|Abstract: ||本研究提出一種由Blackman函數所調變的對稱性漸變波導結構之3-dB分光器，應用在工作波長C+L波段的被動光纖網路裡。此寬頻分光器是使用耦合模理論來進行分析，並且利用三維有限差分波束傳播方法進行模擬。模擬結果發現，在整個C+L波段中，所提出的3-dB分光器的光均勻度，波長相依損失，額外損失和極化相依損失分別都優於2.49E-3 dB、0.018 dB、0.14 dB和0.004 dB。很明顯地，在工作波長C+L波段的被動光纖網路應用裡，此3-dB分光器可以展現良好的性能。|
隨後，我們延伸了上述3-dB分光器的研究，藉由簡單地打破原始設計的對稱性，來獲得不同分光比例的輸出。此不同分光比例的寬頻分光器之數值解決方案是設計波長在1.53~1.57 μm區間。我們一樣是使用BPM來驗證所提出的不同分光比例分光器的性能。經由模擬結果，我們推導出幾何移位與所對應的分光比例的關係，是一個二階多項式的關係。另外，透過這種幾何位移，分光比例可以從50:50調變到90:10。波長在1.53~1.57 μm區間，此不同分光比例分光器的額外損失，串擾值，極化相依損失和波長相依之分光比的偏差值分別都優於0.139 dB、-22.75 dB、0.006 dB和0.335％。明顯可見地，我們所提出的不同分光比例分光器一樣都保留了與對稱設計相同的優點，例如低額外損失，低串擾值，對光極化方向不敏感與對光波長不敏感。
;In this thesis, we propose a coupling-weighted and velocity-tapered 3-dB splitter with a symmetric structure weighted by the Blackman function for C+L-band passive optical network (PON) applications. The broadband splitter is analyzed by the coupled-mode theory and simulated by the use of three-dimensional finite-difference beam propagation method (BPM). It is found that the power uniformity, wavelength dependent loss, excess loss and polarization dependent loss of the proposed 3-dB splitter in the whole C+L-band are better than 2.49E-3 dB, 0.018 dB, 0.14 dB, and 0.004 dB, respectively. It is evident that the 3-dB splitter can achieve the good performances for C+L-band passive optical network applications.
Furthermore, we extend the approach of the above 3-dB splitter to obtain variable splitting ratios by simply breaking the symmetry of the original design. A numerical solution for the broadband splitter with a variable splitting ratio is designed with wavelengths between 1.53 and 1.57 µm. The performance of the proposed splitter is also verified by using the BPM. It was found that a polynomial function of the splitting ratios accompanying a geometrical shift can be derived from the proposed splitter. The splitting ratio can be changed from 50:50 to 90:10 with this geometrical shift. The excess loss, crosstalk, polarization dependent loss, and splitting ratio variations against wavelength of the proposed splitter with wavelengths between 1.53 and 1.57 µm are better than 0.139 dB, −22.75 dB, 0.006 dB, and 0.335%, respectively. Obviously, the proposed splitter with variable splitting ratio retains the advantages of the symmetric design, such as low excess loss, low crosstalk, polarization insensitivity, and wavelength insensitivity.