Comments on "Switching dynamics of short optical pulses in a nonlinear directional coupler"

For original paper see Shum et al., ibid., vol.31, p.190-200 (1995). Shum et al. presented a study of the effects of a dispersive coupling coefficient on the switching dynamics of short optical pulses in a nonlinear two-core directional coupler, in which the authors used the Fourier series analysis method. Xiaoguang Zhang repeats the work using the so-called modified version of the split-step Fourier method. The results were in agreement with the paper by Shum et al. when the dispersive coupling coefficient was R'=0. On the other hand, when the coupling-coefficient dispersion was taken into account, i.e., R'/spl ne/0, the results were just the mirror inversion of those of the paper by Shum et al. in the time domain.