Stimulated Brillouin Scattering Amplification in Directly Written As2S3 Waveguides

High Resolution Distributed Fiber-optic Sensors of Strain and Temperature for Aerospace and Civil Engineering Applications

Optical Engineering, Feb. 26, 2014Yair Antman, David Elooz, Avi ZadokFaculty of Engineering, Bar-Ilan University, Ramat-Gan 52900, IsraelAvinoam.Zadok@biu.ac.il

OutlineWhat is distributed Brillouin sensing?Commercial equipment: specification, deployment examplesNew applications: improve resolution towards cm-scaleSolution principleExperimental resultsOngoing work: integration of high-resolution distributed measurements within composite materials.2Dr. Avi Zadok, Bar-Ilan Univ., COST Technical Meeting, Oct. 2013Stimulated Brillouin scattering3Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014

Image curtsy of Luc Thevenaz, EPFL SwitzerlandBrillouin Fiber Sensing4Localization and measurement of strain variation

Source: www.neubrex.comPumpProbeRepeat for various positions, frequency offsetsDr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014Commercial Deployment ExamplesOmnisens, Switzerland.Focus on Energy Sector. Pipeline integrity monitoring:5Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014

Commercial Deployment ExamplesOmnisens, Switzerland.Undersea cables monitoring:6Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014

Commercial Deployment ExamplesOmnisens, Switzerland.Downhole monitoring:7Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014

Commercial Deployment ExamplesOmnisens, Switzerland.Power plants and cables8Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014

B-OTDACW probe amplified by counter-propagating, pulsed pumpMost widely known and employed Brillouin analysis schemeLong range: towards 100 km!For a given frequency offset, one scan maps out the entire fiber That scan can be very fast (towards hundreds of Hz at 1 km)Resolution (of classic scheme): on the order of 1 meterMany elaborate configurations for resolution enhancement: pre-excitation, multiple pulse widths, etc. Centimeter-scale resolution is challenging 9Y. Peled, A. Motil, and M. Tur, Opt. Express 20, 8584-8591 (2012) S. M. Foaleng, M. Tur, J.-C. Beugnot, and L. Thevenaz, JLT 28, 2993 (2010)Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014Acoustic Field in Space and TimeIntensity of stimulated acoustic field: where and when do the pump and probe waves interact effectively? The B-OTDA case (reference for following schemes): 10

Probe (CW)Pump (pulsed)Output probe is imprinted with SBS gain information that is accumulated over long section Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014MotivationProvide distributed Brillouin sensing with:Centimeter-scale resolutionHundreds of meters range (tens of thousands of resolution points)Reduced acquisition times: simultaneous interrogation of a large number of high-resolution points. 11Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014High Resolution: Correlation DomainDriving force for the acoustic field buildup: inner product of pump and probe 12Analogous to the charging of a capacitor with a time constant . Acoustic field: integrate over driving force cross correlation.Localization of SBS interactions through manipulations of the cross-correlation between pump and probe envelopesB-OCDA (Prof. Hotate, Univ. of Tokyo): Sync. FM of both wavesInner product stable at few correlation peaks, oscillates elsewhereSub-cm resolution. Periodic peaks restrict the unambiguous measurement range to hundreds of resolution points

K. Hotate and M. Tanaka, IEEE Photonics Tech. Lett. 14, 179-181 (2002). Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014PRBS Phase Coding13Y. Antman, N. Primerov, J. Sancho, L. Thevenaz, and A. Zadok, Optics Express 20, 7807 (2013)Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 201413

PRBS Phase Coding: Acoustic FieldSBS interaction is stationary and localizedOutput probe affected by SBS at a single location only 14Pump (fast PRBS phasecode)Probe (fastPRBS phasecode)Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014Difficulties with Phase CodingHigh resolution and (in principle) long range, butOff-peak acoustic fields are non-zero, and contribute parasitic SBS amplification (coding noise). 15Each noise contribution is weak, but there are 10,000 of themLarge number of averagesSBS is built and interrogated one-point-at-a-time(for each frequency offset): Number of scans equals the number of resolution points: long acquisition times

Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014Coding Noise ReductionWeaker coding noise with judicious choice of code. Simulations:16

Y. Antman, N. Levanon, and A. Zadok, Optics Letters 37, 5269-5271 (2012)Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014Coding Noise Reduction (Continued)Experimental results:17

Y. Antman, L. Yaron, T. Langer, N. Levanon, M. Tur, and A. Zadok, Opt. Letters 38, 4701 (2013)Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014

Solution Paths: Interrogation of Multiple PointsUse short phase codes (~ 130 bits): multiple correlation peaks are introduced. 18Pump (fast and short PRBS phasecode)Probe (fastand shortPRBS phasecode)Output probe is again amplified at numerous locations. Wasnt that what we were trying to avoid?Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014

Short Phase Codes with Overlaying Pulsed PumpUse amplitude pulsed modulation of the pump wave on top of the phase codes 19Pump (fast and short PRBS phasecode, withamplitude pulses)Probe (fastand shortPRBS phasecode)Correlation peaks are introduced at different times. Probe amplification can be monitored in time domain, unambiguously. Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014

Experimental Results200 m-long fiber. 127 bits-long phase code. 2 cm resolution.Overlaying pump pulses: 26ns duration Example: output probe power as a function of time20Periodic, isolated peaks repeat every 26 ns (code period), corresponding to SBS gain of individual correlation locations. Phase codes re-timed to move on to next 2 cm-long sections, and so onDr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014Experimental Results: ContinuedA hot spot: one of the peaks is missing, and reappears at a different frequency offset.21

Dr. Avi Zadok, Bar-Ilan Univ., Optical Engineering, Feb. 2014Brillouin Gain MapThis experiment: two spliced fibers, 400 m, 2 cm resolution. All 20,000 resolution points covered with only 130 scans.Acquisition time: 20 minutes, mostly saving of scope traces and equipment switching. Net acquisition time