The non-linear effects of organic based crystals in which the Frenkel type
of excitons are realized were studied. Using the non-equilibrium Green func
tion method it is shown that significant non-linearities can arise in such
type of crystals at moderate pump intensities owing to interaction of excit
ons. The study of transmission the intensive quasiresonant electromagentic
wave by crystal showed that at natural (non-linear) boundary condition the
multistability effects can arise with very sharp and big change of transmis
sion. The switching devices similar to optical key can be realized. (C) 199
9 Elsevier Science B.V. All rights reserved.