  We report that a triangular Fabry-Perot resonator filled with a parity-odd
linear anisotropic medium exhibiting the one-way light speed anisotropy acts as
a perfect diode. A Linear crystal such as the nematic liquid crystals whose
molecular structures break parity can exhibit the one-way light speed
anisotropy. The one-way light speed anisotropy also can be induced in a
non-linear medium in the presence of constant electric and magnetic field
strengths.
