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Semiconductor Science and Technology

Polarization state dynamics induced by the virtual excitation of spin-polarized carriers in semiconductor quantum wells

Eric J. Gansen, Arthur L. Smirl

Published Mar 12, 2004• 0 citations
Publisher

Abstract

By using a circularly polarized pulse that is tuned well below resonance, we create a virtual population of spin-polarized coherent excitons in a GaAs/AlGaAs multiple quantum well, and we study its effects on the polarization state of a weak signal pulse using a combination of time-resolved and spectrally resolved ellipsometric techniques. From these data the polarization state contributions to an all-optical polarization switch, which exhibits a ~415 fs switching time and large contrast ratios, are identified and the performance of the switch is demonstrated.

DOI
10.1088/0268-1242/19/4/122

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Journal of Applied Physics•Feb 15, 2007•22 citations
By using a circularly polarized pulse that is tuned well below resonance, we create a virtual population of spin-polarized coherent excitons in a GaAs/AlGaAs multiple quantum well, and we study its effects on the polarization state of a weak signal pulse using a combination of time-resolved and spectrally resolved ellipsometric techniques. From these data the polarization state contributions to an all-optical polarization switch, which exhibits a ~415 fs switching time and large contrast ratios, are identified and the performance of the switch is demonstrated.
Summary from only given. Recently we have demonstrated an optically-addressed coherent polarization switch that is based on the near-resonant excitation of a spin-polarized population of virtual excitons in MQWs. By taking advantage of the nonlinearities associated with a virtual carrier population, this near resonant device exhibits a pulse-width-limited response; by operating near resonance it is capable of producing relatively large contrast ratios in thin samples; and finally, by generating a spin-polarized carrier population, the device produces a rotation of the signal polarization in unstrained MQWs. Here, we experimentally analyze the switching mechanisms by systematically performing spectrally and temporally resolved differential transmission measurements and by fully determining the polarization state of the transmitted signal as a function of time delay.
Summary form only given. We describe a novel optically-addressed coherent polarization switch that is based on the non-resonant excitation of spin-polarized "virtual excitons" in unstrained MQWs. By operating near (but below) resonance, we achieve nonlinearities that approach the magnitudes of those that can be obtained with resonant excitation, yet we are able to avoid the restrictions that accompany carrier generation, and we take advantage of speeds that are characteristic of non-resonant excitation. Consequently, our device exhibits a pulse-width-limited response that is determined solely by the length of the control and signal pulses and produces large contrast ratios in thin MQW samples.