1,720,974 research outputs found
Inter-channel nonlinear interference noise in fully loaded WDM systems
No full textWe explore the properties of inter-channel nonlinear interference noise in fully loaded WDM systems. We assess the significance of nonlinear phase and polarization-rotation noise and discuss its importance in the evaluation of system performance
Kramers-Kronig coherent receiver
No full textWe review the principles underpinning the Kramers-Kronig (KK) receiver operation and its various implementations. These include direct-detection based schemes, where the information-carrying signal is transmitted along with a CW field that is necessary for the implementation of the KK algorithm, as well as other schemes, where the CW is added at the receiver, owing to the availability of a local oscillator. Polarization-multiplexing with the KK receiver will also be discussed. Finally, an up-to-date review of the experimental implementations of KK transceiver solutions will be presented
Polarization Multiplexing With the Kramers-Kronig Receiver
No full textWe present two schemes extending the KK-receiver so as to accommodate for polarization multiplexed transmission. One of the schemes relies on the Stokes receiver and allows for complex-valued polarization multiplexed transmission without using a local oscillator. This is the first direct-detection-based scheme that allows polarization multiplexing. It uses three photo-diodes and requires three analog to digital converters (ADCs). The other scheme uses a local oscillator, and its implementation is suitable in all cases where the transmitter and the receiver operate at the same wavelength, so that the local oscillator signal can be extracted from the transmitter laser. It uses only two photo-diodes and two ADCs, and does not require optical hybrids. The performance of the first (Stokes-based) scheme is studied numerically, whereas that of the second scheme is studied both numerically and experimentally
Nonlinear phase and polarization rotation noise in fully loaded WDM systems
No full textWe show that nonlinear interference noise (NLIN) produced by faraway WDM channels is dominated by nonlinear phase-noise and polarization-rotations, whereas NLIN produced by nearest channels tends to be more circular. We discuss the impact of these results on nonlinear mitigation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Design of optical space-to-ground links for the international space station
Full text linkInnovative new technologies will have to be developed in near future to satisfy the ever increasing demand on bandwidth coming along with new communication services. Optical free-space laser communication is a promising candidate in this field. While optical space-toground links or optical intersatellite links have been considered since decades, first proof-ofconcept applications of this technology were realized as recently as a few years ago. Establishing an optical link between the International Space Station (ISS) and a ground station could serve as broadband communication link for the scientific experiments aboard the station and could, additionally, extend the operational experience with optical space-to-ground links. Within this thesis, the major concepts and technological requirements for establishing such a communication scenario are presented. The low beam divergence as a consequence of the optical carrier frequency resulting in low link losses is the outstanding advantage of free-space laser communication systems over the widely used radio-frequency technology. Low beam divergence, on the other hand, leads to high technological demands concerning the mutual pointing, acquisition and tracking (PAT) of the communicating terminals. I assess numerical benchmarks for the parameters concerning the link loss, the pointing accuracy and the availability of line-of-sight between the ISS on its low Earth orbit and a ground station. Another issue coming along with a carrier frequency in the optical regime is background radiation from celestial bodies and the atmosphere of the Earth. I calculate the power spectral density accepted by a telescope from the major background sources and assess the impact on the performance of the system. The large distances to be bridged together with the limited transmit power, the high cost of large telescopes and the impossibility of in-line amplification leads to the need for highly sensitive receivers to fully exploit the low signal power available. After comparing different receiver technologies, I focus on optically preamplified direct detection receivers wich combine the advantages of simple setup and the possibility to employ highly developed components employed in fiber-based systems. The design parameters affecting the receiver's performance as well as the influence of the transmitter's properties are investigated by means of simulation employing a detailed model and experiments. Different forms of on-off keying, the standard non return-to-zero (NRZ) format and return-to-zero (RZ) impulsive coding format are employed and the effect on the receiver sensitivity is assessed. By employing RZ coding and optimizing optical and electrical filter bandwidths in the receiver, I experimentally approached the theoretical limit of receiver sensitivity, the quantum limit as close as 1.1 dB. Lately, several applications making use of quantum effects, subsumed under the term quantum communication, have been introduced. I investigate the potential of one of these concepts, quantum key distribution. Employing entangled photons, a cryptography scheme can be established with a privacy provided - in principle - by laws of nature and not to be broken by any measure. There are several aspects equal to classical optical communication, namely PAT, link loss, and background radiation
- …
