All-Optical Regeneration Based on Phase-Sensitive Nondegenerate Four-Wave Mixing in Optical Fibers

An optical regeneration scheme based on nondegenerate phase-sensitive amplification in highly nonlinear fibers is numerically investigated. The proposed regenerator exhibits significant amplitude and phase noise suppression properties and eliminates the need for precise phase and frequency locking with the input return-to-zero differential phase-shift keying signal

Colorless Regenerative Amplification of Constant Envelope Phase-Modulated Optical Signals Based on Injection-Locked Fabry–Pérot Lasers

An efficient phase preserving amplitude noise limiter suitable for constant envelope phase-modulated signals is experimentally demonstrated for 10-Gb/s differential phase-shift-keying (DPSK) signals exploiting injection locking in Fabry–Pérot lasers. The limiter operates successfully over a 16.4-nm tuning range leading to 12 dB of power penalty reduction for 10^-3 of bit-error-rate (BER) performance

V2X Communication over Cellular Networks: Capabilities and Challenges

Vehicular communications is expected to be one of the key applications for cellular networks during the following decades. Key international organizations have already described in detail a number of related use cases, along with their requirements. This article provides a comprehensive analysis of these use cases and a harmonized view of the requirements for the latest and most advanced autonomous driving applications. It also investigates the extent of support that 4G and 5G networks can offer to these use cases in terms of delay and spectrum needs. The paper identifies open issues and discusses trends and potential solutions

Research in parametric optical amplification and injection locking focused on high bit rate optical communication systems applications

In this dissertation, the properties of the all-optical processes of phase sensitive parametric amplification and injection locking, are thoroughly investigated, through numerical simulations and experiments, in order to design integrated optical devices that can improve the performance of coherenct optical communications. Exploiting the phase noise suppression that the phase sensitive parametric amplifier can provide, a novel 40 Gb/s RZ-DPSK regenerator based on the single pump topology is proposed, which adops a realistic solution for the all-optical generation of an idler wave identical to the signal, dealing with the unresolved problem of the practical implementation of the specific devices. Taking into consideration the amplitude noise suppression and the phase replication properties of the injection locked semiconductor laser, we propose the use of the specific device as an alternative solution for (D)PSK and (D)QPSK signal regeneration. From the above properties, the injection locked semiconductor laser is also proposed as an additional unit in a DPSK/ASK receiver in order to provide better discrimination of the two different data streams and improve the performance of the specific modulation format.Στην παρούσα διδακτορική διατριβή μελετώνται διεξοδικά, με τη βοήθεια προσομοιώσεων και πειραματικών μετρήσεων, οι ιδιότητες των διαδικασιών της ευαίσθητης στη φάση παραμετρικής ενίσχυσης και της εγκλείδωσης φάσης με έγχυση οπτικής ισχύος, με σκοπό τον σχεδιασμό ολοκληρωμένων οπτικών διατάξεων, οι οποίες θα προσφέρουν βελτίωση των επιδόσεων των σύμφωνων συστημάτων επικοινωνιών. Εκμεταλλευόμενοι την ιδιότητα της συμπίεσης του θορύβου φάσης που προσφέρει ο ευαίσθητος στη φάση παραμετρικός ενισχυτής προτείνεται και μελετάται ως προς τις επιδόσεις του, με τη βοήθεια προσομοιώσεων, ένας πρωτότυπος αναγεννητής 40 Gb/s RZ-DPSK σημάτων, βασισμένος στην τοπολογία μονής άντλησης, ο οποίος υιοθετεί μία ρεαλιστική τεχνική για την αμιγώς οπτική παραγωγή συμφασικού, ως προς το σήμα, συζυγούς κύματος, επιλύοντας έτσι το πρόβλημα της πρακτικής υλοποίησης τέτοιων διατάξεων. Λαμβάνοντας υπ’ όψιν τις ιδιότητες της συμπίεσης θορύβου πλάτους και της αναπαραγωγής των χαρακτηριστικών φάσης του εγχεόμενου πεδίου που προσδίδει η εγκλείδωση φάσης σε ένα ημιαγωγικό laser, προτείνεται η χρήση του τελευταίου ως μία εναλλακτική διάταξη για την αναγέννηση (D)PSK και (D)QPSK σημάτων. Από τις ιδιότητες αυτές προέκυψε και η εναλλακτική χρήση του εγκλειδωμένου ημιαγωγικού laser ως μία επιπρόσθετη βαθμίδα στον δέκτη DPSK/ASK σημάτων για τον καλύτερο διαχωρισμό των δύο διαφορετικών ροών πληροφορίας και τη βελτιστοποίηση των επιδόσεων του συγκεκριμένου συστήματος μετάδοσης

