The unique ability of slot and sub-wavelength grating (SWG) waveguides to confine light outside of the waveguide core material has attracted significant interest in their application to chemical and biological sensing. However, a high sensitivity to sidewall-roughness-induced scattering loss in these structures compared with strip waveguides casts doubt on their efficacy. In this article, we seek to settle the controversy for silicon-on-insulator (SOI) photonic devices by quantitatively comparing the sensing performance of various waveguide geometries through figures of merit that we derive for each mode of sensing. These methods (which may be readily applied to other material systems) take into account both modal confinement and roughness scattering loss, the latter of which is computed using a volume-current (Green’s function) method with a first Born approximation. For devices based on the standard 220 nm SOI platform at telecommunication wavelengths ($\lambda =1550\mathrm{nm}$), whose propagation loss is predominantly limited by random line-edge sidewall roughness scattering, our model predicts that properly engineered TM-polarized strip waveguides claim the best performance for refractometry and absorption spectroscopy, whereas optimized slot waveguides demonstrate $>5\times$ performance enhancement over the other waveguide geometries for waveguide-enhanced Raman spectroscopy.

中文翻译：

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狭缝和亚波长光栅波导在传感方面是否优于带状波导？

缝隙和亚波长光栅（SWG）波导将光限制在波导核心材料外部的独特能力吸引了人们对其在化学和生物感测中的应用的极大兴趣。然而，与条形波导相比，这些结构对侧壁粗糙度引起的散射损失的高灵敏度使人们对它们的功效产生怀疑。在本文中，我们通过对每种传感模式得出的品质因数进行定量比较，以解决绝缘体上硅（SOI）光子器件的争议。这些方法（可以很容易地应用于其他材料系统）同时考虑了模态限制和粗糙度散射损失，后者是使用具有第一Born近似的体积电流（格林函数）方法计算的。对于在电信波长下基于标准220 nm SOI平台的设备（$\lambda =1550\mathrm{纳米}$），其传播损耗主要受随机线边缘侧壁粗糙度散射的限制，我们的模型预测，经过适当设计的TM偏振条形波导在折光率和吸收光谱方面要求最佳性能，而优化的缝隙波导证明 $>5\times$ 与其他用于波导增强拉曼光谱的波导几何形状相比，其性能得到了提高。