超密波長分工及次載波有線電視系統的基本限制

Abstract

本論文研究超密波長分工系統及次載波有線電視系統的基本限制. 主要分為四個部份: 在第一部分中, 我們分析了2.5 及10 Gb/s的超密波長分工系統在不同單模光纖中的傳輸限制並分析了週期性放大的系統在C波帶的各項基本限制及最佳色散補償比例. 第二部分, 我們發現在1550nm 外調式類比有線電視系統中, 自發性及外加相位調變必須同時考慮才能精準地預測二階拍差, 特別是當外加相位調變的調變深度或頻率高的時侯. 這個結果對長距離1550nm 外調式光發射機的設計有很重要的影響. 第三部分, 我們證明了用多個CW載波來模擬測試M-QAM次載波有線電視系統的準確度是在量測誤差的範圍內. 最後, 我們架設了世界第一個類比的光纖循環迴圈並創造了78個頻道64-QAM 1550nm次載波系統的最長傳輸記錄-740km.

This thesis investigates fiber nonlinearity limitation in both ultra dense wavelength division multiplexing (U-DWDM) digital systems and subcarrier multiplexing analog lightwave transmission systems. The main research results are organized into four parts. First of all, transmission performance of ultra-dense 2.5 and 10 Gbps NRZ IM/DD wavelength division multiplexing systems in various single-mode fibers is investigated. Fundamental limiting factors and their remedies by using optimum dispersion compensation for periodically amplified systems in C-band are presented. Second, we found that the combined effects of self- and external-phase modulations must be considered in order to precisely predict the CSO distortions in a long-distance 1550 nm externally-modulated AM-CATV system, especially when the applied phase modulation index and modulating tone frequency to the integrated phase modulator are high. This result has important implications to the optimum design of 1550 nm transmitter for long-distance AM- and QAM-CATV systems. Third, the validity of using multiple CW tones as the signal source to test the linearity of a multichannel M-ary quadrature-amplitude-modulation (M-QAM) subcarrier multiplexed (SCM) lightwave system was investigated. We consider the following representative optical fiber system nonlinearities: (1) laser clipping, and (2) the combined effect of laser frequency chirp and fiber dispersion. The results show that, if all orders of nonlinear distortions (NLDs) in a signal bandwidth are included in the total NLD power, the error caused by replacing M-QAM signals with CW tones can be within measurement uncertainty. Finally, a long-distance 1550 nm subcarrier multiplexed lightwave trunk system which transported 78 channels of 64-QAM signals was demonstrated in a recirculating loop experiment. Each channel can achieve a carrier-to-(noise + nonlinear distortion) ratio of 30 dB after 740 km transmission through conventional single-mode fiber without dispersion compensation.