| 摘要: | 由於絕緣體層上鍍矽晶片(Silicon-on-insulator, SOI)與微電子技術的高度相容性，SOI也逐漸成為平面光路(Planar Lightwave Circuit, PLC)的主要應用平台。然受制於矽材與空氣、二氧化矽之折射率反差過大，SOI平板波導(Slab waveguide)之單模孔徑僅達0.2 μm，造成極嚴重的光纖耦合問題。我們利用脊形波導(Rib waveguide)結構的特性，在特定結構下，可以抑制波導的高階模態產生，可以達到具 10×6 μm2之大孔徑(Large Cross Section)，且經由計算其與單模光纖的直接耦合 (Butt-joint) 效率可高達-1.25 dB，使其易於與光纖連結並增加實用性。 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(Phase Compensation)的方式，在彎曲過程中，經由空氣柱微稜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。 我們也利用導波共振結構(Guide-mode Resonance, GMR)的特性，將SOI脊形波導與GMR光柵積體化，可以達到濾波器之效果。我們設計了一個單一週期雙填充率之非對稱性光柵結構，作為一強調制之濾波器，可以分離通訊用波長1310 nm與1550 nm之訊號。在PLC上將GMR與脊形波導整合之整體(monolithic)積體化元件，具有相當吸引人的應用價值。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. 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. In the last section of this paper, a monolithic integration of guide-mode resonance (GMR) filter and rib waveguide is proposed and analyzed. This GMR with structure of grating and waveguide can be directly fabricated by dry-etching process on the top Si layer of SOI. A 1310/1550 nm filter by this monolithic structure is designed. Strong modulation in the grating structure with two-filling factor design can enlarge the operating wavelength window to more than 40 nm, which can avoid general wavelength shift by temperature variation. |
