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1 CSIC-JSPS International Smart Infrastructure Symposium Innovative sensors for infrastructure monitoring, Monday, 12 Nov., Leslie Stephen Room of Trinity Hall, University of Cambridge Fibre Optic Nerve Systems for Smart Structures and Smart Materials Kazuo Hotate Department of Electrical Engineering and Information Systems The University of Tokyo

2 Fiber Optic Nerve Systems for Smart Materials and Smart Structures Bridges F.O. Nerve Systems Mountains Space crafts Aircrafts Airports River Levee Highways Slopes CCTV カメラ CCTV カメラ Buildings CCTV カメラ 路側通信サーバ 霧 Tunnels Roads F.O. Nerve Systems Trains, Rail-roads Ports, Ships Disaster prevention Maintenance 16

3 Fiber Optic Nerve Systems Distributed and Multiplexed Optical Fiber Sensing Multiplexed Sensing Source Circulator Optical Fiber Sensors; FBG, etc. Multiplexing; WDM, TDM, Correlation Domain, etc. Detector, DAQ Distributed Sensing Source Circulator Sensing Optical Fiber Mechanisms; Scattering, Mode Coupling, etc. (Brillouin, Raman, Reighley) Distribution; Time Domain, Correlation Domain, etc. (BOCDA, BOCDR, BOTDA, BOTDR, etc.) Detector, DAQ Quasi-distributed Sensing Source Circulator Optical Fiber Sensors; Long-length FBG, etc. Multiplexing; Correlation Domain, FMCW, etc. Detector, DAQ

4 Brillouin scattering (1/2) Spontaneous Brillouin scattering Pump f f 0 Thermal oscillation of SiO 2 Acoustic wave (t A = ~10 ns) Periodical refractive-index change Diffraction grating (moving) f 0 - f B Scattering (with Doppler shift : - f B ) f B = 10.85GHz (= 0.1nm) Reflectivity R SpBrillouin = ー 90dB/m 4

5 Brillouin scattering (2/2) Stimulated Brillouin scattering Pump f Probe wave Probe f 0 f Excitation of the grating 0 - f B Mode coupling Energy transition f 0 - f B from pump wave to probe wave Much larger output signal Reflectivity it R StBrillouin = ー 50dB/m 5

6 Brillouin scattering; application to strain/temperature sensing ty f B f B in ntensit BGS 11GHz 30MHz pump GHz 1) freq. strain * BGS Brillouin gain spectrum cf. 1) T. Horiguchi et al., IEEE Photon. Tech. Lett. 1, 5 (1989). Doppler shift f B strain magnitude f B : strain or temperature? 6

7 Limitation in Basic Time Domain Techniques Optical pulse generator Detector f 0 f 0 -f B Strain FUT Heat Spontaneous BS Trade-off between spatial resolution and strain accuracy in time domain. 1m pulse 100MHz width 30MHz Spatial resolution is limited to ~ 1m 7

8 Brillouin optical time-domain analysis (BOTDA) Recent achievements Manipulation of pulse shape: Spatial resolution improvement (1) Pulse-PrePump (PPP) BOTDA (2) Double-Pulse BOTDA + X. Bao, et al, OPTICS LETTERS, 24, 8 (1999). + L. Che-Hien et al., IEICE OFT (2005). + Y. Koyamada et al., IEICE OFT (2007). (3) Differential pulse-width pair BOTDA (4) Dark-Pulse BOTDA + Wenhai Li, et al, OPTICS EXPRESS, 16, 26 (2008). + A. W. Brown et al.,, J. Lightw. Technol. 25,, 1 (2007). (5) Brillouin Echoes BOTDA + Stella M. Foaleng, et al, JLT, 28, 2 (2010). (6) Dynamic Acoustic Grating Based BOTDA + K. Y. Song et al., Optics Lett. 35, 1 (2010). 8

9 Optical Correlation Domain Techniques Time domain techniques have been much improved. - Spectral shape - Specialty fiber - Higher speed electronics for better resolution Optical Correlation Domain Techniques : (continuous wave tech. without high speed electronics) Measurement mode Random accessibility Spatial resolution Measurement speed 1.6 mm 1kHz for single point, 200Hz with random accessibility, 20Hz with total distributed-measurement 9

