台灣留學生出席國際會議補助

2009年7月14日 星期二

CD-Insensitive PMD Monitoring of an 80-Gb/s Polarization-Multiplexed RZ-DPSK Channel Using a Polarizer and a Low-Speed Detector

論文發表人: 楊政源 (南加州大學電機系博士班)
 
Optical performance monitoring (OPM) has emerged as an exciting topic for enabling future robust, high-performance optical communication systems. Ideally, OPMs should isolate the specific effect that is degrading a data stream, such as deleterious chromatic dispersion (CD), polarization-mode dispersion (PMD), nonlinearities, or low optical signal-to-noise ratio (OSNR). However, as progress is made in advanced OPM functionality, optical systems themselves are transmitting data formats that are ever-more complex. This extremely important trend in advanced data modulation formats is driven by the desire for: (i) better receiver sensitivity and tolerance to nonlinearities, as with differential phase-shift-keying (DPSK), and (ii) better spectral efficiency and tolerance to chromatic dispersion, as with differential quadrature PSK (DQPSK).
A technique that has gained much interest for doubling the system capacity and spectral efficiency is the use of polarization-multiplexing (Pol-Mux) of two independent data streams. Although this format is inherently more sensitive to the PMD effects than other types of formats, it is a viable and relatively straightforward option for high-capacity transmission systems. Given this trend and the increased sensitivity to PMD, it could be quite valuable to investigate optical-performance-monitoring methods to monitor the accumulation of PMD in a high-rate pol-muxed system, especially in a manner that is insensitive to chromatic dispersion. To date, there has been little reported on PMD monitoring in a pol-muxed system.
We experimentally demonstrate a new chromatic dispersion insensitive technique for monitoring differential-group-delay (DGD, i.e., first-order PMD) on a pol-muxed channel. We show monitoring results for an 80-Gb/s pol-muxed RZ-DPSK channel, in which the monitor consists of a polarizer, low-speed detector, and RF power meter. The polarizer is aligned along one data stream of the pol-muxed RZ-DPSK channel and thus the RF power increases with the accumulated DGD, which can be used for monitoring. The RF power is measured at low frequency content (e.g., several hundreds of Megahertz), indicating that the monitored RF power is less sensitive to chromatic dispersion [4]. Monitored power increment of 16.2 dB, insensitive to CD of 0~100 ps/nm, is achieved in the presence of up to 12-ps DGD value. This technique is simple, no high-speed components are required for measurements, and this technique is potentially applicable to 100-Gb/s pol-muxed RZ-DQPSK channel
 
光系統性能監測已經成為一個任人振奮的研究題目去達到未來穩定的和高性能的光纖通訊系統。 理想的情況下,光系統性能監測器可以區分開毀壞光訊號的特定效應,比如光纖色散,偏振色散,非線性光學效應,還有低光訊噪比率。 然而,在邁向更高階的光系統性能監測的功能性,光系統本身正傳輸著比以往更複雜的光訊號調制格式。 這個關於光訊號調制格式的趨勢變得非常重要因為以下的需求:(1)更好的光訊號接收器敏感度還有非線性光學效應的容忍度,比如使用二相位調制訊號;(2)更好的光纖頻譜利用率還有光纖色散的容忍度,比如使用四相位調制訊號。
使用偏振合併調制兩個獨立的光訊號流的技術,來達成雙倍的光纖傳輸系統容量還有頻譜利用率,最近得到學術研究上的關注。 即使這個光訊號調制格式跟其他的調制格式比較起來,本質上對於偏振色散比較敏感,採用這個光訊號調制格式對於高容量傳輸系統來說是非常有價值的、直接的選項。 關於這個趨勢還有對於偏振色散所增加的敏感度,研究探討光系統性能監測技術去監測在高速偏振合併調制系統中所累積的偏振色散變得非常有學術上的價值,尤其是這些技術對於光纖色散可以不敏感。 至今,只有少數的研究報告關於監測偏振合併調制系統中的偏振色散。
我們實驗操作量測一個新技術去監測偏振調制系統中的偏振色散(一階色散),而且這個技術可以對於光纖色散不敏感。 我們展示對於80-Gb/s偏振合併調制的RZ-DPSK訊號通道。 監測器包含偏振片、低速光接收器、電訊號功率量取器。 調整偏振片的方向去對到偏振合併調制訊號中的一路偏振方向,然後所量到的電功率隨著所累積的偏振色散增加,這個變化的趨勢便可以使用來做監測的功能。 電功率在低頻分量部分被量取(也就是幾百萬赫茲),以致於所監測到的電功率比較不敏感於光纖色散。 監測量取到16.2 dB的功率增加量可以用來監測0~12 ps的偏振色散值,並且對於0~100 ps/nm的光纖色散不敏感。 這個技術提供簡單的操作,並不需要高速的儀器,而且這個技術可以適用於更高速100-Gb/s偏振合併調制的RZ-DQPSK訊號通道。