Transparency due to dipole-dipole interaction in photonic crystals doped with nanoparticles

In this paper, we have studied the two-photon absorption process in photonic crystals doped with four-level nanoparticles. It is considered that all the levels of the particles are interacting with the photonic crystal. The decay linewidths of all the four levels are included in the calculations of two-photon absorption process. The effect of the dipole-dipole interaction has also been included in the formulation. Numerical simulations have been performed for the two-photon absorption spectrum on an isotropic photonic crystal. It is found that the system switches between the transparent and the nontransparent states due to the dipole-dipole interaction. The phenomenon of switching depends on the linewidths of these states.