10 Brillouin Optical Correlation Domain Analysis K. Hotate and T. Hasegawa, IEICE Trans. on Electronics, Vol.E83-C, No.3, K. Hotate, K. Abe and K. Y. Song, IEEE PTL, Vol.18, No.24, Intensity modulation SSB modulator Microwave ~ ν B Probe Polarization diversity FM DFB LD IM 90/10 EOM 2 EDFA λ PSW Δf sync. 1.9 MHz SSBM Correlation peak FUT RF ~ f m RF ~ f m EOM 1 EDFA Pump EOM: electro-optic modulator PSW: polarization switch SSBM: single-sideband modulator IM: intensity modulator FUT: fiber under test Delay fiber (~ 10 km) 5.8 MHz Lock-in PD amplifier Data acquisition 3.9 MHz Beat lock-in 10

11 Brillouin Optical Correlation Domain Analysis Probe Strain Freq. probe pump position Probe Propagation of the pump and the probe Pump p p p 11

12 BOCDA Technique Output : Summation of Brillouin gain along the fiber Spatial resolution: Δz = c Δν B 2π n f Δf m - The gain in the position where the correlation is highest can be generated exclusively - The position can be moved by the FM frequency Distributed strain measurement can be realized The University of Tokyo 12

13 Application to Smart Materials Sample used in this study K. Hotate and M. Tanaka, IEEE PTL, Vol.14, No.2, with 1cm spatial resolution!! The University of Tokyo 13

14 Multi-point simultaneous dynamic strain sensing at arbitrarily selected points 3000 Video Clip :0219kobe001.mpg 3000 BGS measurement :Movie_BGS_kobe.wmv Strain [με] 0 Strain [με] Strain gauge pos. 3 Optical fiber pos. 3 Residual strain (gauge) Residual strain (fiber) Strain gauge pos. 4 Optical fiber pos. 4 residual strain Time [s] Time [s] Random accessibility!! University of Tokyo and Kajima Corp. dynamic sensing pts 14

15 Demonstration of mm order spatial resolution K.-Y. Song, Z. He and K. Hotate, OSA Optics Letters, Vol.31, No.17, Translator 3 mm Translator Fiber under test 1 SMF1 0 MHz 3 SMF2 (10 mm) -20 MHz SMF1 0 MHz 5 epoxy epoxy DSF (3 mm) -300 MHz 2 DSF (3 mm) -300 MHz 4 ~ 45 mm ν B [GHz z] Position [mm] rillouin freq quency [GH Hz] μm 90 μm 60 μm 30 μm mm resolution!! B Position [mm] 15

16 Elongation of measurement range by Temporal-Gating Scheme Step: 2 cm K. Hotate, H. Arai and K.-Y. Song, SICE J. of Control, Measurement and System Integration, Vol.1, No.4, 2008 <Invited>. requency [GHz] Brillouin fr Position [m] Brillouin fre equency [GHz] Position [m] requency [GHz] Brillouin fr Position [m] Step: 5 m Br illouin frequ uency [GHz z] Position [m] 7cm resolution / 1,030m range Ratio: 14,700 16

17 1 KHz sampling with simplified BOCDA K.-Y. Song and K. Hotate, IEEE PTL, Vol.19, No.23, Brillouin fr requency [GHz z] Time [ms] Brillouin fr requency [GHz z] Time [ms] 100 Hz signal 100 Hz & AM 10 Hz signal 1 KHz sampling with BOCDA 17

18 SOCF High speed random accessibility with S-BOCDA Phase change: position shift DFB LD Active Adder 50/50 Random accessibility!!, y y,, 10 khz EOM Delay line (~ 10 km) EDFA K. Hotate, M. Numasawa, M. Kishi, and Z. He, 3rd Asia Pacific Optical Sensors Conference, WB-3, Sydney, Australia, Probe Coherence peak FUT Pump Pump Probe 10 khz EOM EDFA f L f sweep Amplitude change: spectrum shape Data acquisition f ref Lock-in amplifier PD VOA 18

19 Dynamic strain sensing at 4 points with random accessibilityy 200 Hz total sampling with Random Accessibility 2H 10Hz 2Hz FUT 5 4 AB C D A B D C [GHz] BFS [GHzz] C D B A K. Hotate, M. Numasawa, M. Kishi, and Z. He, 3rd Asia Pacific Optical Sensors Conference, WB-3, Sydney, Australia, Time [s]

20 High speed total distribution measurement by BOCDA The Univ. of Tokyo & Chung-Ang g Univ. Optical freq quency DFM-BOCDA f m Principle: Differential Frequency Modulation (DFM) Correlation peaks (stationary) (moving) f m + δ f m Position Sweeping correlation peaks are generated LD by Differential Frequency Modulation! Moving speed: V = 2 δ f + δ m c n Peak to peak distance: R = 2 1 f + δ m c n K.-Y. Song, M. Kishi, Z. He, and K. Hotate, OSA Opt. Lett., Vol.36, No.11, PPT by K.-Y. Song

