作為傳遞訊息鏈上的一個元件，密分波多公具有耦合數個特定波長輸入訊號(多公器)和再將訊號分成多個輸出(解多公器)的亮眼表現。密分波多公顧名思義就是擁有較密集的通道間距，這樣的設計是被認為能夠克服當前對巨大數據容量的需求。然而這樣的設計也會有高鄰近通道串擾和高成本的作業系統的後果。我們相信在密分波多工元件中的每個通道都設計成皆為平頂帶寬傳遞通帶，這樣能緩解對於波長需要非常精準以及偏振的需求。因此，在不需要使要波長精準雷射光源的情況下，花費就能有效率的減少。考慮到其關鍵的功能，在這篇論文中的研究重點是如何設計出一個具有低的傳輸損耗、低串擾並具有平頂帶寬傳遞通帶的1x5之密分波多工。所有的模擬皆是使用Photon Design的商業軟體，利用其中的兩套軟體FIMMWAVE和EPIPPROP互相搭配來得到模擬結果。
在設計密分波多工之前，經過觀察，發現了對降低相鄰通道串擾具有顯著影響的參數，進行初步研究以實現優化之目的。各個輸出波導是沿著羅蘭(Rowland)圓作為擺放設計，藉由調整這些波導的位置來觀察對減少串擾的影響。結果顯示出，將波導設計在羅蘭圓上角度較高的位置能有效的減少波導線寬和相鄰通道的串擾。再進一步模擬，發現使用較窄的波導線寬和啁啾型的光柵都同樣能顯著地降低雜訊。
現今有很多種方式已經被發表是產生出低傳輸損耗和低相鄰通道串擾的平頂帶寬傳遞通帶。一般來說，可以藉由波導的幾何形狀或調整光柵焦點以達到平頂帶寬傳遞通帶。本論文中，我們將光柵面的原始方向多轉了一個角度來達到平頂帶寬的通帶。藉由此方式，衍射光的焦點將會產生位移，此時輸出波導中的模會因為位移的訊號和原本的訊號產生傅立葉轉換中的折積(Convolution)現象，進而產生出平頂帶寬的通帶。然而此技術到目前為止依然有較高的傳輸損耗問題尚未解決。這次所提出的方式也有與傳統使用多模干涉儀耦合器所產生出之平頂帶寬結果作比較，轉光柵面角度相較於多模干涉儀耦合器是前者方式具有較好的通道隔離度(±39 dB)，我們在其中使用較窄的線寬於入射波導的條件是不適用於多模干涉儀耦合器的設計。

DWDM (Dense Wavelength Division Multiplexing) owns a promising performance in coupling many numbers of input signals with the certain designated wavelength (multiplexing) and splitting them again into several outputs (de-multiplexing). The dense channel spacing of DWDM is capable of overcoming the massive demand of data capacity needs nowadays. However, this easily causes high adjacent channel crosstalk. It is believed that the flat transmission passband of each channels in DWDM device would relax the need of precise equipment and polarization performance. Thus, the flat passband would effectively reduce the operational cost. In consideration of its critical functions, this thesis will focus on how to develop 1x5 DWDM with low insertion loss, low crosstalk, and flat passband transmission. All simulations were run through Photon Design commercial software, EPIPPROP collaborated with FIMMPROP.
At beginning, the study was conducted to optimize the parameters that have significant impact in reducing the adjacent channel crosstalk. Various output waveguide position along the Rowland circle was tuned to observe its effect in crosstalk reduction. The results showed that putting the waveguides at the higher angle position of Rowland circle would effectively reduce the channel linewidth and the adjacent channel crosstalk as well. Then further simulation showed that using the narrow waveguide width and chirped grating also offer a significant noise floor reduction.
Several techniques have been proposed to obtain the flat passband transmission with low insertion loss and low adjacent channel crosstalk. In general, one can modify the waveguide geometry or tune the grating focal point to flatten the passband transmission. In this thesis, a new approach of passband flattening have been simulated by intentionally tilting the grating facet more to the certain degree. By such, the focal point of diffracted light would be shifted and result in a flat passband once it is convoluted by the output waveguide mode. However, this technique still suffer from high insertion loss. This proposed approach performance was also compared to the MMI coupler method that has been widely utilized in the passband flattening and demonstrated a better channel isolation (± 39 dB) by using narrow width on the input waveguide, which cannot be implemented in the MMI coupler method.

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