Abstract
在光纖通訊領域,強度調制直接偵測(IM/DD)的技巧很受歡迎並且廣泛地使 用在高速的資料傳輸上.這是因為(IM/DD)簡單且在架設的花費上比其它的 技巧便宜的多.然而同調偵測技巧吸引了很多人的注意並應用在光纖通訊 上因為同調偵測系統的接收敏感度遠大於(IM/DD)系統.使用在同調偵測系 統上,有三種調制的方式如振幅平移鍵控(ASK),頻率平移鍵控(FSK),相位 平移鍵控(PSK),在這三種方式中相位平移鍵控(PSK)內差式接收器有著最 佳的接收敏感度.在解調方面此內差式接收系統需要鎖相迴路來補償雷射 相位雜訊.平衡式鎖相迴路和非線性鎖相迴路最常使用在相位平移鍵控( PSK)內差式偵測系統上.非線性鎖相迴路可分為Costas鎖相迴路跟決定驅 動鎖相迴路.Costas鎖相迴路結構上比平衡式鎖相迴路複雜,但它沒有資料 鎖相的雜訊產生且它對雷射線寬的要求比平衡式鎖相迴路寬鬆.所以它廣 泛地使用在相位平移鍵控內差式接收系統上.另外Costas鎖相迴路在上下 臂的輸入功率比對系統性能的影響亦在本章的探討範圍內.在本論文中,我 們探討雷射相位雜訊,偵測器雜訊,光放大器雜訊,對Costas鎖相迴路接收 系統性能的影響.其目的在於估計由雷射相位雜訊所引起的功率損耗,並找 出在光放大器雜訊影響下的雷射線寬要求,本論文分四章:第一章簡介,第 二章Costas鎖相迴路系統性能的分析與理論,第三章計算系統的功率損耗 和雷射線寬的要求,第四章討論,第五章結論. In the field of optical fiber communications, intensity modulation/direct detection (IM/DD) techniques are popular and have been widely used for high-bit-rate data transmission. This is because an IM/DD technique is simple and thus imposes less cost on system implementation than any other techniques. On the other hand, coherent detection techniques have attracted much attention and applied to optical fiber comm- unications. Since the receiver sensitivity in a coherent detection system is much higher than that an IM/DD scheme can offer, a longer span between adjacent optical amplifiers in a long-haul system can be achieved by using the coherent detection technique. In applying coherent detection techniques, three modu- lation formats, such as ASK, FSK and PSK, are commonly used. Among those present detection schemes, the PSK homodyne rece- iver offers the best receiver sensitivity. In the stage of demodulation, however, the receiver needs a phase-locked loop (PLL) circuit to compensate for the effect of laser phase noise. Two types of PLL's are currently employed for PSK homodyne detection in either experimental or theoretical works: balanced PLL's and nonlinear PLL's. In this study, we investigate the system performance of Costas PLL receivers accounting for the effects of laser phase noise, detector shot noise and optical amplifier noise. The focus is aimed to the estimation of power penalty incurred by laser phase noise and to finding the laser linewidth require- ments under the influence of optical amplifier noise. The rest of this paper is organized as follows. Chapter two gives a background theory for system performance analysis. Compu- tational results showing system power penalties and laser linewidth requirements are presents in Chapter three. Chapter four shows the methods to get laser linewidth requirements. Then chapter five concludes this paper.