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- Front Matter: Volume 6619
- Special Session: Market Opportunities
- Invited Talks
- Special Paper
- Physical and Mechanical Sensors
- Chemical, Environmental, Biomechanical, and Medical Sensors
- Electromagnetic, Interferometric, Polarimetric, New Concepts, and Devices for Sensors
- Distributed, Multiplexing, System Applications, and Field Trials
Front Matter: Volume 6619
Front Matter: Volume 6619
Show abstract
This PDF file contains the front matter associated with Proceedings of SPIE Volume 6619, including the Title Page, Copyright information, Table of Contents, Conference Committees listing, Introduction, and Conference Sponsors listing.
Special Session: Market Opportunities
Fiber optic sensing technology: emerging markets and trends
Show abstract
Recent technical advances in fiber optic sensor technology have brought fiber sensors into the mainstream. Using a wide
variety of sensing elements, and interrogation techniques, these devices are finding applications in fields from power line
management to homeland security. A variety of fiber sensor technologies, applications, and markets are discussed.
Market potential for optical fiber sensors in the energy sector
Show abstract
For a long time electric power was taken as a natural unlimited resource. With globalisation the demand for energy has
risen. This has brought rising prices for fossil fuels, as well as a diversification of power generation. Besides
conventional fossil, nuclear plants are coming up again. Renewable energy sources are gaining importance resulting in
recent boom of wind energy plants. In the past reliability and availability and an extremely long lifetime were of
paramount importance. Today this has been added by cost, due to the global competition and the high fuel costs. New
designs of power components have increased efficiency using lesser material. Higher efficiency causes inevitably higher
stress on the materials, of which the machines are built. As a reduction of lifetime is not acceptable and maintenance
costs are expected to be at a minimum, condition monitoring systems are going to being used now. This offers potentials
for fibre optic sensor application.
Photonic sensing technology: currents and trends
Show abstract
Photonic sensing technology and in particular the field of fiber optic sensing, has entered a period of dynamic
market growth. Studies of anticipated world demographic shifts and climate change projections suggest areas in which
significant opportunities for the use of the technology exist and will continue to grow. In this paper, the general currents
and trends in photonic/fiber optic sensor technology will be discussed with a focus upon fiber optic biosensors. In 2004,
the fiber optic biosensor market was estimated to be in the $6-8B range, while this year, its value is projected to be in the
$7-11B range, an annual growth rate of between 6 and 10% during the period. The market is substantial with continued
growth expected over the next 5 years at least. It is large enough and growing fast enough to offer a significant
opportunity for penetration by appropriate fiber optic biosensor products.
Fiber Bragg grating sensors: a market overview
Show abstract
Over the last few years, optical fiber sensors have seen increased acceptance and widespread use. Among the multitude
of sensor types, FBG based sensors, more than any other particular sensor type, have become widely known and popular.
Given their intrinsic capability to measure a multitude of parameters such as strain, temperature, pressure, chemical and
biological agents - and many others - coupled with their flexibility of design to be used as single point or multi-point
sensing arrays and their relative low cost, make of FBGs ideal devices to be adopted for a multitude of different sensing
applications and implemented in different fields and industries.
However, some technical hurdles and market barriers need to be overcome in order for this technology - and fiber
sensors in general - to gain more commercial momentum and achieve faster market growth such as the need for industry
standards on FBGs and FBG-based sensors, adequate packaging designs, as well as training and education of prospective
customers and end-users.
Standards and guidelines: Could they enhance user confidence in fiber sensor technology?
Show abstract
Different experience from fibre sensor applications on-site has revealed the need of guidelines for developers,
manufacturers, suppliers as well as users. Although best knowledge and well-founded experience are available in the
fibre sensor community, a lack of technical instructions for all persons involved can lead to unreliable measurement
results or even damage of sensing components. In contrast, manufacturing and application procedures according to
generally binding technical rules will ensure long-term stable sensor systems and reliable measurement results. These
rules have to include definitions of particular terms to describe the sensor and sensor system characteristics as well as
methods to validate and use sensors properly.
Because FBG sensors are the most popular sensing techniques in very different fields, important aspects to structure a set
of technical recommendations will be discussed, especially for the use of FBG sensors in experimental stress analysis
and for structure monitoring.
The evolution and exploitation of the fiber-optic hydrophone
Show abstract
In the late 1970s one of the first applications identified for fibre-optic sensing was the fibre-optic hydrophone. It was
recognised that the technology had the potential to provide a cost effective solution for large-scale arrays of highly
sensitive hydrophones which could be interrogated over large distances. Consequently both the United Kingdom and
United States navies funded the development of this sonar technology to the point that it is now deployed on submarines
and as seabed arrays. The basic design of a fibre-optic hydrophone has changed little; comprising a coil of optical fibre
wound on a compliant mandrel, interrogated using interferometric techniques. Although other approaches are being
investigated, including the development of fibre-laser hydrophones, the interferometric approach remains the most
efficient way to create highly multiplexed arrays of acoustic sensors. So much so, that the underlying technology is now
being exploited in civil applications. Recently the exploration and production sector of the oil and gas industry has begun
funding the development of fibre-optic seismic sensing using seabed mounted, very large-scale arrays of four component
(three accelerometers and a hydrophone) packages based upon the original technology developed for sonar systems. This
has given new impetus to the development of the sensors and the associated interrogation systems which has led to the
technology being adopted for other commercial uses. These include the development of networked in-road fibre-optic
Weigh-in-Motion sensors and of intruder detection systems which are able to acoustically monitor long lengths of
border, on both land and at sea. After two decades, the fibre-optic hydrophone and associated technology has matured
and evolved into a number of highly capable sensing solutions used by a range of industries.
Market opportunities on fiber optic sensors for aeronautics and aerospace applications
Jose M. Menendez
Show abstract
Since the appearance of fiber optic sensors in the late 1970s, fiber optic sensing has been considered one of the most
promising technologies to be used in structural health monitoring for aerospace applications. The irruption of advanced
composites in space and military applications along this decade, and the posterior generalization in airliners along the
1980s was considered as an opportunity for these sensors, due to their up to date unique capability to be embedded in this
materials with moderate intrusivity. The appearance of fiber Bragg gratings in late 1980s seemed to confirm an easy
incorporation to the aerospace market. However, today, the use of fiber optic sensors on board of aircrafts is still little
more than symbolic, and the obstacles for this slow application are still important: qualification of sensors and
demodulator for on board operation, demonstration of reliability of measurements done by bonded or embedded sensors,
demonstration of health monitoring capability in real scenarios, and demonstrate cost-effectiveness.
Invited Talks
Surface plasmon resonance biosensors
Show abstract
This contribution reviews the present state of the art in the development of surface plasmon resonance (SPR) (bio)sensor
technology, discusses emerging trends, and presents recent results of research into SPR biosensors at the Institute of
Photonics and Electronics, Prague. The developments discussed in detail include a high-performance SPR sensor for
parallelized observation of biomolecular interactions, a miniature fiber optic SPR sensor for localized measurements, and
sensing based on localized surface plasmons on gold nanoparticles.
3D femtosecond laser microfabrication of photonic biochips
Show abstract
Three-dimensional microfabrication of photostructurable glass by femtosecond (fs) laser direct writing is demonstrated
for manufacture of photonic biochips. The fs laser direct writing followed by annealing and successive wet etching can
fabricate the hollow microstructures, achieving a vareiety of microfluidic components and microoptical components in a
glass chip. The optical waveguide written by the fs laser direct writing without the annealing and the successive etching
can be integrated into these microfluidic and microoptical circuits. Such an integrated microchip is of great use for
biochemical analysis and medical inspection based on photonic sensing. Furthermore, as one of the interesting and
important applications, the microchips fabricated by the present technique are applied for inspection of living
microorganisms.
Chiral fiber gratings: perspectives and challenges for sensing applications
Show abstract
Chiral fiber gratings are produced in a microforming process in which optical fibers with noncircular or nonconcentric
cores are twisted as they pass though a miniature oven. Periodic glass structures as stable as the glass material itself are
produced with helical pitch that ranges from under a micron to hundreds of microns. The geometry of the fiber cross
section determines the symmetry of the resulting structure which in turn determines its polarization selectivity. Single
helix structures are polarization insensitive while double helix gratings interact only with a single optical polarization.
Both single and double helix gratings may act as a fiber long period grating, coupling the core and cladding modes. The
coupling is manifested in a series of narrow dips in the transmission spectrum. The dip position is sensitive to fiber
elongation, twist and temperature, and to the refractive index of the surrounding medium. The suitability of chiral
gratings for sensing pressure, temperature and liquid levels is investigated. Polarization insensitive single helix silica
glass gratings display excellent stability up to temperatures of 600°C, while a pressure sensor with dynamic range of
nearly 40 dB is demonstrated in polarization selective double helix gratings.
Molecularly imprinted polymers as biomimetic receptors for fluorescence-based optical sensors
María C. Moreno-Bondi,
Javier L. Urraca,
Elena Benito-Peña,
et al.
