Advanced measurement techniques in optical fiber sensor and communication systems

ADVANCED MEASUREMENT TECHNIQUES IN OPTICAL FIBER SENSOR AND COMMUNICATION SYSTEMS HU JUNHAO NATIONAL UNIVERSITY OF SINGAPORE 2011 ADVANCED MEASUREMENT TECHNIQUES IN OPTICAL FIBER SENSOR AND COMMUNICATION SYSTEMS HU JUNHAO (B Eng., Huazhong University of Science and Technology, China) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF ELECTRICAL AND COMUPTER ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2011 Acknowledgement Many people have inspired, guided and helped me during my four years PhD study in National University of Singapore I would like to thank them all Firstly, I would like to give my special thanks to my supervisor, Dr Changyuan Yu, for his professional guidance and enthusiastic support during my PhD study It is him who has opened the door of research and illuminates my future In the last four years, sometimes, I might feel depressed and lose the confidence to continue my PhD study; it is him who encouraged me and gave me the confidence to continue And I also want to thank Dr Chen Zhihao for his help on my research in optical fiber sensor systems He gave me a lot of guidance and help on the experiment of long distance FBG sensor system He gave me the direction of research on how to improve the performance of experiment Without his help, I cannot finish this project I am also fortunate enough to work with many outstanding students and research staffs in our group I take this opportunity to thank Dr Yang Jing for her beneficial suggestions and encouragement in my study and life Finally, my deepest gratitude goes to my parents Their support and encouragement are always here whenever I encounter any difficulties And I also want to thank my girlfriend for her support With their help, my PhD experience has been the most rewarding and pleasant i Table of Content Acknowledgement i Table of Content ii Summary vi List of Figures x List of Tables xvi List of Abbreviations xvii Introduction 1.1 Pulse generation and measurement techniques 1.1.1 Pulse train generation using SWNTs as saturable absorber 1.1.2 Pulse measurement techniques 1.1.3 Limitation of conventional second-harmonic generation autocorrelator 1.2 Review of optical fiber sensors 1.2.1 Fiber Bragg grating sensor system 11 1.2.2 Long distance FBG sensor system 14 1.3 Performance monitoring in optical communication system 15 1.4 Focus and structure of the thesis 18 Pulse Generation based on Carbon Nano-tube fiber laser 20 2.1 Background and methods 21 2.1.1 Working principle of Q-switched laser system 21 ii 2.1.2 Fabricating single-wall nanotube saturable absorber with low insertion loss 24 2.2 Tunable wavelength CNT-SAs Q-switched fiber ring laser 26 2.3 Tunable wavelength, tunable repetition rate linear cavity CNT-SAs Q-switched fiber laser 31 2.3.1 Experimental setup of the linear cavity fiber laser 32 2.3.2 Experimental results and discussions 33 2.4 Tunable repetition-rate FBG linear cavity CNT-SAs Q-switched fiber laser 36 2.4.1 110-cm length FBG linear cavity fiber laser setup 37 2.4.2 Experimental results and discussions 38 2.5 Comparison 41 Pulse measurement based on degree of polarization (DOP) autocorrelation method 44 3.1 Experiment setup and operation principle 46 3.2 Simulation results 48 3.2.1 Chirp effect to the pulse width measurement 48 3.2.2 Misalignment effect to the pulse width measurement 53 3.3 Experimental results 55 3.4 Comparison and conclusions 57 Long distance fiber Bragg grating sensor system based on Raman amplification 60 4.1 Background and operation principle 62 4.1.1 Spontaneous vs stimulated Raman scattering 62 4.1.2 Operation principle of 100-km long distance fiber Bragg grating sensor 66 4.1.3 Operation principle of 150-km long distance fiber Bragg grating sensor 68 iii 4.2 150-km multi-point temperature and vibration sensor system 70 4.2.1 Multi-point long distance FBG sensor system 70 4.2.2 Long distance temperature sensor system 73 4.2.3 Long distance vibration sensor system 75 4.2.3.1 Vibration sensor based on tunable filter 75 4.2.3.2 Vibration sensor system based on matching filter demodulation 76 4.2.3.3 Experiment results of vibration sensor system 79 4.3 Conclusions 80 CD monitoring based on delay tap sampling with low bandwidth receiver 81 5.1 Principle of Delay-tap Sampling Plot 83 5.2 Delay tap sampling methods based on low bandwidth balanced receiver of 50-Gbit/s RZ-QPSK signal 86 5.2.1 Simulation results 86 5.2.2Experiment results of using low bandwidth balanced receiver 89 5.2.3 Comparison between the results of high bandwidth balanced receiver and our method 92 5.3 Delay tap sampling method based on single low bandwidth receiver 95 5.3.1 Simulation results based on one low bandwidth receiver 96 5.3.2 Experiment