Propagation of single-mode 1.5-μm gain-switched semiconductor laser pulses in normally dispersive fibers

The behavior of gain-switched semiconductor laser pulses propagating in normally dispersive fibers is analyzed both theoretically and experimentally. A simple gain switch model is analytically derived from rate equations including gain compression effects in order to predict the instantaneous optical intensity and frequency during the pulse. A great deal of attention is given to the phase equation. It is shown that carrier dependence of the phase-amplitude coupling factor α must be taken into account to accurately describe experiments. By means of an Er³⁺ doped amplifier, nonlinear propagation of such pulses in normally dispersive fibers is experimentally studied for various peak powers up to 3.2 W. Large Kerr-induced spectrum narrowing is demonstrated together with the production of pulses of adjustable width from 3 to 12 ps. Corresponding time-bandwidth products measured between 0.4 and 0.8 are close to the Fourier transform limit. These results are successfully compared to theory by means of computer simulation involving both the gain-switch model and the nonlinear propagation in the fiber