Show abstract
Molecularly imprinted polymers (MIPs), human-made polymers capable of recognizing a particular molecule in the
presence of others due to the selective cavities of the material, have been successfully applied to the development of
chromatographic and solid phase extraction methods. They have also been applied to the development of
electrochemical, piezoelectrical and optical sensors. In parallel with the classification of biosensors, MIP-based devices
can work according to two different detection schemes: (1) affinity sensors ("plastic-bodies") and, (2) catalytic sensors
("plastic-enzymes"). In the first case the change in a characteristic optical property, most frequently fluorescence, of the
analyte or of the polymer is monitored, upon their mutual interaction. Alternatively, a fluorescent analogue of the target
analyte can also be used to develop sensors based on competitive assays (MIAs). Optimization of the polymer
composition and, in particular, a proper choice of the nature of the functional monomers involved in the polymerization
process, is critical to prepare materials able to selectively interact with the analyte in aqueous media and with the fast
kinetics required for analytical applications. Moreover, a rational design of fluorescent analogues of non-naturally
fluorescent templates or of fluorescent monomers able to change its property upon interaction with the analyte, is also a
bottle neck for wide application of this recognition elements in optical sensing. In this paper we present several
approaches to address these issues namely the optimization of MIP composition and the design and synthesis of novel
fluorophores for the analysis of antibiotics and mycotoxins in real samples.
Fibre optic distributed scattering sensing system: perspectives and challenges for high performance applications
Show abstract
As fiber optic distributed scattering sensing systems are providing innovative solutions for the monitoring of large
structures, the comparison of the different techniques and solutions is difficult because of the lack of standardized
specifications and the difficulty associated to the characterization of such systems. The article presents a tentative
definition of performance specifications and qualification procedures applicable to fiber optic distributed sensing
systems aiming at providing clear guidelines for their design, specifications, qualification, application and selection.
Fabrication and metrology of micro- and nano-optics
Show abstract
Large scale manufacturing of nano and micro-optics, both free-space and planar waveguide optics, has many technical
challenges. Supporting technologies required for manufacturing of different types of optical devices and modules in nano
and micro scales are being developed. As fabrication technology to support nano and micro optics improves, challenges
associated with metrology of optical feature in nano and micro scales become more apparent. In this paper some
examples of research projects at the University of North Carolina at Charlotte in these areas are presented.
Optical fiber sensors based on nanostructured coatings fabricated by means of the layer-by-layer electrostatic self-assembly method
Show abstract
The Layer-by-Layer Electrostatic Self-Assembly (ESA) method has been successfully used for the design and
fabrication of nanostructured materials. More specifically, this technique has been applied for the deposition of thin films
on optical fibers with the purpose of fabricating different types of optical fiber sensors. In fact, optical fiber sensors for
measuring humidity, temperature, pH, hydrogen peroxide, glucose, volatile organic compounds or even gluten have been
already experimentally demonstrated. The versatility of this technique allows the deposition of these sensing coatings on
flat substrates and complex geometries as well. For instance, nanoFabry-Perots and microgratings have been formed on
cleaved ends of optical fibers (flat surfaces) and also sensing coatings have been built onto long period gratings
(cylindrical shape), tapered fiber ends (conical shape), biconically tapered fibers or even the internal side of hollow core
fibers. Among the different materials used for the construction of these sensing nanostructured coatings, diverse types
such as polymers, inorganic semiconductors, colorimetric indicators, fluorescent dyes, quantum dots or even biological
elements as enzymes can be found. This technique opens the door to the fabrication of new types of optical fiber sensors.
Photonic crystal fibers: new opportunities for sensing
Show abstract
We review exceptional properties of the photonic crystal fibres enabling sensing applications of this new class of fibres.
First, the sensing capabilities of highly birefringent index guided fibres are discussed. This includes dispersion
characteristics of phase and group modal birefringence in different fibre structures, and sensitivity of these parameters to
hydrostatic pressures and temperature. We demonstrate that index guided and photonic bandgap holey fibres of specific
construction can be used as wide-band fibre-optic polarizer. We also show that combining of geometrical and stress
effects makes it possible to design the holey fibres with either zero phase or group modal birefringence at virtually any
given wavelength. Finally, different designs and performance of PCFs suitable for gas sensing are overviewed.
Special Paper
Eat-by-light: fiber-optic and micro-optic devices for food safety and quality assessment
Show abstract
A selection of fiber-optic and micro-optic devices is presented designed and tested for monitoring the quality and safety
of typical foods, namely the extra virgin olive oil, the beer, and the milk. Scattered colorimetry is used for the
authentication of various types of extra virgin olive oil and beer, while a fiber-optic-based device for UV-VIS-NIR
absorption spectroscopy is exploited in order to obtain the hyperspectral optical signature of olive oil. This is done not
only for authentication purposes, but also so as to correlate the spectral data with the content of fatty acids that are
important nutritional factors. A micro-optic sensor for the detection of olive oil aroma is presented. It is capable of
distinguishing different ageing levels of extra virgin olive oil. It shows effective potential for acting as a smart cap of
bottled olive oil in order to achieve a non-destructive olfactory perception of oil ageing. Lastly, a compact portable
fluorometer is experimented for the rapid monitoring of the carcinogenic M1 aflatoxin in milk.
Physical and Mechanical Sensors
Simultaneous independent measurement of temperature and strain using a tilted fibre Bragg grating
Show abstract
A single fibre Bragg grating is used to discriminate between temperature and strain by exploiting the core-cladding mode
coupling of a tilted fibre Bragg grating (TFBG). The core and cladding modes exhibit different thermal sensivities, while
the strain sensivities are approximately equal. Monitoring the core-core mode coupling resonance and the core-cladding
mode coupling resonance within the spectrum of a single TFBG allows the separation of the temperature and strain
induced wavelength shifts.
Radiation effect on PMMA POF under gamma-ray irradiation
Show abstract
An irradiation test was performed for polymethylmethacrylate plastic optical fibers under gamma-ray irradiation in order
to use the fiber in low-level radiation environments. Under gamma-ray irradiation at a high dose rate, only a large
radiation-induced transmission loss at wavelengths less than 700 nm was observed. Under irradiation at a low dose rate,
the loss was small and other two characteristic effects were observed. One is a radiation-induced loss that has peaks in
the near infrared wavelength range, and the other is an improvement in the optical transmission over an entire
wavelength range. The peak intensity depends on the absorbed dose of the gamma ray. Therefore, it is considered that
the absorbed dose can be measured using the peak intensity. Irradiation tests were performed by changing the
configuration of the fiber sample to observe the effect of a bending loss. It was found that the improvement in the optical
transmission is dependent on the configuration of the irradiation sample and that the bending loss can be recovered by
gamma-ray irradiation at a low dose rate.
Temperature measurement by thermo-luminescence of fused silica optical fiber under irradiation environment
Show abstract
Thermo-luminescence behavior of fused silica (SiO2) core optical fibers was studied in the air under the &ggr; ray irradiation.
The thermo-luminescence peak at 1390nm, being attributed to the oxyhydrate (OH) in the fused silica had an expected
temperature dependence of the intensity and could be used as a temperature monitor. A partially replaced core optical
(PARCO) fiber that consists of a fiber doped with high content of OH inserted into a pure silica fiber was proposed to
realize a spatial resolution.
Fiber mode converter incorporated fiber ring-down strain sensor
Show abstract
We present a fiber mode converter incorporated fiber-loop ring-down system for strain measurement. The sensing system
consists of a fiber mode converter and a typical fiber-loop ring-down system including a pulsed VCSEL laser diode at
850 nm, multimode fiber couplers, multimode fiber loop, photo-receiver and high-speed data acquisition and signal
processing. The bending multimode fiber-loop ring-down strain sensor is demonstrated with a resolution of 0.28 &mgr;&Vegr; over a
range of 767 &mgr;&Vegr;.
High radiation tolerance of temperature resistant Bragg gratings written in N-doped silica-core fibers up to MGy dose levels
Show abstract
In situ monitoring of gratings' characteristics during continuous gamma irradiation to a dose of 9 MGy revealed by an
order of magnitude weaker Bragg wavelengths drift as compared to gratings written in Ge-doped silica-core fibres.
An integrated probe design for measuring food quality in a microwave environment
Show abstract
The work presented describes the development of a novel integrated optical sensor system for the
simultaneous and online measurement of the colour and temperature of food as it cooks in a
large-scale
microwave and hybrid oven systems. The integrated probe contains two different sensor concepts, one to
monitor temperature and based on Fibre Bragg Grating (FBG) technology and a second for meat quality,
based on reflection spectroscopy in the visible wavelength range. The combination of the two sensors into a
single probe requires a careful configuration of the sensor approaches in the creation of an integrated probe
design.
Thermal response of tellurite glass optical fibre
Show abstract
We have measured the phase sensitivity to temperature of a fibre Fabry-Perot (FFP) formed by splicing multimode
tellurite (TeO2) glass fibre to singlemode silica fibre. The free spectral ranges of two FFPs of different lengths were
consistent with the values expected from independent determinations of the core refractive indices. The phase sensitivity
was 89.3 ± 0.3rad m-1 K-1 at a central wavelength of 1536 nm, compared with 99.8 rad m-1 K-1 for silica fibre.
Fiber optic probe for local void fraction measurements in bubbly flows
Show abstract
A technique based on Fresnel reflection at the tip of a fiber optic probe is used to investigate local void fractions in
bubbly flows. The fiber optic system with multiplexing scheme is designed for demonstrating the feasibility of
measuring local void fractions in bubbly flows. Processing the signal acquired from the fiber optic system, local void
fractions can be obtained. Linear regression with least square method is applied to analyze data. The correlation
coefficient of 0.94 indicates that the technique seems to be suited for measuring local void fractions in the range from 2% to 20%.
