Shayegannia Moein, Montazeri Arthur O, Dixon Katelyn, Prinja Rajiv, Kazemi-Zanjani Nastaran, Kherani Nazir P
Department of Electrical and Computer Engineering, University of Toronto, Toronto, ON, M5S 3G4, Canada.
Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA, 94720, USA.
Sci Rep. 2021 Jan 12;11(1):669. doi: 10.1038/s41598-020-79815-9.
We delineate the four principal surface plasmon polariton coupling and interaction mechanisms in subwavelength gratings, and demonstrate their significant roles in shaping the optical response of plasmonic gratings. Within the framework of width-graded metal-insulator-metal nano-gratings, electromagnetic field confinement and wave guiding result in multiwavelength light localization provided conditions of adiabatic mode transformation are satisfied. The field is enhanced further through fine tuning of the groove-width (w), groove-depth (L) and groove-to-groove-separation (d). By juxtaposing the resonance modes of width-graded and non-graded gratings and defining the adiabaticity condition, we demonstrate the criticality of w and d in achieving adiabatic mode transformation among the grooves. We observe that the resonant wavelength of a graded grating corresponds to the properties of a single groove when the grooves are adiabatically coupled. We show that L plays an important function in defining the span of localized wavelengths. Specifically, we show that multiwavelength resonant modes with intensity enhancement exceeding three orders of magnitude are possible with w < 30 nm and 300 nm < d < 900 nm for a range of fixed values of L. This study presents a novel paradigm of deep-subwavelength adiabatically-coupled width-graded gratings-illustrating its versatility in design, hence its viability for applications ranging from surface enhanced Raman spectroscopy to multispectral imaging.
我们阐述了亚波长光栅中四种主要的表面等离激元极化激元耦合和相互作用机制，并证明了它们在塑造等离子体光栅光学响应方面的重要作用。在宽度渐变的金属-绝缘体-金属纳米光栅框架内，只要满足绝热模式转换条件，电磁场限制和波导会导致多波长光局域化。通过对槽宽（w）、槽深（L）和槽间距（d）进行微调，场强会进一步增强。通过并列宽度渐变和非渐变光栅的共振模式并定义绝热条件，我们证明了w和d在实现槽间绝热模式转换中的关键性。我们观察到，当槽绝热耦合时，渐变光栅的共振波长对应于单个槽的特性。我们表明，L在定义局域波长范围方面起着重要作用。具体而言，对于一系列固定的L值，当w < 30 nm且300 nm < d < 900 nm时，我们展示了强度增强超过三个数量级的多波长共振模式是可能的。本研究提出了一种深亚波长绝热耦合宽度渐变光栅的新范例，展示了其在设计中的多功能性，因此其在从表面增强拉曼光谱到多光谱成像等应用中的可行性。
