  In the presence of strong magnetic fields, the vacuum becomes a birefringent
medium. We show that this QED effect couples the direction of the polarization
of photons leaving the NS surface, to the direction of the magnetic field along
the ray's path. We analyze the consequences that this effect has on aligning
the polarization vectors to generate large net polarizations, while considering
thermal radiation originating from a thermal hydrogen atmosphere. Counter to
previous predictions, we show that the thermal radiation should be highly
polarized even in the optical. When detected, this polarization will be the
first demonstration of vacuum birefringence. It could be used as a tool to
prove the high magnetic field nature of AXPs and it could also be used to
constrain physical NS parameters, such as $R/M$, to which the net polarization
is sensitive.
