  Square-wave pulse generation with a variable duty ratio can be realized with
the help of ideas of Talbot array illuminators formulated for binary phase
gratings. A binary temporal phase modulation of CW laser field propagating
through a group-delay-dispersion circuit of the fractional Talbot length $P/Q$
results in a well defined sequence of square-wave-form pulses. When $P=1$ a
duty ratio of the pulses $D$ is $1/2$ for $Q=4$ and $1/3$ for $Q=3$ and 6.
Maximum intensity of the pulses doubles and triples compared to the CW
intensity for $D=1/2$ and $1/3$, respectively. These pulses can be used for
return-to-zero laser field modulation in optical fiber communication. For
$D=1/3$ extra features between the pulses are found originating from a finite
rise and drop time of phase in a binary phase modulation. Similar effect as a
benefit of the time-space analogy is predicted for binary phase gratings and
interpreted as gleams produced by imperfect edges of the components of the
rectangular phase gratings.
