Short-Reach Optical Wireless Communication E-Book

Ton Koonen

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 454

Veröffentlichungsjahr: 2025

Beschreibung

A deep dive into indoor optical wireless communication networks

In Short-Reach Optical Wireless Communication: By Directed Narrow Beams, distinguished researcher Ton Koonen delivers an in-depth discussion of the design of indoor optical wireless networks and their key functions. The book explores the steering function for directing beams two-dimensionally to devices, the localization function for device finding and the receive function for devices in order to maximize the range of angles and aperture through which light can be captured.

These functions have been analyzed, designed, realized, and validated, as well as integrated in a laboratory setting for proof of concept of bidirectional all-optical wireless communication.

The book also includes:

• A thorough introduction to how key optical wireless communication techniques are realized and validated
• Illustrative examples of optical wireless technology
• Practical discussions of foundational concepts that underlie optical wireless communication and its expected benefits, and a comparison with radio wireless techniques
• A large collection of figures, including photos of experimental setups, layouts of system concepts, and optical system modelling based on ray tracing analysis using MATLAB

Perfect for academic and industrial researchers with an interest in optical wireless communication, Short-Reach Optical Wireless Communication: By Directed Narrow Beams will also benefit professionals working and studying in the areas of optical communication modules and systems.

Leseprobe

IEEE Press445 Hoes LanePiscataway, NJ 08854

IEEE Press Editorial BoardSarah Spurgeon, Editor-in-Chief

Moeness AminEkram HossainDesineni Subbaram NaiduJón Atli BenediktssonBrian JohnsonYi QianAdam DrobotHai LiTony QuekJames DuncanJames LykeBehzad RazaviHugo Enrique Hernandez FigueroaJoydeep MitraThomas RobertazziAlbert WangPatrick Chik Yue

Short-Reach Optical Wireless Communication

By Directed Narrow Beams

Ton Koonen

Full Professor EmeritusDepartment of Electrical EngineeringEindhoven University of TechnologyEindhoven, The Netherlands

Copyright © 2025 by The Institute of Electrical and Electronics Engineers, Inc.All rights reserved.

Published by John Wiley & Sons, Inc., Hoboken, New Jersey.Published simultaneously in Canada.

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“Numquam minus otiosus sum, quam cum otiosus.”(I am never as busy as during my leisure hours.)after Marcus Tullius Cicero, 106–43 BC, in De Officiis III, 1, 1

Dedicated to Annemie,Martijn, Robin, Laurens,and my parents

About the Author

Ton (Antonius Marcellus Jozef) Koonen was born in Oss on Oct. 20, 1954. He received an MSc cum laude in Electrical Engineering from the Eindhoven University of Technology (TU/e) in 1979. He subsequently worked in applied research at Philips' Telecommunicatie Industrie (1979–1984), AT&T Network Systems (1984–1994), and Lucent Technologies–Bell Laboratories (1994–2000), initially as a Member of Technical Staff and since 1987 as a Technical Manager. Ton was a part-time professor in the Telecommunication Systems group at the University of Twente (1991–2000). He was appointed as a full-time professor of “Breedbandige netwerken” (Broadband Networks) in the Department of Electrical Engineering (EE) at TU/e on Jan. 1, 2001. Ton chaired the Electro-Optical Communication Systems group (2004–2021) in the EE department. He also was vice-dean of the EE department (2012–2020) and Scientific Director of the Institute for Photonic Integration (formerly COBRA; 2016–2019). Ton officially retired on Feb. 19, 2021. After his retirement, he continued research and acquired a PhD in Dec. 2023 with a thesis on optical wireless communication.

