Probe field amplification without population inversion in a one-dimensional photonic crystal (1DPC) doped by
four-level rare-earth ions is proposed. By controlling the intensity of the coupling field, probe field absorption
with population inversion converts to probe field amplification without population inversion. It is found that the
amount of probe field amplification through the photonic crystal doped by rare-earth ions is larger than the
probe field amplification for the same ions in free space. For a particular coupling field intensity, i.e. Ωc = 5.1Γ,
the probe field absorption converts to probe field amplification just by manipulating the probe field detuning.