介電-電漿波導耦合器之研製

Study of Dielectric-Plasmonic Waveguide Coupler

梁廷聰(Ting-Tsung Liang)

指導教授 ： 蔡宛卲

共同指導教授 ： 陳祥(Hsiang Chen)

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(2019年)

https://doi.org/10.6837/ncnu201900219

摘要

光波導是在積體光路元件中連結各種元素的基礎，可以當成通道傳導光的介質，介電波導也是其中一種。環氧樹脂的負性光致抗蝕劑 (SU-8) 廣泛用於微機電系統（MEMS）領域，並且能夠形成高縱橫比(Aspect ratio)和耐化學性的優勢，我們將SU-8做成了脊形的介電通道波導。
表面電漿極化子 (SPP) 能在金屬與介電質的介面傳遞，並具有極快的反應速度、高靈敏度等優點。這幾年來，表面電漿極化子被運用在不同的元件上，如光波導、生物感測、光通訊、光耦合器等電漿波導的設計上。表面電漿極化子藉由一層非常薄的金屬薄膜，上下用對稱(折射率相近)的介電質材料包夾，使金屬與上下層的介電質的介面處產生表面電漿子相互耦合，能夠形成有低損耗且在紅外光波段能夠長距離傳播(約數毫米)的對稱導光模態，因此稱為長距離表面電漿模態。
本研究中，我們製作出複合式介電-電漿波導元件，基於積體奈米光路藍圖為目標。我們結合低損耗介電波導及長傳播距離電漿波導，在矽基板上製作出複合式模態耦合器。本研究動機在於透由微米尺寸的介電波導連接奈米尺寸的電漿波導，期望可以更近一步邁向次世代奈米光路平台發展。為了簡化過程，我們在介電波導及電漿波導中的介電層中都使用相同SU-8高分子介電材料。透過二次光學微影技術製作出能夠連接介電波導與金屬波導的橋樑，金屬波導結構以光學微影定義平躺在SU-8介電層上。SU-8波導結構則在定義好的金屬波導上透過反應式離子蝕刻技術，以乾蝕刻方式定義出脊型。最後我們在四吋矽晶片上製作出複合式電漿-介電波導耦合器，並經由預先冷凍的端面處理後，再依序進行手動切割及端面研磨。波導量測方式為透過端面耦合法，量測複合式介電-電漿波導的極化模態分布。實驗所量測分析的結果並與基於有限時域差分法模擬的結果比較。

關鍵字

介電波導 ； 複合式模態耦合器 ； 積體光路元件 ； 電漿波導

並列摘要

The optical waveguide is the basis for connecting various elements in the integrated circuit components, the medium that can conduct light as a channel is called an optical waveguide. The dielectric waveguide is also one of them. The epoxy-based negative photoresist is widely used within the microelectromechanical systems (MEMS) community and is well known for its ability to form thick layers with high aspect ratios and for its chemical resistance. We made a dielectric ridge-shaped channel waveguide with the SU-8 photoresist.
Surface plasmonics polaritons (SPP) can be transferred between the metal and dielectricinterfaces, and has the advantages of fast response and high sensitivity. In the past few years, surface plasmons have been used on different components, such as optical waveguides for, bio-sensing and optical communication, couplers, etc. For the plasmonic waveguides, with a thin metal slab surrounded by symmetric dielectric structures, two SPPs modes at top and bottom metal-dielectric interfaces can couple and form a symmetric mode with low attenuation and it can propagate at a longer length of a few millimeters in the infrared range. It is thus called the long-range surface plasmon polariton (LRSPP) mode.
In this study, hybrid plasmonic-dielectric devices are proposed towards the aim on integrated nanophotonics route map. We combine a low-loss dielectric waveguide with a LRSPP waveguide as an integrated mode coupler fabricated on a silicon substrate. This study is aiming to bridge the optical waveguides between micro-scale and nanoscale towards the development of the next generation nanophotonics platform. To simplify the fabrication process, the same dielectric material of SU-8 polymer is used for the dielectric waveguide and the dielectric cladding layer of the plasmonic waveguide. Two-step photolithographic process enables the patterning of both dielectric and metallic waveguides on the same substrate. The dielectric ridged SU-8 waveguides are defined by dry etching with the reactive ion etching technique. Finally, the waveguide couplers are cut manually from a 4-inch silicon substrate by pre-frozen end-facet preparation and post-polishing processes. The waveguides are measured through end-fire coupling method for the polarization mode distribution of the dielectric-plasmonic waveguide coupler. The experimental results are compared with the simulation analysis based on the finite difference time domain method.

並列關鍵字

Dielectric waveguides ； hybrid mode coupler ； integrated optics devices ； plasmonic waveguides

參考文獻

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