  A large number of new "black widow" and "redback" energetic millisecond
pulsars with irradiated stellar companions have been discovered through radio
and optical searches of unidentified \textit{Fermi} sources. Synchrotron
emission, from particles accelerated up to several TeV in the intrabinary
shock, exhibits modulation at the binary orbital period. Our simulated
double-peaked X-ray light curves modulated at the orbital period, produced by
relativistic Doppler-boosting along the intrabinary shock, are found to
qualitatively match those observed in many sources. In this model, redbacks and
transitional pulsar systems where the double-peaked X-ray light curve is
observed at inferior conjunction have intrinsically different shock geometry
than other millisecond pulsar binaries where the light curve is centered at
superior conjunction. We discuss, and advocate, how current and future optical
observations may aid in constraining the emission geometry, intrabinary shock
and the unknown physics of pulsar winds.
