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Προηγμένα σχήματα διαμόρφωσης και επεξεργασίας σήματος σε ισχυρά πολύτροπες ίνες
Get PDFΚαθώς η ανάγκη για ιδιαίτερα υψηλούς ρυθμούς μετάδοσης γίνεται πιο επιτακτική, κλασσικά μέσα μετάδοσης, όπως ο χαλκός και ο αέρας, που χρησιμοποιούνται εκτενώς στις ενσύρματες και ασύρματες μεταδόσεις αντίστοιχα, φαίνεται να τείνουν να εξαντλούν τη διαθέσιμη χωρητικότητά τους ή να μην επιτρέπουν την χρησιμοποίηση τους. Η χρήση οπτικών ινών για δίκτυα μικρής κλίμακας είναι πλέον μια πολλά υποσχόμενη λύση, προκειμένου να επιτευχθεί η αύξηση του ρυθμού μετάδοσης με ταυτόχρονη υποστήριξη διάφορων υπηρεσιών, όπως είναι για παράδειγμα η ταυτόχρονη μετάδοση δεδομένων, video, φωνής (λ.χ. VO.I.P, I.P.T.V, H.D.T.V). Ειδικότερα, οι πλαστικές οπτικές ίνες μεγάλης διαμέτρου 1mm SI-POF (Step Index-Plastic Optical Fiber) εμφανίζουν μια σειρά πλεονεκτημάτων, όπως το χαμηλό κόστος στην κατασκευή και τη συντήρησή τους, η αντοχή σε μηχανικές καταπονήσεις, η εύκολη συντήρηση, η ανοχή σε ηλεκτρομαγνητικές παρεμβολές και εύρος ζώνης μεγαλύτερο από τα ηλεκτρικά καλώδια. Από την άλλη πλευρά, τα μειονεκτήματα που παρουσιάζουν συγκριτικά με τις ίνες silica, όπως οι μεγάλες απώλειες οπτικής ισχύος (π.χ. 160-180dB/Km) και το περιορισμένο εύρος ζώνης μετάδοσης, που διαθέτουν (τυπικά περίπου 100MHz/50m), καθιστούν αναγκαία τη χρήση πολύπλοκων σχημάτων διαμόρφωσης και τεχνικών επεξεργασίας σήματος ώστε να υποστηρίξουν ρυθμούς μετάδοσης της τάξης των Gbps. Η μελέτη και η εφαρμογή τέτοιων σχημάτων διαμόρφωσης και τεχνικών επεξεργασίας αποτελεί το αντικείμενο της παρούσας διατριβής. Προτείνονται και εφαρμόζονται νέες τεχνικές διαμόρφωσης πολλαπλών φερόντων σε συνδυασμό με τη διάχυση των συμβόλων (multicarrier spreading modulation schemes), κατάλληλα προσαρμοσμένων για μετάδοση μέσω πλαστικών οπτικών τύπου SI-POF.
As the need for very high bit rate transmission becomes more imperative, conventional transmission media such as copper and air, which are extensively used in wired and wireless transmission respectively, seem to either reach their available capacity or their usage is not advantageous. The use of optical fiber as a medium for short range networks is now becoming a promising solution to achieve increased transmission rate while at the same time supporting different (broadband) services, such as the simultaneous transmission of data, video, voice (e.g., VO.IP, IPTV, HDTV). In particular, plastic optical fibers of large core diameter i.e., 1mm SI-POF (Step Index-Plastic Optical Fiber), exhibit a number of advantages regarding not only low manufacturing cost and maintenance but also immunity to mechanical stress, avoidance of electromagnetic interference and enhanced bandwidth compared to the previous transmission media. On the other hand, compared to silica fibers, limitations on their usage include large optical power loss (e.g. 160-180dB/Km) and limited transmission bandwidth i.e., typically about 100MHz/50m. Therefore, in order to efficiently support transmission rates in the order of Gbps, it is necessary to develop and employ complex modulation schemes together with digital signal processing techniques. The subject of this thesis includes the study, development and deployment of such modulation schemes and processing techniques. New multi-carrier spreading modulation techniques are investigated and proposed, which are then suitably adapted for short range high speed IM/DD optical transmission over SI-POF
Approximate expressions for the estimation of the four-wave mixing efficiency in slow light photonic crystal waveguides
