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Journal of Modern Optics

NONLINEAR OPTICS OF ATOMS AND ELECTROMAGNETICALLY INDUCED TRANSPARENCY Dark resonance based optical switching

Byoung Seung HAM

Published Nov 1, 2002• 19 citations
Publisher

Abstract

An optical switching method based on dark resonance is proposed for ultrafast/ultrawide fibre-optic communications. The proposed switching method is based on dark-resonance induced refractive index changes in a three-level system interacting with two-colour laser lights. Two different mechanisms in the proposed optical switching method are discussed for the use of electromagnetically induced transparency and two-photon coherence induction. They are also compared for suitable applications in fibre-optic communications. Finally, a hyper-THz optical modulator is proposed, limited by current technologies due to carrier lifetime or population relaxation decay time.

DOI
10.1080/0950034021000011301

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An optical switching method based on dark resonance is proposed for ultrafast/ultrawide fibre-optic communications. The proposed switching method is based on dark-resonance induced refractive index changes in a three-level system interacting with two-colour laser lights. Two different mechanisms in the proposed optical switching method are discussed for the use of electromagnetically induced transparency and two-photon coherence induction. They are also compared for suitable applications in fibre-optic communications. Finally, a hyper-THz optical modulator is proposed, limited by current technologies due to carrier lifetime or population relaxation decay time.
Summary form only given. In a three-level system, two resonant optical fields can excite spin coherence on the ground states via two-photon resonance. One of the two-superposition states created by the atom-field interactions is decoupled from the excited state. Thus, the population can be trapped in that state showing non-absorption resonance. The essential feature of this decoupled state is dark resonance. Therefore, the existence of the dark resonance is a basis of non-absorption resonance, coherent population trapping, and electromagnetically induced transparency. In a four-level system, however, the two-laser induced spin coherence can be broken when a third laser is applied. At the same time, new coherence between the third laser and one of the pre-existed lasers is created. This phenomenon is useful for optical switching owing to annihilation and creation of the dark resonance in the four-level system. It is noted that the switching time depends on the dark resonance build-up time, which is inversely proportional to the applied Rabi frequency. Numerical simulations are shown for potentially ultrahigh-speed optical switches. Each diffracted four-wave mixing signal is proportional to the spin coherence strength. For a preliminary experiment, a spectral hole-burning crystal is used. The intensity of the diffracted signals is reversed at line center. This coherence switching effect is based on the dark resonance interactions.
Electromagnetically induced transparency is a promising approach to implement quantumcommunication in quantum system. In this study, quantum coherence and interference in theexcitation pathways of a three-level Λ atomic system leads to the formation of new states of matter(i.e. the dark state). This state decouples itself from the excitation beams leading to phenomenasuch as coherent population trapping (CPT), electromagnetically induced transparency (EIT).Taking into account quantum coherence and interference in an optically dense electromagneticallyinducedtransparent medium, we investigate the non-destructive storage and retrieval of singlephotonquantum states in the dark state of this dense ensemble of gas phase medium. The storageand retrieval process is based on the intracavity electromagnetically induced transparency by whichproperties of a cavity filled with three-level Λ-type atoms are manipulated by an external control field.We demonstrate the peculiar case for the storage and retrieval of time-entangled periodic input pulses(a soliton train) in the dark state by adiabatic photon transfer under conditions of dynamicalimpedance matching. These multiplexed photon states are expected to allow sharing quantuminformation among many users, and are currently of very high demand for applications in longdistanceand multiplexed quantum communication.
Summary form only given. The reduced absorption and enhanced nonlinearity in a three-level electromagnetically induced transparency (EIT) system are very important in achieving an effective all-optical switching action. The Kerr-nonlinear index of refraction of a three-level EIT medium can be greatly enhanced near resonance due to atomic coherence induced in such a system in comparison with a two-level atomic system, as we have shown by using an optical ring cavity. Both the magnitude and sign of the Kerr-nonlinear index change dramatically for different frequency detunings of the controlling (or coupling) or cavity (or probe) field. Bistability and dynamic instability occur when such a three-level /spl Lambda/-type EIT system is placed inside an optical ring cavity and the controlling and cavity input intensities to exceed certain threshold values. In this paper, we present a recent experimental demonstration of controlling the cavity output intensity by modulating the frequency detuning of the controlling beam.