本論文主旨在無線光通訊的架構設計，並且將本論文架構應用在高密度分波多工的雙向傳輸上，不僅可以與現有光纖網路作連接，傳輸速度亦可達到10 Gbit/s以上。本實驗設計的發射端與接收端為對稱架構，架構由光纖準直器、物鏡以及透鏡組成，其累加損耗為1.1 dB。本論文架構使用單模光纖耦光，因此使用光纖準直器來提高耦合效率，且另一個優點在於輸出的光為平行光，會使光經過遠距離傳送之後光的擴散角度不會造成太大的損耗。實驗部分，利用單一波長傳送10 Gbit/s，經過實驗後得到功率總損耗約11.36 dB，由單向與雙向的量測結果圖觀察到單雙向的誤碼率曲線趨近於重疊，可得功率償付值為0.3 dB，進一步進行分波多工雙向傳輸實驗，總共傳送8個波道，傳輸波長從1550.08 nm - 1555.72 nm，且波道間距為0.8 nm，發射端的平均功率為-6.5 dBm，在接收端的功率平均為-24.8 dBm，功率償付值約為0.75 - 1 dB之間，由眼圖以及誤碼率來觀察，可以發現單向雙向的誤碼率數值相近，且此系統總傳輸容量可達到80 Gbit/s。最後，將計算此系統的功率餘裕值與傳送距離的關係，先假設經過發射端的功率為10 dBm，此系統的接收端的最小接收功率為-20.3 dBm，加上元件以及系統的損耗後，可以用公式算出本論文的架構最遠可傳送410 m。本架構可以架設在大樓之間傳遞訊息，減少光纖的鋪設。

Optical wireless gets more and more attention in recent years. Bidirectional transmission, which may save 50% of some optical components and devices, is also attractive to telecommunication companies and people who need such service to save cost. The thesis designs and investigates some structures for optical wireless (or free-space optics, FSO) communication. The performance analysis is according to bit error rate (BER) performance and eye patterns. The structure we proposed is formed by a fiber collimator and an objective lens. The total loss of these elements is about 1.1 dB. The challenge we encounter is to align the light beam into a single mode fiber (SMF) in small numerical aperture and low acceptable angle. Thus, a fiber collimator is used to improve the coupling efficiency. It could help to converge the light beam even although the transmission distance is increases.
In experiment set up, the laser source has an emitting power of -6.5 dBm and the received power is -24.8 dBm, for each channel. The total 18.3 dB loss is attributed to the spitting/insertion loss array waveguide grating (AWG), free-space loss and other components loss. The resulted of bit error rate has a power penalty of 0.9 dB as compares to the back-to-back transmission. For the performance in lightwave subsystem evaluation, bidirectional WDM (with eight-channel for each direction) transmission system is set up. Note that the wavelengths for downstream and upstream signals are identical (i.e., wavelength reused). The wavelength ranges from 1550.08 to 1555.72 nm with channel spacing of 100 GHz (0.8 nm). Then each channel is modulated at a data rate of 10 Gbit/s in non-return-to-zero formats, with a total transmission rate of 160 Gbit/s. The power penalty with and without bidirectional transmission is less than 0.3 dB. For the link budget issue, if launched power is 10 dBm and the required received power is -20.3 dBm for 〖10〗^(-9) BER, then the link budget is 30.3 dB and the predicted longest distance is up to 410 m.

[1]A. Mahdy, J. S. Deogun, “Wireless Optical Communications: A Survey,” Wireless Communications and Networking Conference, 2004.
[2]D. Kedar, S. Arnon, “Urban optical wireless communication networks: the main challenges and possible solutions,” IEEE Communications Magazine, vol.42, pp. S2-S7, 2004.
[3]D. J. T. Heatley, D. R. Wisely, I. Neild, P. Cochrane, “Optical Wireless: The Story So Far,” IEEE Communications Magazine, vol.36, pp 72-74, 79-82, 1998.
[4]G. Nykolak, P. F. Szajowski, A. Cashion, H. M. Presby, G. E. Tourgee, J. J. Auborn, “A 40 Gb/s DWDM Free Space Optical Transmission Link Over 4.4 km,” Proc. SPIE, vol.3932, pp. 16-20, 2000.
[5]P. F. Szajowski, G. Nykolak, J. J. Auborn, H. M. Presby, G. E. Tourgee, E.J. Korevaar, J. J. Schuster, I. I. Kim, “2.4 km free-space optical communication 1550 nm transmission link operating at 2.5 Gb/s – Experimental results,” Proc. SPIE, vol.3532, pp. 29–40, Jan. 1999.