Performance enhancement of point-to-point diffuse links at 265 nm under fog conditions

It is known that the tempting features of free space Non-Line-Of-Sight (NLOS) communications systems operating in the Ultraviolet C-band between 200 and 280 nm are the significantly reduced solar irradiance on ground level, the intense scattering and its combination with strong absorption which ensures the covertness against distant eavesdroppers or jammers. In the majority of the experimental surveys that have been published so far, the performance of point-to-point links has been evaluated under clear atmosphere without taking into account the weather conditions. In this work, it is shown that harsh atmospheric conditions due to fog appearance can be advantageous to short distance NLOS transmissions at 265 nm. Initially, the impact of fog on the losses of the diffuse wireless channels was investigated theoretically. Afterwards, an experimental survey of both the losses and the performance of low rate amplitude signals' transmissions for two atmosphere cases followed. Initially, the satisfactory relation between scattering and absorption at 265 nm was verified by deploying outdoor NLOS point-to-point links under clear atmosphere. The transmitter consisted of 4 Light Emitting Diodes and the optical part of the receiver included a filter and a Photo-Multiplier tube. Then, the beneficial impact of artificially generated fog on scattering was exploited not only to enhance the system performance but also to identify the modification of the conditions. The experimental results showed a clear decrease of both the losses and the Bit Error Rate under fog conditions making such a system a perfect candidate for low rate communications under dense atmosphere

Are EARLINET and AERONET climatologies consistent? the case of Thessaloniki, Greece

In this study we investigate the climatological behavior of the aerosol optical properties over Thessaloniki during the years 2003–2017. For this purpose, measurements of two independent instruments, a lidar and a sunphotometer, were used. These two instruments represent two individual networks, the European Lidar Aerosol Network (EARLINET) and the Aerosol Robotic Network (AERONET). They include different measurement schedules. Fourteen years of lidar and sunphotometer measurements were analyzed, independently of each other, in order to obtain the annual cycles and trends of various optical and geometrical aerosol properties in the boundary layer, in the free troposphere, and for the whole atmospheric column. The analysis resulted in consistent statistically significant and decreasing trends of aerosol optical depth (AOD) at 355 nm of ĝ'23.2 and ĝ'22.3 % per decade in the study period over Thessaloniki for the EARLINET and the AERONET datasets, respectively. Therefore, the analysis indicates that the EARLINET sampling schedule can be quite effective in producing data that can be applied to long-term climatological studies. It is also shown that the observed decreasing trend is mainly attributed to changes in the aerosol load inside the boundary layer. Seasonal profiles of the most dominant aerosol mixture types observed over Thessaloniki have been generated from the lidar data. The higher values of the vertically resolved extinction coefficient at 355 nm appear in summer, while the lower ones appear in winter. The dust component is more dominant in the free troposphere than in the boundary layer during summer. The biomass burning layers tend to arrive in the free troposphere during spring and summer. This kind of information can be quite useful for applications that require a priori aerosol profiles. For instance, they can be utilized in models that require aerosol climatological data as input, in the development of algorithms for satellite products, and also in passive remote-sensing techniques that require knowledge of the aerosol vertical distribution

Three different directions in which the European Union could replace Russian natural gas

Russia's invasion of Ukraine fuelled an energy crisis, which considerably impacted Europe given its heavy reliance on Russian natural gas imports. This study uses an ensemble of four global integrated assessment models, which are further soft-linked to two sectoral models, and explores the synergies and trade-offs among three approaches to living without Russian gas in Europe: (a) replacing with other gas imports, (b) boosting domestic energy production, and (c) reducing demand and accelerating energy efficiency. We find that substituting Russian gas from other trade partners would miss an opportunity to accelerate decarbonisation in end-use sectors while risking further fossil-fuel lock-ins, despite featuring the lowest gas price spikes and potentially reducing heating costs for end-users in the near term. Boosting domestic, primarily renewable, energy production on the other hand would instead require considerable investments, potentially burdening consumers. Energy demand reductions, however, could offer considerable space for further emissions cuts at the lowest power-sector investment costs; nonetheless, an energy efficiency-driven strategy would also risk relocation of energy-intensive industries, an aspect of increasing relevance to EU policymakers.</p