氮化矽逆向梯形波導耦合器之設計、製作與量測

Abstract

本論文研究氮化矽逆向梯形耦合器以及數種交錯元件。在逆向梯形耦合器設計中,我們利用光束傳播法(BPM)模擬逆向梯形耦合器的特性。所設計尖端寬度為0.1以及0.2μm的兩種耦合器，在波長1550 nm下可將模場直徑為5μm的光纖耦合至0.5μm寬、1μm高的波導，其耦合效率分別為0.872以及0.701。我們有實作與量測尖端寬度為0.2μm的逆向梯形耦合器，其耦合損耗在C band中為6.9±0.79 dB，效率不如模擬結果高，可能原因是高深寬比的波導在製程上的不完美結果。雖然如此，耦合器在C band中有平坦的耦合效率，證明其寬帶的特點。此外，亦探討不同元件長度對於耦合效率的影響，由模擬與實作證明了耦合器長度只需100 μm即可有效將模態轉至0.5μm寬波導。除了耦合器之外，我們也實作並量測三種交錯元件。其中前兩種的交錯元件,其損耗在C band中約在0.1至0.3 dB的範圍。而第三種環形陷頻濾波器的部分,自由頻譜間距可以加倍成為17.6 nm。

In this study, the inverted taper couplers and several types of crossing devices based on silicon nitride (SiN) waveguides have been investigated. We used beam propagation method (BPM) to simulate the characteristics of the inverted taper couplers. The inverted taper couplers with 0.1 and 0.2 μm tip widths have coupling efficiencies of 0.872 and 0.707, respectively, from 5-μm-MFD fiber to 0.5-μm-width and 1-μm-thickness waveguide at the wavelength 1550 nm. The inverted taper couplers with 0.2-μm tip width were fabricated and characterized. The coupling loss of the inverted taper coupler was 6.9±0.79 dB in C band, which was not as good as expected. The fabrication imperfection of high aspect ratio waveguides might be the reason for the considerable loss. However, the couplers had rather flat coupling efficiency spectrum over the C band, proving its advantage of having broad operation band. Besides, we also simulated and fabricated the couplers with different taper lengths, and the results showed that a 100-μm taper length was long enough for efficient mode conversion. We also fabricated several types of crossing devices. The insertion losses of two types of crossing devices were in the range of 0.1 to 0.3 dB in C band. For the ring notch filter, the free spectrum range (FSR) was doubled to 17.6 nm in C band.