Yueping Niu

Electromagnetically induced grating in asymmetric quantum wells via Fano interference

We propose a scheme for obtaining an electromagnetically induced grating in an asymmetric semiconductor quantum well (QW) structure via Fano interference. In our structure, owing to Fano interference, the diffraction intensity of the grating, especially the first-order diffraction, can be significantly enhanced. The diffraction efficiency of the grating can be controlled efficiently by tuning the control field intensity, the interaction length, the coupling strength of tunneling, etc. This investigation may be used to develop novel photonic devices in semiconductor QW systems.

Realization of cavity linewidth narrowing via interacting dark resonances in a tripod-type electromagnetically induced transparency system

Cavity linewidth narrowing via double-dark resonances is experimentally observed using the Rb87 Zeeman splitting sublevels. With the steep dispersion led by the interacting dark resonances in the tripod-type electromagnetically induced transparency system, we narrow the cavity linewidth to 250xa0kHz at room temperature. Furthermore, the position of this ultranarrow cavity linewidth can be tuned in a 60xa0MHz coupling field detuning range.

Observation of multi-electromagnetically induced transparency in V-type rubidium atoms

A detailed experimental investigation and theoretical analysis have been made in the V-type Rb atomic medium. Seven induced transparency windows, including a central double-peak-structure, have been observed experimentally when a coupling field and a probe field are applied into the ground and first excited states. By taking into account the hyperfine splitting of the excited state, our theoretical analysis gives good explanation for the observed phenomena.

Cavity linewidth narrowing by optical pumping-assisted electromagnetically induced transparency in V-type rubidium at room temperature

A tunable high resolution frequency reference is constructed using the narrowed cavity-linewidth by the optical pumping-assisted V-type electromagnetically induced transparency (EIT). At room temperature, the optical pumping effect will increase the transparency for the V-type EIT and therefore the cavity-linewidth can be narrowed apparently. For the seven EITs observed in our previous study, cavity-linewidth narrowing is observed in all of them. More importantly, we find that the cavity-linewidth can keep at 1.2MHz in a wide frequency range of 100MHz by utilizing the central EIT. This property provides a novel way for constructing high resolution tunable frequency reference via the intracavity EIT.A detailed experimental investigation is made in the intracavity V-type electromagnetically induced transparency (EIT) of the Rb atomic medium at room temperature. The optical pumping effect will increase the transparency for the V-type EIT at room temperature and therefore the cavity linewidth can be narrowed apparently. For the seven EITs observed in our previous study, cavity linewidth narrowing is observed in all of them. More importantly, we find that the cavity linewidth can keep at 1.2 MHz over a wide frequency range of 100 MHz by utilizing the central double-peak-structure EIT. This property provides a novel way for constructing a high resolution tunable frequency reference via the intracavity EIT.

Laser frequency offset locking via tripod-type electromagnetically induced transparency.

We have demonstrated laser frequency offset locking via the Rb87 tripod-type double-dark resonances electromagnetically induced transparency (EIT) system. The influence of coupling fields power and detuning on the tripod-type EIT profile is studied in detail. In a wide coupling fields detuning range, the narrower EIT dip has an ultranarrow linewidth of ∼590u2009u2009kHz, which is about one order narrower than the natural linewidth of Rb87. Without the additional frequency stabilization of the coupling lasers, we achieve the relative frequency fluctuation of 60 kHz in a long time of ∼2000u2009u2009s, which is narrower than the short-time linewidth of each individual laser.

Controllable twin laser pulse propagation and dual-optical switching in a four-level quantum dot nanostructure

We investigate control of the propagation dynamics of weak twin laser pulses and propose a dual-optical switching scheme in four-level semiconductor quantum dots of diamond configuration. It is shown that the propagation dynamics of the two probe pulses depend not only on the intensity of corresponding control field in each cascade transition path but also on the relative intensities of the two control fields. This property provides the probability for realizing all-optical switching in the quantum dots. Possible all-optical switching operations for any one of the probe fields or both probe fields simultaneously with the same or adverse switching status can be realized by modulating the corresponding control fields. In addition, the relative phase of the laser fields also influences the switching operation and can be used to realize optical switching, which is also discussed in the paper.

Reversible self?Kerr nonlinearity in an N-type atomic system through a switching field

We investigate the self-Kerr nonlinearity of a four-level N-type atomic system in 87Rb and observe its reversible property with the unidirectional increase of the switching field. For the laser arrangement that the probe field interacts with the middle two states, the slope and the sign of the self-Kerr nonlinearity around the atomic resonance can not only be changed from negative to positive, but also can be changed to negative again with the unidirectional increasing of the switching field. Numerical simulation agrees very well with the experimental results and dressed state analysis is presented to explain the experimental results.

Surface plasmon-assisted optical bistability in the quantum dot-metal nanoparticle hybrid system

We theoretically investigated optical bistability (OB) of a coupled excition–plasmon hybrid system in a unidirectional ring cavity. It is found that the threshold and the region of OB can be tuned by adjusting the center–center distance between the quantum dot and metal nanoparticle (MNP), the Rabi frequency of the control field and the radius of the MNP. Due to the significantly enhanced optical nonlinearity by the surface plasmon effect, the threshold of OB can be decreased greatly when the probe field is parallel to the major axis of the hybrid system. The enhanced OB may have promising applications in optical switching and optical storage.

Guiding light by the modulated electromagnetically induced transparency

We propose a scheme for guiding light by the modulated electromagnetically induced transparency (EIT) in a three-level atomic system. By using a periodically modulated control field, the linear and nonlinear susceptibilities are changed cyclically for the probe field, which results in the deflection of propagation direction of the probe beam. Propagation direction/path and output position of the probe soliton in the modulated EIT medium can be controlled precisely via adjusting the modulation period of the control field. By changing its initial amplitude, the probe beam can also be guided to a desired output position in the atomic system, driven by a periodic control field. These properties offer a novel way of soliton control, based on the modulated EIT effect.

All-optical signal amplifier and distributor using cavity–atom coupling systems

We report an all-optical signal amplifier and a signal distributor using cavity–atom coupling systems. In this system we couple atoms with an optical cavity and realize the great enhancement of a control laser by the cavity with the help of two high coupling lasers. By this effect, we can use one weak control field to control another strong target field and the intensity changes are linear with our experimental conditions. This can be used as an all-optical signal amplifier, also known as a transphasor. In our experiment, the gain of the weak field to strong field can be as high as 60. Furthermore, we can realize the distribution of optical signals, if we coordinate multiple cavity–atom coupling systems.