21 Differential Frequency Modulation BOCDA Power [μw] GH 9.3 GHz Linear (~290 με/s) Sinusoidal (1.33 Hz, 650 με) Sinusoidal (1.33 Hz, 650 με) S m S m S3 Probe Pump (0.9 m) (0.9 m) (0.9 m) khz Optical Frequency [THz] DFB LD Probe 50/50 FUT PM Pump VOA The Univ. of Tokyo & Chung-Ang g Univ. PD 40 Hz Waveform generator Function generator Pol. SW Delay fiber (25 km) Sync. EDFA DAQ Δν sweep: 10.6 ~ GHz with 5 MHz step (100 traces) K.-Y. Song, M. Kishi, Z. He, and K. Hotate, OSA Opt. Lett., Vol.36, No.11, PPT by K.-Y. Song

22 Experiment: Measurement result 3D map of strain distribution (1 sec.) 40 Δν B [M MHz] Time [sec] The Univ. of Tokyo & Chung-Ang Univ. Δν B [MHz] Time [sec] Δν B [MHz] traces/sec Time [sec] K.-Y. Song, M. Kishi, Z. He, and K. Hotate, OSA Opt. Lett., Vol.36, No.11, PPT by K.-Y. Song

23 Application of BOCDA to Airplane SHM - Prototype model of BOCDA - On the Ground Operation Distributed measurement In Flight Operation Dynamic strain measurement Wide Area Distributed ib t Strain with high spacial resolution Mitsubishi Heavy Industry The University of Tokyo Yokogawa Electric RIMCOF Strain Position of Sensing Fiber Intact Condition Damaged condition Strain Wing RootPoint Flight Time T. Yari, K. Nagai, M. Ihik Ishioka, KH K.Hotate, and dy Y. Koshioka: 15 15th annual International Symposium on Smart Structures and Materials & Nondestructive Evaluation and Health Monitoring, SPIE , San Diego, Mar

24 Airplane that can feel pain: MU-300 Mitsubishi Heavy Industry Yokogawa Electric The University of Tokyo RIMCOF Business Jet, MU-300 OF sensor OF code Strain gage (back side) T. Yari, K. Nagai, M. Ishioka, K.Hotate, and Y. Koshioka: 15th annual International Symposium on Smart Structures and Materials & Nondestructive Evaluation and Health Monitoring, SPIE , San Diego, Mar

25 Airplane that can feel pain: MU-300 Point 5 Multi-point and Dynamic strain sensing pull-up up 2.7G Distributed strain sensing Before flight Level flight After flight Point 6 Mitsubishi Heavy Industry Yokogawa Electric The University of Tokyo RIMCOF T. Yari, K. Nagai, M. Ishioka, K.Hotate, and Y. Koshioka: 15th annual International Symposium on Smart Structures and Materials & Nondestructive Evaluation and Health Monitoring, SPIE , San Diego, Mar Deformation of skin panel due to the cabin pressure!! 25

26 Laser Brillouin Optical Correlation Domain Reflectometry: BOCDR Y. Mizuno, W. Zou, Z. He and K. Hotate, OSA Optics Express, Vol.16, Issue 16, f = f 0 + Δf sin (2π f m t) IM Ref. Pump Correlation peak Scan f = f 0 + f = f 0 f B + Δf sin (2π f m t + φ ) Δf sin (2π f Stokes m t + ψ ) A φ = ψ + 2π n B φ = ψ + 2π n A B FUT freq. time Beat signal detected PD ESA freq. time Beat signal not detected ESA: electrical spectrum analyzer, FUT: fiber under test, PD: photo-diode 26

27 Origin of the Brillouin gain spectrum shape Coherence degree SOCF Correlation peak Correlation peak (sensing position) Beat amplitude Side lobes Apodization by IM rillouin Intens sity (a.u.) B Signal peak (large strain) Background noise Signal peak (no strain) Noise level Brillouin frequency shift (GHz) Limitation of measurement S. Manotham, M. Kishi, Z. He, and K. Hotate, 3rd Asia Pacific Optical Sensors Conference, Th-C23, Sydney, Australia, 2012.

28 Comparison of BGS (Simulation & Experiment) S. Manotham, M. Kishi, Z. He, and K. Hotate, 3rd Asia Pacific Optical Sensors Conference, Th-C23, Sydney, Australia, 2012.

