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xvi Introduction and preface
still in the research and development stage. It is important to understand the opera-
tion of each new development and to assess the implication of each new component
before any application of the photonic link. (3) Once the RF signal is carried on
an optical carrier, photonic techniques may be used to process the RF signals. An
obvious example is the frequency up- or down- conversion of the RF signal. There-
fore, photonic RF signal processing represents a potential attractive application
area for new applications. However, in photonic RF signal processing, the system
performance will have additional requirements than just the requirements for band-
width, efficiency and dynamic range. For example, the phase noise of the RF signal
becomes an important consideration in sensor applications.
System design consideration and the choice of the technologies and components
to be used in RF photonic links, as well as the evaluation of their performance
characteristics, are very different for analog links than for digital optical fiber links.
For example, the “on–off” threshold switching voltage of a modulator is important
for digital communication systems while the slope efficiency is the important figure
of merit for analog modulation. A thorough understanding of the analog system
issues and component requirements is necessary for a successful system design.
This monograph describes, in detail, the various key components and technolo-
gies that are important in analog RF links. The components are evaluated in terms
of their potential contributions to the RF links, such as RF efficiency, bandwidth,
dynamic range and signal-to-noise ratio. Since the modulation of an optical carrier
is much smaller than its bias for analog links, a special feature of the analyses
presented in this book is the use of small signal approximations with emphasis on
the reduction of nonlinear distortions.
The objectives of this book are: (1) to present to the reader various key tech-
nologies that may be used in RF photonic links: (2) to assess the significant aspects
of various technologies; (3) to explore extant and potential applications of such
technologies; (4) to illustrate specific applications of RF photonic links.
The analyses of basic RF photonic links are presented in Chapter 1. The analyses
show clearly the important figures of merit of various components and the system
objectives of analog RF photonic links. Chapter 2 describes the role of RF subcarrier
links in commercial local access networks. Modulation and detection techniques are
of particular importance in RF photonic links, because they determine the nonlin-
ear distortion, the bandwidth, the efficiency, and, in certain cases, the noise of such
links. Chapters 3 to 7 describe various modulation techniques, including the direct
modulation of semiconductor lasers, the LiNbO
3
external modulators, the traveling
wave modulator, the polymer modulator and the electroabsorption semiconduc-
tor modulator. The basic materials and principles of operation, the performance
expectation and the advantages and limitations of each modulation technique are
presented. In Chapter 8, a description of the key features of various detectors is