Two-axis accelerometer based on multicore fibre Bragg gratings
Show abstract
We report an accelerometer based upon a simple fibre cantilever constructed from a short length of multicore fibre
(MCF) containing fibre Bragg gratings (FBGs). Two-axis measurement is demonstrated up to 3 kHz.
Displacement sensor based on optical fibre with multiple overlapping imperfections
Eli Vilge,
Moshe Levantovsky,
Yoel Arieli,
et al.
Show abstract
The concept of highly sensitive fibre optic displacement sensor is presented. It is based on macrobending step index
polymer optical fibre with multiple overlapping surface-side imperfections. The theoretical principles of optical power
losses in such fibres due to multiple curvatures are based on a surface that serves as a model for an imperfect layer and
has the same optical properties. The sensing element was tested using two different types of roughness topologies and
their combination. The various angles of imperfections (90 and 45 degrees) placed on the fibre's core were evaluated.
We discuss some experimental results that confirm our prediction of considerable dependence of the output signal on the
changing imperfections caused by bending the fibre. It was found that sensitivity to bending of the angular imperfections
could be further increased by implementing multiple overlapping imperfections.
Improved optical fibre sensors using hollow glass spheres with a high-performance CCD spectrometer interrogator
Show abstract
Hollow glass micro-spheres, first used to make fibre optic sensors for high hydrostatic pressure, have been interrogated
using a high-precision CCD spectrometer, to give far better precision than earlier. It is found that these simple, low-cost
micro-sensors have excellent sensitivity to both static and dynamic pressure, and have the advantage of being hermetically
sealed. Many other application areas are foreseen for these low-cost sensors.
Optical fibre Bragg sensor torque transducer
A. J. van Wyk,
M. C. S. Snyman
Show abstract
The benefits of an Optical Torque Transducer (OTT) based on optical fibre Bragg sensors for applications in any
environment prone to electro-magnetic and temperature influences are outlined. By using an optical Rotation
Coupler (RC) the transducer avoids slip rings or telemetry systems. The OTT enables the measurement of both
torque and temperature free from electro-magnetic interference (EMI) in situations conventionally very difficult to
make these measurements. OTT torque measurements compare favorably with that of a dynamometer.
Multi-wavelength fiber-optic confocal position sensor with diffractive optics for enhanced measurement range
Show abstract
A multi-wavelength fiber-optic confocal position sensor, employing a diffractive optical element (DOE), is described.
The DOE was designed with the aim of enhancing the chromatic dispersion of the optics, and thus improving the
measurement range of the technique. A proof-of-principle experiment is presented, yielding a five-fold enhancement in
the dispersion and thus in measurement range in excellent agreement with design simulation.
Cure monitoring of a UV cured epoxy resin using a long period grating Mach-Zehnder interferometer
Show abstract
A cascaded long period grating Mach-Zehnder interferometer is used to monitor the change in refractive index of a UV
cured epoxy resin over a cure cycle. Fourier techniques are used to calculate the phase shift and frequency spectral
amplitude of the associated fringe pattern during the cure. The results are compared with the refractive index change
during cure calculated using a Fresnel reflection based technique.
Effects of temperature on high concentration erbium-doped fiber intrinsic parameters
Show abstract
The effects of temperature on high concentration Erbium-doped fibers are characterized using parameters of
transcendental equation model. The intrinsic parameters (intrinsic saturation power, excited-state lifetime and linear
absorption coefficient) of six Erbium doped and Erbium codoped with Lanthanum fibers have been measured for
different temperatures. The temperature dependence of intrinsic parameter has been compared respect to Erbium
concentration and Lanthanum-Erbium concentration ratio.
Origin of coupling to antisymmetric cladding modes in arc-induced long-period fiber gratings
Show abstract
We study the origin of antisymmetric perturbation of the fiber in arc-induced long-period gratings that couple the core
mode into the antisymmetric cladding modes. We demonstrate that this perturbation is caused by a temperature gradient
in the fiber, which is induced, in turn, by a temperature gradient in the arc discharge.
Temperature independent strain/load sensor using a highly birefringent photonic crystal fibre loop mirror
Show abstract
This work presents a temperature independent strain/load sensor using a highly birefringent photonic crystal fibre loop
mirror. The length of the sensing head is 38 centimetres and its corresponding wavelength spacing between two
interferometer minima is 8 nm. The obtained strain and transverse load sensitivity were 1.21 pm/&mgr;&Vegr; and 0.37 nm/Kg/mm,
respectively, while is insensitive to temperature (0.3 pm/°C).
Obstacle detector for the use with electric windows in vehicles
Show abstract
This paper presents a low cost fiber optic obstacle sensor. The detector is primarily developed for the use in applications
like the electric windows in vehicles. Sensor relies on flexible and all polymer design and it based on micro bend losses
in plastic optical fiber (POF). When designing the sensor high priority was given to the low cost components and
materials that are already in use in the automotive industry.
The durability tests were executed on the detector prototypes by continuously pressing on the same place of the sensing
area, with a force of 50 N, at temperatures near to the maximal operating temperature of the POF. The results show that
the obstacle is clearly detected after more than 10.000 continuous presses. The sensor solution presented in this paper can
be used in other applications where obstacle presence detecting is required like are electric doors on buses, other power
driven automatic doors, In-Circuit Testing devices (ICT), security sensors for windows, etc.
Comparison of FBG wavelengths in the regions of 2/3 of the Bragg wavelength and the Bragg wavelength by piecewise irradiation of a chirped phase mask
Show abstract
By using a simple technique of UV laser irradiation at various regions along a chirped phase mask, the responses in the
region of 2/3 of the Bragg wavelength (i.e. ~1030 nm) and the Bragg wavelength (~1535 nm) are investigated
experimentally and compared. The variation of the wavelength of both transmission dips (in the region of the 2/3 of the
Bragg wavelength and the Bragg wavelength) were proportional to the increase in periodicities of phase mask. The ratios
of these wavelengths, for the irradiation of each phase mask section, showed less than 0.7% variation compared with the
value of 2/3, confirming that features at ~1030 nm are the 3rd harmonic of a grating having the phase mask periodicity.
Localized strain measurements using an integration method to process intensity reflection spectra from a chirped FBG
A. Nand,
D. J. Kitcher,
S. A. Wade,
et al.
Show abstract
A chirped fiber Bragg grating was used to measure the non-uniform strain profile of a notched aluminum specimen used
to simulate a cracked structure. The specimen was subjected to tensile tests that produced regions of non-uniform strain
near the notches. Analysis of power reflectance spectra from the grating, through the use of an integration method,
enabled the strain profile near the notches to be determined. Unlike other intragrating sensing methods, this method did
not require a disturbance hypothesis to be postulated. The strain profile results from this intragrating sensor were in
reasonable agreement with predictions from modeling conducted using the finite element method.
Durability under fatigue loading of optical fibres applied to fibre reinforced plastic composites
Show abstract
This paper summarises ongoing research conducted at the Cooperative Research Centre for Advanced Composite
Structures (CRC-ACS) on the durability to fatigue loading of optical fibre sensors, which were surface mounted or
embedded in fibre reinforced plastic composites. The objective of the research is to quantify the parameters affecting the
fatigue performance of such optical fibres. Signal degradation of surface mounted and embedded Bragg grating sensors
has been studied for a number of configurations. For some configurations, preliminary results indicate significant signal
degradation on tension loaded optical fibres after 50,000 cycles strained to 4000 &mgr;&Vegr; and this degradation has been linked
with fibre cracking. No such cracking was observed in compression loaded optical fibres. The durability of the bonding
at various interfaces of the optical fibre / composite system has been investigated for various polyimide coated fibres.
After one million cycles to 3000 &mgr;&Vegr;, 150 &mgr;m diameter optical fibres exhibited significant disbonding in the
coating / cladding interface of the optical fibre. Special 52 &mgr;m diameter optical fibres also exhibited significant
disbonding but to a lesser degree than that in the larger fibres. Stripped fibres exhibited no disbonding at the optical fibre
to composite interface.
Measurements of adsorption strain in porous silicon by Raman scattering
Show abstract
The stress in porous silicon during exposition to a liquid is investigated by an approach based on Raman scattering.
When the porous silicon structure is exposed to isopropanol or ethanol, a reversible blue shift of the Raman spectra is
observed. The blue shift of Raman scattering is ascribed to the contraction induced by the liquids that fill the pores.
A thin foil optical strain gage based on silicon-on-insulator microresonators
Show abstract
We present a novel type of optical strain gage. The strain gage consists of a thin polyimide foil with an integrated optical
circuit. The strain sensing elements are optical microresonators. The optical response to strain of these microresonators is
a wavelength shift of the resonance wavelength. The optical circuit includes several of these resonators to measure strain
in different directions. The strain sensor is read-out using a single-mode optical fiber. Because the different
microresonators in the optical circuit have different resonance wavelengths, they can be read out using the same fiber.
Our strain sensor is some kind of a cross between electrical resistance foil gages and fiber Bragg grating (FBG) sensors.
