利用兩次光載波抑制訊號升頻技術於光纖微波傳輸系統之研究

Signal Up-conversion for Radio-over-Fiber Transport System Using Twice Optical Carrier Suppression Technique

張鈺蓬(Yu-Peng Chang)

指導教授 ： 何文章

國立臺北科技大學/電資學院/光電工程系研究所/碩士(2013年)

摘要

在本論文中所提之串級式單電極強度調變器四倍頻率微波訊號傳輸系統，其藉由利用強度調變器展頻之相位特性，配合簡單之電元件處理，即可產生四倍於RF訊號源之高頻下行光訊號，如此一來傳輸系統可完全免去光濾波器的使用。論文第一部份，利用串級式單電極強度調變器產生四倍頻光微波，將兩顆調變器之直流偏壓操作在傳輸特性曲線之低點(minimum transmission point)形成光載波抑制（optical carrier suppression, OCS）。透過光頻譜分析儀及電頻譜分析儀之量測，利用電相位位移器（electrical phase shifter）對時間延遲作調整，我們可以得到最佳化的光載波抑制比為40.4 dB。
論文第二部分，我們將運用直接調變與外部調變兩種方式將基頻訊號升頻，透過四倍頻之光微波載波產生機制形成倍頻訊號。我們以資料速率622 Mbps(字元長度27-1)之偽隨機位元序列（Pseudo Random Bit Sequence, PRBS）下行信號傳輸10公里及20公里距離之單模光纖；另一方面，同樣以資料速率1.25 Gbps(字元長度27-1)之偽隨機位元序列下行訊號傳輸10公里及20公里距離之單模光纖，觀測兩種不同調變方式所形成最佳化之光載波抑制比。兩種調變方式之升頻訊號經傳輸10公里及20公里後，均以-5 dBm的光功率進入用戶端量得之誤碼率（Bit Error Rate , BER）可達10-9 內及得到清晰之眼圖（Eye Diagram），而功率損耗（Power Penalty）均保持在1 dB以內。

關鍵字

光纖微波系統 ； 四倍頻 ； 光強度調變器 ； 直接調變 ； 外部調變

並列摘要

In this thesis, signal up-conversion for Radio-over-Fiber (RoF) transport system using twice optical carrier suppression (OCS) is proposed. The proposed scheme can produce four times frequency of the RF signals for downstream optical signal by using phase characteristics of the intensity modulated spread spectrum and with using simple electrical components processing. As a result, the optical filter can be completely removed from the use of the transmission system.
First, we employ cascade two single drive intensity modulators to generate frequency quadrupling optical microwave. The two modulators were biased at the minimum transmission point to form the optical carrier suppression (OCS). We measured the spectrum at different points of transmission system by optical spectrum analyzer (OSA) and electrical spectrum analyzer (ESA), respectively. Here, the most optimum optical carrier suppression ratio of 40.4 dB was obtained when using an electrical phase shifter to adjust the time delay.
Second, two modulated methods, direct modulation and external modulation, to up-convert the baseband signals are demonstrated. The up-converted signals were formed through the frequency quadrupling technique mechanism. 622 Mbps and 1.25 Gbps Pseudo Random Bit Sequence (PRBS) downlink signals are transmitted and characterized through 10 km and 20 km of single-mode fiber (SMF), respectively, which the optimum optical carrier suppression ratio of these modulation methods are compared. After 10 km and 20 km of signals transmission, bit error rate (BER) of 10-9 can be achieved and the clear eye diagrams are obtained. Nevertheless, the power penalties are still maintained at less than 1 dB.

並列關鍵字

Radio-over-Fiber ； Frequency quadrupling ； Optical intensity modulator ； Direct modulation ； External modulation

參考文獻

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