results of using a single low bandwidth receiver 98 5.3.3 Comparison between high bandwidth receiver and our method 100 5.3.3.1 Simulation results of CD monitoring scheme using one 40-GHz bandwidth receiver 101 5.3.3.2 Experiment results of CD monitoring scheme using one 40-GHz bandwidth receiver 101 5.4 Conclusions 103 Conclusions and Future Works 104 iv 6.1 Conclusions 104 6.2 Future Works 106 6.2.1 Improvement on autocorrelator based on DOP measurement 106 6.2.2 Improvement on the long distance FBG sensor system 107 6.2.3 Improvement on CD monitoring system based on low bandwidth delay tap sampling method 107 Bibliography 109 Publication list 130 v Summary In 1870, John Tyndall demonstrated that light can follow a specific path by using internal reflection This is the first concept that fiber can be used to guide the light As the development of fiber, glass fiber is proposed However, the losses of these fibers are too large to transmit signals over long distance fibers Later, in 1960s, Charles Kao and his co-workers demonstrated that the high-loss of fiber comes from impurities in the glass, not the glass itself From this concept, using fiber as a telecommunication medium has been realized Optical fiber has a lot of applications; and the two main applications are optical fiber communication and fiber optic sensors However, there are still many problems to be solved in these two main applications For optical fiber communication system, there are a lot of effects that can affect the system performance, such as the chromatic dispersion (CD), polarization mode dispersion (PMD), optical signal noise ratio (OSNR) and other nonlinear effects In order to improve the performance, many techniques are proposed to monitor and measure these effects Taking CD monitoring as an example, there are radio frequency power fading method, additional pilot tone method, delay-tap sampling plots method and others For the fiber optic sensor system, there are also a lot of problems to be solved Take the gas and oil pipeline leakage monitoring sensor as an example; it should be long distance, high vi robustness and low cost In this thesis, several advanced measurement techniques in optical fiber communication and fiber optic sensor systems are introduced Firstly, pulse train generation and measurement techniques are introduced Qswitched single wall nanotubes (SWNTs) fiber laser with low insertion loss is firstly demonstrated in this thesis As we know, a saturable absorber is the key component of passive Q-switched laser to generate the pulse trains These saturable absorbers are normally semiconductor saturable absorber and crystal saturable absorber, which is not friendly using to fabricate all-fiber lasers Later, in 2008, SWNTs is firstly used to generate a tunable wavelength mode-locked fiber laser; and it is published on Nature Nanotechnology Nowadays, SWNTs are widely used to generate ultra-short pulse width mode-locked lasers But Q-switched SWNTs all-fiber lasers have never been demonstrated before In this thesis, we firstly reduce the SWNTs insertion loss from dB to 0.7 dB Then we introduce three different SWNTs based Q-switched fiber lasers They are C+L band tunable wavelength SWNTs all-fiber ring laser, tunable wavelength tunable repetition rate linear cavity SWNTs fiber laser and tunable repetition rate FBG linear cavity SWNTs fiber laser After introducing the pulse generation based on SWNTs, a low power autocorrelator is proposed based on degree of polarization (DOP) measurement Firstly, the chirp factor and mismatching angle is studied in simulation It is found that the pulse widths almost have the linear relationship with the chirp factors, which means our method can be used to measure the chirp factor if the original pulse width is known And vii the small effects of mismatching angle on pulse width measurements prove the high misalignment tolerance of the system Compared with the traditional second harmonic generation (SHG) autocorrelator, which requires very rigid alignment and high laser power, this method can measure -60 dBm power pulse train with shorter time The sensitivity of our method has been increased to 10-20 W2, compared with the SHG autocorrelator 10-7 W2 After introducing the pulse width measurement, the measurement techniques in fiber optic sensor system are introduced As we know, there are many problems in the fiber optic sensor system, such as the measurement length, cost and robustness In this thesis, a simple and cost effective method is proposed to solve the measurement length issue of the FBG sensor systems A novel 150-km multi-point long distance FBG temperature and vibration fiber sensing system is demonstrated based on Raman amplification In addition to a Raman laser at 1395 nm and a laser at 1480 nm, the 