# Localized Surface Plasmon Fields Manipulation on Nanostructures Using Wavelength Shifting
## 4 Discussion  
When designing a plasmonic circuit, two factors are considered, which are the propagation and confinement of surface plasmon polaritons (SPPs). As the propagation length and confinement of SPPs are in a complementary relation, we should compromise between the two factors depending on the purpose when designing a plasmonic circuit. Usually, plasmonic waveguides are designed to pursue maximized propagation length, however, confinement of SPPs at a desired position is required rather than propagation length or strength of confinement, for example, when it is employed for switching schemes in plasmonic circuits by providing dynamics on a static circuit, or in few tens of nanometers nanostructure-based circuit parts since it also supports the confined SPPs volume under the diffraction limit. In this regard, three different nanostructures composed of different orientations of metallic rods, I-, T-, and Y-shaped nanostructures, were prepared as plasmonic platforms to provide more dynamics in the confinement position of the field. The LSPs field distributions on the metallic nanostructures were simulated and explored the feasibility of manipulating the LSPs field using incident-wavelength shifting. The distributions of localized electromagnetic fields were mainly manipulated by four different selected wavelengths of incident light source. The LSP distributions were generated well on the I-, T-, and  
Figure 6: The effects of the incident light source orientation while maintaining TM mode and the incident angle as 60\({}^{\circ}\). The schematic images of the front and bottom views are shown on the left. In the bottom view, the thick red arrows with respect to the direction of the incident light source and the black of the lowercase label identify the direction of the incident angle on the xy-plane and match the calculation results on the right side marked with the same label **(a–j)**. In the calculation data, the angle written in white indicates the orientation of the incident light source in xy-plane which measured from horizontal \(x\)-axis. Y-shaped metallic platforms, interestingly, the LSPs field positions differently depending on the incident wavelength. Notably, the positions of the LSPs field were dramatically switched by the incident wavelength, which means, we could control the position of the propagating surface plasmonic fields at a specific position with a high energy level by incident wavelength switching. By exploiting this scheme, the feasibility of application for the dynamic plasmonic circuits by switching the localized position of SP fields was explored. Moreover, these results enable the building of advanced plasmonic circuits by collaborating with a polarization-dependent plasmonic switching scheme. It could be also suggested for highly sensitive plasmonic sensors and high-performance optical imaging, for instance, plasmonic nanomanipulation-based enhanced Raman spectroscopic sensing and imaging [44; 45; 46], by spatially illuminating the target sample with illumination volume under diffraction limit which is capable of scanning mode illumination function with a tunable laser source. Tuning of confined fields can be applied for fascinating research based on bio/chemical reaction such as high-throughput light-induced tailoring by utilizing surface chemistry [47]. Conceptualization, H.S., J.-r.C. and K.K. ; methodology, H.S., H.A. and T.K. ; software, H.S. and H.A. ; validation, H.S. and J.-r.C. ; formal analysis, H.S. and J.-r.C. ; investigation, H.S., H.A. and T.K. ; resources, H.S., H.A. and T.K. ; data curation, J.-r.C. and K.K. ; writing--original draft preparation, H.S. and J.-r.C. ; writing--review and editing, H.S., J.-r.C. and K.K. ; visualization, H.S. ; supervision, J.-r.C. and K.K. ; project administration, K.K. ; funding acquisition, K.K. All authors have read and agreed to the published version of the manuscript. This research was funded by National Research Foundation of Korea (NRF) (2017M3 DI1A1039287, 2018R1A4A1025623, 2020R1A2C4002732).