Studies on the readability and on the detection rate in a Mach-Zehnder interferometer-based implementation for high-rate, long-distance QKD protocols

We study the way that chromatic dispersion affects the visibility and the synchronization on Quantum Key Distribution (QKD) protocols in a widely-used setup based on the use of two fiber-based Mach-Zehnder (MZ) interferometers at transmitter/receiver stations. We identify the necessary conditions for the path length difference between the two arms of the interferometers for achieving the desired visibility given the transmission distance -- where the form of the detector's window can be considered. We also associate the above limitations with the maximum detection rate that can be recorded in our setup, including the quantum non-linearity phenomenon, and to the maximum time window of the detector's gate. Exploiting our results we provide two methods, depending on the clock rate of the setup, to perform chromatic dispersion compensation techniques to the signal for keeping the correct order of the transmitted symbols. At the end, we apply our theoretical outcomes in a more realistic QKD deployment, considering the case of phase-encoding BB84 QKD protocol, which is widely used. Our proposed methods, depending on the transmission distance and on the photon emission rate at transmitter station, can be easily generalized to every fiber-optic QKD protocol, for which the discrimination of each symbol is crucial.Comment: 14 pages, 12 figure

Enhancing dynamic student learning by teamwork in innovative projects at an Erasmus Mundus master subject adapted to the EHEA (EEES)

The EHEA (EEES in Spain) is creating common academic degree standards comparable and compatible between the European countries. The definition of the new Credit unit, the ECTS, focused on the hours of study devoted by the students, is also promoting the renovation of the educational process at the higher studies of Graduate Degree and Master. We describe the experience of innovation of the teaching practice of the “Fibres & Telecommunications” subject of the Master PhotonicsBCN (part of the Erasmus Mundus Master EUROPHOTONICS), by introducing team9 working techniques for promoting: the development of cooperative learning, interpersonal skills, and positive interdependence among the students, not forgetting the individual initiative and responsibility. The teamwork is oriented to small innovation projects (inspired in state9of9the9art research challenges faced by the European FP7 EURO9FOS Network9 of 9Excellence) promoting interactive and dynamic student learning process. Each team member is spontaneously encouraged to learn as much as possible on both: the area of his task inside the common project, and also the influence of his task in the over all results of the project. This is implemented by the use of commercial software for professional systems deployment (VPIphotonics TM ), which allows each team to check the real viability of their innovative solutionPostprint (published version

Optical terabit transmitter and receiver based on passive polymer and InP technology for high-speed optical connectivity between datacenters

We demonstrate the hybrid integration of a multi-format tunable transmitter and a coherent optical receiver based on optical polymers and InP electronics and photonics for next generation metro and core optical networks. The transmitter comprises an array of two InP Mach-Zehnder modulators (MZMs) with 42 GHz bandwidth and two passive PolyBoards at the back- and front-end of the device. The back-end PolyBoard integrates an InP gain chip, a Bragg grating and a phase section on the polymer substrate capable of 22 nm wavelength tunability inside the C-band and optical waveguides that guide the light to the inputs of the two InP MZMs. The front-end PolyBoard provides the optical waveguides for combing the In-phase and Quadrature-phase modulated signals via an integrated thermo-optic phase shifter for applying the pi/2 phase-shift at the lower arm and a 3-dB optical coupler at the output. Two InP-double heterojunction bipolar transistor (InP-DHBT) 3-bit power digital-to-analog converters (DACs) are hybridly integrated at either side of the MZM array chip in order to drive the IQ transmitter with QPSK, 16-QAM and 64-QAM encoded signals. The coherent receiver is based on the other side on a PolyBoard, which integrates an InP gain chip and a monolithic Bragg grating for the formation of the local oscillator laser, and a monolithic 90° optical hybrid. This PolyBoard is further integrated with a 4-fold InP photodiode array chip with more than 80 GHz bandwidth and two high-speed InP-DHBT transimpedance amplifiers (TIAs) with automatic gain control. The transmitter and the receiver have been experimentally evaluated at 25Gbaud over 100 km for mQAM modulation showing bit-error-rate (BER) performance performance below FEC limit

Απεικόνιση δομών και διεργασιών του νηματοειδούς C. elegans με χρήση μη γραμμικής μικροσκοπίας

