A compact high precision Fabry-Perot interferometer for monitoring Earth deformation

Transcription

1 A compact high precision Fabry-Perot interferometer for monitoring Earth deformation Han Cheng SEAT M. Cattoen, F. Lizion, O. Bernal G. Ravet, L. Michaut Consortium ANR LINES & FUI MIRZA Laboratoire conventionné avec l Université Fédérale de Toulouse Midi-Pyrénées

2 Summary 1. Extrinsic fiber Fabry-Perot interferometer (EFFPI) development Operating principles Modulation-based EFFPI sensor Characteristics 2. Fiber interferometric long-baseline hydrostatic leveling sensor (ihls) 3. Fiber interferometric optical borehole tiltmeter (iobt) 4. Fiber interferometric gravimeter (igravi) 5. Fiber interferometric seismometer (isismo) 6. Conclusions & Perspectives 2

3 EFFPI Operating Principles λ=1310 nm DFB-LD Photodetector Fiber coupler or circulator Output arm Sensing arm Target object d Interference signal I Air cavity Collimator Sensing fiber R 2 + R 1 I R I S Δd I = I R + I S + 2 I RI S cos( Δθ ) V = m V0 + V cos( Δθ ) Δθ = 4 pπn Δθ calculated modulo π directional ambiguities Δd λ p = number of reflections 3

4 Modulation-based EFFPI Experimental schematic of modulation-based EFFPI sensor d+ Δd LD : Laser Diode FC : Fiber Circulator/Coupler ISO : Isolator TEC : Thermo-Electric Controller C : Collimator DAQ : Data AcQuisition PD : Photodetector SF : Sensing Fiber T : Target surface (mirror) 4

5 Modulation-based EFFPI: quadrature signals Generating quadrature interference signals target direction Multiplexed output interference signals Δλ π Δ θ = 4πnd 2 = λ 2 Quadrature condition V y and V x quadrature pair Modulation at frequency f 1 Δ λ 2 = λ 1 8nd Vx= V0 x+ Vmxcos( θ) Vy= V0 y+ Vmysin( θ) Phase diagram of in-quadrature signals V y vs V x Modulation f 1 at 25 khz & d ~25 mm Δi(t) ~0.48 ma Δλ ~4.3 pm 1 interference fringe Δd = λ 4n 5

6 EFFPI for quasi-static displacments Generating "reference displacement" weak (λ/4) and quasi-static displacement or stationary target Demodulated V y and V x in quadrature Phase condition Δλ λ 2 1 2nd Lissajous phase diagram (V y vs V x ) Modulation f 2 at ~1 Hz (d ~25 mm) Δi(t) ~1.94 ma Δλ~17.19 pm 6

7 EFFPI characteristics: static & dynamic Displacement calibration against reference Polytec PI piezo-electric transducer V y V x D calp = µm D refp = µm ΔD i max = µm Dynamic displacement measured against PZT Δ D mean = µm Static displacement (step mode) precision ~2 nm ( Hz) range 2 nm 5 µm (limited by PZT linearity) Inset: max. error (~46 nm) at PZT translation limit Dynamic displacement EFFPI amplitude ~5.155 µm (c.f. reference amplitude µm) error ~2 nm (0.04%) 7

8 EFFPI characteristics: drift & stability Drift & stability characterization with differential probes Displacement measurements from Probe 1 and Probe 2 Difference displacement (Probe 1 Probe 2) Probe 1 and Probe 2 displacements ~14 nm 16.5 mins of data extracted at 1 khz Difference max: < 1 nm min: ~0.15 nm Possible causes: temperature-induced perturbations, wavelength variations 8

9 EFFPI characteristics: temperature sensitivity Temperature sensitivity: equivalent displacement Differential displacements Differential configuration in controlled temperature chamber relative temperature increase over ~1 hr period (~ 0.1 C) temperature variation by independent sensor (AD592 temperature sensor: 3.9 mv/ C) Probe1 & Probe2 displacements ~25.82 nm thermal expansion of steel cage system ~25.6 nm (stainless steel 410 ~10.5 µm/m/ C) Temperature variation 9

10 Applications in Geophysics: ANR LINES Development & installation of 3 instruments at LSBB test site since Feb 2012 Seismometer (isismo) Long baseline hydrostatic leveling sensor (ihls) LSBB geo-location in the Vaucluse Borehole tiltmeter (iobt) LINES-related components for seismometer (isismo), bore-hole tilemeter (iobt) and long baseline hydrostatic levelling sensor (ihls) 10

11 Applications in Geophysics: ihls Fiber interferometric long-baseline hydrostatic leveling sensor (ihls) Long baseline hydrostatic inclinometer ihls Differential optical probes ihls incorporating EFFPI in differential configuration Target mirror LVDT reference sensor Sensing fibers (2 x 270 m and 2 x 120 m) ihls liquid level variations tilt typically 1 nrad ~variation of 1 mm/1000 km! combined baseline 150 m precision ~10-11 radians frequency domain: 10-5 several Hz transfer to industry ongoing 11

12 ihls response and noise level ihls frequence response: comparison with HLS-Fogale, LILY tiltmeter, GPS HLS 140 m Fogale capacitive sensor used by the CERN 150 m ihls used at LSBB site LILY electrolytic borehole tiltmeter GPS measurement GPS measurement Summary of comparison frequency domain: Hz from ~10-5 Hz ihls ~10 times less noisy than HLS- Fogale ihls >20 times better than LILY higher frequencies (from 10-2 Hz) ihls ~100 times better than HLS- Fogale and LILY in precision ihls also less sensitive to atmospheric noise compared to GPS systems & LILY (local pressure variations) 12

