Abstract

We propose a simple scheme for highly efficient nonlinear interaction between two weak, orthogonally polarized, optical fields. The principles of this scheme are as follows: Two weak optical fields E_a = ê_xE_a and E_b = ê_yE_b, having orthogonal linear π and σ polarizations along the ê_x and ê_y axes, respectively, propagate in the atomic medium along the ê_z axis. A single σ-polari zed driving field E_d = ê_yE_d and a static magnetic field H oriented along the ê_x axis, which removes the magnetic- sublevel degeneracy of two F = 1 atomic levels, axe applied. Two A systems, Λ_a = |1〉 ↔|4〉 ↔ |2〉 and Λ_b≡ |1〉 ↔|5〉 |3〉, sharing ground state |1〉, are simultaneously formed in the presence of E_d(ω_d) and give rise to electromagnetically induced transparency [1] for the E_a(ω_a) and E_b(ω_b) fields, respectively. Transitions |2〉 → |6〉 and 3〉 → |6〉 serve to cross-couple Λ_a and Λ_b with the ω_b and ω_a photons, respectively. Thereby, the two fields propagate in the atomic vapor with slow and equal group velocities and interact through their cross-coupling for a very long time. Under the proper conditions (discussed below), this can yield conditional cross-phase modulation [2] of the order of π along with vanishing absorption.

© 2001 EPS