連結光纖與奈米矽波導的逆向梯形波導耦合器之優化

Abstract

在本論文中，我們利用超短的逆向梯形矽波導設計了一個光纖與奈米矽波導之間的光耦合器。藉由探討逆向梯形波導耦合器在基本模態下的各項損耗，我們發現必須最小化模態不匹配損耗與模態轉換損耗之和才能得到具有最低耦合損耗的結構。故利用此法，我們優化了所設計的逆向梯形波導耦合器在輸入端的各項結構參數，並且利用有限時域差分法模擬元件的特性，這個只有10μm長的耦合器可將模場直徑為2μm的光纖耦合到450nm寬、220nm高的矽波導，在光波長為1550nm下，耦合損耗只有0.3dB，而元件操作頻寬則遠大於150nm，且對於製程失誤與對光失誤的容忍度很高。

An ultra-short silicon inverse taper is proposed for coupling between fiber and silicon wire waveguide. After considering all kinds of fundamental-mode losses in the inverse taper coupler, we found that minimizing the summation of mode mismatch loss and mode conversion loss is the only way to achieve the lowest coupling loss. By doing so, we optimized the input facet structure of the designed coupler. The performance of this device is simulated by using Finite Difference Time Domain method. The 10μm-long inverse taper coupler has a coupling loss of 0.3 dB from 2μm-MFD fiber to 450 nm by 220 nm waveguide at the wavelength of 1550 nm; moreover, it has a bandwidth of >150 nm, and high fabrication and alignment tolerances.