yonas seifu phd proposal

7/30/2019 Yonas Seifu PhD Proposal

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Yonas Seifu, PhD Research Proposal

Hybrid Brillion/FBG Sensors for Simultaneous Distributed Temperature andDynamic Strain Sensing on Single Mode and Multimode Fibers

The proposed research work focuses on contributions on new schemes in distributed sensors based onBrilloin Scattering and Hybrid Brilloin/FBG sensors, that utilize the benefits of optical pulse codingtechniques for performance enhancement over single-mode and multimode fibers. After a briefintroduction to fiber-optic sensors and the current state of the art of research in the field, the areas offocus of the proposed research is explained, in each case providing the ground that motivated the workincluding some related, previously made contribution.

The measurement of physical parameters such as temperature and strain in fiber-optic sensors is basedon two basic type of sensing, namely distributed and discrete sensing ([2]). In distributed sensing,scattering phenomena in the fiber such as Raleigh, Raman and Brilloin Scatteirng are used to determinethe measurand (temperature, strain) and the fiber is used to continuously determine the value of theparameter along the entire sensing span. In discrete (point) sensing, however, the measurement ofparameters is performed at predetermined points along the fiber where Fiber Brag Gratings (FBGs) areplaced. Fiber-optic sensors could also be static or dynamic based on whether or not they can capturefast changes in the measurand.

So far, all the above types of sensing systems were widely studied, with spatial and measurandresolution, acquisition time and the sensing length being the main parameters of improvement amongsubsequent implementations. The study of distributed and FBG-based sensors includes differentschemes for the source and receivers, frequency and time domain multiplexing of a number of FBGsas well as hybrid distributed/FBG sensor schemes using common set of source and receiver.

Most notably, recent developments include the use of optical pulse codes, instead of a single pulse inconventional sensing systems, to improve the SNR of the reflected signal at the receiver, there bysignificantly enhancing the sensing distance or the spatial/measurand resolution. Recently, in [3] anovel technique is introduced that uses 63- bit distributed cyclic codes in SMF to reduce the attainabledynamic strain resolution to 380 n/Hz from 1.40 u/Hz, while the sensing distance is increased by15km due to coding.

The proposed research work includes investigating and developing Brilloin based distributed sensorsthat utilize pulse coding over SMF, which makes it possible that fiber already deployed for telecomapplications could be used for sensing without redeployment. Most previously implemented distributedtemperature sensors used MMFs, which are characterized by higher back-scattering coefficients andalso allow for higher input peak power levels before the onset of non-linear effects. The use of opticalpulse coding on SMF is already demonstrated to be very important in distributed temperature sensing(DTS) as shown in [4], where a long range Raman DTS with meter-scale spatial resolution is shownover 26km SMF.

Another component of the proposed work includes the theoretical and experimental demonstration ofthe application of different types of pulse coding techniques to distributed temperature and dynamicstrains sensors based on Spontaneous and Stimulated Brillouin Scattering in both SMF and MMF.These types of distributed sensors, including Brillouin Optical Time Domain Reflectometery (BOTDR)


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and Brillouin Optical Time Domain Analysis (BOTDA) techniques have wide spread applications,because of the higher back-scattered power than Raman Scattering and the lower sensitivity towavelength dependent losses.

For instance, A long range BOTDA system employing pulse coding is demonstrated in [5], where anenhanced SNR for measuring the Brilloin Gain Shift along the sensing fiber is obtained. The use ofcoding helped extend the sensing range by about 40km while maintaining high spatial resolutioncompared to conventional single pulse systems, without significant modification of the setup. Theproposed work includes investigating methods to avoid the use of heuristics in determining the type ofpulse codes utilized in the BOTDR/BOTDA sensors so that it is possible to algorithmically determinethe coding scheme that gives the best performance from among a number of possible coding types.

A very important part of of the proposed work , however is the study of long range Hybrid Brillouinbased/FBG sensors that share similar resources at the transmitter and receiver to simultaneously

measure distributed temperate along the fiber and dynamic strain or temperature at distinct points alongthe sensing span. The scheme is much more compact compared to two separate sensing schemes andalso more cost effective since the optical source, the sensing fiber and receiver stage are all sharedamong two separate schemes. So far, hybrid sensors based on Brillouin scattering have been based onlyon BOTDA ([6]), which requires a number of averaging for several minutes for determining thetemperature along the span, while there were no previous demonstrations of hybrid BOTDR/FBGsensors based on optical pulse coding in SMF.

