- 學位論文
矽線波導與光纖間的二維光學模態轉換耦合器
Two-Dimensional Optical Mode Converters for Fiber and Silicon Photonic Wire Coupling
摘要
矽積體光學近年來由於光通訊的發展而成為一個熱門的研究主題， 我們可以利用SOI 晶圓的高折射細數相差之特性來製作波導使光訊 號在傳遞時不會損耗至基材或是空氣之中。在此我們提出利用光柵耦 合器可以選擇特定之週期使輸入之光訊號可以為通訊波長為1550nm， 並且結合了二維錐形光學耦合器使入射訊號由光纖輸入時(core 大小 為10um)可以減少與積體光學元件(大小為1um)的耦合損耗。我們 可以利用相位匹配之公式算出矽光柵之週期為1.22um再利用 Finite-Difference Time-Domain(有限時域差分法)來計算出真正符 合的週期為1.15um且高度為50nm；並且利用PECVD 沉積出折射率介 於1.57~1.58 的SION(氮氧化矽)使其可以與SU-8 所製成的三維錐形 光學耦合器折射率相同。最後量測出元件的輸入損耗最好的位置是在 1552nm 損耗為-14.7db 並且其頻寬達到了80nm，並且其TE 極化與TM 極化的耦合效率相差了100 倍；而利用SU8 所製作之耦合器經由實驗 的量測可以提升了10db 的輸入損耗並且在位置位移的量測當中再X 方向的容忍度可以達到4um且Y 方向之容忍度可以達到6um。
並列摘要
Silicon photonic integrated circuits have received a lot of attention recently. Due to high-refractive-index contrast between silicon and silicon dioxide, silicon-on-insulator photonic devices usually can be made very compact and easily extend to a large-scale system. However, the light coupling between silicon photonic wire and fiber is a critical issue. Here we present a two-step coupler which can be used to efficiently couple the light from fiber to silicon photonic wires. Because the difference between the waveguide core (about 1um) and fiber core (about 10um) dimension is very large, we utilize SU8 photoresist to fabricate a 3D adiabatic taper for reducing the coupling loss between the fiber and an intermediate waveguide as the first-step coupling. After coupling to the intermediate waveguide, the optical wave is further transferred to the silicon photonic wire through a grating-assisted directional coupler. We use FDTD to analyze the grating period for wavelength around the communication band at 1550nm and the grating period was calculated to be 1.15um and 50nm in height. We use PECVD(plasma enhanced chemical vapor deposition) to deposit SiON for the intermediate waveguide. In the measurement, we have fiber end-to-end insertion loss about -14.6db at 1552nm. Polarization extinction ratio between TE and TM is around 20dB. The misalignment tolerance of 3dB decay is 4m in horizontal direction and 6um in vertical direction.