Ton is a Bell Labs Fellow (1998, the first one in Europe), IEEE Fellow (2007), Fellow of OPTICA (formerly OSA, the Optical Society of America, nowadays OPTICA; 2013), and High-Level Visiting Scientist at Beijing University of Posts and Telecommunications (111 Program, 2018–2023). He was a principal investigator in the Dutch Gravitation programs “Center for Integrated Nanophotonics” and “Networks” (both running from 2013 to 2024). He is a co-initiator and co-leader of the Dutch NWO Perspective program “FREE – Optical Wireless Superhighways” (Sep. 2021–Aug. 2026). Ton received the Dutch ICT Regie Award in 2009. In 2012, he acquired the prestigious Advanced Investigator Grant of the European Research Council on optical wireless communication, followed by a Proof-of-Concept Grant in 2018. With this research, Ton was one of the six finalists in the national Huibregtsen prize competition in 2018. At his valedictory lecture on Sep. 24, 2021, he received the honorable Dutch Royal distinction “Ridder in de Orde van de Nederlandse Leeuw” (“Knight in the Order of the Dutch Lion”).

Ton Koonen initiated and managed a wide range of national and international projects in optical systems research and secured more than € 30M in funding. He has authored and co-authored more than 750 conference and journal papers, with 13,531 citations, and h‑index of 54 (according to Google Scholar, Feb. 20, 2025), and he filed/holds 13 patents. His research interests include optical fiber communication networks, fiber-to-the-home, indoor networks, spatial division multiplexing, radio-over-fiber techniques, and most recently optical wireless communication.

Preface

Optical wireless communication (OWC) brings a number of distinct advantages beyond radio-based wireless communication (such as 4G and 5G mobile, Wi-Fi): the visible and near-infrared (near-IR) optical spectrum offer orders of magnitude more bandwidth than the radio frequency (RF) spectrum (even in the THz frequency bands), crosstalk between users is eliminated by using narrow beams and/or opaque walls, neither the connection is hampered by electromagnetic interference nor does it generate EMI itself, and by steering the narrow beams the energy can be brought only to those places where and when needed, thus yielding high energy efficiency. The small footprints of the beams also support a high user density. By deploying near-IR light such as commonly used in fiber-optic communication, relatively high beam powers (up to 10 mW at wavelengths beyond 1.4 μm) can be used without eye safety issues, and OWC systems can build on the vast set of mature optical modules already widely used in fiber-optic networks. In contrast to systems using widely diverging beams (such as LiFi systems), systems using narrow (nearly) collimated beams ensure a good link power budget that enables high-capacity connections with a longer reach at high user densities and with enhanced privacy.

This book surveys research efforts in high-capacity, beam-steered OWC systems, zooming in on those using narrow two-dimensionally (2D) steered infrared beams for indoor (/ short-to-medium range) service delivery. After discussing the indoor OWC network architecture and its design aspects, it summarizes the key functionalities required, gives a non-exhaustive concise review of the research efforts for these functionalities reported in the literature, and presents the novel solutions we propose for their realization:

2D steering of multiple narrow beams by means of a passive diffractive unit

(containing a pair of crossed gratings, or alternatively a high-port-count arrayed waveguide grating router) and remotely tuning the wavelength of each beam’s signal.

Accurate and autonomous localization of the OWC receivers

in order to aid the beam steering for downstream and upstream communication, by means of passive optical retro-reflector techniques and single-sided beam scanning algorithms without the need for a pre-existing return channel to confirm adequate beam alignment.

Broadband wide aperture and wide Field-of View (FoV) energy-efficient optical receivers

, which are based on scalable two-dimensional matrices of photodiodes followed by a single preamplifier.

The solutions have been designed, analyzed both analytically and numerically, and implemented, and first implementations have been experimentally validated in laboratory demonstrator systems, culminating in bidirectional optical wireless links with an FoV of up to ±10° (full angle) that can bring data at Gigabit Ethernet speeds to up to 128 densely spaced users individually, e.g., for real-time streaming of high-definition video content.

Gratefully I would like to acknowledge the funding received from the European Commission, in particular in the Advanced Investigator and Proof of Concept personal grant programs of the European Research Council (ERC), and the funding from the Dutch Government, in particular in the Gravitation program of the Dutch Research Council (NWO). The funding enabled the research work described in this book.

