976 publications from this institution
Second-order polarization mode dispersion (PMD) is a major limitation to the transmission capabilities of analog systems and of high bit rate digital systems. Basically, the effect of second-order PMD is the same as that of chromatic dispersion. However, like all polarization effects in standard single-mode fibers, the effects of second-order PMD are stochastic, due to the random polarization mode coupling that occurs in such fibers. Hence, the effects of second-order PMD fluctuate with time. The purpose of this article is to present a description of the phenomenon and of its effects on analog and digital signals, to propose definitions, to discuss some orders of magnitudes and to present some numerical simulations and experimental results. Some general understanding of the phenomena of first-order PMD are assumed.
Quantum communication is built on a set of disruptive concepts and technologies. It is driven by fascinating physics and by promising applications. It requires a new mix of competencies, from telecom engineering to theoretical physics, from theoretical computer science to mechanical and electronic engineering. First applications have already found their way to niche markets and university labs are working on futuristic quantum networks, but most of the surprises are still ahead of us. Quantum communication, and more generally quantum information science and technologies, are here to stay and will have a profound impact on the XXI century.
No abstract is provided for this article.
General Trojan horse attacks on quantum key distribution systems are analyzed. We illustrate the power of such attacks with today's technology and conclude that all system must implement active counter-measures. In particular all systems must include an auxiliary detector that monitors any incoming light. We show that such counter-measures can be efficient, provided enough additional privacy amplification is applied to the data. We present a practical way to reduce the maximal information gain that an adversary can gain using Trojan horse attacks. This does reduce the security analysis of the 2-way {\it Plug-&-Play} system to those of the standard 1-way systems.
Advances in quantum cryptography extend from commercial demonstrations and quantum random number generators to improved detectors, new protocols and architectures, and even to quantum teleportation and quantum memories. We discuss our recent results in this field.
We present two interferometric techniques for the measurements of the polarization mode dispersion of standard (i.e. circular) single-mode fibers. The first method uses an interferometric loop and works in the frequency domain. The second uses a polarization maintaining Michelson interferometer and works in the time domain. Their output are related by a Fourier transformation. Both techniques provide information about the entire statistical distribution of the polarization mode delays. Also, both techniques can be applied to the characterization of installed lines. The setups are presented, the principle of the measurements are discussed and examples of results are shown.
Quantum Cryptography over 23km of installed Telecom fiber using a novel interferometer with Faraday mirrors is presented. The interferometer needs no alignment nor polarization control and features 99.8% fringe visibility. A secret key of 20kbit length with a error rate of 1.35% for 0.1 photon per pulse was produced.
The structure of Bell-type inequalities detecting genuine multipartite non-locality, and hence detecting genuine multipartite entanglement, is investigated. We first present a simple and intuitive approach to Svetlichny's original inequality, which provides a clear understanding of its structure and of its violation in quantum mechanics. Based on this approach, we then derive a family of Bell-type inequalities for detecting genuine multipartite non-locality in scenarios involving an arbitrary number of parties and systems of arbitrary dimension. Finally we discuss the thightness and quantum mechanical violations of these inequalities.
No abstract is provided for this article.
A method for measuring the delay between polarization eigenmodes in either high- or low-birefringence fibers is described. The main advantage of this interferometric method is its ability to perform the measurements without the use of any polarizing device. This results in particularly easy handling and makes this technique very suitable for systematic fiber controls. The obtained accuracy using an all-fiber setup is 0.02 ps/m for highly birefringent fibers and 0.003 ps/m when the birefringence is low.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Summary form only given. The potential of nonlinear polarization rotation (NPR) in waveguides is huge as it can be exploited for a large variety of ultrafast devices like optical switches, logic gates, intensity discriminators, nonlinear filters, or pulse shapers. However, an inherent problem to all this applications is the stability of the output polarization state. Fluctuations of the linear birefringence caused by temperature changes, drafts in the fiber environment, and vibrations generally disturb a proper functioning. We propose an elegant method to remove these detrimental fluctuations in a passive way by employing a Faraday mirror (FM) and a double pass of the fiber where NPR takes place. The proposed stabilization scheme has the additional advantage that the double pass allows for a reduction of the fiber length times pump intensity value by almost a factor of two. A model is developed that allows for an intuitive understanding of the action of the linear and nonlinear birefringence during the go- and return-path. Besides giving good insight in the underlying physical processes, it directly shows that the effect of NPR adds whereas the detrimental effects of the (fluctuating) linear fiber birefringence are removed.
