techniques. Also a blue shift of excited state transitions has been observed in photoreflectance spectra. Generally, a stronger blue shift for the ground state transition than for excited state transitions has been observed. Additionally, oscillator strengths for all quantum well transitions have been determined from photoreflectance spectra. It has been found that the oscillator strength is constant for all quantum well transitions despite of modification of the quantum well profile.
    Źródło:
    Acta Physica Polonica A; 2002, 102, 4-5; 649-657
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    GaAs-Based Quantum Well Exciton-Polaritons beyond 1 μm
    Autorzy:
    Pieczarka, M.
    Podemski, P.
    Musiał, A.
    Ryczko, K.
    Sęk, G.
    Misiewicz, J.
    Langer, F.
    Höfling, S.
    Kamp, M.
    Forchel, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1399094.pdf
    Data publikacji:
    2013-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    73.21.-b
    78.67.-n
    78.67.Pt
    Opis:
    Realization of the Bose-Einstein condensate can provide a way for creation of an inversion-free coherent light emitter with ultra-low threshold power. The currently considered solutions provide polaritonic emitters in a spectral range far below 1 μm limiting their application potential. Hereby, we present optical studies of InGaAs/GaAs based quantum well in a cavity structure exhibiting polaritonic eigenmodes from 5 to 160 K at a record wavelength exceeding 1 μm. The obtained Rabi splitting of 7 meV was almost constant with temperature, and the resulting coupling constant is close to the calculated QW exciton binding energy. This indicates the very strong coupling conditions explaining the observation of polaritons at temperatures where the exciton dissociation is already expected, and allows predicting that room temperature polaritons could still be formed in this kind of a system.
    Źródło:
    Acta Physica Polonica A; 2013, 124, 5; 817-820
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Temperature Dependence of Photoluminescence from Epitaxial InGaAs/GaAs Quantum Dots with High Lateral Aspect Ratio
    Autorzy:
    Musiał, A.
    Sęk, G.
    Maryński, A.
    Podemski, P.
    Misiewicz, J.
    Löffler, A.
    Höfling, S.
    Reitzenstein, S.
    Reithmaier, J.
    Forchel, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1492876.pdf
    Data publikacji:
    2011-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.67.Hc
    65.80.-g
    Opis:
    Hereby, we present a study of a thermal quenching of emission from self-assembled epitaxial highly asymmetric quantum dots in InGaAs/GaAs material system for both ensemble and single dot regime. Pronounced interplay between the intensity of wetting layer and quantum dots originated emission was observed as the temperature was increased, evidencing a thermally activated energy transfer between the two parts of the system and an important role of the wetting layer in determining the optical properties of these anisotropic nanostructures. The carrier activation energies have been derived and possible carrier loss mechanisms have been analyzed. Single dot study revealed activation energies slightly varying from dot to dot due to size and shape distribution. The problem of the shape uniformity of individual quantum dot has also been addressed and possibility of additional carrier localization within the investigated structures has been found to be insignificant based on the recorded spectroscopic data.
    Źródło:
    Acta Physica Polonica A; 2011, 120, 5; 883-887
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-12 z 12

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