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Berlin, Germany

Arsenijevic D.,TU Berlin | Kleinert M.,TU Berlin | Kleinert M.,Heinrich Hertz Institute | Bimberg D.,TU Berlin | Bimberg D.,King Abdulaziz University
Applied Physics Letters | Year: 2013

The noise properties of the pulse trains of passively mode-locked 40 GHz quantum-dot lasers subject to optical feedback are investigated in detail. Five different feedback regimes are discovered and the clearly identified regime of resonant optical feedback is further examined. The feedback parameters yielding minimum phase noise are determined. Here, the radio-frequency (RF)-line-width is reduced from its original value by 99% to 1.9 kHz. The corresponding pulse-to pulse jitter of 23 fs is a record low value for passively mode-locked 40 GHz quantum-dot lasers. © 2013 AIP Publishing LLC.

Weber H.G.,Heinrich Hertz Institute
Chemical Physics Letters | Year: 2015

Optical excitation induces a transition in NO2 from a ground state |a> to an excited state |b>. The state |b> is not stable. The molecule evolves irreversibly from |b> to a state |c> in a time τ0 ≈ 3 μs. We investigate the transition from |b> to |c> by analysing results of molecular beam and static gas experiments, and we conclude that the irreversible evolution is either an intramolecular radiationless transition of a symmetric to an asymmetric configuration of the isolated NO2 or the effect of a background cosmic field inducing a parity nonconserving transition from |b> to |c>. © 2015 Elsevier B.V. All rights reserved.

Wunder G.,Heinrich Hertz Institute | Fischer R.F.H.,University of Ulm | Boche H.,TU Munich | Litsyn S.,Tel Aviv University | No J.-S.,Seoul National University
IEEE Signal Processing Magazine | Year: 2013

Energy efficiency matters in future mobile communications networks. The key driving factor is the growing energy cost of network operations that can make up as much as 50% of the total operational cost today [1]. In the context of green information and communication technology (ICT), this has led to many global initiatives such as the Green Touch consortium. © 1991-2012 IEEE.

Boche H.,Heinrich Hertz Institute | Schubert M.,MCI Communications
IEEE Transactions on Signal Processing | Year: 2010

The paper addresses the problem of interference modeling for wireless networks. Two axiomatic approaches are known from the literature: 1) "standard interference functions" proposed by Yates in 1995, and 2) general interference functions proposed by the authors in their previous work. In this paper, both frameworks are thoroughly analyzed and compared. It is shown that every function from framework 1) can be expressed in terms of framework 2). This means that recent structure results for convex interference functions, which were derived for 2), can also be applied to 1). The results provide a bridge between the frameworks 1) and 2), which were studied separately in the literature. Also, new structure results are shown in this paper. For the example of QoS balancing, it is shown that analyzing the structure of interference functions can lead to interesting algorithmic opportunities. The results are potentially useful for the development of physical-layer aware resource allocation algorithms. © 2010 IEEE.

Weber H.G.,Heinrich Hertz Institute
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2015

We show that light-induced coherence between a state |〉 of the electronic ground state X2 A1 and a state |b〉 of the excited electronic state A2 B2 of a laser-induced transition in NO2 affects the evolution of the molecule in the excited state. The optical coherence couples |b〉 strongly with |〉. This optical coupling works against a radiationless process, which is driving the molecule away from the metastable state |b〉 to a final state |c〉. The optical field stabilizes the molecule in the state |b〉 by the coupling to the ground state |〉. This causes the inversion effect in NO2. © 2015 Elsevier B.V. All rights reserved.

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