| 摘要: | 電光調變器效率的提昇，可藉由調變機制設計及適當選擇電光材料來達成。在論文中，提出兩種利用非線性電光有機高分子材料設計與製作的高效率電光調變器，分別利用耦合波導表面電漿波原理所設計的耦合波導表面電漿子電光調變器及利用最佳化波導層厚度提高兩個表面電漿波耦合程度，所設計的雙表面電漿共振電光調變器。這兩種高分子電光調變器，係利用經過電場極化後的非線性電光高分子材料特有之波克效應及膜層厚度最佳化，藉由稜鏡耦合入射光至高分子波導層，以產生耦合波導表面電漿共振或雙表面電漿共振，並透過外加電壓來動態調變電光高分子的折射率，以改變共振耦合程度，來調變反射光強。耦合波導表面電漿電光調變器之基本架構，係由高折射率稜鏡、金屬薄膜層、電光高分子層及薄金屬電極層所構成。在最佳化高分子膜層厚度，由菲比-泊若干涉效應產生之波導共振模態與薄金屬電極層與空氣層介面之表面電漿波相互耦合，產生一個較佳的調變效率。透過設計，我們發現此新型電光調變器可以利用較低的調變電壓操作，以達到高效率的目的。雙表面電漿共振耦合電光調變器之基本架構，係由高折射率稜鏡、金屬薄膜層、電光高分子層、薄金屬電極層及電光高分子緩衝層所構成。在電光高分子膜層厚度最佳化下，入射光在衰逝全反射架構下，於適當共振角下，將使上金屬薄膜層介面之短距離表面電漿共振與下金屬電極層介面之長距離表面電漿共振相互耦合，以提高反射光場調變效率。由於光源在表面電漿共振型電光調變器內交互作用長度遠低於其他調變器，所以具有低損耗傳輸的優點。 本論文逐一討論電光調變器的基本組成、多層膜色散關係、高分子電光調變器之表面電漿共振應用原理、理論推導及模擬分析光調變器效率與電光高分子層厚度的關係。另製造表面電漿共振型電光調變器所必須量測之多層膜各膜層光學特性，可以直接藉由表面電漿共振角度探測技術及使用我們發展出來的改良式資料分析方法，快速決定各種膜層之折射係數與厚度。採用表面電漿共振角度探測技術，除了可以量測決定多層膜各膜層光學特性外，亦具有量測電光係數及調變效率的能力，故大幅簡化實驗程序。由於電光高分子層的製程簡單及相容於積體化電路的優點，故本文採用兩種電光高分子材料：一種為實驗室自行組合DANS-PMMA 電光高分子及另一種為之側鏈型發色團基之電光高分子。我們也應用前述原理，完成兩種有機高分子材料之耦合波導表面電漿共振的實驗。 The improvement on the efficiency of electro-optic (EO) light modulator can be achieved by the optimal design of EO modulating mechanism and the proper selection of EO materials. In this dissertation, two novel high efficiency EO modulators based on multiple surface plasmon resonance (SPR) effects are presented. One of the proposed EO polymeric modulators is based on a novel design in which the degree of coupling of the collimating monochromatic beam into the coupled waveguide-surface plasmon resonance (CWSPR) is electrically varied in order to enhance the modulation efficiency of the device. The other is so called double surface plasmon resonance (DSPR) and based on increasing coupling effect between two surface plasmon resonances via the optimization of the waveguide layer thickness. Both of EO modulators employed the Pockels effect possessed by the poled nonlinear optical organic polymer (NLOP) and the optimization of the thickness of EO thin film. By applying voltage across EO polymer film to vary the refractive index of the EO polymer, the degree of coupling of CWSPR and DSPR is altered and the reflectivity is modulated. The CWSPR EO modulator consists of a high refractive index prism, a thin metal film, a poled polymer layer, and metal electrode. By optimizing the thickness of the EO polymer, the coupling effect of the SPR and the waveguide coupled resonance (WCR) which induced by the Fabry-Perot (F-P) interference within EO polymer can be enhanced. As a result, the CWSPR EO modulator is able to operate with less modulation voltage and achieves better modulation efficiency. The DSPR EO modulator consists of a high refractive index prism, a thin metal film, a poled polymer layer, thin metal electrode, and EO film. In the same way, by optimizing the EO polymer thickness, the coupling effect of the short-range surface plasmon resonance induced at top metal interface and the long-range surface plasmon resonance induced at bottom metal interface will be enhanced and the modulator then yields a better efficiency. The EO polymer light modulator based on SPR-related principles offer the advantage of less insertion loss due to its shorter interaction length. This dissertation sequentially introduce the principles of SPR, the dispersion relation of multilayer system, the fundamentals of the modulator, the theoretical study and simulation concerning the relationship between the efficiency of modulator and the thickness of EO film. The determination of the refractive indexes and thicknesses for the various films, which is required for the fabrication of EO polymer modulator possessed with multilayer structure, can be achieved by employing the home-made SPR sensing technique and an improved data analysis method. In the similar approach, the SPR sensing technique is also capable of measuring the EO properties of the poled polymer film. This will greatly simplify experimental procedure. Since the NLOPs offer the advantages of having large EO constants, low dielectric constants, the simplicity to be fabricated, low cost, the diversity of synthesis and being compatible with integrated circuits, they are considered to be the most promising materials for the development of EO light modulator. Due to the aforementioned strengths offered by EO polymer, the EO polymers used in this project include two NLOP materials, one nonlinear optical organic polymer is a polymethyl methacrylate polymer (PMMA) side-chained with DANS (4, 4’-aminnonitroazoben­zene) chromophore (DANS-PMMA) which synthesized and fabricated by our lab and the other is a side-chained EO polyimide with 2-(N-ethyl-4-(tricyanovinyl)anilino)ethanol chromophore. Based on using the foregoing principles, we have implemented two CWSPR EO modulators with these two NLOP materials. The modulators are characterized, and their performance is tested, in terms of the optical properties of the polymer thin film, the EO coefficient, the insertion loss, and the modulation index. Additionally, the dynamic response of the EO light modulator is also investigated and discussed. |
