nature photonics technology focus optical fiber sensor

March 2008

Optical-fibre sensors

© 2008 Nature Publishing Group

Also Available: Quantum Dot Polymer Nanocomposites Biocompatible Quantum Dots

Magnetic NanoparticlesMetal Nanoparticles

www.oceannanotech.com Email: [email protected] Phone: 479-444-6028

OCEAN NANOTECH, LLC

Innovation in Quantum Dots for Optoelectronics and Photonics

• High Purity at Electronic Grade

• High Emission Quantum Yield

• Narrow Bandwidth Emission

Optical LiquidsCatalog

Cargille Laboratories Inc.55 Commerce Road, Cedar Grove, NJ 07009973-239-6633 • Fax [email protected] • www.cargille.com

New catalog of specialty optical liquids features high-transmission,safe-handling,laser liquids, plus fused silica matching liquids,and specificrefractiveindex liquids (1.300-2.11 nD).

Now includes comparative diagrams of glasses and optical liquids.

Write or call for free catalog. solutionslaser diode

[email protected]

Looking for a laserdiode solution?

We can design andbuild a laser diode

assembly to maximizethe performance of

your system. We arethe specialists forlaser diodes, laser

modules and custom-designed laser

solutions tailored toyour requirements.

Meet us at LASER 2007Hall 1, booth B1.669+671

0142nphotomar.indd 10142nphotomar.indd 1 19/2/08 11:32:35 am19/2/08 11:32:35 am


nature photonics | VOL 2 | MARCH 2008 143

CONTENTS | TECHNOLOGY FOCUS

W 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 in situ 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 in situ 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.

Cover image Fibre sensors are being used to monitor the structural health of large composite structures such as turbine blades.

Industry Perspective p153

EDITORs: NADYA ANsCOMBE, OlIvER GRAYDON

PRODuCTION EDITOR: ChRIs GIllOCh

COPY EDITOR: ANNA DEMMING

ART EDITOR: TOM WIlsON

[email protected]

REsEARCh hIGhlIGhTs 145 Monitoringpipelines, hydrogenleaks,traffic, andmore

INDusTRY PERsPECTIvE147 Oil and gas applications: Probingoilfields Hilde Nakstad and Jon Thomas Kringlebotn

150 Medical applications: Savinglives Éric Pinet

153 Structural-health monitoring: Asensitiveissue Martin Jones

BusINEss NEWs156 Bigcontracts,morefunding andmarketpredictions

PRODuCT hIGhlIGhTs157 Dynamic,robustand versatilesensorsfor diverseapplications

INTERvIEW158 Educationandregulation Interview with Brian Culshaw

Great potential


mailto:[email protected]

picture is worth a thousandwords. CODE V’s image

simulation feature lets you visualizethe performance of your opticaldesigns directly, as an alternative to traditional charts and tables. It is the ideal tool for communicatingoptical performance to non-opticalengineers.

Image simulation is a diffraction-based computation that includes theeffects of geometrical aberrations,diffraction, relative illuminationvariations, and distortion. Blurringdue to a finite-sized detector can alsobe included. The algorithm uses thepower of the Fast Fourier Transform(FFT) calculation, and is much more efficient and accurate thangeometrical ray-blasting techniques.

If optical performance is critical tothe success of your product, there is only one choice for your opticaldesign software—CODE V.

www.opt icalres .com

OPTICAL DESIGN SOFTWARE

A

What you get iswhat you see

Visualize and communicate optical systemperformance with CODE V ® Image Simulation

Corporate Headquarters: 3280 East Foothill Boulevard, Pasadena, CA 91107-3103 (626) 795-9101Fax (626) 795-0184 E-mail: [email protected] Web: www.opticalres.com

Offices: Tucson, AZ | Westborough, MA

© 2006 Optical Research Associates. CODE V is a registered trademark of Optical Research Associates.

• Obtain fast, accurate visualassessments of system imagequality, including diffraction

• Communicate optical concepts andtrade-offs to non-optical engineersduring design evaluations andproduct presentations

• Improve qualitative understanding of traditional performancemeasures such as MTF and spotdiagrams

• Determine image orientation issuesfor complicated folded systems

Untitled-1 1Untitled-1 1 8/10/07 13:37:188/10/07 13:37:18


RESEARCH HIGHLIGHTS | TECHNOLOGY FOCUS

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.

A new parameterJ. Opt. Soc. Am. (in the press)Researchers in Denmark are proposing the adoption of a new approach for characterizing long-period gratings in photonic-crystal fibre sensors.

Lars Rindorf and Ole Bang from the Technical University of Denmark in Lyngby, have shown that although Bragg gratings in photonic-crystal fibre are best characterized in the usual way, that is, by the sensitivity (defined as the resonant wavelength shift divided by the resonant wavelength), long-period gratings are better characterized by their quality factor (defined as the resonant

wavelength shift divided by the full-width at half-maximum of the resonance dip).Rindorf and Bang explain that formulae used for standard optical fibres do not apply for photonic-crystal fibres, as these fibres are typically made of two materials, such as silica glass and air.

By considering the properties of each material separately, the researchers found rigorous formulae that apply to photonic-crystal fibres. They also identified a term for temperature and strain sensing that was previously unaccounted for.

Finding hydrogen leaksIEEE Photon. Technol. Lett. 20, 1041–1135 (2008)A leak detector that can detect a 1% concentration of hydrogen in air with a response time of less than one second has been developed by researchers in Mons, Belgium. The team, from Materia Nova and Faculté Polytechnique de Mons, used fibre Bragg gratings covered with a catalytic sensitive layer. This was made from tungsten oxide powder doped with platinum, which induces a temperature elevation around the fibre Bragg gratings in the presence of hydrogen in air.

In the past, fibre Bragg gratings covered with palladium have been widely investigated for hydrogen sensing, where the sensing mechanism is based on the swelling of the palladium coating, resulting in a stress on the grating. In practice, the palladium-coated sensors suffer from a variety of problems, including a long response time and measurements affected by hysteresis.

The Mons team claims to have solved these problems with its new sensor design. In the presence of hydrogen in air, the sensitive layer takes part in an exothermic reaction, and the increase in temperature around the fibre Bragg grating is measured through a shift in its central wavelength.

The researchers have demonstrated that a good sensitivity is obtained whatever the relative humidity level of the air. They also showed that the grating length does not influence the temperature delivered by the chemical reaction, and that the sensor has a linear response to varying hydrogen concentrations. This linear response is reversible, so there is no need to recondition the sensor after hydrogen detection. It is also compatible with frequency multiplexing and can be used in quasi-distributed sensors.

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.”

Brill

ouin

gai

n [a

.u.]

