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The identical weak reflection Fiber Bragg gratings (FBGs) with large capacity has become one of the central issues of optical fiber sensing field in the engineering application.Currently,wavelength division multiplexing (WDM) and time division multiplexing (TDM) are two major multiplexing techniques.For a WDM system,the maximum number of FBGs is limited by the spectral bandwidth of laser.So the identical weak FBGs are proposed to break through the limitation of the multiplexing capacity.For large-capacity multiplexing of identical weak FBGs,TDM technique is commonly used.In a TDM system,the spectral information of all FBGs can be obtained by some pulsed light with different wavelengths.However,with increasing the number of identical weak FBGs in TDM system,some problems such as complex demodulation process and slow response time are highlighted in the current various demodulation methods. Thus in this paper we propose a new high-speed demodulation method combined with wavelength-sweep optical timedomain reflectometry (WSOTDR) which is different from the pulsed light in optical time domain reflectometry (OTDR), namely a continuous wavelength-sweep light source is used in WSOTDR.In this method,the reflected signals of identical weak FBG at each position will be distinguished from others in time domain through optical delay effect,hence the location information of each FBG could be acquired,and meanwhile the wavelength information of all the identical weak FBGs could be obtained through high-frequency periodical wavelength-swept spectrum in just one wavelength scanning period.In order to calibrate the error of FBG demodulation which is caused by optical delay at high-speed wavelength sweep,we propose a self-calibration method in which two different wavelength-sweep rates are used to obtain the inherent delay parameters of each FBG.In practical application,we use this self-calibration method in the initial stage of demodulation because the inherent delay parameters are usually stable after the layout of an identical weak FBGs network.So the demodulating speed at the working stage of this system is not affected by this self-calibration method. In this paper,by setting up a Fourier domain mode locking laser as an output of continuous wavelength-sweep and highspeed (3.27×106 and 2.72×106 nm/s) light,an identical weak FBG sensing network which consists of 18 FBGs is tested in three experiments.In the initial calibration experiment,we use the self-calibration method to calibrate the inherent delay parameters of each FBG and to verify the accuracy of the system by comparing with the measurement result of spectrum analyzer.In the temperature experiment,the wavelength of each FBG is demodulated from 30 to 100 ℃ in order to test the demodulation linearity of the system.Then in the vibration experiment,a dynamic measurement of 3.6 kHz vibration of FBG is demonstrated with a demodulating speed as fast as 120 kHz,and a 0-60 kHz frequency spectrum is analyzed to prove the speed.The experimental results show that the demodulation error is less than 15 pm, the resolution is 1pm,the linearity is above 0.998,and the demodulating speed reaches 120 kHz.
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Keywords:
- continuous wavelength-sweep light /
- identical weak fiber Bragg gratings /
- high-speed demodulation /
- calibration of delay error