150km long distance system is constructed only by passive optical components, such as the coupler, SMF and EDF It is an all fiber long distance temperature and vibration sensor system without any electrical components along the 150-km fiber The accuracy of this temperature sensor is about oC; and the vibration measurement range is from Hz to 1000 Hz After introducing the measurement techniques in fiber optic sensor systems, 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temperature and vibration sensor system based on stimulated Raman amplification”, IEEE/OSA Journal of Lightwave Technology, vol 30, no 8, pp 12371243, April 2012 Junhao Hu, Zhihao Chen, and Changyuan Yu, “150-km long distance fiber sensor system based on Raman amplification,” IEEE sensors conference, pp 113-116, October 2011 Bo Dong, Jianzhong Hao, Junhao Hu, and Chin-Yi Liaw, “Short linear-cavity Qswitched fiber laser with a compact short carbon nanotube based saturable absorber,” Optical Fiber Technology, vol 17, no 2, pp 105-107, March 2011 Bo Dong, Junhao Hu, Chin-Yi Liaw, Jianzhong Hao, and Changyuan Yu, “Wideband-tunable nanotube Q-switched low threshold erbium doped fiber laser,” Applied Optics, vol 50, no 10, pp.1442-1445, March 2011 Junhao Hu and Changyuan Yu, “Low power autocorrelation technique based on the degree-of-polarization measurement,” Optics Communications, vol 283, no 24, pp 4928-4932, December 2010 Bo Dong, Jianzhong Hao, Junhao Hu, and Chin-Yi Liaw, “Wide pulse-repetition-rate range tunable Nanotube Q-switched low threshold erbium-doped fiber laser,” IEEE Photonics Technology Letters, vol 22, no 24, pp 1853-1855, December 2010 130 Bo Dong, Chin-Yi Liaw, Jianzhong Hao, and Junhao Hu, “Nanotube Q-switched lowthreshold linear cavity tunable erbium-doped fiber laser,” Applied Optics, vol 49, no 31, pp 5989-5992, November 2010 Junhao Hu, Zhihao Chen, Xiufeng Yang, Junhong Ng, and Changyuan Yu, “100-km Long Distance Fiber Bragg Grating Sensor System Based on Erbium-Doped Fiber and Raman Amplification,”IEEE Photonics Technology letters, vol 22, no 19, pp 1422-1424, October 2010 Changyuan Yu, Jing Yang, and Junhao Hu, “Nonlinear fiber based processing for high speed optical communication and sensor systems,” IEEE Photonics Society Summer Topical Meetings (SUM), TuC2-3, pp 1-2, Mexico, July 2010 10 Junhao Hu, Zhihao Chen, Xiufeng Yang, Junhong Ng, and Changyuan Yu, “100km Long distance vibration sensor,”2nd Asia-Pacific Optical Sensors Conference (APOS), pp 1-2, June2010 11 Junhao Hu, Zhihao Chen, Ju Teng Teo, and Changyuan Yu, “100-km long distance FBG vibration sensor based on matching filter demodulation,” 21st Optical fiber sensors conference (OFS), Proc SPIE 7753, 77538N, May 2011 12 Junhao Hu, Jing Yang, Fang Xu, and Changyuan Yu, “Chromatic dispersion monitoring of RZ-DQPSK signal with low bandwidth detector by evaluating the amplitude ratio of delay tap sampling,” 3rd International High Speed Intelligent Communication Forum (HSIC), May 2011 13 Jing Yang, Junhao Hu, Changyuan Yu, Yong Kee Yeo, and Yixin Wang, “MultiChannel 80-GHz Pulse Train Generation Based on Optical Parametric Process,” Optics Communications, vol 283, no 6, pp 939-945, March 2010, 131 14 Junhao Hu, Zhihao Chen, Xiufeng Yang, Junhong Ng, and Changyuan Yu, “Long Distance Fiber Bragg Grating Sensor System Based on Erbium-Doped Fiber and Raman Amplification,” Asia Communications and Photonics Conference and Exhibition (ACP), TuC5, pp 1-6, November 2009 15 Junhao Hu and Changyuan Yu, “An Improved Autocorrelation Technique Based on the Degree-of-Polarization Measurement,” OptoElectronics and Communications Conference (OECC), ThM4, pp 1-2, July 2009 16 Jing Yang, Junhao Hu, Changyuan Yu, Yong Kee Yeo, and Yixin Wang, “MultiChannel 80-GHz Pulse Train Generation Based on Four-Wave Mixing in Highly Nonlinear Fiber,” OptoElectronics and Communications Conference (OECC), TuA5, pp 1-2, July 2009 17 Jing Yang, Junhao Hu, Changyuan Yu, Yong Kee Yeo, and Yixin Wang, “80-GHz multi-channel RZ pulse train generation based on XPM and FWM in a nonlinear optical loop mirror,” 5thInternational Conference on Materials for Advanced Technologies (ICMAT), pp 1-3, July 2009 132 ... temperature sensor is about oC; and the vibration measurement range is from Hz to 1000 Hz After introducing the measurement techniques in fiber optic sensor systems, measurement techniques in optical communication. .. several advanced measurement techniques in optical communication and fiber sensor systems are introduced, especially in pulse generation and measurement, long distance FBG sensor system and CD... summarized in the 15th Optical Fiber Sensors (OFS) Conference as the technologies involved in Fig 1.3 In section 1.2.1, the most popular topic in optical fiber sensors, fiber grating sensor technology,