It is a thin foil device, with a thickness of a few tens of micrometers, but it is an optical device and can be read out in a
similar way as FBG sensors. We present the working principle, fabrication and first experimental results.
Laser-frequency locking techniques for high-sensitivity strain measurements by high-birefringence fiber Bragg gratings and resonators
M. Salza,
G. Gagliardi,
A. Di Maio,
et al.
Show abstract
A new approach to simultaneously interrogate orthogonal axes of single Fiber-Bragg-Gratings (FBGs) and FBG-Fabry
Perot resonator sensors fabricated in linearly highly birefringent (HiBi) fibre is presented. Novel interrogation techniques
of single Fiber-Bragg-Gratings (FBGs) and FBG-resonator sensors are presented. For a single FBG, we combined a
laser-modulation technique to an electronic feedback loop that keeps the source always frequency locked to one peak of
the sensor's reflected spectrum. Two different lasers, with orthogonally-polarized states, were adopted to monitor
simultaneously both the "fast" and "slow" FBG peaks. The corresponding correction signals from the servo-loop outputs
can be interpreted as strain or temperature induced on the FBG. Detection limits ranging from 1 n&Vegr;/&sqrt;Hz to 100 n&Vegr;/&sqrt;Hz,
for axial dynamic and static deformations, respectively, and of 0.025 °C/&sqrt;Hz for temperature variations, are expected. A
similar approach was developed for sub-pε resolution interrogation of an optical resonator made of a high-reflectivity
FBG-pair, using the Pound-Drever-Hall (PDH) stabilization method..
The effectiveness of metal coating on FBG sensor sensitivity at cryogenic temperature
Show abstract
The very low thermal expansion coefficient of silica at cryogenic temperature prevents the use of Fibre Bragg Grating
(FBG) sensors for high resolution temperature monitoring in cryogenic environments involving liquid gases or space
applications. To overcome such limitations sensors have been coated with different metals to improve the measurement
sensitivity in the very low temperature region, i.e. 4.2-35 K. Various coatings have been deposited by electrowinning on
the external fibre surface after aluminium pre-coating. Full characterization of this new type of sensor is described in the
paper.
Quasi-distributed liquid level measurement with adaptable optical fiber transducers
Show abstract
A level and flexible quasi-distributed liquid sensor based on the changes in the light transmittance in a plastic optical
fiber cable is proposed. The measurement points are constituted by small areas created by side-polishing on a curved
fiber and the removal of a portion of the core. These points are distributed and adapted on each full-turn of a spire of
fiber built on a cylindrical tube vertically positioned in a tank. The changes between the refractive indexes of air and
liquid generate a signal power proportional to the position and level of the liquid. The sensor system was successfully
demonstrated in the laboratory and experimental results of three prototypes with 10, 8, and 5 measurement points and
with bend radius of 5mm are presented in this paper.
Strain characterization of fiber Bragg gratings inscribed by high-intensity femtosecond UV pulses
Show abstract
We report strain characterization of birefringent fiber Bragg gratings fabricated in hydrogen-free photosensitive Ge/B
codoped PS1250/1500 fiber by high-intensity femtosecond 264 nm pulses. These anisotropic FBGs demonstrate high
PDL value of 8 dB but, unlike the FBGs inscribed in PM fibers, show shape preservation under strain of [0, 700 &mgr;&Vegr;] by
interrogation based on broad-band source and optical spectrum analyzer.
Fiber optic temperature sensor depositing quantum dots inside hollow core fibers using the layer by layer technique
Show abstract
CdTe Quantum Dots (4 nm of diameter) have been successfully deposited on the inner part of hollow core fibers using
the Layer-by-Layer Electrostatic Self-Assembly method. The architecture of the sensor consists on a short section of a
hollow core fiber tapered at both ends and spliced to standard multimode optical fibers. Taking advantage of the
dependence on temperature of the green fluorescent emission of the Quantum Dot sensitive nanofilms, optical fiber
sensors were fabricated and experimentally demonstrated.
Transversely loaded fibre Bragg grating for pressure measurements
Show abstract
A fibre Bragg grating (FBG) pressure sensor, based upon the transverse loading of half its length, is proposed and
demonstrated. When a transverse load is applied to half of the length of an FBG, a second Bragg peak is generated in the
reflection spectrum, which separates from the initial Bragg peak. The new peak exhibits a red shift in wavelength as the
load is increased. A new data analysis technique, which improves the minimum detectable pressure is discussed. A
normalised pressure sensitivity of 5.73x10-3 ± 5.23x10-5 MPa-1 was obtained. The technique offers the opportunity to
measure independently pressure and temperature using a single FBG sensor element.
Accessing refractive index of absorptive liquid media with optical fibre evanescent-field sensor
S. Khotiaintsev,
V. Svyryd,
J. E. Morales-Farah,
et al.
Show abstract
This paper presents an optical fibre sensor which can access the refractive index of the external liquid absorptive media.
The sensor employs an evanescent-field intensity-type transparent dielectric detection element of hemispherical form.
For this detection element, the effect of absorption of the external media on the measurement results was quantified. In
order to reduce the measurement errors caused by finite absorption of the external media, we incorporated an
absorption-sensitive optical cell in series with the detection element in the sensor. We describe the new measurement
procedure that allows one to reduce the errors caused by the finite absorption of the external media.
A fiber optic Bragg grating seismic sensor
A. Laudati,
F. Mennella,
M. Esposito,
et al.
Show abstract
Here we present a fiber optic seismic waves sensor based on in-fiber Bragg gratings. Fiber Bragg Grating sensors have
been demonstrated to have very high sensitivity to dynamical strain in the sub-micro-strain range and very extended
dynamical response from static to very high frequency. The seismic sensing system is based on the integration of three
FBGs dynamical strain sensors in a mechanical structure acting as an inverse pendulum. Polar symmetry of the
mechanical system and 120° placement of the FBG sensors guarantee a directional capability of the seismic sensor.
Design, manufacturing and preliminary dynamical testing of the seismic sensor are discussed.
Chemical, Environmental, Biomechanical, and Medical Sensors
29Si NMR investigation of ORMOSIL layers used as luminophores' sol-gel matrices in a UV optical fibre sensor
Show abstract
The paper concerns the results of ORMOSIL layer's applied in an optical fibre ultraviolet sensor Nuclear Magnetic
Resonance investigation. The layer which substituted for optical fibre's cladding in device's sensing part acted as a
matrix for a coumarin's derivative. The dye is able to convert ultraviolet into visible radiation which could be easily
detected. Thanks to the fact that the refractive indices of ORMOSIL layers may be controlled and reach a value
characteristic for the fused silica glass a satisfying sensitivity of the device can be achieved. However it may be expected
that both the structure and the composition of ORMOSIL matrices could influence the organic dye's behaviour. The aim
of the experiment presented in the paper was to prove a relation between the sol's condensation time and a composition
of the obtained gel's structure. The obtained NMR spectra gave the evidence of non-condensed -Si-O-C2H5(H) moieties
existence in the solid gels. Moreover, even a 42-days-long process does not lead to the total condensation of
ethoxysilanes' molecules. It is probable that the remaining ethoxy or silanol groups interact with transducer's molecules
as well as influence the refractive index of the gel layer.
Fibre-optic sensors for the estimation of biofilm thickness on metals
Show abstract
This paper presents an optical approach to estimate the thickness of biofilms on metals in natural aqueous environment.
An in-situ fibre optic sensor is held above the sample surface, to offer real time information continuously by measuring
the spatially resolved profiles of scattered light in biofilms. The optical results correlate well with the biofilm thickness
which is measured using a microscope and a microcapillary with a protruding thin, long flexible wire from the top of the
microcapillary. The biofilm thickness is less than 120 &mgr;m on test material after 20 days. Microscopic image analysis also
provides the evidence to confirm micro colony formation by rod and cocci bacterial species. The species Klebsiella are
found to be dominant on carbon steel. It is observed that measured optical intensity is proportional to the concentration
of organisms.
All-optical fiber hydrogen sensor based on annealed Pd-Au sensing nanolayers
Show abstract
We report an all-optical fiber hydrogen sensor based on absorption changes of evanescent
fields caused by an annealed Pd/Au thin film. The sensor consists of a small piece of standard
single-mode fiber (SMF) coated with a Pd/Au thin film sandwiched between two multimode
fibers (MMFs). Due to core diameter mismatch the SMF cladding guides light. When the
device is exposed to hydrogen the layer refractive index diminishes and causes attenuation
changes of the evanescent fields. Adding gold to palladium allows the fabrication of fast,
durable, and reliable sensors suitable for the detection of hydrogen concentration below the
critical 4%.
High sensitivity near-field opto-chemical sensors based on SnO2 particle layers
Show abstract
In this work, the surprising sensing performances of opto-chemical sensors based on SnO2 particles layers against
chemical pollutants either in air and water environment, at room temperature, are reported. The Electrostatic Spray
Pyrolysis (ESP) method has been used to deposit the sensing coatings upon the distal end of standard fibers. This
technique allows the fabrication of SnO2 layers composed of micron and sub-micron dimensions able to locally modify
the profile of the optical near-field collected in the close proximity of the fiber tip. Such layers morphology leads to
strong surface interactions between sensing coatings, analyte molecules and the evanescent contribute of the field,
resulting in an excellent sensors sensitivity against chemical pollutants, even at room temperature.
