Alcatel-Lucent

About: Alcatel-Lucent is a based out in Stuttgart, Germany. It is known for research contribution in the topics: Signal & Network packet. The organization has 37003 authors who have published 53332 publications receiving 1430547 citations. The organization is also known as: Alcatel-Lucent S.A. & Alcatel.

Grating resonances in air-silica microstructured optical fibers.

Abstract: We report what is believed to be the first demonstration of optical fiber gratings written in photonic crystal fibers. The fiber consists of a germanium-doped photosensitive core surrounded by a hexagonal periodic air-hole lattice in a silica matrix. The spectra of these gratings allow for a detailed characterization of the fiber. In particular, the gratings facilitate coupling to higher-order leaky modes. We show that the spatial distribution and the effective index of these modes are determined largely by the design of the lattice and that the grating spectra are unaffected by the refractive index surrounding the fiber. We describe these measurements and corresponding simulations and discuss their implications for the understanding of such air-hole structures.

Intersubband absorption at λ∼1.55 μm in well- and modulation-doped GaN/AlGaN multiple quantum wells with superlattice barriers

Abstract: Intersubband optical absorption around 1.55 μm has been measured in GaN/AlGaN multiple quantum wells (MQWs) grown by molecular-beam epitaxy. First, peak absorption wavelengths as short as 1.41 μm are reported for ultranarrow, ⩾11 A wide, well-doped MQWs with high, 85%, AlN mole-fraction barriers. Second, in order to enable modulation doping as well as the use of lower AlN mole-fraction barriers, we designed and fabricated QWs embedded in barriers consisting of a short period superlattice of narrow GaN QWs and only 65% AlN mole-fraction barriers. The resulting electron Bragg confinement allows peak absorption wavelengths as short as 1.52 μm. Furthermore, the structures can now be modulation doped through doping of the narrow superlattice wells and subsequent charge transfer into the active well. We observe a reduction of the absorption linewidth, from ∼200 to ∼130 meV, for these structures.

Massive MIMO: How many antennas do we need?

Abstract: We consider a multicell MIMO uplink channel where each base station (BS) is equipped with a large number of antennas N. The BSs are assumed to estimate their channels based on pilot sequences sent by the user terminals (UTs). Recent work has shown that, as N grows infinitely large, (i) the simplest form of user detection, i.e., the matched filter (MF), becomes optimal, (ii) the transmit power per UT can be made arbitrarily small, (iii) the system performance is limited by pilot contamination. The aim of this paper is to assess to which extent the above conclusions hold true for large, but finite N. In particular, we derive how many antennas per UT are needed to achieve \eta % of the ultimate performance. We then study how much can be gained through more sophisticated minimum-mean-square-error (MMSE) detection and how many more antennas are needed with the MF to achieve the same performance. Our analysis relies on novel results from random matrix theory which allow us to derive tight approximations of achievable rates with a class of linear receivers.

Effect of nonlinear gain reduction on semiconductor laser wavelength chirping

Abstract: A simple wavelength chirping formula is presented which includes small nonlinearities in the net gain such as spectral hole burning. The two dominant terms are a laser‐structure‐independent derivative or ‘‘transient’’ chirp and a structure‐dependent ‘‘adiabatic’’ chirp, each with distinctly different lightwave system consequences. The two chirp contributions are indirectly related through their mutual association with relaxation oscillations. Time‐resolved spectral measurements on a number of different laser structures support the results.

Capacity Demand and Technology Challenges for Lightwave Systems in the Next Two Decades

Abstract: Ten to 20 years from now, optical networks will have to carry vastly increased amounts of Internet traffic. Today's knowledge (2006) already points to ultimate technology limits in the physical layer, foretelling the end of the so-called "Optical Moore's Law." Such an observation is discordant with the generic and optimistic view of a "virtually infinite" optical bandwidth combined with unlimited Internet-traffic growth. In order to meet long-term needs and challenges, therefore, basic research in wideband optical components and subsystems must be urgently revived today