Two-Photon Excited Fluorescence (TPEF) and Second-Harmonic Generation (SHG) are relatively new promising tools for the imaging of biological structures and processes at the microscopic level. The combination of the two contrast modes in a single instrument can provide unique and complementary information concerning the structure and the function of tissues and individual cells. In the present study a compact, inexpensive and reliable setup was developed for the simultaneous TPEF and SHG imaging of biological samples. By means of the developed setup, high-resolution mapping of the nematode C. elegans in both its anterior and posterior body part, was achieved. Numerous strains, expressing Green Fluorescent Protein (GFP) were investigated, and the two touch receptor neurons of the nematode at its posterior body part (PLM) were localized. Optimum conditions for the detection of the exogenous SHG signal, arising from the GFP molecules, attached to transmembrane proteins of the PLM neurons, were found. Plans for future work for monitoring the membrane potential of the PLM neurons by means of SHG measurements are describedΟ Διφωτονικά Διεγειρόμενος Φθορισμός (ΔΦΔΦ) και η Γέννεση Δεύτερης Αρμονικής (ΓΔΑ) είναι δύο νέα σχετικώς εργαλεία για την απεικόνιση σε μικροσκοπικό επίπεδο βιολογικών δομών και διαδικασιών. Ο συνδυασμός τους σε ένα κοινό απεικονιστικό σύστημα είναι δυνατόν να προσφέρει μοναδικές και, το σπουδαιότερο, συμπληρωματικές πληροφορίες σχετικά με τη δομή και τη λειτουργία ιστών, αλλά και μεμονομένων κυττάρων. Στα πλαίσια της παρούσας εργασίας αναπτύχθηκε μία εύχρηστη, αξιόπιστη και χαμηλού κόστους διάταξη για την ταυτόγχρονη απεικόνιση βιολογικών δειγμάτων, με χρήση των μη γραμμικών φαινομένων ΔΦΔΦ και ΓΔΑ. Χρησιμοποιώντας αυτήν τη διάταξη, επιτεύχθηκε η χαρτογράφηση του εμπρόσθιου και του οπίσθιου μέρους του νηματοειδούς C. elegans, με υψηλή διακριτική ικανότητα. Μελετήθηκαν πολλά γεννετικά μεταλλαγμένα είδη C. elegans, τα οποία εξέφραζαν σε διαφορετικά σημεία και με διαφορετικό τρόπο, μόρια της φθορίζουσας στο πράσινο πρωτεϊνης GFP. Επιτεύχθηκε, επιπλέον, ο εντοπισμός των δύο νευρώνων (PLM) στο οπίσθιο μέρος του νηματοειδούς που είναι υπεύθυνοι για την αντίδραση του ζώου σε μηχανικά ερεθίσματα. Μελετήθηκαν και βρέθηκαν οι ιδανικές πειραματικές συνθήκες για την ανίχνευση του εξωγενούς σήματος δεύτερης αρμονικής, προερχόμενου από τα μόρια της πρωτεϊνης GFP, τα οποία προσδένονται σε διαμεμβρανικές πρωτεϊνες των νευρώνων PLM. Στην παρούσα εργασία περιγράφονται ακόμη τα μελλοντικά μας σχέδια για την παρακολούθηση και την καταγραφή του ηλεκτρικού δυναμικού της μεμβράνης των συγκεκριμένων νευρώνων με μετρήσεις του σήματος δεύτερης αρμονικής

Nonlinear fiber-based optical circuits for complex signal processing functionalities in optical communication networks

