T.W. Schlereth

University of Wuerzburg, Würzburg, Bavaria, Germany

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Publications (17)37.26 Total impact

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    ABSTRACT: Passive mode-locking of AlGaInAs quantum dots was achieved for the first time at 18.1 GHz with a 4.5 ps pulse length at 929 nm wavelength using a monolithic two section tapered ridge waveguide cavity.
    CLEO: Science and Innovations; 06/2013
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    ABSTRACT: We have carried out a detailed characterization of individual self-assembled InGaAlAs/AlGaAs quantum dots grown on GaAs substrate and emitting in the 680–780 nm spectral range. Exciton, biexciton and charged exciton emission lines originating from the same quantum dot have been identified, and the biexciton and charged exciton binding energies have been derived to be equal ∼ 5 and ∼ 9 meV, respectively. The second-order photon correlation experiments allowed us to show a clear antibunching for exciton emission with a value of g(2)(0) = 0.04±0.02, confirming distinctly that such GaAs-based quantum dots can be considered as single photon quantum emitters in the abovementioned wavelength range.
    AIP Conference Proceedings 01/2013; 1556:540-541.
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    ABSTRACT: Low temperature micro-photoluminecence and second-order single photon correlation experiments were performed on individual self-assembled In0.47Al0.34Ga0.19As/Al0.3Ga0.7As/GaAs quantum dots emitting in the range of 680-780 nm. Emission lines originating from exciton, biexciton, and charge exciton confined in the same dot could be identified. The derived exciton fine structure splitting is similar to 125 mu eV, whereas the biexciton and charge exciton binding energies are similar to 4 and similar to 9meV, respectively. The photon correlation statistics measured for the exciton emission exhibited a clear antibunching with the value of g(X-X)(2)(0) = 0.30 +/- 0.05, confirming unambiguously that such quantum dots act as true single photon quantum emitters. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4750241]
    Applied Physics Letters 09/2012; 101:103108. · 3.52 Impact Factor
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    ABSTRACT: We demonstrate room temperature, continuous wave lasing of laser diodes based on AlGaAswhispering gallery mode(WGM)resonators (microcylinder and microring) embedding a quantum dot(QD)active layer. Using InGaAlAs QDs, high-Q (>60 000) lasing modes are observed around 910 nm, up to 50 °C. Lasing with similar performance is obtained around 1230 nm, using InAsQDs. Furthermore, we show that the current injection in the active part of the device is improved in ring resonators, leading to threshold currents of approximately 4 mA for a device with 80 μm diameter. This geometry also suppresses WGMs with a high radial order, thus simplifying the lasing spectra. In these conditions, stable single-mode and two-color lasing can be obtained.
    Applied Physics Letters 01/2012; 100. · 3.52 Impact Factor
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    ABSTRACT: The monitoring of acetylene (C2H2) concentrations is important for many chemical processes. Industrial trace gas measurements are usually performed using gas chromatographs (GC) which have time constants of several minutes. Optical analyzers are expected to yield faster response times with lower maintenance costs. We investigated the use of quantum cascade laser (QCL) spectroscopy in the 14μm range for the sensitive and fast detection of C2H2. This spectral range is favorable, as it avoids spectral interferences by other components which could be present in typical process gases. We developed new custom DFB QCLs and characterized their spectral properties. We determined the performance of our QCL gas analyzer setup and demonstrate a noise equivalent concentration of 10 ppb in 20 s average time.
    Proc SPIE 01/2011;
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    ABSTRACT: We have measured the variation of the spontaneous emission rate with polarization for self-assembled single quantum dots in two-dimensional photonic crystal membranes. We observe a maximum anisotropy factor of 6 between the decay rates of the two bright exciton states. This large anisotropy is attributed to the substantially different projected local density of optical states for differently oriented dipoles in the photonic crystal.
    Optics Letters 08/2010; 35(16):2768-70. · 3.39 Impact Factor
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    ABSTRACT: We have measured the oscillator strength and quantum efficiency of excitons confined in large InGaAs quantum dots by recording the spontaneous emission decay rate while systematically varying the distance between the quantum dots and a semiconductor-air interface. The size of the quantum dots is measured by in-plane transmission electron microscopy and we find average in-plane diameters of 40 nm. We have calculated the oscillator strength of excitons of that size and predict a very large oscillator strength due to Coulomb effects. This is in stark contrast to the measured oscillator strength, which turns out to be much below the upper limit imposed by the strong confinement model. We attribute these findings to exciton localization in local potential minima arising from alloy intermixing inside the quantum dots. Comment: 4 pages, 3 figures, submitted
    Physical Review B 06/2010; 80:155307. · 3.66 Impact Factor
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    ABSTRACT: We have measured the variation of the spontaneous emission rate with polarization for self-assembled single quantum dots in two-dimensional photonic crystal membranes. We observe a maximum anisotropy factor of 6 between the decay rates of the two bright exciton states. This large anisotropy is attributed to the substantially different projected local density of optical states for differently oriented dipoles in the photonic crystal. Comment: 3 pages, 4 figures
    12/2009;
