turation power of -5 dBm. Moreover, the lifetime of the excited molecules is on the order of the input pulse duration. From the figure, the effect of dynamic gain saturation and the consequent distortion of the output pulse is evident. This distortion, as it can be appreciated from the figure, creates much steeper growing front of the pulse with respect to the input pulse. If the pulse were Technology for Telecommunications: Optical Fibers, Amplifiers, and Passive Devices TABLE 4.7 Parameters for the Two-Level Amplifier Used in the Quantitative Examples of This Section -5.21390228 dBm 5.00E-02W 20 dB 1.00E-09s Pulse envelope (mW) Output Input FIGURE 4.15 Distortion of the pulse at the output of an ideal two- 50 ns level amplifier with the lifetime of the excited state of the same order of the pulse duration. destined to be detected after filtering, part of the power will be rejected by the detection filter due to its high-frequency collocation. Let us now imagine that a pulse train is modulated SO that a pulse represents a bit "one" and the absence of a pulse a bit "zero." In the absence of a pulse, the signal level is assumed constant and very small. In Figure 4.16, the effect of an amplification of such a signal with an amplifier with a lifetime smaller than the bit time is shown. In this case, the bit time is 5ns (corresponding to a bit rate of 200 Mbit/s) and the amplifier lifetime is 1 ns. Moreover, the amplifier works again in deep saturation, with a pulse peak power of 50 mW. FIGURE 4.16 Dynamic range reduction of a return-to-zero (RZ) signal passing through an ideal amplifier with the lifetime of the excited state of the same order of the Time (ns) bit duration. Telecommunication Networks FIGURE 4.17 Instantaneous power of the optical wave after narrowband filtering around the shortest wavelength signal when two signals that are 0GHz distant in frequency are injected into an ideal amplifier; both the signals are amplitude mod- ulated with a train of pulses at 100 Mbit/s. The effect of the amplifier dynami