234 σ.Η ανάπτυξη αμιγώς οπτικών διατάξεων επεξεργασίας σήματος αποτελεί σταθερή ερευνητική επιδίωξη με στόχο την επέκταση της διαφάνειας των οπτικών δικτύων και την πλήρη αξιοποίηση του εύρους ζώνης που παρέχει η οπτική ίνα ως φυσικό μέσο μετάδοσης. Για την υλοποίηση αυτού του είδους των διατάξεων, η αξιοποίηση των μη γραμμικών ινών και γενικότερα των μη γραμμικών μέσων Kerr, αποτελεί βασική επιλογή καθώς διαθέτουν τη δυνατότητα λειτουργίας σε υπερυψηλούς ρυθμούς μετάδοσης λόγω της φύσης του φαινομένου Kerr και της πρακτικά ακαριαίας απόκρισης της αντίστοιχης μη γραμμικότητας. Μέσα σε αυτό το πλαίσιο, η διατριβή εστιάζει στη μελέτη, ανάπτυξη και πειραματική αξιολόγηση πρωτότυπων διατάξεων μη γραμμικών ινών για την οπτική επεξεργασία σήματος, οι οποίες διακρίνονται για τη σύνθετη λειτουργικότητα και τη συμβατότητά τους με καινούργια σχήματα κωδικοποίησης και επιβεβαιώνουν ανεπιβεβαίωτα ως σήμερα εν πολλοίς χαρακτηριστικά των μη γραμμικών ινών, όπως η δυνατότητα πολυκυματικής λειτουργίας και ταυτόχρονης επεξεργασίας πολλαπλών καναλιών WDM. Υπό αυτήν την έννοια, η παρούσα διατριβή αντιπροσωπεύει μία ολοκληρωμένη και καλά ορισμένη ερευνητική προσπάθεια, συμπληρωματική ως προς την πλειονότητα των αντίστοιχων ερευνητικών προσπαθειών κατά την τελευταία δεκαετία, οι οποίες εστίασαν στην υλοποίηση απλούστερων τεχνικών σε διαρκώς υψηλότερους ρυθμούς μετάδοσης ή με τη χρήση ολοκληρώσιμων μη γραμμικών μέσων Kerr. Στα πλαίσια της διατριβής μελετήθηκαν και υλοποιήθηκαν τέσσερα συγκεκριμένα οπτικά κυκλώματα, τα οποία περιλαμβάνουν κύκλωμα πολυκυματικής αναγέννησης καναλιών WDM, κύκλωμα ανάκτησης ρολογιού από σύγχρονα ή ασύγχρονα οπτικά πακέτα μικρού μήκους, κύκλωμα αναγέννησης οπτικών σημάτων DPSK και κύκλωμα ανάδρασης για τον πολλαπλασιασμό ρυθμοδότησης ψευδοτυχαίων δυαδικών ακολουθιών (ΨΔΑ). Το κύκλωμα πολυκυματικής αναγέννησης βασίζεται στην υλοποίηση κατάλληλα σχεδιασμένου χάρτη διασποράς με χρήση συμβατικών ινών μετάδοσης και ινών αναίρεσης διασποράς, ο οποίος μειώνει τη μη γραμμική αλληλεπίδραση των καναλιών WDM επιτρέποντας την ταυτόχρονη αναγέννησή τους με τη βοήθεια του φαινομένου της αυτοδιαμόρφωσης φάσης. Το κύκλωμα ανάκτησης ρολογιού βασίζει τη λειτουργία του στη χρήση φίλτρου Fabry-Perot και περιοριστή οπτικής ισχύος μη γραμμικής ίνας. Ο περιοριστής οπτικής ισχύος δέχεται την έξοδο του φίλτρου Fabry-Perot, καταπιέζει δραστικά τη διακύμανση πλάτους που αυτή παρουσιάζει, και αποδίδει κατά αυτόν τον τρόπο ανακτημένο σήμα ρολογιού υψηλής ποιότητας. Το κύκλωμα αναγέννησης οπτικών σημάτων DPSK βασίζει τη λειτουργία του στην αποκωδικοποίηση των εισερχόμενων σημάτων και την εκ νέου διαμόρφωση κατά φάση ενός καινούργιου φέροντος με τη βοήθεια συμβολόμετρου Sagnac μη γραμμικής ίνας. Η συγκεκριμένη διαδικασία εκμεταλλεύεται τη μη γραμμικότητα του συμβολόμετρου Sagnac, έτσι ώστε να καταπιέσει το θόρυβο φάσης και πλάτους των εισερχόμενων σημάτων και να εξασφαλίσει την αναγέννησή τους. Τέλος, το οπτικό κύκλωμα ανάδρασης χρησιμοποιεί τη συγκεκριμένη τοπολογία ανάδρασης, καθώς και την οπτική υλοποίηση πύλης OR με χρήση συμβολόμετρου Sagnac μη γραμμικής ίνας, και επιτυγχάνει τον πολλαπλασιασμό ρυθμοδότησης ΨΔΑ με μεγαλύτερη ευελιξία, ευνοϊκότερους κανόνες κλιμάκωσης και υψηλότερη ποιότητα λειτουργίας σε σύγκριση με τις αντίστοιχες συμβατικές (γραμμικές) διατάξεις πολλαπλασιασμού ρυθμοδότησης. Και τα τέσσερα κυκλώματα επιδείχθηκαν πειραματικά στην περιοχή ρυθμών μετάδοσης των 40 Gb/s, αλλά η δυνατότητα επέκτασης της λειτουργίας τους σε υψηλότερες ταχύτητες είναι δεδομένη. Η πρακτική εφαρμογή τους αφορά οπτικά δίκτυα επικοινωνιών πρώτης, δεύτερης και τρίτης γενιάς, καθώς και συστήματα μετρήσεων και ελέγχου λειτουργίας άλλων οπτικών στοιχείων, διατάξεων, υποσυστημάτων και συστημάτων.The development of all-optical signal processing techniques and circuits has attracted particular interest over the last decades, aiming at the enhancement of optical networks transparency and the exploitation of the huge bandwidth, being made available by the optical fiber as a transmission line. One of the most preferable options for the implementation of this type of circuits is the use of nonlinear fibers, and in general of nonlinear Kerr media, mainly due to their potential for high-speed operation that originates from the nature of the Kerr effect itself and the practically instantaneous response of the Kerr nonlinearity. Within this framework, the thesis focuses on the study, development and experimental demonstration of novel, nonlinear fiber-based, all-optical signal processing subsystems that exhibit a high-degree of network functionality and compatibility with novel modulation formats, and additionally verify further characteristics of the fiber-based processors, such as their capability of multi-wavelength operation and thus, of simultaneous processing multiple WDM channels. In this sense, the present doctoral thesis represents a complete and well-defined research effort, complementary to other efforts over the last decade that have been aiming at implementing simpler concepts at increasingly high data rates and with the use of advanced Kerr media and integrated circuits. Within the framework of the thesis, four particular circuits were studied and experimentally demonstrated for the first time. These include a multi-wavelength regeneration circuit for on-off keying (OOK) signals, a clock recovery circuit for ultra-short, synchronous or asynchronous optical packets, a circuit for regeneration of optical differential phase-shift keying (DPSK) signals and a feedback