Introduction

Microwave links serve important communication, signal processing and radar functions in many commerical and military applications. However, the attenuation of microwave RF signals in cables and waveguides increases rapidly as the frequency of the signal increases, and it is specially high in the millimeter wave range. Optical fibers offer the potential for avoiding these limitations for the transmission of RF signals.

Photonic microwave links employ optical carriers that are intensity modulated by the microwave signals and transmitted or distributed to optical receivers via optical fibers. Since the optical loss for fibers is very low, the distance for photonic transmission and distribution of microwaves can be very long. When the modulation of an optical carrier is detected at a receiver, the RF signal is regenerated. Figure 1.1 illustrates the basic components of a simple photonic microwave link.

Since the objective of a photonic microwave link is to reproduce the RF signal at the receiver, the link can convey a wide variety of signal formats. In some applications the RF signal is an unmodulated carrier – as for example in the distribution of local oscillator signals in a radar or communication system. In other applications the RF signal consists of a carrier modulated with an analog or digital signal.