1,720,980 research outputs found
Photonic reservoir computing based on optical filters in a loop as a high performance and low-power consumption equalizer for 100 Gbaud direct detection systems
No full textWe propose and numerically simulate a passive neuromorphic processor performing equalization in C-band IM-DD links, that employs a spatial reservoir computing scheme based on recurrent optical filters. Followed by a feed forward equalizer, the system achieves sub HD-FEC performance up to 60km in 224 Gbps/λ
Ultrafast all-optical matrix-vector multiplication based on four-wave mixing
No full textWe propose a nonlinear optical approach for ultra-fast, matrix-vector multiplications as required in machine-learning tasks. Optical multiplication is experimentally demonstrated, with less than 0.05% classification accuracy reduction compared to digital results on the MNIST dataset
ML-assisted Equalization for 50-Gb/s/λ O-band CWDM Transmission over 100-km SMF
No full textThis dataset supports the publication:
Yang Hong, Stavros Deligiannidis, Natsupa Taengnoi, Kyle R. H. Bottrill, Naresh K. Thipparapu, Yu Wang, Jayanta K. Sahu, David J. Richardson, Charis Mesaritakis, Adonis Bogris, and Periklis Petropoulos
ML-assisted Equalization for 50 Gb/s/λ O-band CWDM Transmission over 100-km SMF
IEEE Journal of Selected Topics in Quantum Electronics
10.1109/JSTQE.2022.3155990</span
ML-Assisted Equalization for 50-Gb/s/λ O-Band CWDM Transmission Over 100-km SMF
No full textWe propose and demonstrate a bidirectional Vanilla recurrent neural network (Vanilla-RNN) based equalization scheme for O-band coarse wavelength division multiplexed (CWDM) transmission. Based on a 4×50-Gb/s intensity modulation and direct detection (IM/DD) system, we demonstrate the significantly better bit error rate (BER) performance of the Vanilla-RNN scheme over the conventional decision feedback equalizer (DFE) for both Nyquist on-off keying (OOK) and Nyquist 4-ary pulse amplitude modulation (PAM4) formats. It is shown that the Vanilla-RNN equalizer is capable of compensating for both linear and nonlinear impairments induced by the transceiver and the single-mode fiber (SMF). As a result, up to 100-km and 75-km SMF transmission can be achieved for OOK and PAM4 transmission, respectively. Furthermore, through the comparison with other equalization schemes, including the linear equalizer, 3rd-order Volterra equalizer, and Volterra+DFE, it is demonstrated that the Vanilla-RNN equalizer achieves the best BER performance. In the meantime, it also exhibits lower implementation complexity when compared to Volterra-based schemes. Our results show that the Vanilla-RNN scheme is a viable solution for realizing simple and effective equalization. This work serves as an exploration and offers useful insights for future implementations of reach-extended O-band CWDM IM/DD systems
Μελέτη διατάξεων λέιζερ κβαντικών τελειών, εγκλείδωσης τρόπων για τηλεπικοινωνιακές και βιο-ιατρικές εφαρμογές
No full textThis work is focused on the experimental and theoretical study of quantum dot passively mode locked lasers. The first part of this thesis is focused on the analytical study of current literature regarding the generation of ultra short optical pulses through the mechanism of passive mode locking in semiconductor lasers. The benefits and drawbacks of this approach are analyzed, whereas the need for implementation of new materials like quantum dots is discussed in detail. In the second part of this thesis a numerical model based on multi-population rate equations has been developed, in order to study the complex dynamics of multiple energy states present in a quantum dot gain medium. Moreover by incorporating delayed differential equations passive mode lockinghas been achieved and the impact of bias conditions on the temporal properties of the pulses is discussed. The possibility of dual state mode locking from different spectral bands, which is a highly required feature for newly emerging applications, is also analyzed numerically. The third part is focused on the experimental verification of the numerical results of the previous section, whereas the experimental investigation allowed new regimes of operation, which could not be predicted numerically. In detail dual wavelength mode locking, alongside the impact of higher energy state emission in the mode locking procedure has been studied. Furthermore dual ground-state emission due to gain saturation effects has