The Dicke effect is examined in an all-optical system of an optical waveguide side coupled to two interacting ring resonators in a liquid crytal environment. The system is shown to exhibit all the signatures of the Dicke effect under an active and reversible control by an applied voltage.
Ability to tune the group velocity of a light pulse is of great importance for optical communication applications and realization of quantum information processing. Tunability of group velocity can be achieved by using either optical or electronic resonances. Tunability of an optical resonance depends on the change in refractive index of the cavity material. However, since electro-optical coefficients of non-engineered materials are quite small, the tuning range of optical resonances by electric field is narrow. This makes tuning by electric field impractical for most applications. Quantum dot (QD) coupled to a photonic crystal cavity is a useful hybrid system exhibiting nonlinear features. In this work, we analyze the use of quantum dot - optical cavity hybrid systems to engineer nonlinear waveguides susceptible to electric fields. We start by theoretically analyzing the optical pulse propagation at low-photon number excitation limit in a periodically arranged strongly coupled quantum dot - photonic crystal system. A one dimensional periodic array of evanescently coupled photonic cavities (coupled resonator optical waveguides, CROWs) containing non-interacting quantum dots allows us to tune the group velocity and the bandwidth of the pulse by adjusting the cavity/QD coupling. Tunable group velocity can be achieved by applying an external electric field which will result in a significant decrease in the cavity/QD coupling because of DC Stark effect. We also show that, using this approach, light pulses can be slowed down or stored by compressing the pulse bandwidth adiabatically and reversibly. Adiabatic bandwidth compression can be achieved by slowly decreasing the coupling strength when the light pulse is inside the coupled resonator optical waveguide. The energy splitting and the coupling constant after applying electric field is calculated by using perturbation theory for two level systems. With our approach, nonlinear materials highly susceptible to electric fields can be engineered in low-excitation regime.
We investigate the electrically tunable Electromagnetic induced transparency (EIT)-like effect of active metamaterial structures composed of a wire and a split ring resonator by the simulation, experiment, and temporal coupled-mode theory. It is illustrated that an EIT-like effect appears as a result of weak coupling between bright and dark resonators. Around the EIT-like peak frequency, the superradiant resonance mode of the bright resonator is highly suppressed by the subradiant resonance mode of the dark resonator, and high transmittance as well as large group delay is manifested. By integrating a varactor diode into the EIT structure and altering the bias voltage, the EIT-like effect can be dynamically tuned. As the bias voltage ranges from 0 V to 8 V, the EIT-like peak frequency exhibits a prominent blueshift of 0.22 GHz and the transmittance experiences a modulation with a modulation depth up to 98%. Using the temporal coupled-mode theory, the transmission spectrum of the EIT structure is predicted and the parameters of the resonator system are retrieved.