Byoung S. Ham

Studies of electromagnetically induced transparency in metamaterials.

We have studied electromagnetically induced transparency (EIT) in metamaterials for various schemes corresponding to those in an atomic medium. We numerically calculate a symmetric dolmen scheme of metamaterials corresponding to a tripod model of EIT-based optical switching and illustrate plasmonic double dark resonances. Our study provides a fundamental understanding and useful guidelines in using metamaterials for plasmonic-based all-optical information processing.

Electromagnetically-induced transparency and slow light in GaAs/AlGaAs multiple quantum wells in a transient regime.

Electromagnetically-induced transparency (EIT) is observed and analyzed for the group velocity of a femtosecond light pulse interacting with GaAs/AlGaAs multiple quantum wells (MQWs) in a transient regime. The calculated slowdown factor of the group velocity inside the medium due to the dynamic refractive index change is approximately 2.10 x 10(3). We discuss the potential of EIT-induced slow light in GaAs/AlGaAs MQWs for ultrafast (approximately 210 GHz) all-optical information processing such as photon routing.

Quantum manipulation of two-color stationary light: Quantum wavelength conversion

We present a quantum manipulation of a traveling light pulse using electromagnetically induced transparency-based slow light phenomenon for the generation of two-color stationary light. We theoretically discuss the two-color stationary light for the quantum wavelength conversion process in terms of pulse area, energy transfer, and propagation directions. The condition of the two-color stationary light pulse generation has been found and the quantum light dynamics has been studied analytically in the adiabatic limit. The quantum frequency conversion rate of the traveling light is dependent on the spatial spreading of the two-color stationary light pulse and can be near unity in an optically dense medium for the optimal frequencies of the control laser fields.

Observations of delayed all-optical routing in a slow-light regime

We report an observation of a delayed all-optical routing/switching phenomenon based on ultraslow group velocity of light via nondegenerate four-wave mixing processes in a defected solid medium. Unlike previous demonstrations of enhanced four-wave mixing processes using the slow light effects, the present observation demonstrates a direct retrieval of the resonant Raman-pulse excited spin coherence into photon coherence through coherence conversion processes.

Control of photon storage time using phase locking

A photon echo storage-time extension protocol is presented by using a phase locking method in a three-level backward propagation scheme, where phase locking serves as a conditional stopper of the rephasing process in conventional two-pulse photon echoes. The backward propagation scheme solves the critical problems of extremely low retrieval efficiency and pi rephasing pulse-caused spontaneous emission noise in photon echo based quantum memories. The physics of the storage time extension lies in the imminent population transfer from the excited state to an auxiliary spin state by a phase locking control pulse. We numerically demonstrate that the storage time is lengthened by spin dephasing time.

Observations of self-induced ultraslow light in a persistent spectral hole burning medium

We present observations of self induced ultraslow light in a persistent spectral hole-burning rare-earth doped crystal. The observed group delay (velocity) is as long as 40 micros (75 m/s), which is comparable to that obtained using electromagnetically induced transparency or coherent population oscillations. We analyze the observed ultraslow light as a function of frequency detuning, light intensity, and atom population (oscillator strength). The present observation of ultraslow light in a persistent spectral hole-burning medium gives potentials to all-optical information processing such as on-demand all-optical buffer memories.

Optical properties of an N-type system in Doppler-broadened multilevel atomic media of the rubidium D2 line

We report the observations of Mollow sideband-like transparency windows in a Doppler-broadened four-level N-type system of the rubidium D2 line. A pair of enhanced transparency windows across an electromagnetically induced transparency line centre results from dressed state interactions of two coupling fields. The present observations have potential applications of using the symmetric transparency windows for optical quantum information processing such as multiple optical buffer memories and double slow-light-based enhanced cross-phase modulation. We also discuss the quantum coherent control of absorption cancellation, absorption enhancement and probe gain in a closed N-type four-level model introducing the atom flow rate determined by the population decay rate and control field intensity.

Investigation of quantum coherence excitation and coherence transfer in an inhomogeneously broadened rare-earth doped solid

Quantum coherence excitation onto spin ensembles by resonant Raman optical fields and coherence transfer back to an optical emission are discussed in a three-level optical system composed of inhomogeneously broadened spins, where the spin decay time is much slower than the optical decay time. Dynamic quantum coherent control of the spin excitations and coherence conversion are also discussed at a strong coupling field limit for practical applications of optical information processing.

Detuned slow light in the Doppler broadened multi-level D2 line of Rubidium

We observed a detuned slow light phenomenon based on electromagnetically induced transparency in (87)Rb D2 line composed of multiple excited-hyperfine states within a Doppler-broadened linewidth. The results show that the maximum group delay of a probe occurs at off-detuned two-photon resonance frequency. The observed detuned group delay is analyzed with numerical calculations for a probe pulse interacting with the neighboring excited-states-modified Doppler broadening atoms for a fixed coupling field. The experimental results are in good agreement with the numerical calculations.

Investigation of extraordinary optical transmission and Faraday effect in one-dimensional metallic-magnetic gratings

We have investigated extraordinary optical transmission (EOT) with enhanced Faraday effect in one-dimensional metallic-magnetic slit arrays under polar magnetization using the rigorous coupled-wave analysis performed by the Airy-like internal reflection series. The roles of surface plasmon polaritons and quasi-guided waves are studied in which the latter plays a key role. Based on the mechanism of EOT with an enhanced Faraday effect, both enhanced transmittance and enhanced Faraday effect are optimized by adjusting the geometric parameters of slit arrays evaluated by the figure of merit.