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arXiv 1009.0253physics.optics
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纳米硅波导中的方向相关光模

Direction-dependent Optical Modes in Nanoscale Silicon Waveguides

Jacob T. Robinson, Michal Lipson

摘要:

片上光子网络具有比电子电路更有效地传输和路由信息的潜力。近年来,已经报道了许多基于硅的光学器件,包括调制器、缓冲器和波长转换器。然而,在将这些设备组合成网络级架构之前,需要克服许多技术挑战。特别地,由于半导体波导的芯和包层之间的高折射率对比,沿着波导的纳米级缺陷通常将光散射到反向传播模式中。这些反射可能导致对光源的不希望的反馈或双向互连中的串扰,诸如光纤网络中采用的那些。通常假设这些反射波在空间上与前向传播波重叠,使得难以实现基于光的传播方向分离或衰减光的光学环行器或隔离器。在这里,我们单独识别和映射的近场模式配置文件的前向传播和反射光的单模硅波导使用基于传输的近场扫描光学显微镜(TraNSOM)。我们发现,与光纤波导,高折射率对比度和纳米尺度的半导体波导创建反向传播波与不同的空间近场分布。这些近场差异是纳米级光限制的一个以前未观察到的结果,可以为新型元件过滤反射光的前向传播提供基础。

英文摘要:

On-chip photonic networks have the potential to transmit and route information more efficiently than electronic circuits. Recently, a number of silicon-based optical devices including modulators, buffers, and wavelength converts have been reported. However, a number of technical challenges need to be overcome before these devices can be combined into network-level architectures. In particular, due to the high refractive index contrast between the core and cladding of semiconductor waveguides, nanoscale defects along the waveguide often scatter light into the backward-propagating mode. These reflections could result in unwanted feedback to optical sources or crosstalk in bidirectional interconnects such as those employed in fiber-optic networks. It is often assumed that these reflected waves spatially overlap the forward-propagating waves making it difficult to implement optical circulators or isolators which separate or attenuate light based on its propagation direction. Here, we individually identify and map the near-field mode profiles of forward-propagating and reflected light in a single-mode silicon waveguide using Transmission-based near-field scanning optical microscopy (TraNSOM). We show that unlike fiber-optic waveguides, the high-index-contrast and nanoscale dimensions of semiconductor waveguides create counter propagating waves with distinct spatial near-field profiles. These near-field differences are a previously-unobserved consequence of nanoscale light confinement and could provide a basis for novel elements to filter forward-propagating from reflected light.

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