Eur. Phys. J. D 55, 99-109 (2009)
https://doi.org/10.1140/epjd/e2009-00233-3

Dynamics of coupled ultraslow optical solitons in a coherent four-state double-Λ system

¹ Department of Physics, Zhejiang Normal University, 321004 Jinhua, Zhejiang, P.R. China
² Electron and Optical Physics Division, NIST, Gaithersburg, 20899 Maryland, USA
³ State Key Laboratory of Precision Spectroscopy, and Department of Physics, East China Normal University, 200062, Shanghai, P.R. China

Corresponding author: ^a hjli@zjnu.cn

Received: 30 April 2009
Revised: 16 June 2009
Published online: 15 August 2009

Abstract

We present a systematical investigation, both analytical and numerical, on the dynamics of two nearly lossless and distortion-free weak nonlinear optical pulses in a cold, lifetime-broadened four-state double-Λ system via electromagnetically induced transparency. Starting from the equations of motion of atomic response and probe fields, we give a detail derivation of two coupled nonlinear Schrödinger equations that control the nonlinear evolution of two probe field envelopes by means of a standard method of multiple-scales. We show that stable optical solitons with very slow propagating velocity can be generated under very low input light intensity when working in the transparency window of probe absorption spectrum induced by two continuous-wave control fields. We demonstrate that coupled optical soliton pairs are possible in the system through cross-phase modulational instability and mutual trapping effect of solitons. We provide various coupled optical soliton pair solutions explicitly and analyze their stability numerically.