Nature Photonics Technology Focus Optical Fiber Sensor

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Transcript of Nature Photonics Technology Focus Optical Fiber Sensor

March 2008

Optical-fibre sensors

2008 Nature Publishing Group

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2008 Nature Publishing Group


Great potentialCover image Fibre sensors are being used to monitor the structural health of large composite structures such as turbine blades. Industry Perspective p153EDITORs: NADYA ANsCOMBE, OlIvER GRAYDON PRODuCTION EDITOR: ChRIs GIllOCh COPY EDITOR: ANNA DEMMING ART EDITOR: TOM WIlsON [email protected]


e have been hearing about the great potential of fibre sensors for many, many years. There is no doubting that the technology can bring benefits to a wealth of applications, ranging from insitu sensors in the medical industry for monitoring important biological functions (page 150), through to vast distributed sensors in the oil industry (page 147). But despite their advantageous features, such as their immunity to electromagnetic interference, compact size and the ability to make distributed measurements, market penetration has been slower than expected in many areas. Although deployments are now starting to rise and the market outlook over the next few years is optimistic (page 156), the question is why has it taken so long? The main reason is often nothing to do with the performance of the actual sensors themselves. For example, fibre Bragg grating technology has survived the rigours of scientific scrutiny and has proved itself in many field trials. The problem is largely a lack of awareness of the technology, a shortage of regulations to establish what measurements they should be used for and ultimately a question of cost (page 158). The creation of standards and regulations is very important for encouraging or even demanding the use of sensors. For example, regulation demanding insitu lifetime monitoring of structures such as bridges would have an immediate impact on the fibre-sensor market and help avoid catastrophic accidents. Industry standards and regulation would also help bring down cost another barrier to growth. At present, sensor systems are often heavily customized and contain proprietary technology. The adoption of some common standards would help reduce costs. The bottom line is that increased regulation and standards, rather than new technology, are critical to the future success of fibre sensors.

REsEARCh hIGhlIGhTs145

Monitoringpipelines, hydrogenleaks,traffic, andmore

INDusTRY PERsPECTIvE147 Oil and gas applications:

Probingoilfields HildeNakstadand JonThomasKringlebotnMedical applications:


Savinglives ricPinet


Structural-health monitoring:

Asensitiveissue MartinJones

BusINEss NEWs156

Bigcontracts,morefunding andmarketpredictions Dynamic,robustand versatilesensorsfor diverseapplications



Educationandregulation InterviewwithBrianCulshaw

nature photonics | VOL 2 | MARCH 2008

143 2008 Nature Publishing Group


What you get is what you see

Obtain fast, accurate visual assessments of system image quality, including diffraction Communicate optical concepts and trade-offs to non-optical engineers during design evaluations and product presentations Improve qualitative understanding of traditional performance measures such as MTF and spot diagrams Determine image orientation issues for complicated folded systems

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2008 Nature Publishing Group


Sensor checks pipeline integritySmart Mater. Struct. 17, 015006 (2008) Researchers in Naples, Italy, have shown that optical-fibre sensors can be used to monitor the structural integrity of a pipeline, as well as the deformations of the rock or soil surrounding the pipeline. They found that, by measuring normal strain using stimulated Brillouin scattering along three longitudinal directions running down the pipeline, they could measure the amount of pipeline dislocation and its direction. Other researchers have shown that it is possible to use a distributed Brillouin fibre sensor system to measure large compressive strain and detect pipeline buckling. Romeo Bernini from the Institute for Electromagnetic Sensing of the Environment and his colleagues from the Second University of Naples, however, have gone one step further and shown that it is also possible to retrieve more detailed information about the pipeline dislocation. This is very important in order to realize a real-time intelligent monitoring system useful for early detection of events eventually leading to pipeline rupture, he says. In their laboratory, Bernini and his colleagues attached three fibres to the circumference of a test pipeline, reciprocally displaced by 120. We have focused on improving the accuracy and the spatial resolution of the Brillouin fibre sensor, says Bernini. We developed a measurement set-up that worked in the frequency domain and used synchronous signal detection. We also devised algorithms that are able to process the optical signals acquired in the frequency domain. The group is currently working to improve the performance of the sensor even further. In particular they plan to extend the maximum sensing length, which is currently limited to a few tens of kilometres.

Dynamic analysis of the impact of trafficSmart Mater. Struct. 17, 015003 (2008) Researchers in Canada have used embedded fibre sensors to monitor impact waves in concrete slabs resulting from highway traffic. Xiaoyi Bao and colleagues from the Universities of Ottawa and Sherbrooke, monitored distributed impact waves due to traffic in real time, using stimulated Brillouin scattering. This type of sensor system can usually only measure static temperature and strain, because the system response time is in the range of minutes. We used the polarization dependence on the stimulated Brillouin scattering in the fibre to detect the sudden birefringence change induced on the sensing fibre, said Bao. This allows us to demonstrate the impact wave response with a distributed dynamic sensor for the first time. The concrete slabs were reinforced with fibre-reinforced polymer, but this has a serious drawback because impact damage substantially reduces the compressive strength. Impact damage is hidden and cannot be detected by visual inspection or standard strain monitoring. The sensing fibre used for impact-wave detection was attached to fibre-reinforced polymers, which were embedded in eight0.04

Brillouin gain [a.u.]

0.03 0.02 0.01 0.00 0.01 70 50 Distance (m) 30 10 0 0.4 0.8 1.6 1.2 Time (s) 2.0 2008 IOP

full-scale continuous reinforced concrete slabs on Highway 40 in Montreal. The data (pictured) showed peaks in the Brillouin scattering that have a height proportional to the stress in the concrete slab. High peaks represent trucks and lower peaks represent cars. Our current distributed dynamic sensor system requires access to the sensing fibre from both ends; the next phase of the research is to make a sensor system with one-end access, said Bao. We also need to improve the signal-to-noise ratio of the sensing system to reduce the signal processing time further and increase the measurable frequency range. In the past, fibre Bragg gratings covered with palladium have been widely investigated for hydrogen sensing, where the sensing