Carbon dioxide detection at 2 µm using an integrating sphere as an optical absorption cell
Show abstract
This paper describes a multipass absorption sensor based on an integrating sphere. The sphere has an internal coating
which is highly reflective (over 95%) in the near infrared region and this allows the detection of carbon dioxide (CO2)
gas at 2 &mgr;m. CO2 was detected using a light emitting diode as the emitter and a photodiode as the detector. A two inch
(50.8 mm) diameter integrating sphere was used as an absorption gas cell. A method of calculating the effective path
length of the integrating sphere is also presented. The latter is shown to be dependant on the reflectance of the sphere's
internal surface, the sphere's port fraction and the level of attenuation of the optical signal due to the gas present in the
sphere. Effective optical path lengths of 40 cm at the 2 &mgr;m region are reported. Experimental results demonstrating the
detection of CO2 using a two inch diameter integrating sphere are presented and these are compared to simulation results
based on a CO2 absorption over a 40 cm path length at 2 &mgr;m.
Hydrogen detection using a transmission-based optical fibre sensor in the VIS spectrum
Show abstract
Results are presented for a transmission based optical fibre hydrogen sensor using a thin film layer of Palladium as the
sensing element. The thin palladium film was deposited onto a glass substrate via thermal vacuum evaporation. The
sensor was tested by exposing the palladium film to 5% Hydrogen gas in a Nitrogen atmosphere. The absorption and
desorption of hydrogen causes the optical properties of palladium to change depending on the concentration of hydrogen
present in the atmosphere. Using a deuterium/halogen light source in conjunction with a UV/VIS spectrometer the
changes in the optical transmittance in the visible spectra of the Pd film was monitored for 5% hydrogen in a nitrogen
atmosphere. A comparison of different wavelengths in the VIS spectrum is presented. The response and recovery time
for the sensor is shown to be 4-5 seconds and 35 seconds respectively. The sensor is capable of responding to changes of
up to 15% and the sensor shows good repeatability to continuous exposure cycles to 5% hydrogen using nitrogen as the
carrier and recovery gas.
Deep-UV-based differential optical absorption spectroscopy (DOAS) system for the monitoring of nitric oxide
Show abstract
The development of an Ultra Violet (UV) Differential Optical Absorption Spectroscopy (DOAS) fibre-optic sensor for
the monitoring of nitric oxide gases is described in this paper. Experimental results describing the operation of this
sensor with cylinder gases are presented. These experimental results are compared with existing published spectroscopic
absorption measurements. The sensor was developed to operate within an exhaust environment and demonstrate a low
susceptibility to interferences from other gases present. A LabVIEW program was created to interrogate the highest
absorbing wavelength for nitric oxide and calculate the concentrations present before outputting them to the user. The
lower limit of detection for the sensor was found to be 5ppm with response times of 3.4 seconds.
An infrared surface plasmon resonance tilted fibre Bragg device for biological and biochemical sensing
Show abstract
We demonstrate the use of tilted fibre gratings to assist the generation of infrared surface plasmon resonances with short
propagation lengths, resulting in a high index resolution of 2×10-5 in the aqueous index regime. It was also found that the
resonances could be spectrally tuned over 1000nm at the same spatial region with high coupling efficiency (in excess of
25dB) by altering the polarisation of the light illuminating the device.
New optical hydrogen sensor with fast response time based on multilayer palladium-nickel-PTFE thin film for explosion-proof detection of high H2 concentrations of 1-100%
Show abstract
Hydrogen detection is of great interest in many fields such as hydrogen concentrations around the explosive limit of 4%
or in areas where strong electrical fields are present. Optical sensors have the advantage that they are not affected by
these conditions. A comparison of three thin film sensors made of Pd, Pd Ni and Pd Ni / PTFE to detect H2 is made. The
double-sided samples are purpose built by plasma sputtering, with a thickness of 4nm on each side. It is shown that the
signal of a pure Pd deposit is strong but it cannot resist higher H2 concentrations. The Pd Ni deposit has shown good
results and is able to resolve even higher concentrations of 10% H2 but cannot resist high concentrations of H2 over many
cycles. The new Pd Ni / PTFE deposit can be used many times for concentrations up to 100% without any damage and
can detect concentrations of 1-100% of H2. Furthermore the response time for deposits of different thickness is tested.
Orthodontic forces sensing with polymer PCF
Show abstract
Orthodontic forces are measured using a polymer photonic crystal fibre sensor. Transversal pressure deforms the fibre
structure proportionally to the applied load causing light to leak out. The characterization for transversal pressure
demonstrates linear behaviour within the studied load range 0.09 to 4.7 N. For the orthodontic measurements the sensor
is placed between the orthodontic appliance and only one tooth. Loads ranging over 0.98 to 8.82 N, simulating extra oral
appliances, are applied over the orthodontic system at the first molar region. The surface of the tooth experiences forces
ranging from 0 to ~0.63 N compatible with forces required for dental movement.
Multi-channel fibre optic dosimeter based on optically stimulated luminescence for dose verification during radiotherapy treatments
Show abstract
A multi-channel fibre optic OSL dosimeter system is developed by the CEA LIST for quality control in cancer radiation
therapy, in the framework of the European Integrated Project MAESTRO.
Design and optimization of slotted multimode interference devices for chemical and biochemical sensing
M. Mayeh,
J. Viegas,
P. Marques,
et al.
Show abstract
The major achievements in the field of optical sensors in the past two decades have remained mostly limited to the
laboratory demonstrations. There are very few examples of optical sensors, which have been reduced to practice, and
have established themselves in major markets. The main bottleneck in this field is the issue of manufacturability. In this
paper we present optical sensors based on slotted multimode interference waveguides. We show that the sensitivity
increases proportionally to the number of slots. The sensor can be tuned to highest sensitivity in the refractive index
ranges necessary to detect protein-based molecules or other water-soluble chemical or biological materials. The material
of choice is a sol-gel (ORMOCER) matrix that after completion of the process becomes mostly glass and it is highly
stable. Sensors made with this technology are suited to high volume manufacturing.
Cadmium arachidate single-walled carbon nanotubes composites as sensitive coatings for high sensitivity fiber optic chemo-sensors
Show abstract
In this work, the feasibility to exploit optoelectronic chemo-sensors based on cadmium arachidate (CdA)/single-walled
carbon nanotubes (SWCNTs) composites for detection of chemical pollutants both in air and water environments has
been investigated. The nanocomposite sensing layers have been transferred upon the distal end of standard optical fibers
by the Langmuir-Blodgett (LB) technique. Single wavelength reflectance measurements (&lgr;=1310 nm) have been carried
out to monitor chemicals concentration through changes in the optical length of the Fabry-Pérot (FP) cavity induced by
the interaction of the sensitive layer with the analyte molecules. The preliminary experimental results evidence the good
potentiality of these fiber optic nanosensors to detect toluene and xylene at ppm level both in air and water environments
at room temperature.
True challenges of disposable optical fiber sensors for clinical environment
Show abstract
Medical applications represent a unique chance of expansion for the optical fiber sensors (OFS) market that was
confined so far mostly in niche applications where higher technological costs were justified by OFS distinctive
advantages. Single use medical devices integrating OFS could however generate a significant growth for this type of
technology. Thanks to cost reductions derived from the success of optical fiber used in the telecom industry, it is now
possible to produce competitive disposable OFS for clinical environment. Cost reduction is nevertheless not the only
challenge for this type of application: materials bio-compatibility and sterilization resistance, packaging issues, design
considerations for end-user acceptance and operational simplicity, technology reliability including connectivity and
sensor performances, manufacturing process monitoring and outstanding quality control, are among few of the problems
that have to be considered to address correctly the complex medical market with successful disposable OFS devices.
With a clear understanding of the needs and challenges of clinical applications, it is easier to respond to this reality and
to offer commercially suitable solutions.
Optical fibre sensors embedded into medical textiles for monitoring of respiratory movements in MRI environment
A. Grillet,
D. Kinet,
J. Witt,
et al.
Show abstract
The potential impact of optical fibre sensors embedded into medical textiles for the monitoring of respiratory movements
in MRI environment is presented. Preliminary investigations of the feasibility of sensing respiration movements with a
POF OTDR are reported. In addition, a macro-bending sensor based on a periodic design is demonstrated and
successfully implemented using a narrow fabric production process. It allows monitoring human abdominal breathing
movements with a very simple monitoring set-up.
DL-UWTs: novel devices for chemical and biological sensing
Show abstract
Although many optical fiber sensors have been proposed for chemical, environmental or biological measurements, it
seems that the potential of this kind of devices has not been fully exploited. In this paper we discuss the possibilities of
doubly-deposited uniform-waist tapered fibers (DL-UWTs) for the development of new sensors that can become a new
standard in the field of Surface Plasmon Resonance (SPR) based sensors and contribute to the extension of the range of
application of fiber technology to the mentioned fields. We also compare different configuration and evaluate some
relevant features of DL-UWTs, as the possibility of fully independence of polarization or the excitation of multiple
plasmons.
