Radio over Fiber for Wireless Communications: From Fundamentals to Advanced Topics

Chapter 2Important Fi-Wi Link Elements

This chapter describes the main elements of an ROF Fi-Wi system and how their characteristics influence the transport of radio signal(s) for wireless communications. Note that the objective of this chapter (or the book for that matter) is not to provide detailed information on all the characteristics of fiber-optic or wireless communication devices. There is plenty of information available on these topics in the literature, and the reader is expected to have a basic knowledge of fiber optics and wireless communications. This chapter focuses on specific characteristics of the Fi-Wi link elements that are relevant to the focus of the book only.

There are a few figures of merit associated with ROF link performance which affect a wide variety of applications. These are RF gain, noise figure (NF), bandwidth, and spurious free dynamic range (SFDR).

2.1 RF-Optical Modulation

RF-optical modulation can be done either by directly modulating the optical source (the laser diode or occasionally an LED, see Fig. 2.1) or by externally modulating the optical carrier after generation. There are benefits and drawbacks to each of these approaches. Note that both direct and external techniques can be used to modulate the intensity (optical power) or the amplitude and phase of the optical carrier. These are called ‘intensity modulation’ and ‘coherent modulation,’ respectively. The associated detection processes are called ‘direct detection’ and ‘coherent detection,’ ...