SOI脊型波導之彎曲結構與濾波器在晶片內光學連結應用;SOI-based Rib Waveguide Bends and Filters for Intra-chip Optical Interconnects

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题名:	SOI脊型波導之彎曲結構與濾波器在晶片內光學連結應用;SOI-based Rib Waveguide Bends and Filters for Intra-chip Optical Interconnects
作者:	鐘敏豪;Ming-hao Chung
贡献者:	光電科學研究所
关键词:	轉折;濾波;波導;filter;waveguide;bend
日期:	2009-07-02
上传时间:	2009-09-22 10:37:24 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	由於SOI晶片與微電子技術的高度相容性，SOI逐漸成為平面光路的主要應用平臺。然而受制於矽材與空氣、二氧化矽之折射率反差過大，SOI平板波導在紅外光波段之單模孔徑僅達0.3微米，如此，在光纖與平板波導間會造成極嚴重的耦合問題。因此，我們利用脊形波導結構的特性，在較大的結構尺寸下，仍然可以抑制高階波導模態的產生，經由設計我們製作出一個具有2.5 × 2 平方微米孔徑之脊形波導，其與透鏡型單模光纖的直接耦合效率可達 -4.2 dB，根據此結果，單模脊形波導已具備可以與光纖連結之特性。在此篇論文中，我們以黃光製程技術將光學元件包括彎曲與濾波結構設計在單模脊形波導上，並以此為出發點進行研究。為了實現將積體光學元件高密度化的目標，將光路彎曲具有其必要性，然而若要在很小的尺度內將光路彎曲，因折射率反差所造成的光強損耗將無可避免。在本篇論文中，我們提出用相位補償的方式，在波導彎曲處以電感耦合電漿式反應性離子蝕刻製作出空氣柱，並經由在空氣柱中填入聚醯亞銨或環苯丁烷(BCB)後所形成的微透鏡，讓波導之特徵模態得以維持，也希望減少在彎曲處因繞射所造成的損耗。我們以10.46微米之彎曲半徑設計了幾組不同的彎折角度包括10,30,40,48,55以及60度，其平均彎曲效率約為10 dB. 另外因應光通訊之分波的需要，我們也提出了在脊形波導上製作出結合Fabry-Perot共振腔與分佈式布拉格反射器(DBR)所形成之濾波器，以分佈式布拉格反射器當作此共振腔的反射層，並藉由改變布拉格反射器中矽與空氣層的層數，調制此濾波器的濾波帶寬，進而達到微型化晶片內濾波波導的設計。此濾波波導的製作是先用電感耦合電漿式反應性離子蝕刻出寬度1.5微米脊形波導，再蝕刻出布拉格反射器中的空氣槽。假使我們稱一層空氣層加上一層矽層稱為一對式布拉格反射器，那麼由模擬可計算出在兩對式布拉格反射式濾波波導中，我們可以得到一個穿透效率為0.96且頻寬為5奈米的穿透光光譜。由以上的轉彎以及濾波技術，在實驗室將來的研究中，希望得以發展出在單一矽晶片內的分波收發模組，更使此研究成果具有應用性。Silicon-on-insulator (SOI) material has received much attention as a platform for planar lightwave circuits (PLCs) due to the compatibility with complementary metal oxide semiconductor (CMOS) technologies and high possibility to integrate other optoelectronic devices within a single chip. SOI’s intrinic high index contrast between silicon and oxide/air causes single-mode core size less than 0.3 μm for a simple slab-type waveguide, and then serious coupling loss from fibers is inevitable. Therefore, rib-type waveguide is usually adopted not only to provide a larger core size but also to maintain single-mode operation. Furthermore, PLCs-related devices such as bends, beam splitters, or filters based on SOI-based rib waveguide have become essentional research issues in these years. In this thesis, we focus on both waveguide bending and filtering applications with ultra-compact and monolithic characteristics. The individual detail for both devices is briefed as follows: Ultra-compact waveguide bend is very important to achieve devices with high-density integration. SOI-based rib waveguide is a great platform to perform a wild-angle bending with high bending efficiency via reflection mirror, corner mirror technologies. However, these technologies for waveguide bends are short of an efficiently optimal design rule for arbitrary bending angles. Here, a compact SOI rib waveguide bends with benzocyclobutene (BCB) microprisms are proposed. The microprism is designed by using the phase compensation rule and monolithically integrated in the bending area of an optical waveguide to correctly tilt the wavefront of eigen-mode and suppress the radiation loss. The microprism can be realized by dry-etching an air trench in the bent corner and filling it with the BCB polymer material. A very compact bending radius of 10.46 μm is implemented to various bending angles including 10, 30, 40, 48, 55, and 60 degrees with averaged experimental bending loss of 10.48 dB. In addition, the core size of this rib waveguide can be expanded to 2.5 × 2 μm2, resulting in coupling loss less than 4.2 dB. Wavelength-Division Multiplexer plays an important role in optical communication, which converge signals carried by different wavelength, and then separates it into different terminations. Different kinds of optical filters such as thin film filters and grating filters were broached to serve the demand of multiplexer. However, these technologies are deficient in large working area or the huge packaged size. Therefore, a compact SOI-based rib waveguide with distributed-Bragg-reflector (DBR) structures are also proposed, the DBR layers from one to three pairs are designed for incident wave to resonate and filter through a narrow bandwidth and high transmission efficiency of transmitted wave. The transmission efficiency is as high as 0.96 with FWHM (full width half maximum) of 5 nm, which is achieved by two-pair air trench of DBR filter. According to the bending and filtering technique as mentioned above, the approach to a compact intra-chip wavelength division multiplexer would be expected, and makes the research more applicable.
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