The work could not have been done without the invaluable support of my colleagues at the Eindhoven University of Technology. In particular, I would like to thank Dr. Ketema Mekonnen for his great technical support and Dr. Eduward Tangdiongga for his valuable discussions, as well as the PhD students who I had the privilege to guide for their great work in the exciting domain of OWC: Dr. Zizheng Cao, Dr. Joanne (Chin Wan) Oh, Dr. Xuebing Zhang, Dr. Ngoc Quan Pham, Dr. Yu Lei. Furthermore, I thank the postdoctoral researchers Dr. Fausto Gomez Agis and Dr. Amir Khalid, and technician Mr. Frans Huijskens for their valuable work. I am also indebted for the careful reading and the scrutinizing of my text by Prof. Dominic O’Brien, Prof. Volker Jungnickel, and Prof. Sonia Heemstra de Groot. I owe very much to my father and mother, who supported me unconditionally. And last but certainly not least, my gratitude and love goes to my “homefront”: my three sons and daughters-in-law Martijn and Annemarie, Robin and Eva, Laurens and Misha and our little grandson Quin; and above all my wife Annemie for all their support and endless patience.

Ton Koonen

List of Acronyms and Symbols

Acronyms

2D

two dimensional

ADR

angular diversity receiver

AoA

angle of arrival

ASE

amplified stimulated emission

AWGR

arrayed waveguide grating router

BER

bit error ratio

BFL

back focal length

BROWSE

Beam-steered Reconfigurable Optical-Wireless System for Energy-efficient communication (ERC Advanced Grant project)

BS-ILC

beam-steered infrared light communication

BW

bandwidth

CapEx

Capital Expenditures

CC

corner cube

CCC

central communication controller

CMOS

complementary metal oxide semiconductor

CoG

center of gravity

CPC

compound parabolic concentrator

CWDM

coarse wavelength division multiplexing

CW

continuous wave

DBR

distributed Bragg reflector

DMT

discrete multi-tone (modulation)

DS

downstream

DSB

double side-band

DWDM

dense wavelength division multiplexing

EDFA

Erbium-doped fiber amplifier

EFL

effective focal length

EMI

electro-magnetic interference

ERC

European Research Council

FoV

field of view

FP

Fabry Perot (cavity)

FSR

free spectral range

FttH

fiber-to-the-home

FttR

fiber-to-the-room

FWHM

full width at half maximum

GPON

gigabit passive optical network

GEPON

Gigabit Ethernet Passive Optical Network

HD

high definition (video)

IEEE

Institute of Electrical and Electronics Engineers

IM

intensity modulation

IoT

Internet of Things

IR

infrared

ISM

Industrial, Scientific and Medical (frequency bands)

ITU

International Telecommunication Union

LD

laser diode

LED

light-emitting diode

LiFi

light fidelity

LO

local oscillator

LoS

line of sight

MD

mobile device

MDU

multi-dwelling unit

MEMS

micro electro-mechanical system

MGDM

mode group division multiplexing

MIMO

multiple input multiple output

MMF

multi-mode fiber

MZI

Mach Zehnder Interferometer

MZM

Mach Zehnder Modulator

NA

numerical aperture

NLoS

non-line-of-sight

NPV

net present value

NRZ

non-return-to-zero (modulation)

NWO

Nederlandse Organisatie voor Wetenschappelijk Onderzoek (Netherlands Organization for Scientific Research)

O/E

optical-to-electrical (conversion)

OOK

on–off keying (modulation)

OPA

optical phased array

OpEx

operating expenses

OWC

optical wireless communication

OXC

optical cross-connect

PAA

phased array antenna

PAM

pulse amplitude modulation

PD

photodiode

PDL

polarization-dependent loss

PIC

photonic-integrated circuit

PMMA

polymethylmethacrylate

POF

plastic optical fiber

PON

passive optical network

PRA

pencil radiating antenna

PRBS

pseudo-random bit sequence

P2P

point-to-point

P2MP

point-to-multipoint

QAM

quadrature amplitude modulation

RAP

radio access point

REAM

reflective electro-absorption modulator

RF

radio frequency

RG

residential gateway

RoF

radio over fiber

RR

retro-reflector

RSS

received signal strength

Rx

receiver

SDM

spatial division multiplexing

SGC

surface grating coupler

SLM

spatial light modulator

SMF

single-mode fiber

SOA

semiconductor optical amplifier

SSB

single sideband

TDM

time division multiplexing

TDMA

time division multiple access

TIA

transimpedance amplifier

TRL

technology readiness level

TRx

transceiver

TTD

true time delay

Tx

transmitter

US

upstream

USP

unique selling point

UTC

uni-traveling-carrier (photodiode)

