| 摘要: | 在通訊領域中，隨著人們對傳輸速率的要求越來越高，且相較於銅線，光波導有更高的傳輸速率以及更寬的頻寬，並且降低了損耗，所以矽光子學的應用成為了一個不錯的選擇，其運作系統包括用於傳輸的光子電路以及用於計算的電子電路。首先以雷射調製器將電訊號轉換至光訊號，再以光纖以及光波導傳遞光訊號，最後由光接收器將光訊號轉回電訊號。高功率寬頻的光源在光纖通訊都有如光學放大器、拉曼雷射、醫學或光譜學等領域有重要應用。除此之外，近年來利用晶載系統產生光學非線性訊號已被廣泛應用，然而要在光波導上產生非線性特性也需要較高的光功率。
在量測光纖對波導的耦合中，當輸入光的功率達到一定的強度時，會在光纖上產生機械振動(mechanical vibration)，影響量測結果。V型槽(V-Groove)與U型槽(U-groove)皆為很好的解決方案。U-Groove最開始的做法為片外(off-chip)的形式，而隨著U-Groove在積體光路的應用越來越多，逐漸發展為片上(on-chip)的形式。在以往on-chip的製程經驗中，U-groove皆是在製作完波導後製作。本論文嘗試新的製程步驟:事先製作U-groove的製程步驟(Groove-first)。可以在製作U-Groove時同時避免氮化矽應力問題，並且可以避免掉氧化矽的蝕刻同時量產出多片U-Groove試片。在波導方面，避免一些對波導產生影響的步驟，可以突破MA6曝光機的解析度極限，製作出天然的倒錐形波導(inverse taper)。
此論文利用矽基板上蝕刻出U-groove，再以此試片製作出氮化矽波導(silicon nitride-based waveguide)，來達成與單模光纖之被動對準(Passive Alignment)。最後，我們確認雷射可以從光纖耦合進入Groove-first試片之波導，量測到波導模態。並且確認機械振動造成的量測影響在輸入光功率達到800mW的情況下維持在10%以內。
;In the communications field, the need for high-speed transport and large-bandwidth data communication is increasing rapidly. Comparing to the copper conductor in electrical communication, the optical waveguide provides higher speed, wider bandwidth, and lower loss. Thus, the application of silicon photonics become a good candidate for the next generation communication. The basic operation system includes photonics circuit for communication and electronics circuit for computation. The electrical signal is converted into optical signal by modulating either the intensity or the phase of a laser. Then, the optical signal is transported by the optical fiber externally and the optical waveguide internally. For the receiver, the optical signal is converted back into electrical signal by an optical receiver. Besides, for high-power optical sources, there are significant applications in various domains including optical amplifiers, Raman lasers, medicine, and spectroscopy. Recently, these studies have been investigated in on-chip systems, especially for generating optical nonlinear signals.
To study optical nonlinearity, high optical power is a must. However, during the measurement of optical fibers coupling to waveguides with high input power, the mechanical vibration of the optical fiber would be a critical problem for coupling stability. Traditionally, it can be compromised by fabricating either V- or U-Groove structures. U-Groove was first made in the off-chip type. As the demands for photonics increase, U-Groove is gradually developed into the on-chip type. In the past, these on-chip U-Grooves are widely used and patterned after the waveguide formation. In this thesis, we present a new fabrication process, Groove-first, which U-Grooves were formed before the waveguide formation. Groove-first process can solve the problem of silicon nitride film stress by combining the strain-relaxed pattern during U-Groove formation. Also, this process can prevent the etching of silicon oxide and mass produce U-Groove chips. In terms of waveguide, unwanted process onto the waveguide structure can be avoided. The natural inverse taper waveguide can be formed by MA6 which break its resolution limit.
In the first part of this thesis, we will discuss the fabrication and process optimization of U-grooves before patterning the waveguide. Second, silicon nitride-based waveguides were chosen to be the photonic platform for fiber-waveguide interconnection. Last, we will show that the measurement error caused by the mechanical vibration could be released comparing to the traditional coupling without the grooves and the power variation is found to be below 10% even with the input power up to 800mW. |