13 ihls for earth deformation & hydrology ihls for Earth deformation Long baseline hydrostatic inclinometry LVDT & ihls Difference LVDT ihls Earth tides M8.7 Sumatra event Earth deformation precision ~ 2 x rad diff. ihls LVDT < 0.2% before quake diff. ihls LVDT ~3% during quake 13

14 ihls for accelerator alignment at CERN ihls for particle accelerator & collider alignment at CERN (µm) West Detected earth tides ihls HLS-Fogale TT1 (140 m long) 15 Center 6.25 µm -15 Comparison between ihls-lines and HLS-Fogale (stability) 65 (µm) (µm) East 05/09/ /09/ /10/16 Evaluation of ihls at CERN TT1 test tunnel HLS Fogale ihls Results 3 ihls deployed at CERN diff. ~ 6.25 µm at centre position continuous operation for ihls but regular disruption to HLS-Fogale 14

15 Applications in Geophysics: iobt Fiber interferometric optical borehole tiltmeter (iobt) iobt iobt pendulumn principles tri-axial probes spaced at 120 d 1 + d 2 + d 3 = constant Sensing fibers (3 x 270 m) Borehole (hidden) Tri-axial measurement of displacements d 1, d 2 and d 3 redundancy measurement compensates atmospheric noise corrects for system drifts dynamic range ~ ±1 mm frequency domain: Hz transfer to industry ongoing 3 Optical probes iobt in borehole iobt incorporating 3-axis EFFPI sensor probes Moving / Laboratoire d analyse et d architecture mass des systèmes du CNRS 15

16 iobt response and sensitivity to earth tides iobt frequence response from squarewave excitation induced by PZT plate & earth tide detection Measurement of earth tides with iobt over 10 days Filtered displacement Resultant response 0.6 Hz frequency band denotes fundamental oscillating mode 12 Hz and 26 Hz bands indicate rod s vibration modes remaining frequency bands caused by parasitic movements Resolution ~ 1 nm Earth tide detection 10 days observation of earth tides displacement resolution ~1 nm corresponding tilt resolution ~1 nrad 16

17 iobt redundancy capability iobt: validation of redundancy via tri-axial displacement measurement d 1 + d 2 + d 3 Validation of redundancy capability M5.8 Japan earthquake 29 Feb 2012 d 1 + d 2 + d 3 = ~ 10 nm over 800 s 17

18 iobt for earth deformation: 2D movement iobt for earth deformation Earth tides 2D observation orientation along N-S amplitudes ~ nm (3-axis) Oscillation of iobt with earth tides 2D movement Earthquake observation Argentina earthquake 5 Mar 2012 magnitude ~M6.1 amplitudes ~15-24 µm (3-axis) iobt response to seismic activities (M 6.1 Argentina earthquake) Reconstructed 2D movement 18

19 Applications in Geophysics: igravi Fiber interferometric gravimeter (igravi) Measurement of x(t) to obtain g x = ½ g*t 2 Displacement (µm) Measurement of g from free-fall of mass x(t) Response of x(t) during free-fall time (ms) Displacement (µm) Drop chamber with sensor detecting free-falling mass igravi preliminary results mgal precision (10-5 m/s 2 ) under unoptimized laboratory conditions TRL 3 industrial partners: Aquitaine Electronique, etc 19

20 Applications in Geophysics: isismo Fiber interferometric seismometer (isismo) Exploded view of L22 used in isismo Mirror surface Collimator Toroidal joint isismo configuration/specifications based on L22 Hz seismometer mobile mass structure modified for interferometric probe L22 inductive output used as reference movement of mobile mass displacement velocity (or acceleration) upon differentiation resolution of isismo ~ 1 nm in displacement ~ nm/s in velocity application frequency domain: Hz (> 1Hz) isismo at isismo with 1 km fiber for remote sensing LSBB test site 20

21 isismo response to natural oscillation isismo frequency response 0-10 DSP of displacement (db): DSP of displacement reference (db): 1 nm ref 2 used /Hz 1 nm 2 /Hz isismo noise analysis typical operating range: Hz noise level corresponds to precision of < 2 nm over 5 khz bandwidth comparable to best commercial seismometer (Streckeisen STS2) Frequency (Hz) Frequency (Hz) Spectral analysis of oscillatory noise level over 0 5 khz bandwidth (LAUM-ESEO results) 21

22 Conclusions Precision: < 2 nm over Hz bandwidth Dynamic range: 2 nm ~8 mm at 4 mm/s (Nyquist limit) Alignment tolerance: > ± 1 (with < 10 nm error; double reflection) Stability & temperature sensitivity: nm/ C (1-axis) & 1 nm/ C (differential) Basis for 4 opto-geophysics instruments: ihls: resolution rad over bandwidth of 0 several Hz iobt: resolution 1 nrad over bandwidth of 0 10 Hz (with tri-axial redundancy) igravi: precision ~mgal (10-5 m/s 2 ) isismo: displacement resolution < 1 nm & velocity resolution ~ 10-9 m/s over 2 Hz 5 khz bandwidth currently only relative measurement! 22

23 Perspectives & Future Work Technology transfer for industrial development & commercialization (work in progress FUI MIRZA) Laser wavelength locking to increase sensor resolution dynamic Low-power consumption for autonomous deployment Absolute measurement of distance (work in progress) Thank You 23