circuit for rate multiplication of pseudo-random binary sequences (PRBS). The multi-wavelength regeneration circuit is based on the implementation of a carefully designed dispersion map that allows for the elimination of the nonlinear interaction between the WDM channels and for their simultaneous regeneration by means of the self-phase modulation effect. The clock recovery circuit is based, in turn, on the use of a Fabry-Perot filter (FPF) and a subsequent optical power limiter, which drastically suppresses the intense amplitude modulation of the FPF output and delivers the high-quality signal of the recovered clock. The DPSK regenerator relies on the decoding of the input data streams and the phase re-modulation of a new optical carrier using a nonlinear fiber-based Sagnac interferometer. The concept exploits the nonlinear transfer function of the Sagnac gate and offers the possibility for suppressing both the phase- and the amplitude-noise of the input signals, thus resulting in their regeneration. Finally, the all-optical feedback circuit exploits the feedback topology and the functionality of an optical OR gate to achieve the data rate multiplication of PRBS with higher flexibility, favorable scaling laws and higher operation quality as compared to the conventional, linear techniques. The optical implementation of the OR gate relies again on the nonlinear fiber-based Sagnac interferometer. All four circuits were experimentally demonstrated at 40 Gb/s data rate range, but the capability of extending their operation at higher data rates is given. Their practical significance refers to their potential for deployment in first-, second- and third-generation optical communication networks, as well as in test & measurement systems for the performance evaluation of a variety of optical elements, circuits, subsystems and systems.The development of all-optical signal processing techniques and circuits has attracted particular interest over the last decades, aiming at the enhancement of optical networks transparency and the exploitation of the huge bandwidth, being made available by the optical fiber as a transmission line. One of the most preferable options for the implementation of this type of circuits is the use of nonlinear fibers, and in general of nonlinear Kerr media, mainly due to their potential for high-speed operation that originates from the nature of the Kerr effect itself and the practically instantaneous response of the Kerr nonlinearity. Within this framework, the thesis focuses on the study, development and experimental demonstration of novel, nonlinear fiber-based, all-optical signal processing subsystems that exhibit a high-degree of network functionality and compatibility with novel modulation formats, and additionally verify further characteristics of the fiber-based processors, such as their capability of multi-wavelength operation and thus, of simultaneous processing multiple WDM channels. In this sense, the present doctoral thesis represents a complete and well-defined research effort, complementary to other efforts over the last decade that have been aiming at implementing simpler concepts at increasingly high data rates and with the use of advanced Kerr media and integrated circuits. Within the framework of the thesis, four particular circuits were studied and experimentally demonstrated for the first time. These include a multi-wavelength regeneration circuit for on-off keying (OOK) signals, a clock recovery circuit for ultra-short, synchronous or asynchronous optical packets, a circuit for regeneration of optical differential phase-shift keying (DPSK) signals and a feedback circuit for rate multiplication of pseudo-random binary sequences (PRBS). The multi-wavelength regeneration circuit is based on the implementation of a carefully designed dispersion map that allows for the elimination of the nonlinear interaction between the WDM channels and for their simultaneous regeneration by means of the self-phase modulation effect. The clock recovery circuit is based, in turn, on the use of a Fabry-Perot filter (FPF) and a subsequent optical power limiter, which drastically suppresses the intense amplitude modulation of the FPF output and delivers the high-quality signal of the recovered clock. The DPSK regenerator relies on the decoding of the input data streams and the phase re-modulation of a new optical carrier using a nonlinear fiber-based Sagnac interferometer. The concept exploits the nonlinear transfer function of the Sagnac gate and offers the possibility for suppressing both the phase- and the amplitude-noise of the input signals, thus resulting in their regeneration. Finally, the all-optical feedback circuit exploits the feedback topology and the functionality of an optical OR gate to achieve the data rate multiplication of PRBS with higher flexibility, favorable scaling laws and higher operation quality as compared to the conventional, linear techniques. The optical implementation of the OR gate relies again on the nonlinear fiber-based Sagnac interferometer. All four circuits were experimentally demonstrated at 40 Gb/s data rate range, but the capability of extending their operation at higher data rates is given. Their practical significance refers to their potential for deployment in first-, second- and third-generation optical communication networks, as well as in test & measurement systems for the performance evaluation of a variety of optical elements, circuits, subsystems and systems.Χρήστος Β. Κουλουμέντα