Polymer optical fibre sensor to monitor skin moisture
Show abstract
We present a polymer optical fibre sensor to sense skin moisture and droplet formation when sweating occurs. The
sensor used evanescent field attenuation, by exploiting a moisture sensitive cladding with moisture indicator
(fluorescein) contained within a porous cladding (HEMA). The sensor was designed to be comfortable to wear and
unobtrusive, hygienic, with sterilised interchangeable sensing elements. It had maximum sensitivity between 98% and
100% humidity, and response time of 24 seconds.
Ethanol concentration measurement by Raman spectroscopy in liquid-core microstructured optical fiber
Show abstract
A liquid-core air-clad microstructured fiber has been developed for determination of ethanol concentration in aqueous
solutions by Raman spectroscopy. The sensor shows a linear response and a low ethanol concentration solution has been
characterized using the calibrated sensor. The configuration used for light and liquid injection is stable and robust,
making the sensor useful for on-line measurements.
Evaluation of coupling losses in hollow-core photonic crystal fibres
Show abstract
Hollow-core photonic crystal fibres have a high potential for gas sensing applications, since large light-gas interaction
lengths can be effectively attained. Nevertheless, in order to enhance effective diffusion of gas into the fibre hollow-core,
multi-coupling gaps are needed, which raise coupling loss issues that must be evaluated prior to the development of
practical systems. In this communication we present a study on the coupling losses dependence on lateral and axial gap
misalignment for single-mode fibre and two different types of hollow-core photonic crystal fibres. In addition,
experimental results on the splicing of these fibres are also presented.
Optical fiber pH sensors based on self-assembled multilayered Neutral Red coatings
Show abstract
The Electrostatic Self Assembly Layer-by-Layer (ESA) technique has been already used for the fabrication of optical
fiber pH sensors, the properties of the resultant pH sensitive coatings has been found to be strongly dependent on the
fabrication parameters, especially on the pH of the polyelectrolyte solutions used for the deposition of the coatings. In
this work the resulting properties of the sensitive coatings have been optimized by changing the parameters of
fabrication. Techniques as AFM, for studying the thickness and morphology of the sensing films, and spectroscopy, for
studying the composition of the films, were used for the characterization of the devices. Optical fiber pH sensors with
response from pH 3 to pH 7 were successfully fabricated.
High spectral power density supercontinuum source at 1.3 µm suitable for optical coherence tomography applications
Show abstract
The generation of a continuous-wave pumped supercontinuum source at 1.3 &mgr;m is described. The device makes use of a
tunable Yb-doped fiber laser, a cascade of fiber Bragg-grating mirrors and a concatenation of standard silica fibers with
stepwise decreasing dispersion. The generated supercontinuum spans from 1280 to 1513 nm, shows and average output
power of 1.34 W and exhibits >0 dBm/nm spectral power density over 200 nm.
Simultaneous determination of oxygen and temperature using quantum dots and a ruthenium complex
Show abstract
An all-optical scheme for simultaneous determination of oxygen and temperature is presented. A ruthenium complex
immobilized in a non-hydrolytic sol-gel matrix is used as oxygen sensor. Temperature information is provided by CdSe
quantum dots immobilized in the same material. While the dye luminescence is quenched by oxygen and temperature,
the nanocrystals luminescence depends only on temperature. Results presented demonstrate that the combined
luminescence response allows to simultaneously assess both parameters using a single optical fiber system.
Optical fiber pH sensor based on poly (p-phenylene vinylene)
J. Goicoechea,
M. Esparza,
I. R. Matias,
et al.
Show abstract
Poly(p-xylene tetrahydrothiophenium chloride) was successfully deposited on tapered ends of optical fiber by means of
the Layer-by-Layer Electrostatic Self-Assembly method. A posterior thermal curing at low temperatures (around 100°C)
is necessary for the synthesis of the conjugated polymer poly (p-phenylene vinylene), (PPV). The fluorescence of this
polymer has shown dependence to pH. Optical fiber pH sensors were experimentally demonstrated for the working range
from pH 3 to pH 8.
Optical psychrometer for relative humidity measurement in non-conventional environments
S. Pirrotta,
E. Guglielmino
Show abstract
The aim of this study has been the introduction and calibration of a novel Relative Humidity meter, based on optical
sensors. It consists of a psychrometer, whose temperature measurements are performed by means of two Fiber Bragg
Grating sensors, working as dry-bulb and wet-bulb thermometers. Their preliminary calibration permits to convert Bragg
wavelengths into temperature values with high repeatability and accuracy: hence, the local relative humidity can be
evaluated, using thermal gradient and dew point temperature, by a psychrometric table implemented as analytic function
inside a processing algorithm. The proposed sensor presents all the typical advantages of the optical devices, especially
the immunity to electromagnetic disturbances and to corrosion, allowing to measure humidity in aggressive
environments as meteorological off-shore stations, marine structures and vehicles.
Microalgal fiber-optic biosensors for water quality monitoring
Guillermo Orellana,
Laura Villén,
David Haigh,
et al.
Show abstract
Novel fiber-optic biosensors have been developed for the analysis of pesticides in water based on Chlorophyceae
microalgae immobilized into a porous silicone layer as recognition element, and on measurements of the photogenerated
O2 as chemical transducer. The inhibition of O2 production by the photosynthetic green algae in the presence of the
pesticide (simazine) was used as the biological signal. Luminescent thin films and a dedicated optoelectronic unit based
on emission phase-shift measurements provide the tools for the sensitive O2 measurements. Fluctuation analysis allows
selection of sensitive and resistant microalgae mutants without genetic manipulation for maximum biosensing selectivity.
In-vivo characterization of a microdialysis-based pH sensor
Show abstract
A pH sensor based on optical fibres was developed. The analysed sample is the interstitial fluid drawn from the adipose
tissue by means of a microdialysis catheter. The pH sensing layer is constituted by a pH indicator, phenol red, directly
immobilised onto the internal wall of a glass capillary. The interrogation of the glass capillary is performed by an
optoelectronic unit, developed in our laboratory, which makes use of a light emitting diode at 590 nm as source and a
photodiode as detector. A suitable animal model was developed and in-vivo tests on pigs were carried out.
Optical PMMA chip for multianalyte detection
Show abstract
In the present work an optical platform is described for the interrogation of a multichannel array for chemical and
biochemical parameters. A fluorescent sensing layer is immobilised on the internal wall of the channel and the emitted
light travels along the thickness of the channel and is detected with an optical fibre connected with a spectrum analyzer.
A compact optical system for the interrogation of microcantilevers
Show abstract
The present paper is concerned with the development of an optical system capable of interrogating an array of silicon
microcantilevers. The use of a laser line-generator and of a CCD camera allows the simultaneous interrogation of the
eight cantilevers of the chip without movable parts. The resolution achieved in terms of displacement of each cantilever
end is better than 7.5 nm. As an example of the operation, the system has been characterized as a refractometer by filling
the cell with liquids having different index of refraction.
LPG-based PVA coated sensor for relative humidity measurement
Show abstract
A long period grating (LPG)-based optical fiber sensor, coated with polyvinyl alcohol, has been developed for relative
humidity (RH) measurement over the range from 33% RH to 97% RH, for which the grating response has been
monitored. The fiber optic sensor using the LPG has been designed to monitor the change in resonance loss which is
then related to the humidity measured through calibration of the sensor with a series of materials of known refractive
index. Results on the calibration and use of the sensor are reported and considered in this work, in light of other grating-based
methods for humidity measurement.
Integrated optic surface plasmon resonance measurements in glass substrates
A. Parisi,
F. P. D'Aleo,
S. Guarino,
et al.
Show abstract
The surface plasmon resonance (SPR) technique is an optical method that can be used to measure the refractive index of
organic nano-layers adsorbed on a thin metal film. Although there are many techniques for measuring biomolecular
interactions, SPR-based techniques play a central role in many current biosensing experiments, since they are most suited
to sensitive and quantitative kinetic measurements. Here we give some results from the analysis and numerical
elaboration of SPR data regarding the flow of different solutions with refractive indexes in the range of interest (1-1.4).
After a brief discussion of the principles of SPR and of waveguide fabrication technique, we give a description of
system setup and some results regarding the real time waveguide output intensity monitoring to measure the interaction
between the gold thin film and the analyte.
Tunable diode laser spectroscopy for industrial process applications
Show abstract
An alternative approach to signal recovery in tunable diode laser spectroscopy with wavelength modulation is proposed
and investigated. Measurements of transmission spectra of methane in nitrogen are compared with equivalent data in the
HITRAN data base and curve fitting of HITRAN data to that measured have been used to obtain gas concentration and
pressure. The results validate the new technique and demonstrate that absolute measurements of rotation / vibration gas
line transmission functions, gas concentration and gas pressure can be made accurately without the need for calibration.
Electromagnetic, Interferometric, Polarimetric, New Concepts, and Devices for Sensors
WLI high voltage optical fiber sensor systems with compensation for optical power fluctuations
Josemir C. Santos,
José C. J. Almeida,
Luiz P. C. da Silva
Show abstract
Two versions of opto-electronic signal processors applied to demodulating the output signal of a White Light
Interferometry (WLI) based optical sensor, designed to measure ac high voltages, are presented. Both processors
incorporate schemes to compensate optical power fluctuations caused by changes of attenuations and losses in
components of the optical fiber sensor systems. The strategy adopted in the first signal processor is based on the precise
detection of the peaks and valleys values present in the output signal of a modulated recover interferometer, which signal
contains desired information about the ac high-voltage applied to a specially designed Pockels cell used as sensor
interferometer. The second signal processor uses a reference sample of the optical power delivered in the output of the
sensor interferometer to normalize the output signal of an unmodulated recover interferometer. Prototypes for both signal
processors were developed and subjected to tests conducted to measure ac high voltages up to 110 kVpp and to verify the
stability of the measurements under conditions of optical power attenuations up to -8.66 dB introduced in the link.
