以偏振態控制表面電漿子傳遞方向之研究

Polarization Controlled Directional Control of Surface Plasmon Polaritons

特杜吾(Tyagi, Dhruv)

指導教授 ： 黃承彬

國立清華大學/其它/跨院國際博士班學位學程/博士(2020年)

摘要

我們通過數值和實驗證明了功能等離子超表面，旨在實現多方向SPP操縱。取決於激發光源的偏振，SPP可以被定向到至少七個單向狀態和一個分裂狀態。我們還以數值方式展示了用於將SPP路由到三個獨立方向的納米級蝕刻三角形陣列。此處介紹的工作為實現下一代光學納米電路開闢了新途徑。

關鍵字

等離子體 ； 光

並列摘要

Surface plasmon polaritons (SPPs) are electromagnetic excitations whose propagation is confined along the interface of a metal and a dielectric as a result of electromagnetic fields coupled to oscillating electrons. SPPs exhibit unique optical properties in metallic nanostructures which has opened up the possibilities of their applications in many fields such as bio-sensing, photovoltaics, near-field microscopy, integrated optics and sub wavelength optical manipulators. Directional steering of light using plasmonic structures is desirable for next-generation optical nano circuits. Metallic nanostructures support surface plasmon polariton (SPP) propagation under optical excitations at sub-wavelength regimes. SPPs can be launched by coupling free space light into SPP modes using a variety of techniques such as by using prisms and gratings. For efficient manipulation and launch of SPPs metasurfaces with nanostructures in a metal film such as a subwavelength slits and apertures has been demonstrated in past. Directional control over the beam propagation has the potential to enable the development of various highly efficient nanodevices such as plasmonic transmitters, receivers and sensors. Both solid and etched structures have been investigated in the past for achieving unidirectional plasmonic routing. But, very few successful attempts have been made in obtaining polarization sensitive unidirectional routing with more than one directions in a single device. To control the propagation direction of the SPPs, the primary and thus the most important aspect is the ability to control the spatial and temporal phases. To achieve this, metasurfaces can be used since the subwavelength components in a metasurface can be optimized for the enabling polarization dependent field enhancements in the aspired direction. The interference effects between two coupled SPP launch sources can be used for achieving unidirectionality for an orthogonal polarization. An assembly of these components placed at strategic locations can provide with the functionality for direction the SPP launch in the direction of choice based on the polarization of the exciting source. However, controlling the SPP launch in all the directions still remains challenging. We numerically and experimentally demonstrate a functional plasmonic metasurface designed to achieve multi-directional SPP steering. Depending on the polarization of the exciting light source, SPPs can be directed to at least seven unidirectional states and one split state. We also numerically demonstrate a nanoscopic etched triangle array for routing SPPs to three independent directions. The work presented here opens a new avenue for realization of of next-generation optical nanocircuits.

並列關鍵字

Plasmonics ； Optics ； Coherence Control

參考文獻

References

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[3] A.D. Boardman, Electromagnetic Surface Modes, John Wiley & Sons, New York (1882).

[4] G. Boisde, A. Harmer, Chemical and Biochemical Sensing with Optical Fibers andWaveguides, Arthech House, Boston, (1996).