  The well known Lambda-system using two ground state hyperfine levels, F=1 and
F=2 of 5S1/2 and one hyperfine level, F=2 of excited state of 5P3/2 of 87Rb has
been recently studied using two counter- propagating control lasers [1]. The
experiment shows conversion of electromagnetically induced transparency (EIT)
into electromagnetically induced absorption (EIA) because the doubly driven
Lambda-system forms various sub-systems. We here present detailed theoretical
study of the different possible sub-systems created by this configuration. We
also explore the possibility of tuning the strength of individual sub-systems
by changing the polarization of the control lasers.
