FEATURES OF THE PROPAGATION AND INTERACTION OF OPTICAL SIGNALS IN SINGLE-FIBER TRANSMISSION-SYSTEMS WITH WAVELENGTH-DIVISION MULTIPLEXING

The problems that arise when designing highly efficient long-distance optical communications lines have been widely discussed in the scientific journals, both in this country and abroad. Each fiber in the cables should be used as completely as possible. The use of optical-fiber transmission systems with wavelength division multiplexing for long-distance communications enables their carrying capacity to be increased considerably [11]. To obtain high technical and economic efficiency it is best to use the duplex method of data transmission on several optical carriers using a single monomode optical fiber [8], employing semiconductor lasers with a high emission power, with the optical carriers situated in one of the transparency windows of the optical fiber. However, as results of numerous investigations have shown [1-13], the relatively high optical power densities in the fiber give rise to considerable nonlinear effects. In an optical-fiber transmission system with wavelength division multiplexing the effect of amplification due to Raman scattering, which arises as a result of resonance interaction between the optical carriers and optical phonons of the fiber material [1-12], has the greatest effect. As a result of the Raman effect in monomode optical fibers, ''interaction'' is observed between the optical signals of different optical channels. This manifests itself as a reduction in the powers of the optical carriers with shorter wavelengths and a corresponding increase, as a result of this, in the power of the optical carriers with longer wavelengths, which, in the final analysis, distorts the form of the optical-signal envelopes. In this paper we present the results of investigations of the interaction between oppositely propagating optical carriers which occurs when single-fiber optical-fiber transmission systems with wavelength division multiplexing are employed. The results obtained are important when designing the linear channel of these systems.