2. Modulated optical sources

In 2003, the principle used in optical transmissions was amplitude modulation of the optical carrier. For long-distance transmission or network applications, studies have been undertaken in other types of modulation (optical frequency modulation, phase modulation, etc.). The advent of erbium-doped fiber amplifiers (EDFAs) has considerably reduced the interest of these studies for telecommunications applications. By reducing insertion losses, optical amplification has made it possible to reduce additional link noise and thus increase sensitivity without having to resort to optical coherence or frequency modulation techniques, which are very difficult to implement. However, for certain analog applications, frequency modulation has proven to be robust against noise. What's more, some publications tend to show that better dynamic range can be achieved with this type of modulation.