29 1-cm spatial resolution with optimized IM (~7000 με ) S. Manotham, M. Kishi, Z. He, and K. Hotate, 3rd Asia Pacific Optical Sensors Conference, Th-C23, Sydney, Australia, 2012.

30 Brillouin Dynamic Grating generated with Stimulated Brillouin Scattering Process Acoustic wave is generated through the stimulated Brillouin scattering by x-polarized light. pump probe beat x y x acoustic grating acoustic resonance energy ν = Bragg condition: βa = 2βx = 2βy n n x y = or n f = n f λ λ x y 2 n V / λ x x x B eff a op x x y y Song, Zou, He, Hotate, Song and Hotate, OFS19, Opt., Lett., 33, 9, Perth, Y-polarized light is found to be reflected by the acoustic grating with a Bragg condition. B f = f f = f yx y x x ny frequency deviation 30

31 Experimental results: existence of Brillouin Dynamic Grating (BDG)* * Detected by OSA while y-polarized light is manually tuned to satisfy Bragg condition. Optical power (db Bm) All on w/ filter Readout only All on w/o filter Pump power: ~23 dbm Probe power: ~-1 dbm Readout power: ~19 dbm Birefrengence-induced shift ~30 db Brillouin frequency shift cal power (dbm) Optic ASEFilter ASE ~20 GHz Filter presion ratio (db) Supp -75 Optical frequency (THz) Filter s reflection spectrum Optical frequency (THz) B fyx = fy fx = fx 44.0 GHz B = n y Birefringence-determined frequency deviation 4 Song, Zou, He, Hotate, Opt., Lett., 33, 9,

32 BGS and BDG characteristics on strain and temperature FUT: ~32-m-long Fujikura PANDA-PMF u.) Brillo ouin gain (a BGS Strain dependence d strain increase Brillouin frequency (GHz) uin gain (a.u u.) Brillo W. Zou, Z. He and K. Hotate, OSA Optics Express, Vol.17, No. 3, Temperature dependence d temperature increase BGS Brillouin frequency (GHz) (a.u.) Diffra acted power BDG strain increase Frequency deviation (GHz) (a.u.) Diffra acted power 5 temperature increase BDG Frequency deviation (GHz) 32

33 Discriminative measurement of strain and temperature W. Zou, Z. He and K. Hotate, OSA Optics Express, Vol.17, No. 3, ΔT C ε ν C ε f Δ ν B C C Δ ε ε T B ν ν = ε T Δf yx Cf C f Δ T : MHz/ με : 0.890MHz/ με C C T ν ε f :1.058MHz/ o C : MHz/ o C Δε T T δε 1 C C δν f ν B = ε T T ε ε ε δt C C f ν f Cν C f C f C δ ν yx δν B = 0. 1MHz δf yx = 4MHz δε = 3.1με δt o =0.021 C 33

34 Simultaneous measurement of strain and temperature with correlation-based continuous-wave technique W. Zou, Z. He, and K. Hotate, IEEE Photonics Technology Letters, Vol. 22, No. 8, y microwave, ν z EDFA polarizer PM-ISO x 3dB PC DFB-LD1 SSBM PMF fiber delay Δf B EOM EDFA PM-CIR computer PC Sync. chop polarizer PBS/C Δf D LIA1 PD1 DAQ VOA Bias T ramp sweep LIA2 PD2 TBF PC DFB-LD2 EDFA polarizer R PM-CI 34

35 Distributed Measurement of BGS and DGS 2.3m (a) Fiber samples Readout (y) A B C D E F G H I Probe (x) Pump (x) of ν B (MH Hz) Change (MHz) Cha ange of f yx 150 (b) Distributed ν B (a) 150 W. Zou, Z. He, and K. Hotate, IEEE Photonics E Technology Letters, Vol. 22, No. 8, D 30 A B C F H B 30 D G I F H 0 A C G I Change of ν B (MHz) Change of f yx (MHz) Position (m) (c) Distributed f yx E (b) A C E G I No change at A, C, G, I Temperature increase atbdefh B,D,E,F,H Temperature Strain and strain -500 A B B C D F G H I applied at E Position (m) Position (m) Temperature 35

36 ΔT [ o C] Δε [μ με] A Simultaneous measurement of strain and temperature distribution Case 1: No strain applied on E portion Case 2: Strain applied on E portion B D E F H C G W. Zou, Z. He, and K. Hotate, IEEE Photonics Technology Letters, Vol. 22, No. 8, (a) I Temperature No change at A, C, G, I 0 Temperature increase at B,D,E,F,H Temperature and strain (b) applied at E 2000 E A B C D F G H I Strain Position [m] 36

