  The analysis of optical pulse generation by phase modulation of narrowband
continuous-wave light, and subsequent propagation through a
group-delay-dispersion circuit, is usually performed in terms of the so-called
bunching parameter. This heuristic approach does not provide theoretical
support for the electrooptic flat-top-pulse generation reported recently. Here,
we perform a waveform synthesis in terms of the Fresnel images of the
periodically phase-modulated input light. In particular, we demonstrate
flat-top-pulse generation with a duty ratio of 50% at a quarter of the Talbot
condition for the sinusoidal phase modulation. Finally, we propose a binary
modulation format to generate a well-defined square-wave-type optical bit
pattern.