0.04

0.03

0.02

0.01

0.00

–0.01

7050

3010 0 0.4

0.81.2

1.62.0

Distance (m)Time (s)

RESEARCH HIGHLIGHTS | TECHNOLOGY FOCUS

Smart 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 eight

Dynamic analysis of the impact of traffic

© 2

008

IOP

nature photonics | VOL 2 | MARCH 2008 | www.nature.com/naturephotonics 145


http://www.nature.com/naturephotonics

Nature Publishing GroupCovering the spectrum in the physical sciences

VOL.7 NO.1 JANUARY 2008www.nature.com/naturematerials

GLOBALIZATION OF RESEARCHFriendly competition

NAFIONA clear diffusion model

DIAMONDOIDSOut of the sludge

Charge order takes a slide

Branestorm

VOL.4 NO.1 JANUARY 2008www.nature.com/naturephysics

QUANTUM OPTICSFew-photon fluorescence

SUPERCONDUCTIVITYCharge without spin

QUANTUM MOLECULAR DYNAMICSExplosive simulations

BIOTECHNOLOGYNanomagnetic switches for cells

LITHIUM BATTERIESSilicon nanowires show their potential

MAGNETOELECTRICITYNew effects from first principles

Colossal predictions for platinum nanowires

VOL.3 NO.1 JANUARY 2008www.nature.com/naturenanotechnology

SILICON PHOTONICS Signal regeneration

SPECTROSCOPY Real-time Raman

BIOLUMINESCENCE Firefly efficiency

Waveguiding in photonic crystals

VOL.2 NO.1 JANUARY 2008www.nature.com/naturephotonics

OWEN FRACTURE ZONE Plate boundary revealed

METEORITE IMPACTSA boon for a change

CLIMATE CHANGE Expanding tropics

Glacial water drives the flow

VOL.1 NO.1 JANUARY 2008www.nature.com/naturegeoscience

Nature Publishing Group offers a range of journals in the physical sciences – from the broad scope of Nature to specifi c titles in physics, photonics, materials, nanotechnology, geosciences, chemical biology and, new for 2009, chemistry. Each journal carries a mix of research papers, reviews, news and views, and commentaries that keeps you up-to-date with the latest research in your area.

Visit www.nature.com to:

- register to receive table of content e-alerts- sign up for RSS feeds- enter a personal subscription- recommend the journals to your library

*Journal Citation Reports, Thomson, 2007

Impact factor:

12.409*

Impact factor:

12.040*

Launched in

January 2008

Launching 2009Impact factor:

19.194*

www.nature.com

13470-01 PS cluster ad 2008.indd 113470-01 PS cluster ad 2008.indd 1 17/1/08 10:35:0217/1/08 10:35:02



INDUSTRY PERSPECTIVE | TECHNOLOGY FOCUS

Hilde Nakstad and Jon Thomas KringlebotnOptoplan, Haakon VIIs gate 17 A, 7041 Trondheim, Norway

e-mail: [email protected]

F inding oil is one of today’s toughest engineering challenges. And once an oil field has been found, extracting

all of the oil is an even bigger challenge. Optical-fibre sensors are important for helping the oil industry to locate and monitor reservoirs and to efficiently recover the largest possible percentage of oil and gas with minimal environmental impact. Such sensors are being used to map reservoirs, understand how they develop and to monitor the processes used to separate oil, gas and water.

The recovery rate from oil reservoirs at present is of the order of only 40–50% before they are abandoned. Reservoir monitoring is needed to enhance this rate. Any increase in the oil recovery rate will, in addition to the increased profit, have a considerable positive effect on the environment, as the remaining oil from marginal fields can be extracted with the existing infrastructure.

Over the past 20 years, increasingly sophisticated optical instrumentation for permanent in-well monitoring has been made available to reservoir engineers, including pressure, temperature, flow and seismic sensors. Pressure and temperature measurements are used to characterize oil production and the effect it is having on the reservoir. Flow measurements determine both the total flow through a producing pipe and the phase fractions of oil, gas and water. The use of several flow meters in one well can tell the reservoir engineer from which zone in the well the oil is produced and where water is penetrating.

Seismic measurements are used to globally image and characterize the geophysical properties of rock formations, and are extensively used in exploration surveys to locate reservoirs. In recent years, seismic measurement systems have been installed permanently in-well and

on the seafloor for reservoir monitoring. However, most of these systems have been electrical, with fibre-optic systems now starting to emerge.

Over the past 10 years the ability to control production has improved, with extraction from multiple zones within a well and the use of downhole control valves to open and close access for production from each individual zone. As experience has been gained, the feedback loop, from measurements through model development and prediction to control, has become increasingly more efficient, and the demand for more measurements has increased. Whereas wells with permanently installed sensors were rarely seen 15–20 years ago, it has become a necessity today, and hardly any well is without some form of instrumentation.

Fibre-optic technology provides several advantages over electrical instrumentation for permanent reservoir

monitoring applications in the oil and gas industry. Fibre-optic sensors are highly reliable. They also have an ultralong range, and a large number of similar or different sensors can be multiplexed on one fibre.

For in-well applications, fibre-optic sensors offer high reliability owing to their passive nature. Within wells, the environmental conditions are challenging, with temperatures in excess of 100 °C and even as great as 200 °C, and the reliability of conventional electrical sensors suffers under such conditions. The passive nature of fibre-optic sensors is also an advantage when the sensors are located beneath the sea, eliminating failures caused by electronic components exposed to water. The small size and weight of fibre sensors are added benefits, enabling sensors to be located at otherwise inaccessible sites. In addition, the low loss and large bandwidth of optical fibres enables transmission of huge amounts of data over tens of kilometres. In the case of subsea wells, the fibre can provide a connection to the topside facility without the need for any electronics beneath the surface. The use of optical-amplifier and multiplexing technology, initially developed for telecommunications, can enhance the range and bandwidth of optical-sensor systems even further.

Several different fibre-optic sensors are available today. The first fibre-optic sensor to be installed in an oil well in 1993 was based on fibre-coupled micromachined silicon resonators, and was used to measure temperature and pressure. The silicon resonator was excited using modulated light, and the vibration induced by this light was measured using interferometric techniques. Today most of the fibre-optic sensors available to the oil and gas industry are intrinsic, that is, the sensing element is the fibre itself and the light does not have to exit and re-enter the fibre core (see Box 1).

Although most fibre-optic sensors for the oil and gas industry have been made for in-well sensing, there is growing interest in fibre-optic monitoring systems for subsea and sea-bottom applications.

Optical-fibre sensors have become an indispensable tool in the oil and gas industry, helping engineers to not only locate wells, but also get the most out of them.

Oil aNd gas applicaTiONs

Probing oil fields

Pressure and temperature (pT)

Flow and phase fraction

Seismic

Distributed temperature sensor

Cable

Seismic array

pT guage

Distributed flow sensors

Oil and gas reservoirs are drained using several wells from one topside facility. The well heads can be located several kilometres from the platform below the sea. Based on data provided by distributed flow sensors and pT guages, the production from each well and each zone within a well is controlled using downhole control valves.