Influence of the pre-stress in Terfenol-fiber Bragg grating integrated magnetic field sensors
Show abstract
This paper presents the first results on the use of the pre-stress to improve the performance of a magnetic field sensor
based on a Terfenol-Fiber Bragg Grating integrated device. Indeed, since the pre-stress modifies the response of the
magnetostrictive material, this should allow to fit the performances of the sensor to different operative conditions or to
exploit also the stress as a control variable to optimize the design of the sensor.
New approach for optical resonances in dielectric circular cylinder based on whispering gallery mode
Show abstract
We describe, first to our knowledge, optical resonances of Transverse Electric (TE) and Transverse Magnetic (TM) wave
propagations in dielectric micro-circular-cylinder. New Asymptotic approaches have been developed based on TE and TM
waves. Size parameter (pi times diameter divided by wavelength of the light) is phenomenal to demonstrate Whispering
Gallery Mode (WGM) in dielectric circular cylinder. The developed expressions for size parameter for both TE and TM
waves are very simple and can be used to characterize the resonances in dielectric micro-circular-cylinder. Asymptotic
expressions have been developed based on Electro-Magnetic (EM) wave theory derivations which are mathematically
robust than existing approaches presented in the literatures, and can be used to develop optical sensors by characterizing
resonances in dielectric micro-circular-cylinders. The solutions are shown to be very accurate for large size parameters.
Gamma radiation and low-temperature effect on a low-birefringence fibre for current sensing application in plasma burning reactors
Show abstract
We evaluate the possibility to use a low-birefringence fibre for current sensing application in harsh environmental conditions as expected in quasi steady plasma burning reactor. Experimental results show that the Faraday rotation of the low-birefringence fibre is not significantly degraded by a gamma irradiation upto 5.4 MGy and when the fibre is kept at ambient temperature.
Comparative analysis of the DFB fiber laser and fiber-optic interferometric strain sensors
Show abstract
The DFB fiber laser strain sensor is shown to provide an improvement in the minimum detectable length
change by a factor of 275 at 2 kHz for an applied strain when compared with an interferometric sensor interrogated by an
equivalent DFB laser. This corresponds to a strain resolution enhancement by a factor of 18, if the strain is applied over a
10cm length of fiber. The ability of the fiber laser sensor to operate in its thermodynamic noise limit is shown to be the
primary reason for this enhanced sensitivity. Thermodynamically limited noise performance is demonstrated with three
interrogation methods.
Identification near-field seismic rotational events by fibre-optic rotational seismometer
Show abstract
The paper presents new results about identification near-field seismic rotational events by a fibre-optic rotational
seismometer. The Sagnac interferometer with 2&sgr; sensitivity equal to 4.27 10-8 rads-1 has been used as rotational
seismometer, which can detect rotational events in a direct way. The theoretic investigation of obtained results show
that such events can be treatment as the seismic rotational waves. The paper presents the experimental results
obtained simultaneously by a fibre-optic and a standard rotational seismometers installed in the Ojcow seismic
observatory. The main advantage of such an approach is a possibility to recognize the velocity of seismic rotational
waves, which is different from the velocities of other seismic waves.
Fiber optic differential distance measurements based on a dual fringe synthesis technique
Seiichiro Kinugasa
Show abstract
A new type of stable interferometric fiber optic sensor based on the amplitude modulation (AM) technique is applied to
the differential distance measurements. By synthesizing interferograms from two interferometers, output signal shows an
AM waveform in the optical frequency domain. By extracting the low frequency interval, the imbalance of optical path
differences (OPDs) can be extracted. This unique sensor system is described in detail with some experimental results.
Study of LPG-assisted fibre modal Michelson interferometers with coherence addressing and heterodyne interrogation
Show abstract
In this work, the LPG-assisted fibre Michelson modal interferometer is studied as a sensing structure for
environmental refractive index, temperature and liquid level when coherence addressing and heterodyne interrogation are
considered. The effects on measurand sensitivity of the order of the cladding mode excited by the LPG, of the degree of
etching of the sensing fibre and of the fibre type used are investigated.
Modal interferometer based on a single non-adiabatic fibre taper
Show abstract
In this work it is presented a novel in-fibre modal interferometer based on a non-adiabatic biconical fused taper that
couples light between the cladding and the core, combined with the Fresnel reflection at the fibre end. It is observed
that the returned light from this fibre structure shows a channelled spectrum similar to that of a two-wave Michelson
interferometer. The application of this device as a fibre optic flowmeter sensor is demonstrated.
In-fibre Mach-Zehnder configuration based on fibre multimode interference structure combined with a long period grating
Show abstract
A novel Mach-Zehnder interferometer based on a fibre multimode interference structure combined with a long period
fibre grating is proposed. The multimode interference is achieved through the use of a multimode fibre section spliced
between two single-mode fibres, with a length adjusted to couple a fraction of light into the cladding modes. A LPG
placed after the multimode fibre couples light back into the fibre core completing the Mach-Zehnder interferometer. This
novel configuration was demonstrated as a bending sensor.
Design, development, and analysis of crossover-free fiber optic gyroscope sensor coils
Show abstract
We describe experiments of fiber coils using different lengths, coil diameters, and configurations wound on a innovative
winder. Geometric and polarimetric analyses of coils and effects on Sagnac area and bending induced birefringence are
examined.
The detection of ultrasound using fibre optic sensors
Show abstract
Ultrasound is a valuable tool for the detection of damage in structures and the characterisation of material properties. Its
detection is conventionally done by piezoelectric transducers, however fibre optic sensors can operate over a greater
range of frequencies and also yield information on the direction of wave propagation. The interaction between fibre
sensors and ultrasound both demonstrates the integrating features of intrinsic fibre optic sensors and presents new
opportunities in ultrasonic detection, offering enormous diversity in polar and frequency response. This paper
summarises the interaction mechanisms between ultrasound and fibre sensors and confirms their functional flexibility.
We use these results to demonstrate the practical use of these sensors to detect and locate damage in a sample.
Design of a multi-wavelength fibre laser using an intra-cavity phase modulator and Sagnac loop filter for sensor applications
Show abstract
This paper describes the design of an all-fibre multiwavelength erbium doped fibre laser operating at room temperature.
By using a Sagnac loop filter, multiple wavelength channels are obtained with 0.8nm spacing in the C-band and
simultaneous multiwavelength operation is achieved through an intracavity sinusoidal phase modulator. A polarization
controller inside the filter is helpful in controlling the multiwavelength operation. The effects of modulation frequency,
modulation index and pump power on the multiwavelength operation are experimentally investigated. The fibre laser
has potential applications in fibre Bragg grating sensors and fibre optic spectroscopy.
Miniaturized optical fiber sensor interrogation systems for potential aerospace applications
Show abstract
Optical fiber sensors have shown great potentials for aerospace applications. But two issues need to be addressed before
these applications can be realized. One is how to reliably implement optical sensors in the air vehicles. The other is the
need of compact, low weight sensor interrogation systems. We propose to use planar lightwave circuits (PLC) to address
the second issue. In this article, we report some of our results on the development of both echelle diffractive gratings
based sensor interrogator and arrayed waveguide gratings based sensor interrogators. Both approaches offer miniaturized
solutions for the development of optical fiber sensor interrogation systems.
Global optimization of multimode interference structure for ratiometric wavelength measurement
Show abstract
The multimode interference structure is conventionally used as a splitter/combiner. In this paper, it is optimised as an edge filter for ratiometric wavelength measurement, which can be used in demodulation of fiber Bragg grating sensing. The global optimization algorithm-adaptive simulated annealing is introduced in the design of multimode interference structure including the length and width of the multimode waveguide section, and positions of the input and output waveguides. The designed structure shows a suitable spectral response for wavelength measurement and a good fabrication tolerance.
Tilted-fibre-Bragg-grating-based 800nm WDM interrogation system for strain, temperature, and refractive index sensing
Show abstract
We report the implementation of a low-cost high-resolution WDM interrogation system operating around 800nm region
with bandwidth up to 60 nm and resolution of 13 pm by utilising a tilted fibre Bragg grating as an out-coupling device
and a CCD-array detector. The system has been evaluated for interrogating fibre Bragg grating based strain, temperature
sensors, giving sensitivities of 0.6 pm/&mgr;&Vegr; and 5.6 pm/°C which are in good agreement with previously reported values.
Furthermore, the system has been utilised to detect refractive index change of sample liquids, demonstrating a capability
of measuring index change as small as 10-5.
Comparison between a symmetric bidirectional-pumping and a unidrectional-pumping configurations in an erbium fiber ring laser
Show abstract
An experimental comparative study between two wide-band wavelength-tunable erbium doped fiber ring lasers
(EDFRLs) with the same active fiber length but with two different pumping configuration (forward unidirectional
pumping and symmetric bidirectional pumping) is reported in this paper. Both fiber lasers cover almost the whole C-band
and L-band with a single setup laser. The signal wavelength can be tuned in a wide range of 60 nm with the two
presented lasers. Nevertheless, experimental results verify that a higher output power is obtained with the bidirectional
pump configuration.
