In 2017, the value of the global market for free space optical communication technology was 9.2 million and it is expected to grow at a compound annual growth rate of 34% during the years 2018-2023. North America and Asia-Pacific are ranked successively the two major global markets. The high demand for fast, flexible wireless technology among all industries including reconnaissance, last and first mile connectivity, backhaul and internet of things are major drivers for the expected growth of free space optics. Moreover, security and high-speed wireless communication, as well as the emerging need for higher flexibility modules, are also key factors that enhance the growth of the global free space optics market. All of these factors are the major forces behind this book’s investigation of the performance of FSO under severe conditions and environmental impairment, and how FSO systems can be integrated to enhance the next 5G networks revolution. This book provides an in-depth insight of free space optics already applied in military data security as well as in daily data exchange. This system offers several more advantages compared to other technologies such as low cost, mobility equipment’s or security. Moreover, this technology has the potential of becoming an integral and indispensable part of data-processing architectures and telecommunications in the very near future. The book also provides a review of the history of wireless optical telecommunications, together with a synopsis of the application of the principles of electromagnetism in free-space optics. FSO Features and applications are also presented together with an overview of the potential challenges. The environmental impairment itself, which is the key challenge, is put under deep scrutiny. Special attention too is given to the possible mitigation solutions to overcome possible impairments.

Text sample: Chapter 2.2 Overview of FSO Technology: FSO technology consist of the transfer of data/information between two points using optical radiation as the carrier signal through unguided channels. The transported data is modulated on the intensity, phase, or frequency of the optical carrier. An FSO link is fundamentally based on line-of-sight (LOS) transmission with no obstruction along the propagation path, thus ensuring very high data rate transmission in the absence of any multipath induced dispersion [59, 60]. The unguided channels could be any, or a combination of, space, sea-water, or atmosphere. The focus in this work is on terrestrial FSO and, as such, the channel of interest is the atmosphere. (Figure 2-1: Setup of the FSO Sender and receiver) FSO systems allow the use of narrow divergence, directional laser beams, which provide high security with a low probability of interception or detection features that can be desirable in many applications. Narrow and highly focused optical beams are also important in situations where the channel is not clear due to fog. For example, penetration of dense fog over a kilometre distance is achievable at Gbps data rates with a beam divergence of 0.1 mrad. Furthermore, the tight antenna patterns of FSO links allow considerable spatial re-use, and wireless networks using such connectivity are highly scalable, in marked contrast to ad-hoc RF networks, which are non-scalable [61, 62]. The basic features, areas of applications, and the description of each fundamental block of an FSO system are further discussed in the following sections. 2.3 Features of FSO: Several typical features of FSO technology are presented below: i. Huge modulation bandwidth – The frequency range of an optical carrier spans from 10¹²-10¹6 Hz, which corresponds to 2000 THz bandwidth. This is a key feature since the amount of data that can be transmitted is directly related to the bandwidth of the carrier. Optical communication permits a far greater information capacity compared to RF technology, with an operational frequency bandwidth, which is relatively lower by a factor of 105 [60, 63, 64]. (Figure 2-2: The overview of the EM spectrum with ist nominated frequency bands) ii. Unlicensed spectrum – FSO utilises the visible to far infrared (FIR) bands of the electromagnetic spectrum, as shown in Figure. 2-1. The optical carrier frequencies have a very small footprint at this spectrum range, and therefore, FSO systems are not significantly affected by signals from other bands. However, this is not the case with the RF spectrum, where adjacent bands are susceptible to interference. Therefore, regulatory authorities, such as the Federal Communication Commission (FCC) in the US, and the Office of Communication (Ofcom) in the UK, have put stringent regulations in place [67]. Obtaining a slice of the RF spectrum is costly and could take a long time. However, this is not the case with the FSO spectrum, which is free, relatively inexpensive compared to the RF spectrum, and can be rapidly installed. Iii. Narrow beam size – Optical radiation is well known for ist extremely narrow beam size, which typically ranges between 0.01 and 0.1 mrad [65]. This implies that the transmitted power is concentrated within a very small area. The tight spatial confinement also permits parallel transmission of a number of laser beams at the same, and/or different wavelengths, which is not possible in RF-based systems. Iv. Cost-effective – The cost of utilisation of FSO systems is lower than that of an RF system for a given data rate. FSO can deliver similar bandwidth to optical fibres, but without the additional cost of right-of-way and trench digging, especially in urban areas [68]. V. Quick to deploy and redeploy – FSO offers quick deployment and can be operational in just a few hours, from installation to link alignment, which is desirable in emergency situations where there is an urgent need to establish a high bandwidth communications link. The most important requirement in FSO deployment is the achievement of an unobstructed LOS between the Tx and the Rx. FSO modules can also be taken down and redeployed in different locations [64, 69]. Vi. Weather dependent – Atmospheric conditions have a huge impact on the performance of terrestrial FSO communication links due to the presence of atmospheric absorption and scattering. These ‘undetermined’ characteristics of the FSO channel undoubtedly pose the greatest challenge. Nevertheless, this is not particular to FSO, since RF and satellite communication links are also subject to link unavailability due to heavy rain, and snow [96, 123].

• Optical wireless communication

• Free space optics

• 5G

• Internet of things

• Laser communication

• Visible light communication

• IoT

Dr. Aymen Gatri, born in Tunis, Tunisia, has received his first engineering degree from the University of Wuppertal in Germany and his PhD in Physics, Mathematics and Electrical Engineering with a focus on Optical Wireless Communications from the Northumbria University Newcastle, UK. He has more than 14 years of professional experience in various industries and positions including IT, automotive, defense, raw materials and energy. Dr. Gatri has conducted several research projects at the School of Northumbria Communications Research Lab., Optical Communications and the Bonn Rhein Sieg University of Applied Sciences. His research focus is digital transformation among various industries, in particular how digital transformation is driving 5G, IoT and futuristic Cybersecurity strategies.