148� nature photonics | VOL 2 | MARCH 2008 | www.nature.com/naturephotonics

INDUSTRY PERSPECTIVE | TECHNOLOGY FOCUSINDUSTRY PERSPECTIVE | TECHNOLOGY FOCUS INDUSTRY PERSPECTIVE | TECHNOLOGY FOCUS

These include ocean-bottom seismic cable (OBC) systems, for example, where the large-scale multiplexing capability and passive nature of fibre-optic sensing systems can be fully exploited. An OBC system comprises thousands of seismic stations placed in trenches at the bottom of the ocean. Each station (commonly called a 4C station) includes four components: one fibre-optic hydrophone and three fibre-optic accelerometers for the measurement of pressure waves and vibrations. The sensors are installed on the seafloor in a regular pattern, and seismic signals are generated using an airgun in the water. Each sensor measures the direct pressure wave from this airgun as well as the reflection of this wave from the rock formation underneath the sensor. Differing physical properties of the formation affect the reflected signals. By appropriate signal processing and interpretation it is possible to predict the location of oil and gas reservoirs and, by repeating these surveys over time, it is possible to monitor dynamically the effect of oil production on the reservoir, so-called 4D monitoring. With thousands of sensors installed on the seafloor it is possible to cover a large area of the subsurface, providing the reservoir engineer with a global view of the reservoir.

Optoplan has developed a fibre-optic OBC system, which features hydrophones and accelerometers based

on interferometric fibre Bragg grating (FBG) sensors (see Box 1). The fibre-optic hydrophone converts pressure waves into a change in the fibre length, while the fibre-optic accelerometer modulates the fibre length as the sensor is exposed to acceleration. An advanced optical

interrogation system is used to read out the optical signals from a large number of sensors with the required resolution, crosstalk and harmonic distortion. A typical system comprises approximately 2,000 4C stations with a total of 8,000 sensor channels covering a seabed area of typically 30–40 square kilometres.

The sensors are linked together using several fibres and a combination of time- and wavelength-division multiplexing is used to distinguish their respective signals. Excellent performance has been verified in several field tests and comparisons with state-of-the-art electrical systems. The performance of the fibre-optic system is comparable to these electrical systems, but in addition the potential for superior reliability using the fibre-optic system is significant. For permanently installed sensor systems this is crucial. Once installed on the seafloor a sensor system will remain there as long as oil and gas is produced from that field, providing seismic data on demand. All that is needed for a future round of measurements is a seismic source as the sensors are already there, ready to measure any change in the response from the rock formation.

Following field tests, Optoplan’s fibre-optic OBC system is now ready for deployment offshore. In spring 2008, 200 stations will be installed in a pilot installation in the North Sea. Although it is a relatively small installation,

There are two main optical-fibre sensor technologies available to the oil industry — sensors based on FBGs and sensors based on light scattering (Raman and Brillouin) in the fibre itself.

An FBG is a periodic modulation of the index of refraction of an optical fibre over a length of about 1 cm, and causes reflection at wavelengths that match the period of the index variations. As the period changes with temperature and the strain on the fibre, the reflected wavelengths vary. By proper design of the sensor element, the Bragg grating can be used to monitor temperature, pressure or strain. These sensors can be very accurate, with some capable of detecting the reflected wavelengths with an accuracy of 1 pm, corresponding to an accuracy in temperature and strain measurements of 0.1 °C and 1 µstrain, respectively.

Fibre Bragg gratings are also used in interferometric sensor systems, where the parameter to be measured changes

the phase delay between the light waves reflected from two FBG reflectors at different positions. Minute changes to the fibre length, and hence phase delay, can be detected with extremely high resolution. By proper design of the sensor element, it is possible to measure a variety of parameters — anything that can be converted into a change in fibre length. Interferometric sensors are best suited for dynamic measurements as the absolute fibre length is more difficult to determine with interferometric techniques. Reflective interferometric sensors can also be made without the use of FBGs. In these systems reflectors are created using mirrors and the partial coupling ratios are created using couplers. Interferometric sensor systems based on fibre Bragg gratings are commercially available for flow and phase fraction measurements and for in-well and sea-bottom seismic sensing.

In FBG-based sensor systems numerous distinct wavelengths can be used to multiplex several sensors along a single fibre (each FBG sensor is designed to respond to a different wavelength).

Fibre-optic distributed temperature sensors based on Raman and Brillouin scattering offer unique, truly distributed sensing along a standard optical fibre, and do not have an electrical equivalent. In a Raman-based system a high-intensity light pulse is sent along a fibre. As it propagates, some of the light is back-scattered along the fibre in two spectral bands. By monitoring the amplitude ratio of these bands as a function of distance it is possible to derive a temperature profile along the fibre. The temperature and spatial resolution of such measurements are moderate, typically 1–2 °C and 1–2 m, with long measurement times, but the information provided to the reservoir engineer is valuable because of the truly distributed nature of the measurements.

Box 1 Types of optical-fibre sensors

a fibre-optic ocean-bottom seismic system. Thousands of sensors are trenched in the seafloor and connected back to topside facilities for monitoring.

opto

plan





it is expected to provide useful data to the reservoir engineers. The system will have a cable connecting it to the fibre-optic interrogation system on an off-shore platform several kilometres away. The signals from the 200 stations (800 channels) will be converted to seismic formats and transferred to shore for processing and interpretation.

To commercially succeed with such large-scale systems, an efficient manufacturing system is mandatory. High yield and repeatable manufacturing is important for all parts of the system, including manufacture of the FBGs used in the system and the mechanical parts required to assemble a seismic station. Optoplan, with its owner Wavefield Inseis, has developed a manufacturing system that can handle the manufacture of several systems every year, each featuring at least 2,000 4C seismic stations. The first full-scale fibre-optic OBC installation will be ready for deployment within 1–2 years.

By combining the information provided by these permanently installed fibre-optic OBC systems with the measurements available from in-well sensors that measure flow, pressure and temperature, the reservoir engineer

will be able to get a detailed model of the hydrocarbon reservoir, where the reserves are and how the reservoirs respond to production. Only by

optimizing oil production this way can the reservoir engineers expect to increase the oil recovery rate from today’s low of around 50%.

a fibre-optic four-component seismic station. Three identical accelerometers are placed orthogonal to each other inside a sensor package together with a hydrophone. The sensor package is spliced into the cable, and several thousands of these stations are connected in a full-scale OBc system.

opto

plan


INDUSTRY PERSPECTIVE | TECHNOLOGY FOCUSINDUSTRY PERSPECTIVE | TECHNOLOGY FOCUS INDUSTRY PERSPECTIVE | TECHNOLOGY FOCUS

Éric PinetFISO Technologies, 500-195 Avenue St-Jean-Baptiste, Québec G2E 5R9, Canada


O ptical fibres helped revolutionize medicine when they were first used to illuminate endoscopes in the 1960s.

The result was the development of minimally invasive tools that have become essential for medical diagnosis and surgery. But optical fibres offer the potential for much more than simple illumination or imaging tasks. For example, they can also sense many physiological parameters, such as temperature, pressure, oxygen concentration and applied forces.

In medical applications, optical-fibre sensors offer many advantages over conventional sensors: they are small, immune from electromagnetic interference (EMI), have increased sensitivity and are very robust. But until recently, the medical community has not been able to benefit from these advantages, mainly because of the cost factor. Market penetration has been slow because optical-fibre sensors and their interrogation units are often quite expensive when compared with traditional sensors, in particular electrical sensors. As a result, optical-fibre sensors have so far been mostly confined to expensive medical devices (for instance in neurology or cardiology) where they have distinct advantages over traditional sensors.

