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Journal of Experimental and Theoretical Physics Letters

Transient and steady-state properties of asymmetric semiconductor quantum wells at telecom wavelength bands

Hamid Reza Hamedi

Published Sep 1, 2014• 5 citations
Publisher

Abstract

The transient and steady-state dispersion and absorption properties of a three-subband asymmetric semiconductor quantum well system are investigated. In the steady-state regime, it is shown that by increasing the strength of Fano-interference as well as enhancement of energy splitting of two excited states the slope of dispersion changes from negative to positive which is corresponding to a switch between superluminal to subluminal light propagation. At the same time, the probe absorption reduces at telecommunication wavelength λ = 1550 nm. The influence of incoherent pumping fields on time-dependent susceptibility is then discussed. It is found that due to more transfer of population to the upper levels, increasing the rate of incoherent pump field leads to the reduction of probe absorption. In addition, it is realized that incoherent pumping has a major role in converting fast to slow propagation of light at long wavelength. We also introduce an extra controllability for the light pulse to be slow downed at Telecom wavelength just through the quantum interference arising from incoherent pumping fields. The obtained results may be practical in telecommunication applications.

DOI
10.1134/s0021364014130049

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The transient and steady-state dispersion and absorption properties of a three-subband asymmetric semiconductor quantum well system are investigated. In the steady-state regime, it is shown that by increasing the strength of Fano-interference as well as enhancement of energy splitting of two excited states the slope of dispersion changes from negative to positive which is corresponding to a switch between superluminal to subluminal light propagation. At the same time, the probe absorption reduces at telecommunication wavelength λ = 1550 nm. The influence of incoherent pumping fields on time-dependent susceptibility is then discussed. It is found that due to more transfer of population to the upper levels, increasing the rate of incoherent pump field leads to the reduction of probe absorption. In addition, it is realized that incoherent pumping has a major role in converting fast to slow propagation of light at long wavelength. We also introduce an extra controllability for the light pulse to be slow downed at Telecom wavelength just through the quantum interference arising from incoherent pumping fields. The obtained results may be practical in telecommunication applications.
Abstract: A theoretical investigation is carried out into the impact of incoherent pumping fields and quantum interference induced by incoherent pumping fields on the Kerr nonlinearity in a three-level asymmetric semiconductor quantum well system. It is found that Kerr nonlinearity is so sensitive to the rate of incoherent pumping fields, but insensitive to the quantum interference induced by incoherent pumping fields. In addition, it is demonstrated that an enhanced Kerr nonlinearity with reduced absorption can be achieved just via the strength of Fano- type interference and without applying any coherent laser field. The obtained results are very different from the conventional schemes which coherent coupling fields are used to control the Kerr nonlinearity. This advantages make our electronic medium much more practical than its atomic counterpart due to its flexible design and the controllable interference strength.
The transient and steady-state behaviour of the absorption and the dispersion of a probe field propagating at λ = 1.55 μm 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. The linear dynamical properties of the double coupled quantum well by means of perturbation theory and density matrix method are discussed. 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. 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.
Abstract In this paper, we investigate the absorption and dispersion properties of a weak probe field in a triple quantum well nanostructure by using the incoherent pumping fields. A deep 7.1 nm-thick GaAs well is coupled, on one side, to two shallow 6.8 nm-thick Al 0.2 Ga 0.8 As wells by a 2.5 nm-thick Al 0.4 Ga 0.6 As barrier. The two shallow wells are separated by a 2.0 nm-thick Al 0.4 Ga 0.8 As barrier. Both sides of quantum well contact with 36 nm Al 0.4 Ga 0.6 As. Therefore, this type of triple quantum well nanostructure can be used as a suitable medium for studying the effect of spontaneously generated coherence (SGC) and interference between incoherent pumping fields on absorption and dispersion properties of weak probe light. We find that the interferences from spontaneous emission and incoherent pumping processes can change the slope of dispersion and group velocity of the probe light from slow to fast or vice versa. Moreover, it is demonstrated that the group velocity of the light pulse can be controlled with the rates of incoherent pumping fields.
We investigate the strength of Fano interference effects on the probe absorption spectra in asymmetric semiconductor quantum wells driven coherently by a probe laser field. We find that the probe absorption can be dramatically reduced due to the strength of the Fano interference, and the effect of the energy splitting on the probe absorption is also discussed. Our study is much more practical than its atomic counterpart due to its flexible design and the controllable interference strength. Thus it may provide some possibilities for technological applications in optoelectronics and solid-state quantum information science.
The transient and steady-state behavior of the absorption and the dispersion of a probe pulse laser field propagating through an InGaAs\InP double coupled quantum well are studied. The effect of terahertz radiation excitation, electron tunnelling and incoherent pumping on the optical properties of the probe field is discussed. In the terahertz (30~300 μm or 1~10 THz) intersubband transition, the incoming photon energy is (4~41 mev) 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 and this process inhabits the correct optical switching in terahertz applications. 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 and tunnelling between the quantum wells. The required switching time is calculated and we find it between 3 to 26 picoseconds.