We report the first demonstration of 640-Gb/s return-to-zero ON-OFF keying channel transmission over a 100-km standard single-mode fiber link employing midspan phase conjugation. A frequency-degenerate conjugate field spanning more than 20 nm is created in a low-birefringence parametric mixer for the first time. Physical separation of the conjugate field from the original field is enabled by utilizing pump polarization nondegeneracy. Rigorous link characterization using a high-quality 640-Gb/s transmitter and a high-sensitivity receiver revealed error-free (bit error ratio <;10^-9) performance, eliminating the need for impractical fiber length control or electronic signal processing. The compatibility of wavelength-transparent conjugation with spectrally inefficient channel implies that channels with higher bit rates and better spectral efficiency can also be compensated.

This paper analyses how digital technologies implementation in the maritime transport sector companies can help in achieving the Blue Economy goals. Previous research offering a comprehensive overview of digital technologies in the maritime transport sector within the context of the Blue Economy is scarce. To fill this research gap, the economic effects of maritime transport are investigated, and the positive impacts of digital technologies on maritime transport are analyzed, all in the context of the Blue Economy. The authors have concluded that by implementing digital technologies in the maritime transport sector, the Blue Economy goals related to maritime transport (for example transport cost reduction, decreased harmful emissions generated during the voyage and at the berth) can better be achieved, etc.

In nautical tourism, Croatia has great potential for further development; from the conditions of navigation, safety, destination content, traffic accessibility, natural beauty, traditional hospitality and gastronomic offer of island and coastal places, etc. Its features, at the same time, are the advantages of competing countries: purity of the sea and coastal places, beauty and preservation nature, climate, security, hospitality, country image and spatial layout of the marina. The disadvantages relate to insufficient availability and nautical ports equipment, insufficient education, low level of technical service at nautical ports. The research aimed at analysing the current state of nautical tourism in Croatia. The methods used, based on the collected data, have been analysed. The results of the analysis rely on the existing state of nautical tourism, which determines the importance of additional investment in this form of tourism. The aim of the research is to define and shape the necessary measures and development strategies to achieve the purpose of research: the development of nautical tourism contributes to the growth of Croatia’s economy.

The fourth industrial revolution is already a fact. It is manifested in the emerging automation of many processes in shipping, which until recently have been highly dependent on the competence of the people who manage them. The analysis of navigational accidents invariably touches the human factor and involves it in the reasons for their occurrence. The statistics are discouraging and the lack of competence of seafarers is always present in the reports of the investigating authorities. The idea of creating and implementing autonomous ships is cited as a lifeline to overcome the shortcomings that disturb the industry due to the human factor. A few authors in their publications point out many unresolved issues, one of which is related to the education and competence of service personnel. The existing International Convention for Standards of Training, Certification and Watchkeeping of Seafarers does not cover unmanned ships. The mandatory and recommended competencies in it are addressed to the people on board. Some maritime educational institutions have introduced the concept of “autonomous ship” in their curricula, such as Nikola Vaptsarov Naval Academy, Varna and Faculty of Maritime Study, Split. There are probably others who think ahead, but this approach is not enough because unmanned ships are already a fact in the maritime industry. This article aims at exploring the possibilities for supplementing the curricula of maritime training institutions with appropriate subjects for the new realities in shipping.

We present a theoretical analysis describing the spectral dependence of phase noise in one-pump fiber parametric amplifiers and converters. The analytical theory is experimentally validated and found to have high predictive accuracy. The implications related to phase-coded sensing and communications systems are discussed.