UWB

ultra-wideband (radio)

VCSEL

vertical cavity surface emitting laser diode

VIPA

virtually imaged phased array

VLC

visible light communication

WDM

wavelength division multiplexing

Wi-Fi

radio-based wireless connection standard

XG-PON

10-Gigabit-capable passive optical network

Symbols

α

CC

side length of corner cube

α

incidence angle (of optical beam)

△

λ

tun

wavelength tuning range

△

λ

FSR

wavelength Free Spectral Range

η

A

fill factor of area

η

AP

fraction of number of rays captured by an aperture

η

antenna

radiation efficiency of antenna

η

CC

fraction of incident power retroreflected by corner cube

η

matrix

fill factor of photodiode matrix

λ

wavelength (of light, or radio wave)

φ

,

ψ

beam steering angles (in two dimensions)

ω

radial frequency

c

0

speed of light (in vacuum)

C

d

capacitance of photodiode

D

A

directivity (of an antenna)

D

beam

beam diameter

D

lens

lens diameter

f

focal length (of a lens)

G

A

antenna gain

H

room height

K

numbers of rays in a beam (in ray tracing)

K

,

M

dimensions of matrix (of photodiodes)

L

length and width (of square area covered by optical beam steerer)

M

,

N

dimensions of matrix (of fibers in AWGR optical beam steerer)

m

order of interference

p

defocusing parameter

P

beam

power of a beam

responsivity (of a photodiode)

R

d

resistance (parallel resistance in photodiode)

R

s

resistance (serial resistance in photodiode)

T

eq

equivalent beam-to-photodiode power coupling factor

w

0

mode field radius (of Gaussian beam at its minimum width)

1Introduction

1.1 Motivation

Since its first introduction in field trial networks in the early 1970s, optical fiber has rapidly become the medium of choice for data transport in communication networks, starting with long-distance links, then in regional and metropolitan networks, and in recent years conquering the last kilometers to the home. Fiber widely outperforms copper-based cables by its very low losses and low dispersion and has pushed the transport capacity of communication networks to great heights. Moreover, its wavelength dimension provides a multiplicator for transport capacity, as well as extra traffic routing functionalities. Recently, exploiting the spatial dimension in few-moded fiber has raised the capacity and flexibility even further.

The powerful Internet as we know it today would not have been possible without fiber. Fiber has already arrived at the doorstep of many households. Extending its potential into the home, however, has not truly happened. The outdoor fiber highway is handed over to a variety of copper- and radio-based indoor networks, and only part of the fiber's high-bandwidth potential is experienced by indoor users.

On the other hand, there is a fast rise in capacity demand by the users and their devices. The variety of services offered by the Internet is booming, encompassing tele-shopping, tele-education, teleconferencing, entertainment, ultrahigh-definition video streaming, large file transfer, and many more; the traffic volume they generate is enormous (Fig. 1-1). The number of users of the Internet is increasing fast (Fig. 1-2), and most of them access the Internet by wireless devices (such as laptops and smartphones). In particular, video-based services require a large share of the capacity of the home access network. Moreover, there are also intra-home data transport needs, such as posed by the transport of broadband data streams and large files between in-home laptops, tablet computers, smartphones, video and audio sets, network-attached storage (NAS) units, scanners, printers, etc., as well as by transport of bursty, low-volume data between various home devices that are part of the Internet of Things (IoT; see Fig. 1-3). The volume of intra-home traffic may exceed the traffic volume going into/out of the home, making the load on the in-home network even heavier.

Fig. 1-1 What happens on the Internet worldwide in 2023 in every minute

(source: eDiscovery Today & LTMG)

Hence, following their successes in the public network, photonic solutions should also be considered for the indoor network. Moreover, the use of multiwavelength technology can enable the convergence of different service families within a single fiber infrastructure, which saves indoor network installation costs.

