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Tunable all-optical delay via nonlinear optical processes in semiconductor quantum wells.

机译：通过半导体量子阱中的非线性光学过程可调谐的全光延迟。

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摘要

The dramatic experimental demonstration of slow light in atomic vapors via electromagnetically induced transparency (EIT) has stimulated considerable interest in the dynamic control of the group velocity of light and in the development of tunable all optical delays. This dissertation presents experimental studies of all-optical tunable delays via nonlinear optical processes in semiconductor quantum wells (QWs). Two different approaches have been pursued. The first employs EIT arising from electron spin coherence in semiconductors and the second is based on efficient carrier induced exciton dephasing in QWs.; The EIT-based approach takes advantage of the spin-orbit coupling in the valence band to couple two electron spin states to a common light-hole valance band state in a GaAs QW waveguide. Induced transparency due to electron spin coherence in optical absorption has been demonstrated by investigating both the polarization and magnetic field dependence of the induced transparency. Signature of Rabi oscillations for excitonic transitions has also been observed. The relatively small transparency, however, has limited the fractional delay that can be achieved. Nevertheless, our studies have shown a novel approach for inducing and manipulating electron spin coherence in a semiconductor with neither external nor effective internal magnetic fields.; We have overcome the shortcomings of the EIT-based approach by exploiting unique incoherent nonlinear optical processes in semiconductors. In this approach, a control laser beam injects free carriers above the band gap of a GaAs QW. Strong Coulomb interactions between excitons and free carriers lead to highly efficient broadening and bleaching of the exciton absorption resonance, effectively modifying the group velocity of a signal pulse propagating near the exciton resonance. Fractional delay exceeding 200% has been obtained for an 8 ps optical pulse tuned near the heavy-hole exciton resonance, representing an improvement of more than one order of magnitude in terms of both fractional delay and signal bandwidth for tunable optical delays in semiconductors. In addition, pulse reshaping and pulse breakup observed near the exciton absorption line center also motivate further investigation of coherent propagation effects such as self-induced transparency in semiconductors.
机译：通过电磁感应透明性（EIT）进行的原子蒸气中慢速光的戏剧性实验演示，引起了人们对动态控制光的群速度以及开发可调谐的所有光学延迟的极大兴趣。本文通过半导体量子阱中的非线性光学过程，对全光可调延迟进行了实验研究。追求两种不同的方法。第一种方法是利用半导体中电子自旋相干产生的EIT，第二种方法是基于量子阱中有效的载流子激子相移。基于EIT的方法利用价带中的自旋轨道耦合将GaAs QW波导中的两个电子自旋态耦合到公共光孔价带态。通过研究诱导的透明性的极化和磁场依赖性，已经证明了由于光吸收中的电子自旋相干引起的诱导的透明性。也已经观察到激子跃迁的拉比振荡的特征。但是，相对较小的透明度限制了可以实现的分数延迟。然而，我们的研究表明，在既没有外部磁场也没有有效内部磁场的情况下，可以在半导体中诱导和操纵电子自旋相干的新颖方法。通过利用半导体中独特的非相干非线性光学过程，我们克服了基于EIT的方法的缺点。在这种方法中，控制激光束在GaAs QW的带隙上方注入自由载流子。激子和自由载体之间的强大库仑相互作用导致激子吸收共振的高效拓宽和漂白，从而有效地改变了在激子共振附近传播的信号脉冲的群速度。对于在重空穴激子共振附近调谐的8 ps光脉冲，已经获得了超过200％的分数延迟，这在半导体的可调光延迟的分数延迟和信号带宽方面都表现出超过一个数量级的改善。此外，在激子吸收线中心附近观察到的脉冲整形和脉冲破裂也促使人们进一步研究相干传播效应，例如半导体中的自感应透明性。

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  • 作者

    Sarkar, Susanta Kumar.;

  • 作者单位

    University of Oregon.;

  • 授予单位 University of Oregon.;
  • 学科 Physics Optics.
  • 学位 Ph.D.
  • 年度 2006
  • 页码 137 p.
  • 总页数 137
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 光学;
  • 关键词

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