Abstract
We present a convenient way to obtain an optical power limiting behavior in a quantum dot molecule system, induced by an interdot tunneling. Also, the effect of system parameters on the limiting performance is investigated; interestingly, the tunneling rate can affect the limiting performance of the system so that the threshold of the limiting behavior can be a function of the input voltage, allowing the optimization of the limiting action. Furthermore, by investigating the absorption of the probe field, it is demonstrated that the optical limiting is due to a reverse saturable absorption mechanism; indeed, analytical results show that this mechanism is based on a cross-Kerr optical nonlinearity induced by the tunneling. Additionally, the limiting properties of the system are studied by using a Z-scan technique.
Highlights
We present a convenient way to obtain an optical power limiting behavior in a quantum dot molecule system, induced by an interdot tunneling
One of the mechanisms that may lead to a nonlinear absorption effect is reverse saturable absorption (RSA), referred to as excited-state or two-photon absorption, in which the absorption cross section from excited-state energy levels is significantly higher than the ground-state absorption cross s ection[4,8,13]; RSA, being one of the major optical limiters (OLs) mechanism, has been reported for applications in efficient OLs14–20, with compounds such as organic and inorganic m aterials[21,22], liquid c rystal23, nanocomposites24, nanoparticles[25] and thin film[26]
We present a convenient way to generate an optical power limiting in a four-level quantum dot molecule (QDM) system being induced by the interdot tunneling which can be controlled by applying a gate voltage
Summary
Let us consider a couple of lateral self-assembled (In,Ga)As/GaAs quantum dots with different band structures; the self-assembled lateral QDMs can be produced by the combination of molecular beam epitaxy and atomic layer precise in situ etching on GaAs(001) substrates, which can provide a low density about 5 × 107 cm−2 homogeneous ensemble of QDMs consisting of two dots aligned along the [11 ̄0] direction[44]. The state |2 shows a state that an electron is excited to the conduction band in one of the QDs to generate an exciton in such a way that the other QD does not excited. The electron transfers to the conduction band of the second QD, via the interdot tunneling, to generate an indirect exciton which is shown by the state|3. We assume that a coupling laser field of frequency ωc (with Rabi frequency c ) is applied on the transition |2 ↔ |1 while, the transition |4 ↔ |3. Note that the interdot coupling occurs only for two nearly degenerate quantum states, which can be prepared by applying an external static gate voltage to the QDMs. The Rabi frequencies of the coupling and probe fields, respectively, are c = Ecμ21/ħ and p = Epμ43/ħ , with μij being as the dipole momentum matrix element from|i to|j. Throughout the paper, the tunneling detuning is assumed to be zero or negligible in such a way that the system can have a stationary steady-state
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