The users increasingly prefer wireless service delivery instead of wire-bound delivery, thus getting more freedom in their mobility and reducing installation efforts of the indoor physical cabling infrastructure. Radio-based wireless indoor networks are widely deployed, in particular Wi-Fi based networks that are operating in the 2.5 and 5 GHz bands. The use of mm-wave and microwave technologies (e.g., 60 GHz and sub-THz) is being considered for providing extra bandwidth and for creating pico-cell network architectures in order to increase the network's aggregate capacity by spatial multiplexing. Radio-over-fiber for such high frequencies can combine the best of two worlds, and photonic integrated circuitry enables powerful microwave signal processing capabilities [1-1, 1-2]. The load on radio-based networks is booming, fueled by the growth of the number of IoT devices, as well as the increasing bandwidth needs of broadband services. This growth is leading to radio spectrum congestion and incidentally, even resulting in service denials. Optical wireless communication (OWC) by means of dedicated free-space optical technologies can open a huge amount of additional spectrum and enhance wireless service delivery capabilities in many domains [1-3 – 1-5].

Fig. 1-2 Growth of the number of individuals using the Internet

(source: ITU, Dec. 2022)

Fig. 1-3 Growth of the Internet of Things

(source: NCTA)

Indoors, OWC can counteract the congestion of the radio spectrum and offload much traffic from the radio-based network [1-6]. It also offers enhanced privacy and reduces crosstalk from/into neighboring rooms as it does not penetrate walls. Another advantage is that the additional optical spectrum needs no licenses. Moreover, OWC is immune to electromagnetic interference (EMI) and does not generate EMI itself. OWC, however, needs line of sight (LoS), which Wi-Fi technology does not. In OWC, even with nondirective receivers, LoS is needed, as the reception of LoS signals is much stronger than that of diffuse non-LoS signals. When using mm-waves (with frequencies in the range of 30–300 GHz), LoS is also needed, as these waves need directional antennas with high gain for establishing the transmission link power budget according to Friis' transmission equation [1-7]

(1-1)

where PT is the power fed into the transmitter antenna terminal, PR is the power out of the receiver antenna terminal, GT and GR are the gain of the transmitter and receiver antennas, respectively, d is the length of the mm-wave propagation path, and λ is the (short) wavelength of the mm-wave. Wi-Fi typically uses frequency bands in the 2.5 and 5 GHz region and thus has lower radio path losses than mm-waves; these Wi-Fi frequencies can even penetrate through walls (which compromises privacy). By offloading the broadband traffic, the OWC network creates adequate room for the radio wireless network to handle a large amount of lower volume (bursty) traffic flows, particularly the traffic for IoT devices, which may need to operate in non-line-of-sight (NLoS) conditions [1-8].

Outdoors, OWC can also bring a range of benefits and can offer relief for overloading of the radio spectrum and other issues. Unlike in indoor networks, atmospheric effects (such as fog, rain, snow, and air turbulence) can hamper the optical path, causing loss and phase fluctuations in it (scintillation [1-9]). For the particular case of underwater communication, radio transmission is not feasible and compared to sonar, OWC can provide transmission at higher data rates which, for example, is useful for video inspection and controlling unmanned underwater maintenance/repair robots [1-10]. While the short reach of OWC links for indoor applications typically ranges from a few meters to some tens of meters, the range can be considerably longer for outdoor applications. Medium reach free-space optics (FSO) applications include fixed optical wireless access to remote buildings, backhaul links for mobile telephony base stations, mobile communication on the road between vehicles and vehicle-to-roadside communication, street-level communication, inter-drones communication, communication in large outdoor areas such as sports stadiums and outdoor festivals. Examples of long to ultra-long FSO applications are ground-to-airplane communication, ground-to-satellite communication, and inter-satellite communication [1-11]. Medium- to ultra-long optical wireless links can be established with OWC technologies deploying narrow (nearly) collimated optical beams that are carefully steered to their receiver destinations. The reach of wide, diverging beams is strongly power limited. The steering of narrow beams needs to be highly accurate and their divergence must be very small, especially for establishing long-reach links. This requires sophisticated beam-steering and beam-shaping techniques. On the other hand, the Field-of-View (FoV) of the receiver typically does not need to be as large as for short-reach indoor communication, as long-reach links typically use only a single beam (or very few beams) and the incident angle at the receiver varies only over a tiny range.