[6]F. Marioni, Z. Sodnik, F. E. Zocchi, “2.5-Gb/s free-space optics link over 1.1 km with direct fiber coupling to commercial devices,” Proc. SPIE, vol.5550, pp. 60–69, 2004.
[7]G. Nykolak, P. F. Szajowski, J. Jacques, H. M. Presby, J. A. Abate, G. E. Tourgee, J. J. Auborn, “4 × 2.5Gb/s 4.4 km WDM free-space optical link at 1550 nm,” Proc.OFC, vol.Supplement, pp. PD11/1-PD11/3, 1999.
[8]P. L. Chen, S. T. Chang, S. T. Ji, S. C. Lin, H. H. Lin, H. L. Tsay, P. H. Huang, W. C. Chiang, W. C. Lin, S. L. Lee, H. W. Tsao, J. P. Wu, J. Wu, “Demonstration of 16 Channels 10 Gb/s WDM Free Space Transmission Over 2.16 km,” IEEE/LEOS Summer Topical Meetings, pp. 235-236, 2008.
[9]W. O. Popoola, ”Subcarrier Intensity Modulated Free-Space Optical Communications Systems,” University of Northumbria, Newcastle, 2009.
[10]H. Willebrand, B. S. Ghuman, “Free Space Optics: Enabling Optical Connectivity in today's network,” Sams publishing, 2002.
[11]O. Bouchet, H. Sizun, C. Boisrobert, F. De Fornel, P. Favennec, “Free-Space Optics: Propagation and Communication,” ISTE Ltd, 2006.
[12]R. M. Gagliardi, S. Karp, “Optical Communications, 2nd ed,” John Wiley, New York, 1995.
[13]P. P. Smyth; P. L. Eardley; K. T. Dalton; D. R. Wisely; P. McKee; D. Wood,”Optical Wireless: a prognosis,” Proc. SPIE, vol.2601, pp 212-225, 1995.
[14]洪秀雄，大氣科學概論網路學習網頁，國立中央大學。
[15]I. I. Kim, B. McArthur, E. J. Korevaar, “Comparison of laser beam propagation at 785 nm and 1550 nm in fog and haze for optical wireless communications,” Proc. SPIE, vol.4214, pp. 26-37, 2001.
[16]H. C. van de Hulst, ”Light scattering by small particles,” Wiley, New York, 1957.
[17]H. Hemmati, “Deep Space Optical Communications,” Wiley-Interscience, chapter 3, 2006.
[18]E. Leitgeb, M. Geghart, and U. Birnbacher, “Optical networks, last mile access and applications,” Journal of Optical and Fibre Communications Reports, vol. 2, pp. 56-85, 2005.
[19]M. al Naboulsi and H. Sizun, “Fog attenuation prediction for optical and infrared waves,” Optical Engineering, vol.23, pp. 319-329, 2004.
[20]山下真司著、白中和譯，”光纖通信原理與最新應用技術”，建興文化事業有限公司，臺北，2004。
[21]J. H Franz, V.K Jain, “Optical Communication Components and System,” Alpha Science International Ltd., UK, pp. 700-702, 2000.
[22]S. O. Kasap, ”Optoelectronics and Photonis: Principles and Practices,” Pearson Education International, pp. 1-13, 2001.
[23]S. V. Kartalopoulos, “Introduction to DWDM Technology,” Wiley-IEEE, New York, 2000.
[24]王祥，”線性型單縱模光纖雷射的研製”，國立臺灣科技大學電子工程研究所碩士論文，2010。
[25]許凱翔，”C頻帶波長可調線性型單縱模光纖雷射之研製”，國立臺灣科技大學電子工程研究所碩士論文，2010。
[26]王俊容，”光纖光柵與光循環器組成之光纖雷射：研製與應用”，國立臺灣科技大學電子工程研究所碩士論文，2005。
[27]李揚漢、許立根、譚昌文、洪鴻文、曹士林、楊淳良、趙亮琳，”光纖通訊網路”，五南圖書出版股份有限公司，臺北，第1-101頁，2007。
[28]黃素貞譯，”光纖技術手冊”，全華科技圖書股份有限公司，臺北，第9章，2003。
[29]R. Ramaswami, K. N. Sivarajan, ”Optical Network,” Morgan Kaufmann, USA, pp. 258-263, 2002.
[30]耿繼業、何建娃，”幾何光學”，全華科技圖書股份有限公司，臺北，第11章，2009。