[1] Wang L, Li D S, Ou J P 2011 Adv. Mater. Res. 148 1611
[2] Jiang D S, He W 2002 J. Opt. Laser 13 420(in Chinese)[姜德生, 何伟2002光电子·激光13 420]
[3] Wang F F, Zhang L, Yang L Z, Liu Y Y 2014 Acta Opt. Sin. 34 88(in Chinese)[王斐斐, 张丽, 杨玲珍, 刘艳阳2014光学学报34 88]
[4] Zhou Q, Ning T G, Pei L, Li J, Li C, Zhang C 2012 Opt. Lett. 8 414
[5] Jiang H, Chen J, Liu T, Huang W 2013 Sensor. Actuat. A:Phys. 198 31
[6] Chen D, Fok M P, Shu C, He S 2008 Lasers and Electro-Optics, 2008 and 2008 Conference on Quantum Electronics and Laser Science Canada, May 4-9, 2008 p1
[7] Lee B C, Jung E J, Kim C S, Jeon M Y 2010 Meas. Sci. Technol. 21 094008
[8] Chen D, Shu C, He S 2008 Opt. Lett. 33 1395
[9] Yu H H, Zheng Y, Guo H Y, Jiang D S 2014 J. Funct. Mater. 12 12001(in Chinese)[余海湖, 郑羽, 郭会勇, 姜德生2014功能材料12 12001]
[10] Dai Y, Liu Y, Leng J, Deng G, Asundi A 2009 Opt. Lasers Eng. 47 1028
[11] Li Z Y, Sun W F, Li Z M, Wang H H 2015 Acta Phys. Sin. 64 234207 (in Chinese)[李政颖, 孙文丰, 李子墨, 王洪海2015 64 234207]
[12] Zhang C X, Zhang Z W, Zheng W F, Liu X H, Li Y, Dong X Y 2014 Chin. J. Lasers 41 0405004(in Chinese)[张彩霞, 张震伟, 郑万福, 刘晓航, 李裔, 董新永2014中国激光41 0405004]
[13] Chan C C, Wei J, Ho H L, Demokan M S 2000 IEEE J. Sel. Top. Quant 6 741
[14] Zhang M L, Sun Q Z, Wang Z, Li X L, Liu H R, Liu D M 2011 Laser & Optoelectronics Progress 8 93(in Chinese)[张满亮, 孙琪真, 王梓, 李晓磊, 刘海荣, 刘德明2011激光与光电子学进展8 93]
[15] Hu C W, Wen H Q, Bai W 2014 J. Lightwave Technol. 32 1406
[16] Wang Y, Liu W, Fu J, Chen D 2009 Laser Phys. 19 450
[17] Li Z Y, Liu M Y, Wang Y M, Liu Q, Gong J M 2014 IEEE Photon. Technol. Lett. 26 2090
[18] Yin G L, Dai Y T, Karanja J M, Dai J X 2015 Sensor. Actuat. A:Phys. 235 311
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[1] Wang L, Li D S, Ou J P 2011 Adv. Mater. Res. 148 1611
[2] Jiang D S, He W 2002 J. Opt. Laser 13 420(in Chinese)[姜德生, 何伟2002光电子·激光13 420]
[3] Wang F F, Zhang L, Yang L Z, Liu Y Y 2014 Acta Opt. Sin. 34 88(in Chinese)[王斐斐, 张丽, 杨玲珍, 刘艳阳2014光学学报34 88]
[4] Zhou Q, Ning T G, Pei L, Li J, Li C, Zhang C 2012 Opt. Lett. 8 414
[5] Jiang H, Chen J, Liu T, Huang W 2013 Sensor. Actuat. A:Phys. 198 31
[6] Chen D, Fok M P, Shu C, He S 2008 Lasers and Electro-Optics, 2008 and 2008 Conference on Quantum Electronics and Laser Science Canada, May 4-9, 2008 p1
[7] Lee B C, Jung E J, Kim C S, Jeon M Y 2010 Meas. Sci. Technol. 21 094008
[8] Chen D, Shu C, He S 2008 Opt. Lett. 33 1395
[9] Yu H H, Zheng Y, Guo H Y, Jiang D S 2014 J. Funct. Mater. 12 12001(in Chinese)[余海湖, 郑羽, 郭会勇, 姜德生2014功能材料12 12001]
[10] Dai Y, Liu Y, Leng J, Deng G, Asundi A 2009 Opt. Lasers Eng. 47 1028
[11] Li Z Y, Sun W F, Li Z M, Wang H H 2015 Acta Phys. Sin. 64 234207 (in Chinese)[李政颖, 孙文丰, 李子墨, 王洪海2015 64 234207]
[12] Zhang C X, Zhang Z W, Zheng W F, Liu X H, Li Y, Dong X Y 2014 Chin. J. Lasers 41 0405004(in Chinese)[张彩霞, 张震伟, 郑万福, 刘晓航, 李裔, 董新永2014中国激光41 0405004]
[13] Chan C C, Wei J, Ho H L, Demokan M S 2000 IEEE J. Sel. Top. Quant 6 741
[14] Zhang M L, Sun Q Z, Wang Z, Li X L, Liu H R, Liu D M 2011 Laser & Optoelectronics Progress 8 93(in Chinese)[张满亮, 孙琪真, 王梓, 李晓磊, 刘海荣, 刘德明2011激光与光电子学进展8 93]
[15] Hu C W, Wen H Q, Bai W 2014 J. Lightwave Technol. 32 1406
[16] Wang Y, Liu W, Fu J, Chen D 2009 Laser Phys. 19 450
[17] Li Z Y, Liu M Y, Wang Y M, Liu Q, Gong J M 2014 IEEE Photon. Technol. Lett. 26 2090
[18] Yin G L, Dai Y T, Karanja J M, Dai J X 2015 Sensor. Actuat. A:Phys. 235 311
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