However, recent advances in manufacturing techniques and sensing technologies mean that medical applications for optical-fibre sensors are growing rapidly, and sensors are now even being used in disposable devices.

With the miniaturization of laparascopic tools and catheter-based instruments, practitioners increasingly need to get reliable information about the remote environments they are investigating through small incisions or natural openings in the human body. In particular, there is a need for sensing physical parameters, such as temperature, pressure or applied forces,

at the tip of an instrumented catheter. These are ideal roles for optical-fibre-based point sensors.

The miniature size of fibre sensors (usually between 125 µm and 1 mm for a bare sensor) is probably one of the main reasons for using them in the space-constrained and instrument-crowded environment of the catheter tip. However, there are other benefits as well. Measurements in situ are usually much more precise and more informative than remote sensing, and optical sensors are immune to the EMI generated by electrical instruments in the operating environment. Electromagnetic interference can also be caused by

electrical cauterization tools, as well as radiofrequency or microwave tip probes. This equipment is used for local tissue heating or burning and magnetic-resonance-imaging (MRI) systems, which are starting to be used in the operating theatre. Because the sensing information is carried by photons and not electrons, optical-fibre sensors are intrinsically insensitive to EMI. This in itself is a major advantage, but it also means the sensors do not need to be shielded and can therefore be made much smaller than their electrical counterparts.

In terms of accuracy and sensor drift, optical sensors also often have superior levels of performance compared with

Penetration of optical-fibre sensors into the medical market has been slow because of high costs and long regulatory procedures. Today, however, an increasing number of life-saving medical procedures are benefiting from the advantages that these tiny sensors can bring.

Medical aPPlications

Saving lives

thanks to their miniature size, optical-fibre sensors have real potential in many medical applications, especially in the development of minimally invasive surgical tools.

FISO

Tech

nOlO

gIeS





INDUSTRY PERSPECTIVE | TECHNOLOGY FOCUSINDUSTRY PERSPECTIVE | TECHNOLOGY FOCUS

electrical miniature sensors. In addition, the fact that such optical sensors are mostly made from inert and thermally stable materials, such as glass and selected polymers, makes them attractive for biocompatibility and product certification.

An example of a medical application that benefits from all these advantages is a miniature pressure sensor, which can be used in neurology for intracranial pressure (ICP) monitoring. This is probably the most important application for optical-fibre sensors in the medical market at the moment. Until the use of optical-fibre sensors, the conventional method for measuring ICP was to use fluid-filled catheters and to measure the cerebrospinal fluid pressure externally. Inserting and managing these catheters is a challenging task, and optical-fibre sensors have made this procedure much more straightforward. Using optical-fibre sensors, small disposable catheters (about 1.3 mm in diameter) can be inserted into the brain ventricle to directly measure the ICP. This method, considered the gold standard for measuring ICP, provides an accurate evaluation of this crucial parameter. Indeed, in brain trauma, damaged nervous tissues can swell in the fixed skull volume and thus drastically increase the cerebrospinal-fluid ICP. High ICP is responsible for coma and death in extreme cases. The use of a miniature optical-fibre pressure sensor that could also be combined with a temperature sensor offers an MRI-compatible ICP monitoring tool, without the drawbacks of inserting and managing fluid-filled catheters for external pressure monitoring. Progress in optical-fibre sensor technologies will allow even smaller ICP catheters in the future. For example, FISO Technologies recently developed an ultraminiature (125 µm diameter) prototype optical-fibre pressure sensor made entirely from glass: such a technological breakthrough will open new

avenues for ICP procedures, as well as for pressure monitoring of small animal models used in research to find new drugs.

Another important application for optical-fibre pressure sensors is a cardiac-assist therapy called intra-aortic balloon pumping (IABP). It consists of inserting a disposable catheter terminated by a balloon into the aorta, usually through the femoral artery. The balloon is rapidly inflated and deflated in counter-pulsation with the heartbeat to provide better blood irrigation of the heart and the brain. This life-supporting therapy, developed in the late 1960s, is used to assist patients with heart problems until they recover from heart surgery or disease. Its success relies on synchronizing the balloon pumping with the heartbeat, which can be done either by using electrocardiogram (ECG) signals or an aortic-pressure waveform. Aortic-pressure-waveform monitoring is traditionally performed by an external electrical sensor, which measures pressure transmitted through a fluid-filled catheter. This method has major drawbacks associated with the fluid-pressure transduction, which can suffer from damping effects due to catheter elasticity or the presence of tiny bubbles. Also, the pressure readings are completely obscured if the catheter is vibrating, which is always the case in emergency situations or during patient transportation. These drawbacks are eliminated by the use of an optical-fibre-based pressure sensor mounted at the tip of the catheter. The optical-fibre sensor enables an accurate and direct in situ measurement that can easily detect small pressure changes, such as the ‘dichrotic notch’, which corresponds to an aortic-valve closure event and is used for balloon inflation triggering. As fluid transduction is eliminated, IABP therapy is significantly simplified and, more importantly, the catheter diameter can be further reduced to values that are impossible to reach with non-optical sensing technologies. This drastically lowers the risk of ischaemia (the main risk associated with IABP therapy) because blood flows better through an artery that is less hindered by medical instruments.

Another interesting emerging medical application is surface-temperature monitoring of patients under MRI investigation. For sedated or severely injured patients, temperature is a crucial physiological parameter to follow during MRI procedures, which can typically take 30–60 minutes. Here, the EMI insensitivity and small size of optical-fibre sensors are the main advantages. For instance, small sensors can be packaged more easily and positioned precisely for accurate detection of hot spots. Checking for hot spots is also

important for the validation of MRI-safe implantable devices and for ensuring that they do not heat up while they are under the strong magnetic fields of MRI systems.

Strain and applied forces are other parameters that can easily be measured with optical-fibre sensors. Such sensors, positioned at the tip of instrumented catheters, can give the laparoscopic surgeon valuable information that can be used for feedback in robotized surgical procedures. Disposable medical devices integrating strain and force optical sensors will soon become more widely available as the price of optical sensing technology decreases. Although such devices have already demonstrated real potential during the research and development phase, they will probably become more popular in modern hospitals where their EMI insensitivity makes them attractive.

Most high-volume medical applications for optical-fibre sensors involve measuring physical parameters, but chemical sensing is also a growing market and sensors that detect dissolved oxygen and carbon dioxide or pH are now commercially available. Some catheters are already equipped with fibre sensors offering blood-gas monitoring capabilities, which are crucial for monitoring sedated patients. Optical-fibre sensors based on spectroscopic

optical-fibre sensors can be packaged for skin-temperature monitoring, for example during MRi procedures.