Get PDFWe present approximate analytical expressions for the estimation of the degenerate four-wave mixing conversion efficiency in slow light photonic crystal waveguides. The derived formulas incorporate the different effective modal areas and the frequency-dependent linear and nonlinear parameters of the pump, signal and idler waves. The influence of linear loss, two-photon absorption and free-carrier generation is also accounted for. Numerical solution of the coupled propagation equations is used to verify the validity of the proposed expressions under different values of the linear and nonlinear parameters of the waveguide. It is shown that the derived expressions provide an accurate estimation of the conversion efficiency and are thus expected to be very useful in the design of photonic crystal waveguides for nonlinear signal processing applications
Π.3. ΣΥΜΠΕΡΑΣΜΑΤΑ ΚΑΙ ΠΡΟΤΑΣΕΙΣ : Τελική έκθεση - Μελέτη Τεύχος Β΄: Βιβλιογραφική Ανασκόπηση [του έργου «Εκπόνηση μελέτης για την εφαρμογή των προγραμμάτων επιχειρηματικότητας στη δευτεροβάθμια εκπαίδευση»]
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Προγράμματα σπουδών ενηλίκων:6ος κύκλος Εκπαιδευτικών Προγραμμάτων: Σεπτέμβριος 2014 – Νοέμβριος 2014
Get PDFΠεριλαμβάνονται τα πακέτα εργασίας:
ΠΕ 1.1 - Σχεδιασμός και προγραμματισμός εκπαιδευτικών
προγραμμάτων
ΠΕ 1.2 - Οργάνωση εκπαιδευτικών προγραμμάτων
ΠΕ 1.3 - Υλοποίηση εκπαιδευτικών προγραμμάτων
ΠΕ 1.4 - Αξιολόγηση εκπαιδευτικών προγραμμάτω
Donor-acceptor graphene-based hybrid materials for managing photoinduced electrontransfer reactions
Get PDFGraphene research and in particular the topic of chemical functionalization has been exploded in the last decade. The main aim is to induce solubility and thereby enhance processability of the material, which is otherwise insoluble and inapplicable for technological applications when stacked in the form of graphite. In this frame, initially, graphite was oxidized under harsh conditions to yield exfoliated graphene oxide sheets, soluble in aqueous media and amenable to chemical modifications due to the presence of carboxylic acid groups at the edges of the lattice. Some donor-acceptor hybrid materials with photo- and/or electro-active components were prepared and characterized, while their charge-transfer properties were evaluated. However, it was obvious that the highly defected framework of graphene oxide cannot be really utilized in applications that are governed by charge-transfer processes, for example in solar cells. The alternative route for solubilizing and modifying graphene by exfoliating graphite is the current method of choice for the realization of novel hybrid materials and further boost their direct applicability in artificial photosynthesis and the construction of photovoltaic devices. In this review article, the routes for obtaining donor-acceptor graphene-based hybrid materials for managing charge-transfer phenomena, mainly, but not exclusively, with porphyrins and phthalocyanines are presented. Earlier examples and studies performed on graphene oxide modified with organic electron donors are also given
Protein detection by polymer optical fibers sensitized with overlayers of block or random copolymers
Get PDFIn this study a low cost and low complexity optical detection method of proteins is presented by employing a detection scheme based on electrostatic interactions, and implemented by sensitization of a polymer optical fiber (POF) surface by thin overlayer of properly designed sensitive copolymer materials with predesigned charges. This method enables the fast detection of proteins having opposite charge to the overlayer, and also the effective discrimination of differently charged proteins like lysozyme (LYS) and bovine serum albumin (BSA). More specifically, as sensitive materials here was used the block and the random copolymers of the same monomers, namely the block copolymer poly(styrene-b-2vinylpyridine) (PS-b-P2VP) and the corresponding random polymer poly(styrene-r-2-vinylpyridine) (PS-r-P2VP), of similar composition and roughly similar molecular weight. Moreover, this work focused on the comparison of the aforementioned sensitive materials regarding the way in which they can adapt on sensing optical platforms and constitute functional sensing bio-materials