新穎子載波間干涉雜訊補償技術以及應用在長距離被動式光網路系統

Abstract

為了能有效的降低光通訊系統的成本，採取直接調制的方式將會比外部調制的方式好。目前直接調制大都使用直接對雷射輸入電流進行調制，或是使用EAM進行調制動作。以基頻通訊來說，可使用的頻寬除了由雷射本身的增益曲線決定之外，會隨著光纖傳輸的距離，各元件的chirp factor，而產生一RF衰減。另外，為了有更高的頻譜使用效率，我們使用正交分頻多工 (OFDM) 來調制訊號。因為這樣，子載波間的干涉、子載波與雷射光源間的干涉，對於我們這樣的直接調制基頻光通訊系統是個相當大的課題。基於此，我們藉由數學工具，於解調器運用訊號處理技術以及重復偵測 (iterative detection) ，將因干涉所產生的雜訊於接收端進行補償。另外，多頻帶 (multi-band) 的訊號調制方式，可用來避開因RF衰減所造成的訊號功率損失，也進一步提高頻譜的使用效率。

For the purpose to effectively reduce the cost of optical communication system, directly modulation will be better than external modulation. Most of the case for directly modulation is to modulate the laser bias current directly or to use the Electro-Absorption Modulator to modulate the laser light. In baseband communication, usable band-width is not only decided by laser gain curve, but devices’ characteristics, and the transmission distance. On the other hand, for increasing spectral efficiency, we use orthogonal frequency division multiplexing (OFDM) to modulate the signals. However, the interference between subcarriers to subcarriers, subcarriers to optical carrier, will be a main project to the directly modulated-base band optical communication system. Therefore, we use advanced digital signal processing and iterative detection techniques to compensate the interference-induced noise at receiver port. By the way, multi-band signal subcarrier allocation can avoid the energy loss due to power fading and further increase the spectral efficiency.