FISO

Tech

nOlO

gIeS

the eMi insensitivity of optical sensors is perfectly suited to applications involving high electromagnetic fields, such as in MRi.

lyOn

, Pre

STOn

/neW

ScOM



INDUSTRY PERSPECTIVE | TECHNOLOGY FOCUSINDUSTRY PERSPECTIVE | TECHNOLOGY FOCUS

techniques have the potential to not only sense simple chemicals but also more complex molecules of biological interest (such as glucose, peptides, proteins or DNA). The greatest challenges for chemical sensing are probably related to achieving both selectivity and sensitivity when dealing with complex molecular mixes. The miniature size of the optical-fibre sensor becomes a distinct advantage when the sample size is reduced to a few micro- or even nanolitres, as is usually the case in biochemistry or in drugs research and development. Such tiny sensors could be important for future microchemical diagnosis, for instance at the cell level.

The trend towards miniaturization will also push the industry to offer single-fibre-based optical sensors with multi-parameter sensing capabilities. The size reduction of the optical fibre itself could also contribute to further miniaturization. Although the present standard diameter

is 125 µm, some 80-µm optical fibres are now commercially available. Point sensing is the main application for optical-fibre sensors in the medical market at the moment, but more distributed sensing applications will also emerge in this field, as is already the case for structural health monitoring of smart structures and materials. For example, measuring quasi-distributed strain along an optical fibre incorporated into a mattress can be used for patient monitoring to check movements or even breathing cycles. When inserted into a catheter, distributed strain sensors could be used for stereotactic applications, for example in neurosurgery.

Although there are many motives for the rapid development of optical-fibre sensors in medical fields, the market boom that was predicted more than a few decades ago has not yet happened. Instead, a slow but constant growth has been observed. The main reasons for

this evolution are the industrial maturity of optical-fibre sensor technologies and the difficulties in penetrating a market that requires complicated product qualifications and top-quality manufacturing processes. Not many optical-fibre-sensor companies have the capability to mass-produce and sell in the medical market because medical product development is often a long and expensive process, always application-specific and usually has to be conducted with medical company partners. Obtaining regulatory approval (such as from the US Food and Drug Administration and CE Marking) can also be a long and arduous process.

Like every emerging technology, there is a learning curve for the industry as well as for the end-users. There are many challenges to be overcome: ensuring a clean optical connection is still a practical challenge in the medical field. Unlike technicians working in the telecom industry, medical practitioners do not have the experience, or even the time, to carefully handle an optical-fibre sensor in an emergency situation. The greatest challenge for the optical-fibre-sensor industry is therefore to offer the end-user ‘plug and play’ devices that are easy to use and tolerant to rough handling. Application-oriented customization, reduced cost and robust designs are important for the commercial success of such sensing technology, especially for the medical market.

a miniature optical-fibre-based pressure sensor, shown here in a 24-guage hypodermic needle. this Fabry–Pérot type of sensor can be used to measure the pressure of any bodily fluid and is now used in many medical applications, including life-support devices.

FISO

Tech

nOlO

gIeS





Martin JonesInsensys, 3 Compass Point, Ensign Way, Hamble, Southampton, SO31 4RA, UK


T oday, most aircraft have their inspection, service and lifetime determined by the number of hours

they have flown. It is a logical approach, but flawed. An aircraft that flies in relatively benign conditions, landing on good quality runways, will experience very different loads from the same aircraft if flown in consistently heavy turbulence and landed on substandard, or even grass, runways. The industry understandably takes a conservative approach, assuming a hard set of conditions as the norm and scheduling inspection, service and lifespan accordingly. This results in unnecessary and costly inspection and services, as well as a shorter lifespan for aircraft that may still be airworthy. The use of fibre-optic sensors could change this for the better.

Embedded into the structure of the aircraft, fibre-optic strain-measurement technology provides the aerospace industry with the opportunity to schedule inspection, service and retirement of the aircraft based on the actual loads experienced by the structures. This will bring considerable cost savings for the operators, as well as improved safety for passengers.

The small cross-sectional area (0.25 mm diameter) of fibre sensors means they can be embedded within most composite structures without having any adverse impact on the structure’s mechanical properties. This enables measurement of strain in key locations that were previously out of reach.

Once embedded within a structure, sensors based on fibre Bragg grating technology become permanent installations that are capable of monitoring the structure throughout its entire lifetime. In addition, as many sensors based on fibre Bragg gratings can be written into a single optical fibre, multiple sensors can be deployed without the need for complex wiring. Although the sensors are directional and make measurements along a single axis, it

is simple to deploy several that are aligned in orthogonal directions to allow data collection along a number of axes, and thus torsion can be measured.

Robustness is also an important feature of fibre sensors. As optical sensors do not contain electronics, they are immune to electromagnetic interference and are naturally protected from damage from lightning strikes, radio interference or other forms of electromagnetic radiation. They also have a very high fatigue tolerance and are not susceptible to water ingress or corrosion.

The aerospace industry is now starting to use fibre-sensor technology within prototypes and components where it can prove itself. As a result of being able to embed optical fibres within carbon-fibre composites, companies have, for the first time, been able to validate the internal stresses previously predicted by complex software packages, such as finite-element analysis. So far the embedded fibres have indicated significant differences in certain structures, leading to design change and the recalibration of predictive models.

As well as aeroplane wings and fuselages, helicopter blades are also typically made from composite materials.

Once embedded into the blades, fibre-optic sensors enable maintenance of blades and the replacement of blades based on actual load history rather than flying hours. In addition, an understanding of the load within each blade can be used to determine the lift force generated by the rotor. All of this data will be fed to flight control systems in the future, optimizing helicopter operation and improving safety.

Wind turbines

Wind-turbine blades are another example where embedded fibre sensors are playing a valuable role. As wind turbines get larger many new engineering challenges arise. The power generated from the turbine increases with the square of the rotor diameter, but increased size means significantly greater loads. In fact the increase in the loads is proportional to the third power of the blade diameter.

Fibre sensors provide an understanding of real-time loads and blade load history that is important to manufacturers and wind-farm owners. For the manufacturer, a better understanding of the loads enables improved designs leading to lighter, more efficient blades. For the wind-farm

The aerospace and wind-energy industries, which use composite materials to build aircraft and turbine blades, are beginning to use fibre-optic sensors to monitor the health of these massive structures.

structural-health Monitoring

A sensitive issue

the airbus a380, the largest passenger aircraft in the world, uses composites extensively. airbus is actively investigating the use of fibre-optic sensors on the a380.

Airb

us





operator, understanding loads and load imbalances caused by wind shear and turbulence enables better operation of the turbines in the farm. It also helps to identify potentially damaging situations and provides an early alert to ‘blade throw’ events, which could have catastrophic consequences for anything in the surrounding area.

Understanding the load history, being able to schedule maintenance and repair, and the early identification of problems provides the wind-energy industry with a similar set of drivers to those recognized in the aerospace industry. In considering the application of wind turbines offshore, the need for a system to measure the loads within the turbine blades becomes even more compelling. Once offshore, the wind-farm operator does not have the advantage of relatively easy visual inspection. This factor combined with the massive comparative cost of maintaining and servicing offshore installations, means that early identification of problems and the ability to schedule preventative maintenance, alongside existing servicing schedules, has significant financial and operational benefits.The three factors that drive manufacturers to the fibre-optic solution are fatigue life, ease of installation and, perhaps importantly, the fact that a lightning strike to the blade has no impact on the fibre-optic strain sensor.

