Controlling the optical properties of a laser pulse at λ = 1.55μm in InGaAs\InP double coupled quantum well nanostructure

Abstract

Background: The transient and steady-state behaviour of the absorption and the dispersion of a probe field propagating at λ = 1.55μm through an InGaAs\InP double coupled quantum well are studied. The effect of terahertz signal excitation, electron tunnelling and incoherent pumping on the optical properties of the probe field is discussed. Methods: The linear dynamical properties of the double coupled quantum well by means of perturbation theory and density matrix method are discussed. Results: We show that the group velocity of a light pulse can be controlled from superluminal to subluminal or vice versa by controlling the rates of incoherent pumping field, terahertz signal and tunnelling between the quantum wells. The required switching time is calculated and we find it between 3 to 15 ps. Conclusions: In the terahertz (30 ~ 300 μm or 1 ~ 10THz) intersubband transition, the incoming photon energy is (4 ~ 41mev) and maybe in the order of electron thermal broadening (KT ~ 6 meV-25 meV for 77 K -300 K). Therefore in the conventional structure, the incoming photon can directly excite the ground state electrons to higher energy levels. It is shown that the absorption and the dispersion of the probe field can be controlled by the intensity of terahertz signal and incoherent pumping field.