  We discuss a simple, linear, zero-delay implementation of spectral shearing
interferometry for amplitude and phase characterization of optical frequency
comb sources and arbitrary waveforms. We demonstrate this technique by
characterizing two different high repetition rate (~10 GHz) frequency comb
sources, generated respectively by strong external and intracavity phase
modulation of a continuous-wave laser. This technique is easy to implement,
requiring only an intensity modulator and an optical spectrum analyzer (OSA),
and is demonstrated to work at average power levels down to 100nW (10aJ/pulse
at 10 GHz). By exploiting the long coherence lengths of these frequency combs
and the self-referenced nature of the measurement, we also demonstrate a simple
single-ended measurement of dispersion and dispersion slope in long lengths of
fiber (>25km).