Typically turbines are designed for a 20-year operational life, and during that time the sensor will undergo approximately 60 million cycles. A conventional strain sensor will typically fail after less than 60,000 cycles; the fibre-optic strain sensor shows no degradation in performance after 100 million cycles. So once embedded within the turbine blade, typically during the blade-manufacturing process, the fibre-optic sensor is there for the life of the turbine, with no need for servicing or recalibration.

Perhaps not surprisingly wind turbines are no strangers to lightning. The level of activity depends on where in the world they are situated — Japan is particularly vulnerable in comparison with Europe, and certain parts of the USA are also notorious. Even in Europe there have been some surprises; the offshore wind farm at Horns reef — some 80 turbines in the North Sea off the coast of Denmark — has seen considerably more lightning activity than originally anticipated. The fibre-optic strain sensor survives lightning strikes to the blade until the blade itself suffers significant damage, whereas conventional electric-based strain sensors will typically fail even with low-intensity strikes.

Overall, fibre-optic strain measurement offers the ability to measure strain reliably in harsh environments where previously strain measurement was either impossible or fraught with difficulty. The challenges faced by the technology at the moment are based around the need for lower-cost systems, simplified installation processes and a change in the attitude of engineers who have grown up with traditional electrical strain gauges and are naturally resistant to change.

aerospace applications

Conventional resistive strain gauges have traditionally been the most appropriate way to measure strains in the aerospace industry. There are, however, some significant drawbacks. The resistive strain gauge itself is small and light, but the wiring required, particularly if it is in an area with high levels of electromagnetic interference and requires shielding, adds unwanted weight to the aircraft. For all aircraft programmes — military and civil — weight reduction is a key focus.

Other problems, such as the need for recalibration of resistive strain gauges and their tendency to fatigue, or simply fall off, all help the case for replacing the incumbent technology. That said, perhaps the greatest driver for the adoption of fibre-optic strain gauges is the influx of carbon-fibre technology into aerospace components and airframes. Critical load-bearing structures — for example, wing spars on aircraft such as the Airbus A400 and the entire fuselage in the case of Boeings new 787 — can be monitored throughout their life with fibre optics embedded into the structures during their manufacture. Airbus is actively investigating the use of fibre-optic sensors in its aircraft, including the new A380.

Fibre-optic cable is generally inexpensive at less than $1 per metre, and the cost of ‘writing’ the Bragg gratings and the measurement instrument to input the light and read the optical signal have all fallen sharply in recent years. However, optical sensor technology remains expensive in comparison with traditional resistive strain gauges. As a result the fibre-optic strain-measurement approach needs to sell itself in markets where its unique benefits can command a premium.

The commercial benefits are clear: there are obviously benefits in terms of passenger safety associated with a real understanding of the loads an aircraft has seen over its lifetime and hence its airworthiness. But the road for the adoption of new technology in aerospace is a long one. Although the industry and the regulators see the benefits, there will be a long process of validation and testing before the European Aviation Safety Agency and Federal Aviation Authority will enforce a change from the current tried and tested methods. The change will come about, but it will probably be ten years before you board a plane where the airframe life is being assessed by a fibre-optic strain-measurement system embedded throughout the plane.

german researchers have tested fibre sensors based on bragg gratings in the tail of the new airbus a340/600. the sensors have shown excellent correlation with conventional strain gauges.

optical-fibre sensors are being used in the wind-turbine industry to measure strain in the massive blades of wind turbines. their immunity to lightning strikes is a big benefit.

LM G

LAss

Fib

er

Airb

us



From Semiconductor Lasers, Fundamental

Optics and Lasers to Quantum Optics,

Spectroscopy and everything in between,

Nature Photonics has it covered!

This new monthly journal is dedicated to publishing top-quality, peer-reviewed research across all areas of Photonics & Optoelectronics. Nature Photonics has review articles, research papers, News & Views pieces and Research Highlights summarizing the latest scientifi c fi ndings PLUS articles dedicated to the business side of the industry covering areas such as technology commercialization and market analysis. See for yourself what Nature Photonics is all about. Editor: Oliver Graydon, PhD

www.nature.com/naturephotonics

Today’s research driving tomorrow’s applications.

LASERSVCSELs get a makeover

OPTICAL FIBRESSubwavelength confinement

TERAHERTZ TECHNOLOGY Applications galore

Butterflies inspire optical sensors

VOL.1 NO.2 FEBRUARY 2007www.nature.com/naturephotonics

Semiconductor Lasers

12936-01NPho_Semi(RJFP4C).indd 112936-01NPho_Semi(RJFP4C).indd 1 22/5/07 17:07:3822/5/07 17:07:38


156� nature�photonics�|�VOL�2�|�MARCH�2008�|�www.nature.com/naturephotonics

BUSINESS NEWS�|�TECHNOLOGY FOCUS PRODUCT HIGHLIGHTS�|�TECHNOLOGY FOCUS

Joint venture targets temperature monitoring of power cables

UK company Sensornet and Chinese company Bandweaver have formed a joint venture to supply the global power market with monitoring solutions based on optical-fibre sensors. Sensornet is a supplier of power-cable monitoring solutions based on distributed temperature sensing (DTS) and the joint venture will focus exclusively on providing monitoring solutions for the power utility sector.

This announcement follows a series of big deals for Sensornet, which recently received a multimillion-dollar contract for its DTS system to be used in an offshore oil field and also a deal with a major Asian utility company for monitoring a transmission network.

Sensornet says that its Sentinel DTS-XR system measures temperature with high resolution at distances of up to 30 km. It enables utility companies

to detect potential hotspots in cables and take preventative action before temperatures approach the official ratings.

FISO gets nuclear order

FISO Technologies has been awarded an order of over $300,000 for optical sensors and signal conditioners from a major UK producer of electricity. The products will be used to monitor nuclear power plants. The order, which represents 20 signal conditioners and more than 70 sensors, is to be delivered over a three-month period with an anticipation of future orders from this well-established customer, who has acquired several FISO systems in recent years.

The fibre-optic displacement sensors are installed in nuclear power plants to monitor the dilation of concrete structures surrounding nuclear reactors. The linear displacement sensor, which covers a range of 20 mm, and the universal multichannel instrument system, which has a sampling

rate of 20 Hz, have been used in this application for more than five years.

SensorTran receives fundingSensorTran, a developer of distributed-temperature-sensing technology, has raised $8 million in its latest round of venture capital financing. The round was co-led by new investor Advantage Capital Partners and prior investor Expansion Capital Partners, with all existing investors participating, including WHEB Ventures and Stonehenge Capital Company.

SensorTran’s distributed-temperature-sensing systems are used in several applications, including monitoring transmission and distribution power cables, downhole oil and gas wells, high-temperature vessels, pipelines, storage tanks and climate change.

