矽基片B型抗諧振反射光波導結構光子晶體錐形耦合器之設計、製作與特性量測

Abstract

光子晶體是由擁有不同介電常數的物質週期排列而形成的結構，其具有可以阻止特定 波長的光在晶體中傳導的特性。矽基片B型抗諧振反射光波導結構光子晶體，此結構在水 平方向與垂直方向用來侷限光波的機制分別是利用光子晶體能隙與抗諧振反射，此波導擁 有較厚的核心層厚度使它在垂直方向上對光纖的光源有較好的耦合效率。提升水平方向的 耦合效率，我們設計了一個擁有不同分段長度的光子晶體錐形耦合器，利用多模干涉的原 理設計出各個最優化的分段長度並得到好的耦合效率。此外，為了改善到W1的耦合效率， 我們在結構的通道中加入孔洞，大幅提升其效率。製作完成後的元件量測結果顯示無論是 在頻寬或者耦合效率上，使用上述方法所設計的耦合器都明顯優於未設計過的元件，當波 長為 1.55μm 兩者的能量損耗至少有 6 dB 的差異，此結果也印證使用調整分段長度與 在通道中加入孔洞確實能有效提升光子晶體耦合器的效率。

Photonic crystals (PCs) are optical structures with periodic changes in the dielectric constant and they own the ability to forbid certain frequency of lightwaves to propagate. In this study, the PC tapered couplers based on the type-B antiresonant reflecting optical waveguide (ARROW-B) structures are presented. In this structure, light confinement is provided by photonic band gaps and antiresonance reflection in the lateral and vertical direction, respectively. This PC waveguide (PCW) has relatively thicker core suitable for efficient coupling with single mode fibers in the vertical direction. To improve the coupling efficiency in the lateral direction, a PC tapered coupler with different section length was designed. Due to the increment of mode-matching level, the coupling efficiency between single mode fiber and W1 PCW could be high. Furthermore, point defect was introduced in the W3 section of the tapered coupler to generate one-peak mode distribution, and improve the poor coupling efficiency to the last section of the PC tapered coupler. We manufactured this device and the measurement results showed that the designed couplers own significant performance both on coupling efficiency and broad band characteristics. The coupling loss of the designed couplers is at least 6 dB lower than that of the undesigned couplers. According to the simulations and measurement results, adjusting the section length and adding hole defects within the propagation path can efficiently improve the performance of PC couplers.