Jun Kou

Magneto-optical switching and routing via coherently induced photonic band gaps in a driven Fe = 0↔Fg = 1 transition

In an Fe = 0↔Fg = 1 transition interacting with a weak π-polarized probe and a strong σ-polarized standing-wave coupling, we obtain single or double photonic band gaps depending on the applied magnetic field. Moreover, the coherently induced two-photonic-band gap structure can be tuned by the magnitude of the magnetic field. Such a magnetic-field-dependent feature is exploited to devise magneto-optical switching and routing of two light pulses. The efficient magneto-optical control of light propagation may have applications in an optical network and optical information processing.

Controlled light-pulse propagation via dynamically induced double photonic band gaps

We analyze the optical response of a standing-wave driven four-level atomic system with double dark resonances. Fully developed double photonic band gaps arise as a result of periodically modulated refractive index within the two electromagnetically induced transparency widows. We anticipate that the dynamically induced band gaps can be used to coherently control the propagation of light-pulses with different center frequencies and may have applications in all-optical switching and routing for quantum information networks.

Tunable double photonic bandgaps in a homogeneous atomic medium

Double photonic bandgaps (PBGs) can simultaneously appear when double dark resonances in uniform cold atoms are spatially modulated by a resonance standing-wave. Theoretical calculations show that variable and efficient coherent optical control of the PBGs can be achieved by modulating the coupling field and standing-wave. The structures of double PBGs induced by the atomic coherence effect are better than those obtained in the photonic crystal heterostructures. We anticipate that this scheme has potential applications in optical networks for dual-channel all-optical switching or a dual-frequency optical Bragg reflector.

Switching from subluminal to superluminal light propagation via a coherent pump field in a four-level atomic system

We theoretically investigate the influence of a coherent pump field on the propagation of a weak light pulse of a probe field in a four-level atomic system. Due to the modulation of the pump field, the light pulse can be manipulated from subluminal to superluminal with negligible distortion. This scheme can be realized in both the ultracold and Doppler-broadened atomic systems. We also demonstrate that the spectral linewidth with an anomalous dispersion is reduced by thermal averaging; therefore, one can obtain a larger negative group refractive index in room-temperature vapor than the largest value achieved in ultracold atomic gas.