長距離表面電漿波導之研究

Study of Long-Range Surface Plasmon Polariton Waveguides

黃聖庭(Sheng-Ting Huang)

指導教授 ： 蔡宛卲

國立暨南國際大學/科技學院/應用材料及光電工程學系/碩士(2017年)

摘要

表面電漿子可以在金屬與介電質的界面傳遞，具有高靈敏度、即時反應等優點。近年來，表面電漿子被廣泛應用在各種元件上，如生物感測、光訊號開關及光波導，然而表面電漿子的傳播長度在可見至紅外波段通常為數十至數百微米，藉由一層足夠薄的金屬薄膜，上下以對稱（相近折射率值）的介電質結構包夾，使上下層的金屬與介電界面處的表面電漿子互相耦合，形成非對稱與對稱兩種導光模態。其中的對稱模態具有低損耗及在紅外光波段能夠長距離傳播（約數毫米）。因此它被稱為長距離表面電漿子模態。
在本研究中，我們設計及製作以上下兩層高分子介電質包覆金條紋的長距離表面波導。以光學微影術定義不同線寬的金條紋；並以電子槍蒸鍍系統沉積金膜。材料分析透過表面輪廓儀 (α-step) 和稜鏡耦合器 (prism coupler) 量測高分子覆蓋層的厚度及折射率，並透過原子力顯微鏡(AFM)與掃描式電子顯微鏡(SEM)量測金條紋及元件端面的形貌。光學分析包括傳播距離及導光模態分布的量測。傳播距離的計算是透過分別使用633 nm、785 nm及1550 nm三種不同波長的雷射光源量測散射損耗，再以公式進行計算。導光模態則是透過端面激發耦合方法，在1550 nm波長下量測。我們討論不同線寬的模場直徑、極化消光比及模態重疊積分。模擬計算以時域有限差分法計算元件的光傳播長度及導光模態分布，並與實驗結果比較。由模擬與實驗的結果比較能夠看出兩者的一致性。

關鍵字

積體光學元件 ； 長距離表面電漿子 ； 電漿波導

並列摘要

Surface plasmon polaritions (SPPs) are surface waves that propagate along the metal-dielectric interface. SPPs have the advantages of high sensitivity and real time measurement. In recent years, integrated photonic devices based on SPPs have been fabricated for bio-sensing, optical signal switches and waveguides. However, the propagation lengths of SPPs propagating along a metal-dielectric interface are usually limited to the order of tens to hundreds of micrometers in the visible to near-infrared range. With a metal slab, which is thin enough, surrounded by symmetric dielectric structures (with very close refractive indices), two SPP modes at top and bottom metal-dielectric interfaces can couple and form both asymmetric and symmetric modes. Symmetric mode has the properties of low attenuation and it can propagate at a longer length in the infrared range (a few millimeters). It is thus called the long-range surface plasmon polariton (LRSPP) mode.
In this study, design and fabrication of LRSPP waveguides, consisting of thin gold stripes surrounded by top and bottom polymer claddings, are presented. Gold stripes with different widths are defined by ultraviolet lithography and are deposited by electron-gun evaporation. Thickness and refractive index of the cladding is measured with a surface profiler and a prism coupler, respectively. Material characterization including gold stripe width, thickness, and end-facet quality is performed with atomic force microscope (AFM) and scanning electron microscope (SEM). Optical characterization including propagation length and guiding mode profile is measured. The propagation lengths are characterized at laser wavelengths of 633 nm, 785 nm and 1550 nm based on scattering loss measurement. The guiding mode profiles are measured at 1550 nm using the end-fire coupling method. Mode-field-diameter (MFD), polarization extinction ratio, and overlap integral of the LRSPP waveguides of different stripe widths are discussed. Simulation results based on finite-difference time-domain (FDTD) of propagation lengths and guiding mode profiles are compared with experimental results. Good accordance between experimental and simulation results can be seen.

並列關鍵字

Integrated optics devices ； Long-range surface plasmon polariton ； Plasmonic waveguides

參考文獻

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