been shown, whereas two new regimes of operation related tothis effect has been identified. The first consists of tunable dual wavelength modelocking from the ground state, whereas the second consists of pulse width narrowing in the presence of dual state emission. In addition the dynamic response of several quantum dot mode locked devices have been performed in the presence of varying optical feedback. The analysis consisted on the effect of feedback on both emission bands revealing a variation on the dynamic properties of each state. Moreover inhomogeneous current injection has been applied in a multi-section quantum dot laserenabling new operation regimes like self-pulsations due to inter-state carrier dynamics and chaotic operation without the use of sophisticated feedback-based-setups. Finally the experimental characterization of devices having different structural characteristics allowed the extracture of design guidelines for pulse width and peak power optimization.Η συγκεκριµένη διδακτορική διατριβή πραγµατεύεται την µελέτη ολοκληρωµένων διατάξεων λέιζερ κβαντικών τελειών, για την επίτευξη παθητικής εγκλείδωσης τρόπων και κατ’ επέκταση την παραγωγή οπτικών παλµών µικρού χρονικού εύρους και µεγάλης οπτικής ισχύος. Στα πλαίσια της διερεύνησης πραγµατοποιήθηκε βιβλιογραφική µελέτη για την ανάδειξη των δυνατοτήτων των ηµιαγωγικών λέιζερ όσο αναφορά την ποιότητα της παλµικής λειτουργίας, καθώς και σκιαγραφήθηκαν τόσο τα πλεονεκτήµατα όσο και τα προβλήµατα που παρουσιάζουν. Η βιβλιογραφική µελέτη των συµβατικών δοµών κατέδειξε την αναγκαιότητα για χρήση νέων υλικών όπως είναι η κβαντικές τελείες για την άρση των περιορισµών. Στη συνέχεια αναπτύχθηκε ένα θεωρητικό µοντέλο βασισµένο σε πολυπληθισµιακές εξισώσεις φορέων για την µοντελοποίηση διατάξεων λέιζερ κβαντικών τελειών σε παθητική εγκλείδωση τρόπων. Η θεωρητική µελέτη πουπραγµατοποιήθηκε ανέδειξε εξαιρετικά ενδιαφέροντα αποτελέσµατα όσο αναφορά την επίδραση των συνθηκών πόλωσης στα χρονικά χαρακτηριστικά των παλµών όσο και αποκάλυψε νέες περιοχές λειτουργίας που σχετίζονται µε την ύπαρξη επιπλέον φασµατικών περιοχών εκποµπής. Τη θεωρητική µελέτη ακολούθησε η πειραµατική διερεύνηση διατάξεων λέιζερ κβαντικών τελειών µε αρχικό κίνητρο την επιβεβαίωση των θεωρητικά προβλεφθέντων συµπεριφορών. Στο πρώτο τµήµα της πειραµατικής µελέτης παρουσιάζεται η εξέλιξη µεγεθών όπως είναι το οπτικό φασµατικό εύρος, το ηλεκτρικό φάσµα των διατάξεων καθώς και τα χρονικά χαρακτηριστικά ως προς τις συνθήκες πόλωσης. Στη συνέχεια πραγµατοποιήθηκε πειραµατική διερεύνηση φαινοµένων ταυτόχρονης εγκλείδωσης από δύο ανεξάρτητες φασµατικές περιοχές σε πλήρη συµφωνία µε τα θεωρητικάαποτελέσµατα. Στο επόµενο τµήµα της πειραµατικής διερεύνησης µελετήθηκαν συµπεριφορές, οι οποίες δεν είχαν προβλεφθεί θεωρητικά λόγω απλοποιήσεων που είχαν πραγµατοποιηθεί στο θεωρητικό µοντέλο. Αυτές οι νέες περιοχές λειτουργίας παρουσίασαν έντονο ερευνητικό ενδιαφέρον λόγω των πιθανών µελλοντικών τους εφαρµογών στον τηλεπικοινωνιακό και βιο-ιατρικό τοµέα. Η πρώτη περιοχή λειτουργίας σχετίζεται µε την ύπαρξη δύο διακριτών φασµατικών περιοχών εκποµπής, που οφείλονται σε φαινόµενα κορεσµού της απολαβής και επέτρεψαν την ταυτόχρονη καισυντονιζόµενη εγκλείδωση τρόπων και από τις δύο κορυφές όσο και την µείωση της διάρκειας των παλµών. Επιπλέον µελετήθηκε για πρώτη φορά η ανοχή των διατάξεων κβαντικών τελειών στην ύπαρξη οπτικής ανατροφοδότησης σε όλες τις δυνατές περιοχές εκποµπής και εξάχθηκαν ενδιαφέροντα συµπεράσµατα για τη διαφορετική δυναµική περιοχή λειτουργίας της κάθε φασµατικής περιοχής. Επιπλέον µελετήθηκαν οι επιπτώσεις ανοµοιογενούς άντλησης σε διατάξεις κβαντικών τελειών πολλαπλών τµηµάτων. Η συγκεκριµένη διερεύνηση αποκάλυψε την ύπαρξη εγγενών ασταθειών που δεν σχετιζόντουσαν µε την ύπαρξη οπτικής ανατροφοδότησης αλλά µε τη δυναµική των φορέων, και επέτρεψε την επίτευξη παλµικής λειτουργίας αλλά και χαοτικής λειτουργίας χωρίς τη χρήση επιπλέον διατάξεων. Αυτή η τελευταία εφαρµογή είναι εξαιρετικάσηµαντική και µπορεί να επιτρέψει την χρήση πιο απλών διατάξεων βασισµένων σε κβαντικές τελείες για χρήση σε τηλεπικοινωνιακά συστήµατα που βασίζονται στη χαοτική κρυπτογραφία. Τέλος ο πειραµατικός χαρακτηρισµός ενός µεγάλου εύρους διατάξεων οι οποίες διέθεταν διαφορετικά κατασκευαστικά χαρακτηριστικά επέτρεψε την εξαγωγή σχεδιαστικών κανόνων για τις νέες γενιές λέιζερ κβαντικών τελειών
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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