A related work, which is one of the motivations to the work proposed above, is given in [7] but basedon Raman, as opposed to Brillouin, Scattering where a novel technique is implemented that uses opticalpulse coding. The scheme combines Raman DTS using OTDR techniques with TDM multiplexed

FBG-based point sensors for simultaneous temperature and dynamic strain measurement. I t is shownthat cyclic pulse coding enables a temperature and dynamic strain resolutions of 3K at 10 km and 60n/(Hz)1/2 at 250 Hz, respectively.

Hence, the proposed work aims at theoretical and experimental demonstration of the choice of (sets) ofsuitable optical coding techniques and their integration in to the hybrid Brillouin/FBG sensor schemethat is to be newly designed, for achieving optimum performances in terms of reachable distance,acquisition time and resolution. The scheme will benefit from the gains of optical pulse coding toenhance the sensing distance and resolution in simultaneous temperature and strain measurement, whileat the same time extending the utilization of existing source, receiver and fiber infrastructure for hybridsensing. The effects of including TDM multiplexed FBGs along the fiber and the interaction with the

Brillouin scattering effects, including its impact on over all sensing performance is also to be studiedcarefully.

A common challenge in the implementation of Raman based sensors is the need for a high powersource or an amplifier due to the relatively low back-scattered power, while Brillouin based sensors areknown to have higher back scattered power, allowing the wide application of the system to be designedusing relatively simpler configurations


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Finally, since the availability of compact interrogation units (sources and receivers) is key to the widespread use of the sensors schemes that are to be demonstrated, an important extension to the work canbe the design of efficient and low-cost photonic integrated circuits (PICs) for the respective

components of all the schemes described above.

To recapitulate, the proposed research work includes major contributions in enhanced application ofoptical pulse coding techniques in BOTDR/BOTDA systems in MMF, the study of such systems overSMF, in-depth investigation of new long range hybrid Brillouin/FBG sensors using optical pulse codingtechniques for improved performance over SMF and design of PICs for interrogation units. Thecompletion of the proposed project is expected to have ample contribution to the widespread demandfor distributed and hybrid sensors in such areas as structural health monitoring in smart structures,industrial setting with high voltage and high power machinery, electrical power lines, environmentalcontrol and monitoring and public transportation.

References

[1]. K.T.V Grattan, Dr. T. Sun Fiber optic sensor technology: an overview Sensors and Actuators 82,40-61 (2000)

[2]. Farhan Zaidi, Tiziano Nannipieri,Alessandro Signorini, Mohammad Taki, Valentina Donzella,Fabrizio Di Pasquale (2012), FBG in High performance time domain FBG dynamic interrogationtechnique based on cyclic pulse coding

[3]. Alan D. Kersey, Michael A. Davis, Heather J. Patrick, Michel LeBlanc, K. P. Koo,C. G. Askins, M.

A. Putnam, and E. Joseph Friebele, Fiber Grating Sensors,Journal of Light wave Technology Vol. 15,No. 8 August 1997.

[4]. Marcelo A. Soto Tiziano Nannipieri, Alessandro Signorini, Andrea Lazzeri, Federico Baronti,Roberto Roncella, Gabriele Bolognini,, and Fabrizio Di Pasquale Raman-based distributed temperaturesensor with1m spatial resolution over 26 km SMF using low-repetition-rate cyclic pulse coding

[5]. Marcelo A Soto,Gabriele Bolognini,Fabrizio Di Pasquale and Luc Thevenaz, Long-range Brillouinoptical time-domain analysis sensor employing pulse coding techniques, Measurement Sceience andTechnology, 2010.

[6].Tiziano Nannipieria, Mohammad Taki, Farhan Zaidi, Alessandro Signorini , Marcelo A. Soto, GabrieleBologninic, Fabrizio Di Pasquale. Hybrid BOTDA/FBG sensor for discrete dynamic and distributedstatic strain/temperature measurements

[7]. Iacopo Toccafondo, Mohammad Taki, Alessandro Signorini, Farhan Zaidi, Tiziano Nannipieri,Stefano Faralli, and Fabrizio Di Pasquale, Hybrid Raman/FBG Sensor for Distributed Temperature andDiscrete Dynamic Strain Measurements

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