Aihong Yang

Ultranarrow linewidth and high gain of an optical cavity with enhanced self-Kerr nonlinearity in quantum dot molecules

The enhanced self-Kerr nonlinearity of quantum dot molecules may be used to realize optical cavities with an ultranarrow linewidth and high gain. The resonant tunneling induces constructive interference for the self-Kerr nonlinearity, and then a narrow gain window with large normal dispersion appears with frequency detuning. The competition between linear and nonlinear dispersion leads to strong normal dispersion of the total susceptibility, which significantly narrows the cavity linewidth; the nonlinear gain introduces the total gain effects contributing to high transmission. Simulation results show that the cavity linewidth could be narrowed by nearly 30 times and the transmission peak enhanced about 40 times compared with a linear case.

Enhanced cross-Kerr effect for probing tunnelling in coupled quantum dots

An efficient scheme for probing electron tunnelling is proposed based on the enhanced cross-Kerr nonlinearity in a double–dot system. Due to resonant tunnelling, the cross-Kerr nonlinearity arises in a transparency window. Its intensity is nearly two orders of magnitude greater than that of the self-Kerr effect under any given conditions, where residual absorption is suppressed due to the competition of nonlinear gain and absorption. The enhanced cross-Kerr effect is sensitive to the tunnelling, so the probe spectrum can detect subtle tunnelling changes. The simulation results show that the probe sensitivity of the nonlinear phase shift is about 0.28 rad/μeV.

Tunable, high-sensitive measurement of inter-dot transition via tunneling induced absorption

A tunable, narrow absorption spectrum induced by resonant tunneling is demonstrated and proposed for measuring interdot tunneling. Tunneling-induced absorption (TIA) arises from constructive interference between different transition paths, and the large nonlinear TIA significantly enhances the total absorption. The narrow nonlinear TIA spectrum is sensitive to inter-dot tunneling, and its sensor characteristics, including sensitivity and bandwidth, are investigated in weak-coupling and strong-coupling regimes, respectively.

Voltage-controlled optical precursors in quantum dot molecules

Abstract Optical precursors generated in a quantum-dot-molecule system by an incident square-modulated pulse are theoretically investigated. Voltage-controlled electron tunneling couples two quantum dots instead of a laser field, and a narrow transparency window appears with normal dispersion. The main pulse is delayed due to slow-light effect and the precursor pulses are obtained. We examine the linear susceptibility and find that its one part exhibits normal dispersion and the other one presents anomalous dispersion. Competition between the two parts leads to normal dispersion for the linear susceptibility, which contributes to the above results. Voltage-controlled precursors may be useful to design novel optical devices for generating precursors.

Tunneling-induced coherent perfect absorption in an optical cavity with coupled quantum wells

A scheme of tunneling-induced perfect absorption is proposed in an intracavity quantum-well (QW) system. In the linear case, the cavity transmission is found to be narrowed and weakened with respect to an empty cavity. In the nonlinear case, the resonant tunneling induces constructive interference for the nonlinear absorption, with the total absorption dramatically enhanced. For the cavity modes close to the QW resonant frequency, the cavity field can be completely absorbed, and the tunneling-induced perfect absorption (TPA) effect appears in the cavity transmission. The intensities of the control field and inter-well coupling broaden the TPA bandwidth, and the frequency detuning of the control field shifts the TPA window.

Tunneling induced absorption with competing Nonlinearities

We investigate tunneling induced nonlinear absorption phenomena in a coupled quantum-dot system. Resonant tunneling causes constructive interference in the nonlinear absorption that leads to an increase of more than an order of magnitude over the maximum absorption in a coupled quantum dot system without tunneling. Resonant tunneling also leads to a narrowing of the linewidth of the absorption peak to a sublinewidth level. Analytical expressions show that the enhanced nonlinear absorption is largely due to the fifth-order nonlinear term. Competition between third- and fifth-order nonlinearities leads to an anomalous dispersion of the total susceptibility.

Enhanced gain and narrow linewidth of an optical cavity by the Doppler effect in a four-level atomic system

Abstract A scheme for high gain and narrow linewidth of an optical cavity with a four-level atomic system is proposed by the Doppler effect via active Raman gain (ARG) process. Atomic motion leads to Doppler frequency shift which induces constructive interference for the linear susceptibility. The enhanced normal dispersion greatly narrows the cavity linewidth, and the amplified gain gives rise to a high cavity transmission. Simulation results show that the cavity linewidth based on ARG is about one order of magnitude narrower than that based on electromagnetically-induced transparency under the same conditions, and the cavity transmission intensity could be enhanced by nearly 30 times.