1.2 Scope of the Book

The research described in this book focused on OWC system architectures and techniques to be applied in the domain of short-reach indoor communication. The goal is to enable the delivery of broadband services wirelessly to indoor users and devices at high user densities while complementing radio-based wireless techniques such as the IEEE 802.11 Wi-Fi suite. Such an OWC system should enable the wireless extension of the data highway capabilities of (fiber) access networks to users and devices individually, as well as support intra-building high-capacity data communication.

This research particularly focused on the architecture and enabling techniques for indoor short-reach OWC by means of narrow two-dimensionally (2D)-steered beams, which can bring the powerful functionalities of optical fiber wirelessly. Next to the general advantages of OWC (such as no need for spectrum licensing and the adding of the ample bandwidth available in the optical spectrum), beam-steered infrared light communication (BS-ILC) can bring a number of particularly powerful advantages with respect to radio-based wireless communication and wide-beam OWC:

It can offer very high (fiber-like) capacity to users individually. The transport performance of a narrow infrared beam may theoretically even exceed that of an optical fiber, as, unlike a fiber, an optical beam is not affected by waveguide dispersion. As the beams are highly directive and each follow a single path, no multipath effects and their associated fading occur. The larger bandwidth of the beam link may strongly reduce the signal processing efforts required for compressing the signal's bandwidth, thereby reducing the latency time incurred during that processing. Moreover, the latency of the beam link is about 33% smaller than that of an equally long silica fiber link due to the refractive index of the fiber core glass (which is around 1.5). The latency reduction increases the link capacity in bidirectional operation, such as in machine-to-machine communication.

High user densities. Due to the small footprint of a beam, very small picocells can be created, which enables dense spatial division multiplexing and thus allows narrow spacings between the users.

A high privacy and security level. Light does not penetrate walls, and the small footprint ensures negligible crosstalk with nearby users.

High-energy efficiency. The beams are directed on demand, only to those places where and when they are needed.

Immunity for externally generated EMI, and it also does not generate EMI itself.

It can build on mature optical device technologies already readily available and widely used in optical fiber networks.

BS-ILC also has a few disadvantages:

LoS is needed for a beam to reach a user. Workarounds can be devised, such as applying multiple spatially separated beam steerers, which can create alternative paths and may be arranged in a multiple-input multiple-output (MIMO) setting, or by adaptively relaying the signal by reflective surfaces, at the cost of comprehensive control measures and signal processing.

Accurate beam steering and user tracking are needed, which takes time and compromises the mobility of the user. Therefore, the BS-ILC is mainly intended to serve nomadic and static user devices that do not require connectivity while moving. This operation mode is often applicable in the delivery of broadband services such as high-definition video streaming and the exchange of large data files.

The beam steering and tracking also make the higher layer protocols more complex; extra room (either in-band in the time domain or out-of-band in the frequency domain) is needed to coordinate the network control plane with the data plane.

When using multiple beam steerers, the beam steering needs to be coordinated among themselves to avoid interference; this requires additional protocols.

1.3 Structure of the Book

The research described in this book focuses on the studies done to bring the benefits of optical communication into the indoor domain for individual users, both in their professional work environment and their residential environment. These findings have largely been published in a range of journal and conference papers and have also been laid down in a number of patents. The adjective “indoor” when used in combination with communication networks is used to distinguish it from “outdoor” networks, that is, in an environment not governed by strict regulations of standards and largely set up by the user(s) according to their personal wishes, not hampered by atmospheric effects, and typically involving short reach links (up to a few tens of meters).

