Dhakal Ashim, Wuytens Pieter, Raza Ali, Le Thomas Nicolas, Baets Roel
Photonics Research Group, INTEC Department, Ghent University/IMEC, Gent 9000, Belgium.
Center for Nano- and Biophotonics, Ghent University, Gent 9000, Belgium.
Materials (Basel). 2017 Feb 8;10(2):140. doi: 10.3390/ma10020140.
Recent studies have shown that evanescent Raman spectroscopy using a silicon nitride (SiN) nanophotonic waveguide platform has higher signal enhancement when compared to free-space systems. However, signal-to-noise ratio from the waveguide at a low analyte concentration is constrained by the shot-noise from the background light originating from the waveguide itself. Hence, understanding the origin and properties of this waveguide background luminescence (WGBL) is essential to developing mitigation strategies. Here, we identify the dominating component of the WGBL spectrum composed of a broad Raman scattering due to momentum selection-rule breaking in amorphous materials, and several peaks specific to molecules embedded in the core. We determine the maximum of the Raman scattering efficiency of the WGBL at room temperature for 785 nm excitation to be 4.5 ± 1 × 10 cm·sr, at a Stokes shift of 200 cm. This efficiency decreases monotonically for higher Stokes shifts. Additionally, we also demonstrate the use of slotted waveguides and quasi-transverse magnetic polarization as some mitigation strategies.
最近的研究表明，与自由空间系统相比，使用氮化硅（SiN）纳米光子波导平台的倏逝拉曼光谱具有更高的信号增强。然而，在低分析物浓度下，来自波导的信噪比受到源自波导本身的背景光的散粒噪声的限制。因此，了解这种波导背景发光（WGBL）的起源和特性对于制定缓解策略至关重要。在这里，我们确定了WGBL光谱的主要成分，它由非晶材料中动量选择规则破坏引起的宽拉曼散射以及纤芯中嵌入分子特有的几个峰组成。我们确定在室温下，对于785 nm激发，WGBL的拉曼散射效率在斯托克斯位移为200 cm时的最大值为4.5±1×10 cm·sr。对于更高的斯托克斯位移，这种效率单调下降。此外，我们还展示了使用开槽波导和准横向磁极化作为一些缓解策略。
