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Quantum Electronics and Laser Science Conference

Dark-resonance-based quantum switching

Byoung Seung HAM

Published Nov 13, 2002• 0 citations
Publisher

Abstract

Summary form only given. Dark-resonance-based ultra-high-speed optical switching is demonstrated. This demonstration shows a breakthrough in the limitations of current semiconductor-based optical technologies in fiber-optic communications. The proposed idea of the optical switching is based on the dark resonance interactions and nondegenerate four-wave mixing processes in a four-level system. To demonstrate quantum switching in time domain, 16-density matrix equations are numerically solved for consecutive square pulses. To implement the proposed quantum switch, quantum-well semiconductors having suitable intersubband transitions or other dipole transition solids may be used.

DOI
10.1109/qels.2001.961912

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Summary form only given. Dark-resonance-based ultra-high-speed optical switching is demonstrated. This demonstration shows a breakthrough in the limitations of current semiconductor-based optical technologies in fiber-optic communications. The proposed idea of the optical switching is based on the dark resonance interactions and nondegenerate four-wave mixing processes in a four-level system. To demonstrate quantum switching in time domain, 16-density matrix equations are numerically solved for consecutive square pulses. To implement the proposed quantum switch, quantum-well semiconductors having suitable intersubband transitions or other dipole transition solids may be used.
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.
Summary form only given. Analysis of the physics of current optical switching techniques shows that the possible switching speed is less than THz even if one may use intersubband transitions of semiconductor quantum wells. The author demonstrates that the switching speed can be faster than the population relaxation time T/sub 1/ when quantum coherence is utilized. The observation of optical switching time is ten times faster than the population decay time. A spectral hole-burning crystal of Pr/sup 3+/ doped Y/sub 2/SiO/sub 5/ (Pr:YSO) is used for an initial experimental demonstration.
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.