Chapter 5
Performance of Microwave Photonic Links
5.1. Microwave photonic links: diagrams and definitions
5.1.1. Direct modulation link diagram and definitions
Figure 5.1 helps to define the principal parameters of a microwave photonic link with direct laser modulation without a command amplifier and without an amplifier after photodetection.
The laser is biased by an average current, I0, which determines the average optical power generation POPT0. The RF or microwave pRFE power applied at the input generates a peak alternating current in the laser, which has a peak amplitude iE. At the laser output this alternating current leads to amplitude modulation of the optical power with a power amplitude defined by a peak value pOPT,I. This is a double sideband modulation, as shown in Figure 5.1.
The modulated optical power (average power POPT,I and alternative amplitude power pOPT,I) is injected into an optical fiber where it undergoes an attenuation LOF. In the case of double sideband modulation, the chromatic dispersion of the fiber can induce an additional attenuation. The phenomenon will be examined in detail later. Similarly, the coupling between the laser and fiber in one part and the coupling between the fiber and photodetector in the other part are not perfect and hence introduce attenuations. For the moment, it will be considered that LOF regroups all these attenuations.
The modulated optical power is now injected into a photodetector. The continuous power POPT0,O component ...
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