臺灣博碩士論文加值系統

超寬頻脈衝訊號為短脈衝訊號，具有傳輸速率高、抗干擾性強、寬頻、系統容量大等優點，在無線通訊傳輸上具有極大的潛力，但受限於其傳輸功率必須低於-41.3dBm/MHz，傳輸距離約莫10公尺，需利用光纖來才能達到大範圍的訊號傳輸。
本實驗室提出一個新穎的方法，不需複雜的系統架設即可產生超寬頻脈衝光訊號：利用電致吸收調變器整合錐形耦合器，在電致吸收調變器外加電場的情況下，主動波導的吸收與折射率隨著電場而改變，其耦合的比例與吸收的能量也跟著不同，在元件末端使用單模光纖同時接收主被動波導的能量時，由吸收和耦合的交互作用下而產生正負斜率變化的U型轉換曲線( Power via bias )，並在U型區域輸入高斯脈衝訊號，藉由調整合適的轉換曲線的工作點，將低振幅的電訊號轉換成超寬頻脈衝光訊號，並直接於光纖中傳輸以減少電-光轉換所產生的損耗。
在研究結果方面，雙週期脈衝光訊號的半高寬為75ps，10dB頻寬為7.5GHz，頻寬載波比為125%，且功率頻譜密度小於-41.3dBm/MH，以上皆符合聯邦通訊委員會之規範；另外，在系統測試上已完成訊號眼圖和誤碼率的量測，未來將結合長距離光纖來傳遞超寬頻脈衝光訊號，並比較不同傳輸距離的超寬頻脈衝光訊號，最後藉由誤碼率的量測來驗證超寬頻脈衝光訊號可利用光纖來才能達到大範圍的訊號傳輸。

Ultra Wide Band (UWB) is a short-pulse signal which has extremely potential in wireless communication system due to the advantages of high data rate, better immunity to multipath fading, wide bandwidth, and high capability. According to the Federal Communications Commission (F.C.C.), UWB only can be transmitted in short distance of a few to tens of meters due to low power density (-41.3dBm/MHz). However, optical fiber has low loss and cost and wide bandwidth, so it can be achieved in wide area network.
In this work, we propose a novel method to generate optical UWB doublet pulse without complicated setup. When electroabsorption modulator (EAM) integrating a taper optical directional coupler (TODC) was applied field, the transmission loss and coupling would change resulting from the absorption coefficient and effective index of active waveguide with the applied field. So, we used a single mode fiber collecting the power after the device, we could get the valley shape transfer function. Using the transfer function of electro-absorption modulator (EAM) integrating TODC we inject a Gaussian pulse into the EAM in the range of valley shape, and it can transform an electrical pulse into optical UWB doublet pulse by acceptable operating point. Therefore, the optical signals could be transmitted in optical fiber so that it can reduce loss of the electro-optic transformation.
Experimentally, the full wave at half maximum of doublet pulse, 10dB bandwidth, fractional bandwidth were 75ps, 7.5GHz, 125%, respectively, and power density was less than -41.3dBm/MHz. These were all meeting the F.C.C. standard. In the future, we will use long distant optical fiber to transmitted UWB signal, and compare with different distance. Finally, we will check the UWB signal can be transmitted in optical fiber to achieve wide range signal transmission by bit error rate test.

論文審定書..............................................................................i
誌謝........................................................................................iii
中文摘要................................................................................iv
英文摘要................................................................................vi
第一章 序論..........................................................................1
1.1 研究動機.........................................................................1
1.2 簡介.................................................................................3
1.3 超寬頻系統技術與波形.................................................6
1.4 超寬頻脈衝光訊號之產生方法...................................10
第二章 原理.......................................................................16
2.1 超寬頻雙週期脈衝訊號之產生原理..........................16
2.2 電致吸收調變器與錐型耦合器之結構......................19
2.3 錐型耦合器之工作原理..............................................20
2.4 電致吸收調變器之工作原理......................................23
第三章 特性分析與實驗結果...........................................27
3.1 元件直流特性量測與討論..........................................27
3.2 BPM模擬與討論..........................................................36
3.3 超寬頻訊號之架設與結果討論..................................41
第四章 結論與未來工作.....................................................47
參考資料與文獻..................................................................49

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