Chapter 2 introduces the potential of optical technologies to enhance the performance of indoor communication networks, and among these technologies, the research in OWC described in this book. It discusses how photonic technologies can be introduced in indoor networks in order to bridge the gap between the capacity offered by the optical fiber-to-the-home (FttH) access network and the capacity accessible for the users, as well as to improve the intra-home network performance. Indoor networks have to carry a large variety of services, with widely differing needs regarding for instance bandwidth, quality of service, and reliability. They have to support both wired and wireless connectivity, at low costs and low energy consumption levels. The chapter reviews the architectures, the economics (both from an installation and an operational viewpoint), and the techniques for converged optical fiber indoor networks that are cost- and energy-efficient, and compares them with current copper-based solutions. Particular attention is given to high-capacity multimode (plastic) optical fiber techniques, radio-over-fiber techniques including adaptive radio beam steering, techniques for providing capacity on demand, and OWC techniques. An evolution roadmap is outlined that describes how the growing indoor communication demands can be met by gradually introducing these powerful techniques and network architectures.

Chapter 3 zooms in on OWC as the main topic of this book. OWC offers powerful solutions for resolving the imminent capacity crunch of radio-based wireless networks. OWC is not intended to fully replace radio wireless techniques such as Wi-Fi, but to rather complement these and off-load their high traffic loads. After discussing OWC's strengths in various application domains, a non-exhaustive tutorial overview of two major directions in OWC is provided: firstly, wide-coverage visible light communication (VLC) and LiFi, which are built on LED illumination techniques and share capacity among multiple devices, and secondly, communication with narrow two-dimensionally steered infrared beams that offer the unshared high capacity to devices individually. The latter constitutes the main area of research addressed in this book. A non-exhaustive review of the research on key techniques supporting beam-steered OWC is given: active and passive beam-steering techniques, device localization, and wide Field-of-View (FoV) receivers. Their application in bidirectional hybrid optical/radio networks and bidirectional all-optical wireless networks is discussed. The performance characteristics of beam-steered OWC are compared with those of wide-beam OWC (encompassing VLC and LiFi) and of the radio-based IEEE 802.11 systems (the Wi-Fi suite), regarding sensitivity for EMI, data capacity available per device, latency, and energy efficiency aspects. Photonic integration will become a key enabler for the introduction of indoor OWC; hence, a non-exhaustive review of photonic integrated circuit (PIC) solutions for OWC beam-steered transmitters and receivers is also given.

Chapter 4 outlines the architecture we propose for indoor broadband beam-steered OWC systems, termed the “BROWSE – Beam-steered Reconfigurable Optical-Wireless System for Energy-efficient communication” architecture. The architecture comprises a broadband fiber backbone network that feeds optical data streams to the rooms, in which they are conveyed by optical free-space beams to the individual users/devices. The BROWSE network design guidelines are derived, which serve as the basis for the design of the OWC key functionalities (such as beam steering, localization, and wide Field-of-View reception). The architecture is intended to provide broadband services wirelessly on demand where and when needed to individual users, tailored to their wishes. By using passive modules for the beam steering at the ceiling sites (the network access points), it intends to centralize the active service delivery functions and control functions as much as possible and to locate these remotely from the ceiling sites, in order to ease upgrading and maintenance and reduce energy consumption.

Chapter 5 focuses on techniques for adaptive indoor 2D beam steering to multiple users individually, even when they are not stationary. For downstream communication, beams directed at the users are emitted from a common ceiling unit in a point-to-multipoint scheme. Diffractive techniques are investigated where the wavelength of each data signal fed to the beam steerer determines in which 2D direction the associated beam is steered. Two options are analyzed in depth: using a pair of crossed diffraction gratings that enables semi-continuous steering and using an arrayed waveguide grating wavelength demultiplexer of which the output ports are two-dimensionally arranged in front of a lens shaping the beams enabling discrete steering. Both options include only passive elements that minimize maintenance efforts and failure risks and are readily scalable to serve more users individually by just feeding more wavelengths. Moreover, the signals can be generated remotely by tunable laser diode transmitters, which greatly facilitate system upgrades. For the upstream OWC link, continuous beam steering deploying a 2D electromechanical translator stage is investigated. Laser diodes with an arbitrary wavelength can be used, which is attractive for the cost-sensitive user terminal; there, diffractive steering is less attractive as wavelength tunable sources and their control entail higher costs.

Chapter 6