Abstract
早期的光通訊調變方式一般使用直接強度調變.其本質上是一種振幅調變.其使用範圍受到一些限制。本篇文章就需要所使用的調變系統為相位調變,即相位平移鍵控其主要原因乃在於其有以下一些優點；1:高接收敏感度.2:可增長光放大器間的光纖長度.3:線上光濾波器頻寬限制的降低.4:在多頻道通訊系統中有較高的頻率選擇.除此之外在目前同調檢測方法中內差式相位平移鍵控接收機在訊號傳輸上能提供最佳的系統性能。本文中,我們首先說明平衡式鎖相迴路相位平移鍵控內差式接收系統之0與1間的最佳相位偏移量對系統的重要性。在長途通訊上不可避免地必須使用光放大器.而其自發性發射將會降低同調系統的性能.吾人可算出在使用光放大器下.當不適當使用相位偏移量所造成的訊號功率補償.在一個每秒10G個位元系統中,我們發現其可達到至少1.5分貝的訊號功率補償。第二部份探討有關鎖相迴路所具有的暫態響應延遲效應對訊號失真的影響.因在解調時回授迴路之回授機構本質上會產生響應延遲(包含迴路的傳遞延遲和二階迴路的暫態特性);我們有興趣探討地是後者對訊號的影響.而在此我們討論平衡式和Costas式兩種鎖相迴路.我們可發現在鎖相迴路中,當許多相同位元訊號(0或1)被連續性地傳遞時,平衡式鎖相迴路系統對訊號會造成失真的現象,但Costas系統對訊號的影響則幾乎可以被忽略。In this thesis, we firstly report the importance of theoptimum phase deviation between mark-state and space-statebits in a PSK homodyne system with a balanced phase-locked-loop (PLL) receiver. The signal power penalty incurred byimproper use of phase deviations is evaluated. It is foundthat such power penalty can amount to larger than 1.5 dB in a10 Gbits/sec system. In the second part of this thesis, weexplore the waveform distortion induced by the effect oftransient response delay (TRD) that is inherent in a PLLreceiving system. Phase- locked loops of both balanced andCostas types are considered in this study. It is found thatas a large number of identical bits are consecutivelytransmitted, substantial signal distortion can be induced bythe effect of TRD for a balanced PLL system while the effectof TRD can be neglected for a Costas PLL system.