| 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平板波導之單模孔徑僅達0.2μm，造成極嚴重的光纖耦合問題。我們利用脊形波導結構的特性，在特定結構下，可以抑制高階波導模態的產生，且可達到具有10 × 6 μm 2之大孔徑，經由計算與單模光纖的直接耦合效率可高達 -1.25 dB，使其易於與光纖連結並增加實用性。 製程上為了達到具光學品質脊形波導側壁，我們以電子束微影法來定義結構，並以電感耦合電漿式反應性離子蝕刻可以得到高達3.5μm、無側蝕，且極為光滑的側壁蝕刻結果。利用單模光纖與脊形波導直接耦合之量測結果顯示，一個長度達 1.3 公分的長直波導，其插入損耗可以達到 - 4.46 dB。我們並以一光學放大系統來截取脊形波導的模態場圖，經由分析比對，可以證明該模態與設計結果十分吻合。 為了使微光學元件在平面光路上達到高密度的整合，波導結構需要在小區域裡達到大角度的彎曲。我們利用相位補償的方式，在彎曲過程中，經由空氣柱微透鏡讓波導之特徵模態得以維持。對於上述所提之大孔徑的單模脊形波導，我們設計出具有10°的大角度彎曲波導結構，曲率半徑僅達 27 μm，且彎曲損耗僅達 - 1.61 dB。我們並成功的以聚焦離子束製作出具相位補償之微空氣稜鏡。Silicon-on-insulator (SOI) waveguides have received much attention as a platform for planar lightwave circuits (PLCs) due to their compatibility with complementary metal oxide semiconductor (CMOS) technologies. Light in the silicon layer of SOI is naturally confined in the vertical direction because of the high index contrast between the bottom oxide layer, Si layer, and air. However, owing to the inherently large index contrast between si and air, the core size of a single-mode SOI waveguide is generally less than sub-micro size, resulting in a very serious coupling problem. Rib waveguide with specific structure can provide a core width with large cross-section, but still maintain in single-mode operation. In this paper, a large single-mode rib waveguide is designed and demonstrated. For easily coupling to SMF, the upper silicon layer is chosen to 10 μm, and the corresponding width of core is 6 μm with etching depth equal to 3.5 μm. On the basis of the above design, a calculation results of a butt-joint interconnect from SMF can be as high as -1.25 dB. The polarization-dependence loss is less than 0.01 dB, and wavelength- dependent loss preserves 1 dB variation within 100 nm. E-beam lithography is employed in this fabrication process due to obtain a waveguide sidewall with optical performance. By ICP-RIE dry etching process, the side-wall angle is very close to 90°, which maintains the designed eigen-mode correctly. The smooth side-wall roughness results in the low propagation loss of 0.9 dB/cm. Moreover, the near-field mode pattern is also measured by IR-camera, and it shows highly coincident to the designed eigen mode. For the purpose of high-density integration in PLC, a phase- compensated air-based microprism is introduced to a wide-angle bending rib waveguide. An air microprism, which can be made by directly dry etching up to oxide layer, compensates the phase difference in this rib waveguide bend, and then properly tilts the planar wavefront to the designed bending angle. A 10° bending waveguide with radius of curvature of only 27.1 μm is designed and fabricated. |
