  We introduce a weakly coupled photonic crystal waveguide as a promising and
realistic model for all-optical amplification. A symmetric pillar type coupled
photonic crystal waveguide consisting of dielectric rods periodically
distributed in a free space is proposed as all-optical amplifier. Using the
unique features of the photonic crystals to control and guide the light, we
have properly chosen the frequency at which only one mode (odd mode) becomes
the propagating mode in the coupled photonic crystal waveguide, whereas another
mode (even mode) is completely reflected from the guiding structure. Under this
condition, the all-optical amplification is fully realized. The amplification
coefficient for the continuous signal and the Gaussian pulse is calculated.
