  It is shown that inhomogeneous broadening of the spectral line of active
impurities may sustain simultaneously parity (P) and time (T) symmetries of a
medium, in a finite range of field frequencies, what is forbidden by the
causality principle in media without broadening. If a spectral width of a
propagating pulse is less than the inhomogeneous broadening, the medium for
such a pulse becomes quasi-PT symmetric. The effect of the broadband quasi-PT
symmetry in a finite frequency domain, is illustrated on examples of
unidirectional diffraction of pulses in Bragg and Laue geometries, propagating
in photonic crystals.