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    ABSTRACT: Wavelength control of tapered quantum dot (QD) lasers was achieved by adding a distributed Bragg reflector as wavelength-selective element to the devices. The Bragg wavelength of around 920 nm is matched to the gain of the single layer of InGaAs QDs that is used as active material. Devices with 1.4-mm-long tapers have reached output powers of over 1 W, and over 2 W were obtained from lasers with 3-mm-long tapers. The emission of the devices is restricted to a very narrow spectral range, with side-mode suppression ratios of over 40 dB.
    IEEE Journal of Selected Topics in Quantum Electronics 07/2009; · 4.08 Impact Factor
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    ABSTRACT: By adjusting the Al and In concentration of AlGaInAs quantum dots (QDs), their morphologic and spectral properties (i.e., size, height, density, and emission wavelength) can be engineered partly independently. In this paper, we report that this tunability can be used to improve QD laser properties and to realize QD lasers at wavelengths not achievable with the commonly used (Ga) InAs QDs. We show that using tailored AlGaInAs QDs grown on GaAs substrate, the device properties of QD lasers can be improved with respect to material gain, accessible wavelength range, and temperature stability of the wavelength. In particular, we report that the material gain in QD lasers can be notably increased (by a factor of 2.1). Furthermore, we demonstrate QD lasers with application key wavelengths in the range between 760 and 920 nm. The presented short-wavelength ( ~ 760 nm) QD lasers exhibit characteristics comparable to state-of-the-art quantum well (QW) lasers (light output > 20 mW, sidemode suppression ratios ~ 40 dB, I<sub>tr</sub> = 43 mA). We also demonstrate that AlGaInAs QDs can be used to fabricate QD lasers with extremely high temperature stabilities of the wavelength (0.072 nm/K).
    IEEE Journal of Selected Topics in Quantum Electronics 07/2009; · 4.08 Impact Factor
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    ABSTRACT: We have studied the response of a photonic crystal cavity to changes of the ambient refractive index. Transmission measurements of the cavity under different gaseous environments and pressures showed a linear dependence of the resonance wavelength on the refractive index of the ambient gas. A change of the refractive index by 10−4 leads to a shift of the resonance by 8 pm, which is readily detectable due to the high quality factor of the cavity. The observed wavelength shifts agree well with finite-difference time domain simulations of the cavity.
    Applied Physics Letters 06/2008; 92:261112. · 3.52 Impact Factor
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    ABSTRACT: In this paper, a comparative study of the gain spectra of quantum-well (QW) and quantum-dot (QD) lasers is presented. We point out the differences between the gain function of a QD laser and a QW laser and give a qualitative description of the effect that leads to the high wavelength stability of QD lasers. Furthermore, we demonstrate, by means of the gain spectra of an InGaAs and AlInGaAs QD laser, that devices with a high wavelength stability can be manufactured over a wide range of emission energies. The experimentally obtained data are fitted with a theoretical model that describes the gain of a QD ensemble. The characteristic features resulting in the high wavelength stability of QD lasers of 0.072 nm/K are analyzed and discussed.
    IEEE Journal of Quantum Electronics 03/2008; · 2.11 Impact Factor
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    T W Schlereth, C Schneider, S Höfling, A Forchel
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    ABSTRACT: We present a study of the growth, morphology and optical properties of Al(x)Ga(1-x-y)In(y)As quantum dots (QDs) for a wide range of Al and In concentrations (0≤x≤0.34 and 0.43≤y≤0.60). Short emission wavelengths between 660 and 940 nm and QD surface densities up to 1.1 × 10(11) cm(-2) have been achieved. Our results show that by varying both the Al concentration and the In concentration an independent adjustment of strain and QD band gap is possible. This additional degree of freedom can be employed for tailoring AlGaInAs QDs with the desired emission wavelength, surface density and average size. AlGaInAs QDs thus offer new possibilities for future QD device design.
    Nanotechnology 01/2008; 19(4):045601. · 3.84 Impact Factor
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    ABSTRACT: Single mode emission of tapered lasers was achieved by an on-chip distributed Bragg reflector. The quantum dot based devices show stable single mode emission around 920 nm, good beam quality and output powers up to 2 W.
    01/2008;
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    ABSTRACT: We report on AlGaInAs quantum-dot laser structures emitting at ~760 nm with basic device characteristics comparable to state-of-the-art quantum-well lasers. Distributed-feedback laser diodes have been processed emitting in the center of the oxygen A-absorption band. Typical threshold currents of 34 mA (1-mm-long devices), slope efficiencies of 0.33 W/A per facet, and sidemode suppression ratios of 40 dB have been measured at room temperature in continuous-wave mode. Single-mode emission with a maximum output power ges20 mW has been achieved for temperatures up to 55degC.
    IEEE Photonics Technology Letters 10/2007; · 2.04 Impact Factor
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    ABSTRACT: We fabricated red emitting (763.7 nm) Al<sub>0.13</sub>Ga<sub>0.40</sub>ln<sub>0.47</sub>As quantum dot (QD) distributed feedback (DFB) lasers. The devices exhibit output powers >20 mW, threshold currents as low as 34 mA and side mode suppression ratios of 40 dB.
    Nano-Optoelectronics Workshop, 2007. i-NOW '07. International; 01/2007
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    ABSTRACT: Cited References Count:19|173ZB|AMER INST PHYSICS|CIRCULATION & FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA|Schlereth, T. W.|Schneider, C.|Kaiser, W.|Hoefling, S.|Forchel, A.|ISI Document Delivery No.:173ZB
    Applied Physics Letters 01/2007; 90. · 3.52 Impact Factor