In order to build nanophotonic devices, it is important to understand and ultimately control the optical mode structure within potential components such as nanoscale waveguides. However, experimental characterization of such modes in the optical regime is difficult due to the nanoscale dimensions of such components and the perturbations that would be induced by a near-field probe. Here, we demonstrate a probe-free, far-field method to characterize the optical modes within GaN nanowires (NWs) based on a novel off-axis scanning confocal microscope system. Using this microscope, we observe spectral signatures resulting from lateral leakage of waveguide modes when they exceed their respective cutoff limits. We identify these modes within hyperspectral images using an analytical model coupled with finite element simulations. The model can also be used to predict the spectral signatures for given geometrical and dielectric parameters, which enabled us to deduce the transverse dimension of the NW from hyperspectral images with an accuracy of ${\sim}30\;\text{nm}$.

中文翻译：

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半导体纳米线中横向光学模式的光谱特征

为了构建纳米光子器件，重要的是了解并最终控制潜在组件（如纳米级波导）中的光学模式结构。然而，由于此类组件的纳米级尺寸以及近场探针将引起的扰动，因此在光学方案中对此类模式进行实验表征是困难的。在这里，我们展示了一种基于新型离轴扫描共聚焦显微镜系统的无探针远场方法来表征GaN纳米线（NWs）内的光学模式。使用该显微镜，我们观察到当波导模式超过各自的截止极限时，由于横向泄漏而产生的光谱特征。我们使用分析模型与有限元模拟相结合，在高光谱图像中识别这些模式。$ {\ sim} 30 \; \ text {nm} $。