為了因應光被動網路靈活性、安全性、與存活能力等多樣性需求，本論文提出基於同心圓拓樸(concentric-concentric circles topology)分佈結合光分波與分碼多重擷取(WDMA/OCDMA)機制應用於中央共享式(central-shared)光網路單元(optical network units, ONUs)，且同時運用陣列波導光柵(arrayed-waveguide gratings, AWGs)路由器的循環週期與自由頻寬間距(free-spectral range, FSR)之特性建構於被動光網路中。在提出的架構中，在光網路裡全部的光網路單元根據各自的地理位置分佈適當的半徑組合成一同心圓型式去切割成不同的同心圓光網路單元群組(concentric circles ONU group)，藉由這種同心圓拓樸我們可以固定每一圈同心圓的往返時間(round trip time)而使得系統效能有顯著的提升。

本論文使用一個粗陣列波導光柵(coarse AWG)路由器不僅保留了指配碼正交性也確保平衡檢測器只會發生最小波長的碰撞。接著我們使用延伸性最大長度序列碼(Extended M-sequence code, EMS code )去實現基於陣列波導光柵的編/解碼器將可以獲得更方便又簡單的編解碼過程且全部使用者的訊息可一次全部解碼出來，此外EMS碼可以放鬆碼長限制並且可增加同心圓光網路單元群組的使用者數目。

本論文將分成兩個部份去探討系統效能，第一、探討多重存取干擾(multiple-access interference, MAI)暨相位導致振幅失真(phase-induced intensity noise, PIIN)的效應，本論文提出的同心圓WDMA/OCDMA機制與傳統光頻域振幅分碼多重擷取 (SAC-OCDMA)在錯誤率為10-9的使用者比較之下使用者數目明顯增加並且更適合用於非同步的資料傳送。第二、估計本論文架構的光功率預算(optical power budget)將可以得到在被動光網路上更實際的功率損耗。因此，比較傳統分時、分波、與分碼多工被動光網路機制，本論文提出的同心圓WDMA/OCDMA被動光網路機制將更兼具靈活性、私密性、及方便性機能的另一選擇方案。

In order to realize passive optical networks (PONs) with flexible, confidential and survivable capacities, a hybrid wavelength-division multiple-access and optical code-division multiple-access (WDMA/OCDMA) scheme over central-shared concentric-circles topology optical network units (ONUs) is presented. Importantly, the periodic cyclic and free-spectral-range (FSR) properties of arrayed-waveguide grating (AWG) routers are also exploited. In the current study, the total ONU capacity in the network is appropriately radius to be partitioned into different groups in accordance with the subscribers’ geographical locations. By combining concentric-circles for ONU groups to fix the round trip time from different circles then system performance will be significantly increased.

By using a coarse AWG router, the proposed concentric-circles topology retains not only signatures orthogonality but also minimal wavelength collisions in the photo-detector. We adopt extended M-sequence (EMS) code to correspond to the AWG codecs for the more convenient and simple coding processes. Besides, the EMS code can relax the code-length and accommodate more users in one group.

The proposed scheme will be examined in two separate parts. Firstly, effects of multiple-access interference (MAI) and phase-induced intensity-noise (PIIN) are investigated. The proposed scheme allows a more significant increase in the number of simultaneous active users than the conventional SAC-OCDMA scheme under the specified bit error rate of 10-9. Secondly, estimation of optical power budget offered for the proposed concentric circles optical network will be discussed. Compared to the current TDM-PON, WDM-PON, and CDM-PON schemes, the proposed WDMA/OCDMA scheme is an alternative solution in network flexibility, confidentiality, and convenience.

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