Nonlinear Pulse Reshaping in Optical Fibers

The propagation of ultrashort laser pulses in the optical fibers is connected with a plenty of interesting and practically important phenomena. Unique dispersive and nonlinear properties of the optical fibers lead to various scenarios of the pulse evolution which are resulted in particular changes of the pulse shape, spectrum and chirp. The modern age of the optical fibers starts from the 1960s with the appearance of the first lasers. These fibers were extremely lossy but new suggestion on the geometry with the single mode operation (Kao et al., 1966) which was obtained by theoretical calculations based on the Maxwell’s equations, and the development of a new manufacturing process (French et al., 1974) have led to the achievement of the theoretical minimum of the loss value 0.2 dB/m (Miya et al., 1979). The investigations of the nonlinear phenomena in the optical fibers have been continuously gained by the decreasing loss. Loss reduction in the fibers made possible the observation of such nonlinear processes which required longer propagation path length at the available power levels in the 1970s. Stimulated Raman Scattering (SRS) and Brillouin scattering (SBS) were studied first (Ippen et al., 1972). Optical Kerr-effect (Stolen et al., 1973), parametric four-wave mixing (FWM) (Stolen et al., 1974) and self-phase modulation (SPM) (Stolen et al., 1978) were observed later. The theoretical prediction of the optical solitons as an interplay of the fiber dispersion and the fiber nonlinearity was done as early as 1973 (Hasegawa et al., 1973) and the soliton propagation was demonstrated seven years later in a single mode optical fiber (Mollenauer et al., 1980). Discovery of the optical solitons have revolutionized the field of the optical fiber communications. Nowadays solitons are used as the information carrying ‘‘bits’’ in optical fibers (Hasegawa et al., 2003). This is resulted from unique properties of the solitons. In general, the temporal and spectral shape of a short optical pulse changes during propagation in a medium due to the self-phase modulation and chromatic dispersion. This actually limits the transmission bit rate in optical fibers. Under certain circumstances, however, the SPM and dispersion can exactly cancel each other producing a self-localized waveform called the solitary wave. Due to the particle-like nature of these solitary waves during mutual interactions they were called solitons. Solitons are formed when GVD is