Novel Benes Network Routing Algorithm and Hardware Implementation

Benes/Clos networks constitute a particularly important part of interconnection networks and have been used in numerous areas, such as multi-processor systems, data centers and on-chip networks. They have also attracted great interest in the field of optical communications due to the increasing popularity of optical switches based on these architectures. There are numerous algorithms aimed at routing these types of networks, with varying degrees of utility. Linear algorithms, such as Sun Tsu and Opferman, were historically the first attempt to standardize the routing procedure of this types of networks. They require matrix-based calculations, which are very demanding in terms of resources and in some cases involve backtracking, which impairs their efficiency. Parallel solutions, such as Lee’s algorithm, were introduced later and provide a different answer that satisfy the requirements of high-performance networks. They are, however, extremely complex and demand even more resources. In both cases, hardware implementations reflect their algorithmic characteristics. In this paper, we attempt to design an algorithm that is simple enough to be implemented on a small field programmable gate array board while simultaneously efficient enough to be used in practical scenarios. The design itself is of a generic nature; therefore, its behavior across different sizes (8 × 8, 16 × 16, 32 × 32, 64 × 64) is examined. The platform of implementation is a medium range FPGA specifically selected to represent the average hardware prototyping device. In the end, an overview of the algorithm’s imprint on the device is presented alongside other approaches, which include both hard and soft computing techniques

Enhancing dynamic student learning by teamwork in innovative projects at an Erasmus Mundus master subject adapted to the EHEA (EEES)

The EHEA (EEES in Spain) is creating common academic degree standards comparable and compatible between the European countries. The definition of the new Credit unit, the ECTS, focused on the hours of study devoted by the students, is also promoting the renovation of the educational process at the higher studies of Graduate Degree and Master. We describe the experience of innovation of the teaching practice of the “Fibres & Telecommunications” subject of the Master PhotonicsBCN (part of the Erasmus Mundus Master EUROPHOTONICS), by introducing team9 working techniques for promoting: the development of cooperative learning, interpersonal skills, and positive interdependence among the students, not forgetting the individual initiative and responsibility. The teamwork is oriented to small innovation projects (inspired in state9of9the9art research challenges faced by the European FP7 EURO9FOS Network9 of 9Excellence) promoting interactive and dynamic student learning process. Each team member is spontaneously encouraged to learn as much as possible on both: the area of his task inside the common project, and also the influence of his task in the over all results of the project. This is implemented by the use of commercial software for professional systems deployment (VPIphotonics TM ), which allows each team to check the real viability of their innovative solutio

Fungal Septic Knee Arthritis Caused by Aspergillus fumigatus following Anterior Cruciate Ligament Reconstruction

Postoperative infections after arthroscopic anterior cruciate ligament (ACL) reconstruction (ACLR) represent a rare but severe complication. An extremely rare case of Aspergillus septic arthritis in a 27-year-old patient following arthroscopic ACLR is reported. The patient presented with signs of knee infection 14 days after ACLR. Two consecutive arthroscopic debridements were performed, while eventually histopathology, cultures and multiplex PCR test revealed Aspergillus identified as A. fumigatus by mass spectrometry. The patient commenced long-term treatment with voriconazole. Fungal arthritis or osteomyelitis following ACLR has a mild local and general inflammatory reaction when compared to the bacterial ones. Nevertheless, such infections may lead to aggressive osseous destruction and necrosis. A high index of suspicion is of utmost importance for early detection, while microscopic, histological examination and multiplex PCR may be more helpful for the diagnosis than cultures since cultures are more time-consuming and may vary depending on different factors