Kent Kalar, CEO of SensorTran, said, “The past year was SensorTran’s strongest to date, and this additional capital will empower us to continue expanding our product portfolio, our sales reach, and our global service network.”

The outlook for the fibre-sensor sector is growth towards the billion dollar level, according to the latest set of figures from two organizations. The Optoelectronics Industry Development Association (OIDA) estimates the market for distributed-fibre-sensor systems will reach $550 million by 2010. These are similar figures to those estimated by Global Industry Analysts, which projects that the fibre-optic-sensor market will be worth more than $650 million by 2010.

The two organizations also agree on the main drivers for growth — homeland security and defence. “Many vital assets, which may extend over wide areas, are under constant threat of being attacked or breached,” says David Krohn of Light Wave Ventures, who carried out the market research for the OIDA. “Fibre-optic-sensor technology has the potential for wide usage in this application, but it must be capable of being integrated with other surveillance approaches, such as wireless technology.”

The OIDA’s findings also show that another key market driver is the oil and gas industry. “With the current price of oil up over 300% in the last five years and a limited supply, smart oil and gas wells, as well as reservoir management, are very important,” says Krohn. “The industry has seen some major investment in optical-fibre-sensor technology recently

because no other technology can do what fibre sensors can do in this application.”

But although Krohn’s research has shown that fibre sensors have great potential in these and many other applications, he warns that industry coordination in the development of standards is required to promote market acceptance and growth. “When businesses are heavily customized, they will remain small,” says Krohn. “When an industry is standardized, it is able to grow.”

In Krohn’s opinion a lack of legislation for the monitoring of infrastructure, such as power lines and bridges, has also contributed to slow growth. “I would like to see legislation that ensures all bridges and other important pieces of infrastructure

Distributed fibre optic sensor market

Year

2010

2009

2008

2007

2006

0 700600500400300200100

Smart structures

Market ($ millions)

Distributed temperature sensing systems Industrial Homeland security

MilitaryOil and gas

Legislation and standards needed to drive market growth

OIDA

are ‘smart’,” says Krohn. “A distributed sensing system for a bridge can cost between $50,000 and $300,000, which most construction companies do not want to spend, but replacing a collapsed bridge can cost more than $1 billion. Legislation would encourage the construction industry to invest in a technology, which in the end could save it a lot of money.”

As well as standards and legislation, Krohn believes cost is one of the biggest barriers to growth in the sensor industry. “Fibre-sensor systems are still relatively expensive because many companies have developed proprietary technology and systems are heavily customized,” says Krohn. He feels standardization will help bring costs down.



BUSINESS NEWS�|�TECHNOLOGY FOCUS PRODUCT HIGHLIGHTS�|�TECHNOLOGY FOCUS

nature�photonics�|�VOL�2�|�MARCH�2008�|�www.nature.com/naturephotonics� 157

Interrogation monitor has subpicometre resolution

www.ibsenphotonics.comThe Danish firm Ibsen Photonics has released a 1,310-nm version of its interrogation monitor (I-MON) for monitoring fibre Bragg grating sensors. The latest I-MON builds on Ibsen’s high-resolution spectrometer technology and uses the company’s fused silica transmission gratings. The design allegedly enables a fast measurement frequency and compact size, as well as low power consumption. Ibsen says that the latest product operates with a wavelength range from 1,275 nm to 1,345 nm and suits use not only with fibre Bragg grating sensing, but also high-resolution spectrometer applications. The company also offers the I-MON E series — high-resolution versions designed as stand-alone monitors with a USB interface for easy set up with a laptop. The I-MON E series is compatible with the wavelength range 1,520–1,585 nm, offers high sensitivity, subpicometre resolution and is easy to use.

Portable interrogator has broadband tuning capability

www.fibresensing.comFibreSensing and Micron Optics have collaborated to release a portable measurement unit for sensors based on fibre Bragg gratings. The unit combines Micron Optics’ robust, wide-scanning, high-power, low-noise swept laser source with FibreSensing’s integrated and portable instrument platform.

The instrument is particularly well suited for measurements in remote civil, downhole-oil, and pipeline applications, where both high accuracy and portability are required.

Some of the interrogator’s important features include its broadband tuning capability, battery operation, a built-in NIST traceable wavelength reference, data-logging functions for automated sampling, archiving and transmission, a local database for managing multiple sensor configurations and datasets, and an optical-spectrum analyser function.

Temperature sensor for harsh environments

www.lumasenseinc.comLumaSense Technologies has released its Luxtron 800 series fibre-optic systems for temperature monitoring in harsh environments prone to electromagnetic noise, high voltages and microwaves.

The Luxtron 800 series instruments are industrial-grade and configurable with either one or two measurement channels at frequencies of 4 Hz or 10 Hz. The table-top Luxtron 812 version features an easy to read two-line LED display and is encased in a tamper-proof metal enclosure. The systems have RS-232 or analog output ports for downloading data and integration into industrial control schemes. The 800 Series board-level systems suit integration into OEM products where accuracy, low or no drift and fast measurement speed are required.

The Luxtron 800 series systems are compatible with all of Luxtron’s Fluoroptic (FOT) probes, which are entirely non-metallic and are immune to electromagnetic interference.

Sensor system has multichannel selector functionality

www.advantest.co.jpOver recent years, optical-fibre strain-sensing systems have been used in disaster prevention to monitor signs of impending landslides or structural collapse following natural disasters. With this application in mind, Advantest has launched a multichannel optical-fibre strain-sensing system, the N8511. The system enables the early detection of ground movement and structural strains, and according to Advantest, it is the industry’s first system with multichannel-selector functionality, enabling strain sensing in up to 16 optical fibres. Advantest says that this feature offers a larger operating area and makes the system more cost-effective, as it does not require the optical switches and special software needed by conventional systems to measure multiple fibres.

Sensing system maps fibre position and shape in medical applications

www.lunainnovations.comLuna Innovations has developed a distributed sensing technology for fibre-optic mapping of position and shape in medical and ocean surveillance applications.

Using Luna’s fibre-optic cable during minimally invasive surgery gives surgeons real-time feedback on the position of

the instruments used. The fibre, when embedded or surface-attached to surgical tools or other devices, will monitor the three-dimensional shape of its environment with measurements that are dynamic and independent of the temperature.

In ocean surveillance the technology can be used to gather underwater acoustic data in a variety of applications, including submarine hunting patrols and deep-water search and rescue. The system uses optical-frequency-domain reflectometry, which permits tens of thousands of sensors, with the same nominal reflected wavelength, to be read with very high spatial resolution.

Luma’s special optical fibre consists of high-density linear arrays of fibre Bragg grating strain sensors, which are fabricated in multiple fibre cores and packaged as a monolithic structure. Using advanced algorithms, the strain differential as seen by the fibre-optic sensors is used to calculate the bends at every discrete element along the length. Because of the sensor density, each individual sensing element can be integrated to reconstruct the shape of the fibre.

