  A system with a topological insulator slab sandwiched by two one-dimensional
photonic crystals as a defect is investigated. A giant topological
magnetoelectric effect is proposed which is characterized by two resonant peaks
with half-unit transmissions and rich polarization behaviors in the photonic
band gap. We also predict a giant optical Hall effect in our system, in which
the transverse shift of the transmitted light could be thousand times larger
than the wavelength. These effects are purely from the $\Theta$-domain walls at
the topological insulator interfaces and could be observed easily. These
effects can also be used as the sensitive detection of basic physical
constants.
