下一代40 Gb/s接取網路技術開發和研究

Abstract

爲滿足用戶日益增長的帶寬需求，第一代被動光網路(PON)現在已經被標準化，一些國家已經開始使 用，它同時也是一種光纖到戶(FTTH)的低成本解決方案。它們通常提供在上限20km 範圍内，通過用 戶端的被動分光器和時分多工(TDM)，對共享的32 位用戶提供~2.5Gb/s 下行和~1Gb/s 上行的數據傳 輸。儘管這種被動光網路可以比銅綫網路提供更大的帶寬增長，但是它們並不是網絡供應商所尋求 的最好的降低成本解決方法。因此他們開始提出PON 之後有哪種網路出現的問題。 使用多波長分工(WDM)來增加用戶頻寬是目前普遍被認為下一世代被動光網路的方法。雖然技術 上來說使用多波長分工雷射當作用戶端上傳資料的頻道是可行的，但是用戶端使用昂貴且佈建費用 極高的特定波長雷射並不符合成本效益。因此使用光載子散佈(Optical carrier distribution)架 構被認為是一個有潛力的方式。在此架構中，光載子從中央控制室散佈並分享至用戶端，作為上傳 資料的光載子。使用再調變(Signal-remodulation)的技術可進一步提升載子頻寬的利用率。再調變 技術中，搭載下傳資料的光載子可經由用戶端的調變器再次調變而載入上傳資料，因此一個用戶端 只需要一個波長就可完成上下傳的動作。 數種高速(可高達10 Gb/s)傳輸的再調變被動光網路架構皆已被提出。如今令人感興趣的則是將 傳輸速度提升至40 Gb/s。然而將被動光網路從10 Gb/s 提升至40 Gb/s 是非常具有挑戰性的。此計 畫中，我們將注意力集中在三個階段來達成40 Gb/s 接入網路: (1)首先，我們將調查佈建單一40 Gb/s 頻道系統會遭遇到哪些困難及挑戰。(2)接著，我們將提出一個80 Gb/s/wavelength 訊號再調變架 構的接入網路(使用下傳40 Gb/s DPSK 和上傳40 Gb/s ASK 訊號)。由於我們降低了下傳DPSK 訊號 的調變率(Reduced modulation index)，使得網路剩餘的色散容忍度被大幅提升。由於色散影響被 縮減，也使得經過再調變的ASK 上傳訊號品質能夠提升。此外，我們可以在Mach-Zehnder Interferometer (MZI) 解調器的破壞性干擾輸出端偵測到品質良好的下傳DPSK 訊號。(3)最後將使 用16 個多波長分工頻道的測試平台來完成高達1.28 Tb/s (16 X 80 Gb/s)高傳輸效能的實驗。 此計劃可以為合作夥伴 - 釩創科技股份有限公司建立高速(高達40 Gb/s) FTTH 技術。釩創科技 總部在台北，研發部門位於新竹，釩創科技致力於為客戶提供從儀器設備到系統整合的先進光學和 FTTH 技術。本計劃能促進學術界和業界的合作，令理念和技術在研究人員和工程師之間更好的交流 傳遞。

In order to meet the ever-increasing bandwidth demand by end-users, the first generations of PON have been standardized and deployed in come countries. PONs are also cost-effective access architectures of fiber-to-the-home (FTTH) networks. They typically offer 2.5 Gb/s downstream and ~1 Gb/s upstream, shared among 32 customers via passive optical splitters and a time-division multiple (TDM) access protocol, over a reach of up to 20 km. Whilst these PONs offer significant bandwidth increases compared to copper-based approaches, they may not provide the best ultimate solution for service providers. Hence, the network operators will ask “What comes next after the present PON?” Using wavelength division multiplexing (WDM) is generally considered to be the next step of the present PON to increase the user bandwidth. Although it is technically feasible today if WDM lasers are used to provide the upstream customer data channels, but it is not cost-effective due to the high inventory and deployment costs of using expensive, wavelength-specified laser sources in the customer optical network unit (ONU). A potential solution to this problem is to use optical carrier distribution. In this network, the optical carriers are distributed from a central office (CO), which are shared among, and modulated by the customer ONUs to generate the upstream channels. Bandwidth utilization can be further increased by using signal remodulation, in which the downstream wavelength channel can be remodulated at the ONU to produce the upstream signal, thus, only one wavelength is required for each ONU. Different high speed signal remodulation PON solutions up to 10 Gb/s have been proposed. Researchers are going to further increase the data rate of PON towards 40 Gb/s. However, scaling up from 10 Gb/s to 40 Gb/s PON is very challenging. In this project, we will focus on three areas to achieve the high data rate access network of up to 40 Gb/s per wavelength channel: (1) First, we will study the challenges of deploying single channel 40 Gb/s system. (2) Secondly, we will propose and demonstrate a 80 Gb/s/wavelength (using 40 Gb/s downstream and 40 Gb/s upstream signals) signal-remodulation PON using downstream DPSK and upstream ASK signals. By using the reduced modulation index (RMI) of the downstream DPSK signal, the tolerance to the residual chromatic dispersion can be greatly enhanced. Due to the reduction of the accumulated chromatic dispersion, the quality of the upstream remodulated ASK signal can be improved. Besides, by detecting the downstream demodulated DPSK signal at the destructive output port of the Mach-Zehnder Interferometer (MZI), good quality of the demodulated DPSK signal can still be achieved. (3) Finally, A WDM signal-remodulation PON having a total capacity of 1.28 Tb/s (16 X 80 Gb/s) will also be demonstrated. This project can build up the high data rate (up to 40 Gb/s) FTTH technologies for our partner in this project: PHYTREX Tech. Corp. (headquarter in Taipei, RD team in Hsinchu), which devoted to offer advanced photonic and FTTH technologies from equipments to system integration solutions to customers. This project can also promote the collaboration between academic and industries, allowing idea and technologies transfer between researchers and engineers.