A review of communication-oriented optical wireless systems

This article presents an overview of optical wireless (OW) communication systems that operate both in the short- (personal and indoor systems) and the long-range (outdoor and hybrid) regimes. Each of these areas is discussed in terms of (a) key requirements, (b) their application framework, (c) major impairments and applicable mitigation techniques, and (d) current and/or future trends. Personal communication systems are discussed within the context of point-to-point ultra-high speed data transfer. The most relevant application framework and related standards are presented, including the next generation Giga-IR standard that extends personal communication speeds to over 1 Gb/s. As far as indoor systems are concerned, emphasis is given on modeling the dispersive nature of indoor OW channels, on the limitations that dispersion imposes on user mobility and dispersion mitigation techniques. Visible light communication systems, which provide both illumination and communication over visible or hybrid visible/ infrared LEDs, are presented as the most important representative of future indoor OW systems. The discussion on outdoor systems focuses on the impact of atmospheric effects on the optical channel and associated mitigation techniques that extend the realizable link lengths and transfer rates. Currently, outdoor OW is commercially available at 10 Gb/s Ethernet speeds for Metro networks and Local-Area-Network interconnections and speeds are expected to increase as faster and more reliable optical components become available. This article concludes with hybrid optical wireless/radio-frequency (OW/RF) systems that employ an additional RF link to improve the overall system reliability. Emphasis is given on cooperation techniques between the reliable RF subsystem and the broadband OW system

Saturation in cascaded optical amplifier free-space optical communication systems

The performance of a free-space optical (FSO) communication system in a turbulent atmosphere employing an optical amplifier (OA) cascade to extend reach is investigated. Analysis of both single and cascaded OA FSO communication links is given and the implications of using both adaptive (to channel state) and non-adaptive decision threshold schemes are analysed. The benefits of amplifier saturation, for example in the form of effective scintillation reduction when a non-adaptive decision threshold scheme is utilised at the receiver for different atmospheric turbulence regimes, are presented. Monte Carlo simulation techniques are used to model the probability distributions of the optical signal power, noise and the average bit error rate due to scintillation for the cascade. The performance of an adaptive decision threshold is superior to a non-adaptive decision threshold for both saturated and fixed gain preamplified receivers and the ability of a saturated gain OA to suppress scintillation is only meaningful for system performance when a non-adaptive decision threshold is used at the receiver. An OA cascade can be successfully used to extend reach in FSO communication systems and specific system implementations are presented. The optimal cascade scheme with a non-adaptive receiver would use frequent low gain saturated amplification

Lex Maritima in a changing world: development and prospect of rules governing carriage of goods by sea

This chapter examines the attempts to unifying law governing carriage of goods by sea and the background to these attempts over the past hundred years or so. It finds that a repetition of the current mode of negotiating static conventions will not unify these rules. Moreover, from historic and legal perspectives, the attempts to unify the international carriage of goods by sea regimes in the past century have remained transitional. The active players have shifted from private entrepreneurs to government delegates. This research probes into the new trade practice for the shipping industry in the twenty-first century and argues that new ‘landscape’ calls for innovative modifications of the conventional approach to unifying carriage of goods by sea rules. This research also forecasts the prospects of the Rotterdam Rules and discusses several countries’ current attitudes, including the UK, the Netherlands, Scandinavian countries and, particularly, the USA

All-optical clock recovery from short asynchronous data packets at 10 Gb/s

Abstract—In this letter, we demonstrate clock extraction from 10-Gb/s asynchronous short data packets. Successful clock acqui-sition is achieved from data packets arriving at time intervals of only 1.5 ns, irrespective of their precise phase relation. The clock recovery circuit used consists of a Fabry–Pérot filter and an ultra-fast nonlinear interferometer gate and requires very short time for synchronization. Index Terms—Burst mode, clock recovery, optical packet/burst switching, semiconductor optical amplifier (SOA), ultrafast non-linear interferometer (UNI). I