ANALYTICAL EVALUATION TECHNIQUE OF SELF-PHASE-MODULATION EFFECT ON THE PERFORMANCE OF CASCADED OPTICAL AMPLIFIER SYSTEMS

We propose an approximate analytical evaluation technique of Self-Phase-Modulation (SPM) in cascaded optical amplifier systems. The effect of SPM on optical pulse distortion is represented by the increase in the alpha-parameter of the transmitter. The waveform distortion is approximated by assuming that the pulse is transmitted over a dispersive fiber without nonlinearity. This technique greatly reduces the calculation time, and is especially useful in designing cascaded amplifier systems, evaluating theoretical maximum transmission distance, and so on. Also, this technique is applicable to a wide range of parameters such as amplifier output power and dispersion, even in dispersion shifted fiber (DSF) and non-dispersion shifted fiber (NDSF). It can handle the nonuniformity of system parameters in a system, such as the variation of dispersion values along the transmission fiber, non-equal amplifier spacing, and differences in amplifier output powers. In this paper, we derive an expression for the alpha-parameter alpha(SPM), which represents the magnitude of nonlinear waveform distortion, and we show the accuracy of our technique. We give three examples of applications of this technique: 1) Derivation of theoretical maximum transmission distance of cascaded amplifier systems with nonnegligible SPM, 2) statistical evaluation of transmission distance when fiber dispersion values are random, and 3) dispersion compensation characteristics. To our knowledge, they are the first analytical evaluations of these applications.