Medical pressure sensor

www.opsens.comCanadian company Opsens claims that its MEMS-based optical-fibre pressure sensor is the smallest available on the market. Aimed at medical applications and with a diameter of just 400 µm, it permits the reduction of catheter size and enables less invasive catheterization practices.

The company claims that the sensor’s design resolves two important issues facing the industry — temperature and moisture-induced signal drift. Opsens says that its sensor experiences no hysteresis, motion artefacts, bend effects or signal drift in time. Designed as a catheter-tip sensor, the OPP-M sensor provides a high-frequency response and accurate pressure readings.

The OPP-M sensor has a pressure measurement range from –50 mm Hg to +300 mm Hg and a resolution of 0.5 mm Hg. Combined with Opsens’s White Light Polarization Interferometric, this new blood-pressure transducer delivers high-fidelity and artefact-free pressure measurement in harsh environments.

IBSE

N

OpSE

NS


http://www.advantest.co.jp

http://www.fibresensing.com

http://www.lumasenseinc.com

http://www.advantest.co.jp

www.lunainnovations.com

http://www.opsens.com

INTERVIEW | TECHNOLOGY FOCUS

What are the current trends in the optical-fibre-sensor market?The optical-fibre-sensor market is amazingly diverse, so identifying trends is difficult. However, one notable point is that market penetration has been, from a researcher’s perspective, a bit disappointing. Fibre sensors have the potential to bring significant operational advantages to many applications, but the sensors are often used in industries that are very conservative. Many of the underlying technologies and principles have not changed much since optical-fibre sensors were invented — gratings are still gratings, and fibres are still fibres — we have, however, seen many improvements in applications engineering. Systems for the interrogation of fibre Bragg gratings have improved, for example, and the use of spectroscopic signatures has become more sophisticated. In fact, much of the technological development has been at the detector and signal-processing end, rather than within the sensors themselves.

What needs to happen to speed up market penetration?Education and regulation. These aspects have nothing to do with the science and technology of sensors, so often get overlooked by engineers, but education and standards are very important. The people who could use the technology need to be educated in how to use it and what benefits it can bring; and we need to establish standards and regulations to ensure a common language and understanding. Getting industry to take on a new technology can be an arduous task. Modern aircraft and many satellites now use optical-fibre gyroscopes for navigation and stabilization, but the evolution from mechanical spinning-mass systems took 20 years. Fibre gyroscopes succeeded because they are less dependent on very-high-precision mechanics and offer a much wider range of operating conditions. The key to success with optical-fibre sensors is finding those applications where the fibre sensor can do things that other sensors cannot.

Regulations are needed because nobody measures something unless they have to or they perceive a significant

economic advantage. For example, there have been several instances of bridges collapsing. These could possibly have been avoided if the structural health of those bridges had been continuously monitored. However, there is no regulation in place that states the structural health of a building needs to be continuously monitored so construction companies and bridge owners avoid the expense.

Two other important aspects of fibre-sensor development, which many technologists under-rate, are packaging and interface. It is important to collaborate with the people who will be using their products to find out how the product should be packaged and how the interface can be designed to make it user-friendly. If the developers get this right, customers will be more likely to buy the technology.

What are the most interesting emerging applications?The aerospace industry is starting to use or investigate fibre-optic sensors. But it is a very conservative industry and, although I find this frustrating, I am pleased by this conservatism every time I fly. However, I do believe fibre-optic technology will succeed in the aerospace industry. The timing will depend on how the technology will fit into the regulatory framework and on the perceived benefit to manufacturers and passengers.

The technology is making inroads into medical instruments, and can be found at the heart of optical-coherence-tomography probes, producing unparalleled images from within the eye and immediately below the skin. Industrial applications include the monitoring of currents and voltages in overhead electrical power transmission lines; looking at concentrations of hazardous gases in the atmosphere; monitoring gas concentrations in hydrogen fuel cells; and discerning food quality through highly precise colour measurements. In all of these applications, however, fibre-optic sensors are used in relatively modest total volumes.

One of the great advantages that fibre-optic sensors have over other types of sensors is that they can be networked and perform distributed measurements. For example, they can be used in tunnels over many tens of kilometres mapping temperature changes with a resolution of about one metre, making them ideal for monitoring outbreaks of fire. A recent report by the Optoelectronics Industry Development Association (OIDA) in the USA is very optimistic that the prospects offered by distributed techniques will soon totally dominate fibre-sensor applications.

What will be the most significant developments over the next few years?The majority of present fibre sensors are based on very well established concepts, such as interferometry, diffraction and spectrometry. At this level, little is likely to change. However as an optical community we are continuing to perfect ever more elegant tools to handle light. It certainly isn’t clear at present where new concepts, such as photonic crystals, slow light and all-optical switches, may find applications in sensing. However, as we learn more about how to manipulate light, these techniques will find their roles in sensor technology. We need to be well versed in the progress in optical techniques and technologies outside our own specialist fields and be able to spot the opportunity to use them. Nadya Anscombe is a freelance science and technology journalist based in the UK.

Sensor expert: Brian Culshaw.

Fibre-optic sensors have been around for many years, but their market penetration has been slow. Nadya Anscombe talks to Brian Culshaw of Strathclyde University in the UK to find out why.

Education and regulation




www.naturechina.com

Supported by

Keep up to date with the latest leading research from Mainland China and Hong Kong by registering forNature China e-alerts. Providing you with weekly research highlights from the region drawn from a variety of publications covering topics including:

• biotechnology• cell & molecular biology• chemistry• clinical medicine• developmental biology• earth & environment• ecology & environment• genetics• materials• neuroscience• physics• space & astronomy

Go to www.naturechina.com and click on the e-alert sign up button for further details

For scientists in Mainland China and Hong Kongplease visit: www.naturechina.com.cn

E-alert sign up

Sign up for Nature China table of contents e-alerts

13293-04 NChina toc ad FP.indd 113293-04 NChina toc ad FP.indd 1 24/10/07 15:23:3624/10/07 15:23:36


B&W Tek is a leading company in engineering

and manufacturing biomedical diagnostic

instrumentation and therapeutic lasers. It has

successfully carried many OED/OEM projects

for world-class biomedical device companies.

ISO 13485:2003 / ISO 9001:2000 Certified

DentistryAestheticsPDT

ENTUrologyGynaecology

OphthalmologyBio-ModulationClinical Diagnosis

Applications

www.BWTEK.com Phone: 1.302.368.7824

[email protected] Fax: 1.302.368.7830

Contract Manufacturing & Engineering forMedical Lasers & Biomedical Instruments

Dental/Aesthetic Laser

Raman Analyzer forNoninvasive Diagnosis

Multi-Channel Laserfor Therapy & Cell

Manipulation

Ophthalmology/PDT

B&W Tek’s in-house, vertically integratedcapabilities meet your needs for:

Fast track engineering and prototyping

Quality assurance and medical regulatory compliance

High volume and value added manufacturing

Unprecedented time to market

19 Shea Way, Newark DE 19803, USA

Untitled-3 1Untitled-3 1 16/1/08 10:28:0916/1/08 10:28:09


nature photonics technology focus optical fiber sensor

Documents