Phase control of linewidth of electromagnetically induced transparency coupled by double fields

The effect of the relative phase on the spectral linewidth of electromagnetically induced transparency is studied in a Λ-type three-level configuration coupled by double coupling fields and the result is presented in this paper. We show that the relative phase between the double coupling fields has a great degree of influence on the spectral width of electromagnetically induced transparency window. The linewidth can be controlled by changing the relative phase. Particularly, as the double coupling fields have opposite phases, the linewidth of EIT window can be extremely narrow distinctly.