  The advantage of optical bistability (OB) using three-level
electromagnetically induced transparency (EIT) atomic system over the two-level
system is its controllability, as absorption, dispersion, and optical
nonlinearity in one of the atomic transitions can be modified considerably by
the field interacting with nearby atomic transitions. This is due to induced
atomic coherences generated in such EIT system. The inclusion of near
dipole-dipole (NDD) interaction among atoms further modifies absorption,
dispersion, and optical nonlinearity of three-level EIT system and the OB can
also be controlled by this interaction, producing OB to multistability.
