  The coupling between the electromagnetic and gravitational fields results in
"faster than light" photons and invalids the Lorentz invariance and some laws
of physics. A typical example is that the first and third laws of geometric
optics are invalid in the usual spacetime. By introducing an effective
spacetime, we find that the wave vector can be casted into null and then it
obeys the geodesic equation, the polarization vector is perpendicular to the
rays, and the number of photons is conserved. That is to say, the laws of
geometric optics are still valid for the modified theory in the effective
spacetime. We also show that the focusing theorem of light rays for the
modified theory in the effective spacetime takes the same form as usual.