37 Measurement range elongation by temporal gating scheme for simultaneous measurement R. K. Yamashita, W. Zou, Z. He and K. Hotate, OFS-21, m range 40 cm resolution BGS Powe r (a.u.) Pump-readout frequency offset (GHz) DGS Powe er (a.u.) Pump-readout frequency offset (GHz) 37

38 Measurement range elongation by temporal gating scheme for simultaneous measurement Simultaneous measurement of strain and temperature R. K. Yamashita, W. Zou, Z. He and K. Hotate, OFS-21, m range 40 cm resolution 38

39 Long length FBG Distributed Sensing with SOCF Co oherence function Distributed measurement Measuring window Position Long-length FBG 10cm Ref flectivity Position Position Strain? Heat? Bragg wavelength Wavelength Bragg wavelength K. Hotate, and K. Kajiwara, Optics Express, 16(11), ,

40 Multiplexed Sensing System 3dB-Coupler Circulator DFB LD IM Isolator Delay Line [Reference] [Signal] Bias Sync FBG f 0 sweep Tee Beat Compensation Array FBG1 CH1 CH2 f A -f B FG1 CG2 FG2 Driver AOM FBG2 Coherence GPIB Peak FBG3 45MHz Isolator PC Bending BPF PD + Loss SQD - Σ f Sensing PD 3dB- A Isolator Coupler Arm f1 = 7.6 [GHz] f2 = [MHz], [MHz], [MHz] (FBG1,2,3) f AOM = [MHz], [MHz], [MHz] (FBG1,2,3) 40

41 Experimental Results (three FBGs) FBG Uniform Heat FBG (~5 C) FBG Epoxy adhesive Strain (~40με) 0 [mm] [mm] [mm] pm 45pm Heat Strain 41

42 Conclusions Brillouin Optical Correlation Domain Analysis + 1.6mm spatial resolution, 1 khz sampling rate, random accessibility have been realized, without high speed electronics. + Random accessibility with 200 Hz sampling rate, and total-distributed measurement with 20 traces/sec. + Applications, such as aircraft SHM, have been demonstrated. Brillouin Optical Correlation Domain Reflectometry + 1.0cm spatial resolution, 50Hz sampling rate, random accessibility have been realized. Brillouin Dynamic Grating and Applications + Discriminative measurement of strain and temperature has been realized. FBG based quasi-distributed sensing +Long-length FBG for short-length distributed measurement head. + Multiplexing of the long-length length FBGs. 42

43 Secure Life and Society with Fiber Optic Nerve Systems Bridges F.O. Nerve Systems Mountains Space crafts Aircrafts Airports River Levee Highways Slopes CCTV カメラ CCTV カメラ Buildings CCTV カメラ 路側通信サーバ 霧 Tunnels Roads F.O. Nerve Systems Trains, Rail-roads Ports, Ships Disaster prevention Maintenance 16

44 44

45 Contents Introduction Fiber Optic Nerve Systems Brillouin Optical Correlation Domain Techniques + Brillouin Optical Correlation Domain Analysis + Brillouin Optical Correlation Domain Reflectometry Brillouin Dynamic Grating and Applications + Discriminative measurement of strain and temperature FBG based quasi-distributed sensing Conclusions 45

46 Temporal gating scheme Measurement range enhancement - Ando Electric and Univ. of Tokyo f m ν m Delay Probe LD Polarization controller Chopping ν 0 Microwave Synthesizer LN Mod (intensity Mod) ν m ν 0 EO.Mod Polarization controller Pump gain ν m Fiber Und der Test ν 0 Lock-in Amp Photo Diode EO.Mod z z 46

47 BCODA with Time-division pump-prove prove generation scheme 10km D elay (0.05m sec) K. Hotate and T. Yamauchi, JJAP, Vol.44, No.32, LD Freq. LD 10kH z & 10M H z Phase: position Direct M od. Gating Phase input output Amplitude : spectrum Time Novel Setup input W/O compensation output Waveform Generator Oscilloscope DFB-LD Optical Slope Filter PD With compensation 47

48 Spatial resolution enhancement by intensity modulation scheme +Side lobes near the correlation peak are reduced by IM for pump and probe. +Length of the localized Brillouin dynamic grating are reduced. 48

49 Spatial resolution enhancement by intensity modulation scheme +Spatial resolution is improved by about 5 times. 49