Distributed Optical Amplification Based on Raman Scattering for DWDM Applications in C, L and U Bands

Nowadays there are a lot of big changes that are completely and radically transforming the world of telecommunications,.
The use and demand for optical fiber, the only way to guarantee huge amounts of bandwidth, have grown exponentially, as well as applications and services (voice, data, video) widespread in our daily lives.
The constant demand of Internet to transport high-capacity data dragged many "just born" inventions out of the labs and directly applied "in the field", many of them improved during their application.
To meet the new needs, the DWDM transmission based on EDFA reached the upper limit of capacity. The EDFA used in DWDM transmission systems are called concentrated amplifiers because the gain is concentrated at one point of the transmission line. Distributed amplifiers, Raman amplifiers such as, but amplify the signal over a long distance transmission line, using the fiber as a means of boosting.
The use of Raman distributed amplification fiber can improve the signal to noise ratio and reduce the impact of nonlinearity on the performance of transmission systems. But there are some problems concerning the phenomenon described: the Rayleigh backscattering that occurs when the light is elastically reflected from inhomogeneities of the optical fiber of the amount of a sub-micron. This can be separated into two main effects: a reflection that propagates back toward the propagation direction, called Simple Rayleigh Backscattering (RBS) and reflection that propagates in the same direction of propagation itself, called Double Rayleigh Backscattring (DRB). This implies a fundamental limit to the gain Raman amplification can provide.
In literature, therefore, the Rayleigh back scattering was always seen as a phenomenon that degrades the performance of Raman amplifier in two ways: degradation of the signal to noise ratio due to the simple Rayleigh backscattering and interference by double Rayleigh backscattering due to multipath.
In the presented work we wanted to take advantage of this "apparently damaging phenomenon" to demonstrate the ability to obtain Raman amplification in the C band (1530-1565 nm), L (1565-1625 nm) and far in U (1625-1675 nm) with a simple and new approach based on standard optical components.
The first chapter shows the current state of the optical network with related systems and components. Pros and Cons of introducing the optical amplifiers used as Raman amplification are also analyzed.
The second chapter describes the scattering and Raman amplification emphasizing the fundamental theory and applications. They also analyzed the various aspects of noise and bias.
In the third chapter is an account of experiments conducted in the laboratories of Optical Communications Institute of Communications and Information Technology (ISCOM), a body of the Italian Ministry of Communications Research.
Performance has been tested on the Rome-Pomezia cable using 100 km of fiber-Step Reduced (SR) with excellent results in terms of Q factor and eye diagram.
The use of this cable is of fundamental importance because it allowed the verification of the proper functioning of the system on a real DWDM link.