Nanocoating effects on tapered long period fiber gratings
Show abstract
In this work, the experimental analysis of the response of nanocoated Tapered Long Period Gratings (TLPGs) to
Surrounding Refractive Index (SRI) changes is presented. The modal transition is demonstrated to take place in this kind
of devices and to be an effective method to improve their SRI sensitivity. The dip-coating method was carried out by an
automated system and showed to be a reliable technique for the deposition of conformal coatings. A comparison with
traditional UV-written LPGs revealed that a thicker overlay is necessary for the TLPG to tune the transition region in the
same SRI range.
Non-uniform nano-coated long-period fiber gratings for sensing applications
Show abstract
This work numerically and experimentally investigates the spectral modifications due to non-uniform azimuthally
symmetric high refractive index (HRI) nano-coatings deposited on long-period fiber gratings (LPFGs). First, a uniform
overlay was deposited on a LPFG by using electrostatic self-assembling technique, which guarantees a fine control on
the coating thickness. Successively, UV (&lgr;=193nm) laser micromachining was applied to locally and selectively remove
the coating with high spatial resolution and preserving the azimuthal symmetry of the structure. As the overlay removal
was performed starting from the middle of the grating, strong modifications of the LPFG transmission spectrum
occurred. Phase-shift phenomenon and selective fringes generation in correspondence of all the attenuation bands can be
observed. The two-effects occurring are ruled by the longitudinal length of the uncoated region and the overlay features
(thickness and optical properties). The wavelength selectivity, combined with the effects of the HRI coatings on the
cladding modes distribution, can be successfully applied for the development of advanced and high performances
sensing devices.
Nanogrinding of microprofiles and microlenses on optical fibers endfaces for use in optical-fiber sensors
Show abstract
This paper presents nanogrinding as an alternative technique for the fabrication of optical fiber micro profiles. Grinding
of these lenses is carried out on a nanogrinding machine (NGM) specially built for this purpose. Cleaved single mode
optical fibers with core diameter of 9 &mgr;m and outside diameter of 125 &mgr;m were used. Optical fiber endfaces with a
multitude of micro profiles were successfully made. This includes conical lenses, tapered lenses, D-shaped endfaces, and
fibers with oblique endfaces. The results are presented in the form of optical microscopy and scanning electron
microscopy images of the produced lenses.
Technique of FBG fabrication with an arbitrary spectrum
Show abstract
An arbitrary FBG spectrum can be obtained as the addition of the contribution of some concatenated subFBGs written
without phase jump using the same phase mask. An adaptive filter is used in order to obtain, from the desired spectrum,
the parameters of the different subFBGs reproducing the required response.
Micro-structured chirped fiber Bragg gratings: toward new spatial encoded fiber optic sensors
Show abstract
In this work, we report on the investigation of in-fiber photonic devices based on microstructured chirped fiber Bragg
gratings (CFBGs) for sensing applications. The basic device here analyzed consists in a CFBG with single or multiple
defects obtained by a deep and localized stripping of the cladding layer along the grating structure. The effect of each
local thinning along the grating length, properly exploited, basically enables the formation of one pass-band channel
within the pristine grating bandwidth and correspondently in one stop-band out of the pristine grating bandwidth. In
addition, due to spatial encoding in chirped gratings, each channel spectral position exclusively depends on the features
of its own defect (length, depth of the defect and surrounding refractive index) in a well defined location along the
grating. Thus, the spectral properties of each channel are not affected by defects located elsewhere along the grating
structure, enabling the possibility to develop independent multipoint sensors by exploiting a single grating device.
Sensitivity characteristics in thinned long-period tapered gratings
Show abstract
In this work, a comparative study has been carried out to investigate the effects of cladding stripping on the external
refractive index sensitivity in tapered and UV long period gratings. Here, wet chemical etching combined with
microscopic analysis allow us to identify the experimental dependence of the surrounding refractive index (SRI)
sensitivity on the cladding radius for both grating types. The experimental results reveal that although in both cases a
sensitivity enhancement is achieved by reducing the cladding thickness, the tapered devices offer substantially a greater
sensitivity gain in respect to UV written devices.
Improvements in the fabrication of microstructured fiber Bragg grating sensors
Show abstract
In this work, we propose a novel fabrication method as technological assessment for the development of microstructured
fiber Bragg gratings (FBGs) tailorable for specific applications. Micro-structured FBG (MSFBG) relies on the
localized stripping of the cladding layer in a well defined region in the middle of the grating structure leading to the
formation of a defect state in the spectral response. The key feature of this class of devices is the strong dependence of
the defect state generated in the grating spectrum on the optical properties of the medium surrounding the device. In fact,
this property enables the development of tunable devices as well as in fiber refractometers and chemical sensors. One of
the main drawbacks of these devices is the fabrication process requiring a well precise control of the stripped region
dimensions. Here, we demonstrate that the optimization of this device is possible by adopting a fabrication process based
on polymeric coatings and UV laser micromachining. These method combined with wet chemical etching allows the
easy prototyping of MSFBGs with the desired features for specific applications.
Self-assembled optical detectors for optical fiber sensors
Show abstract
Recent work in the fabrication of self assembled quantum dot (QD) detectors for optical fiber sensors is reported in this
paper. The ability to develop the QD based devices and materials via the electrostatic self-assembly (ESA) process has
been demonstrated. The QD precursor nanocluster materials involved in ESA have been designed and synthesized to
proper size, stabilized in an aqueous-based solution, and functionalized to allow self-assembly. The optical fiber sensor
instrumentation has been developed to monitor the reflected optical power with the buildup of the QD layers on the fiber
endface during the ESA process. The results are confirmed by observing the effects of low-finesse QD Fabry-Perot
interferometric cavities formed via such processes on the ends of optical fibers. The photocurrent-voltage characteristics
show a diode-like behavior with linear photocurrent in the reverse bias and nonlinearity in the forward bias. It is
suggested that fast response times can be achieved due to the high carrier mobilities that arise in part due to structure of
the materials formed via the solution-based ESA process.
Effects of thickness and external refractive index in coated tilted fiber Bragg gratings
Show abstract
In this work, an experimental analysis on the spectral effects induced by depositing a uniform high refractive index
(HRI) thin coating on weakly tilted fiber Bragg gratings (TFBGs) is carried out. First, two weakly TFBGs presenting
different tilt angles were fabricated. Successively, by using dip-coating technique, two different coating thicknesses were
deposited on each of them. The transmission spectra of the obtained structures were collected as the surrounding
refractive index (SRI) changed in the range 1÷1.47. The coated gratings present some differences in their spectral
evolution, that can be opportunely exploited. The coated configuration could improve some aspects of previous
demodulation techniques exploited in the case of bare TFBGs. Moreover, an important effect of HRI coatings is to
enhance the SRI sensitivity of the spectral position of the dips corresponding to cladding modes coupling, leading to a
different interrogation method for sensing applications.
Supercontinuum generation with a figure-eight fiber laser
Show abstract
We use a figure-eight fibre laser with a photonic crystal fibre NALM (nonlinear amplifying loop mirror) to produce a
moderate supercontinuum from 1440 nm - 1680 nm in highly nonlinear dispersion shifted fibre. We also observe a 743
nm band in the fluorescence of the erbium doped amplifier outside the figure-eight fibre laser.
High precision and tunable multi-wavelength fiber source based on cascaded four-wave mixing enhanced by Raman
Show abstract
We present a multiwavelength fiber source based on cascaded of four-wave mixing in two semiconductor optical
amplifiers followed by further four-wave mixing in an optical fiber enhanced by Raman amplification. The multiwavelength
source is generated by two initial frequencies detuned 200 GHz and referenced in the absorption lines of the
acetylene 12C2H2, which sweep in frequency keeping the detuning of the lasers constant. With this configuration, we
have achieved a high resolution source with a spectrum of 36 channels centered with adjustable peaks separation. The
source can be employed to interrogate a fiber Bragg grating sensors network and in gas spectroscopy applications.
Temperature compensation technique for Bragg gratings in microstructured optical fibers for sensing applications
Show abstract
The thermal drift of the characteristic wavelength of a Fiber Bragg Grating photowritten in the core of an 18-hole-microstructured
fiber is significantly reduced by inserting a liquid of suitable refractive index into its holes. The
maximum sensitivity is reduced, and the spectral range of variations is divided by a factor of 8, over a temperature range
larger than 20°C. Such passive FBG temperature compensation technique is of great interest for applications involving
accurate sensing free of thermal effects.
Silicon resonant cavity enhanced photodetectors based on internal photoemission effect
Show abstract
In this paper, the design of resonant cavity enhanced photodetectors, working at 1.55 micron and based on silicon
technology, is reported. The photon absorption is due to internal photoemission effect over the Schottky barrier at the
metal-silicon interface. A comparison is presented among three different photodetectors having as Schottky metal: gold,
aluminium or copper respectively. In order to quantify the performance of photodetector, quantum efficiency including
the image force effect, as a function of bias voltage is calculated.
Design of long-period fibre grating refractometric sensors with linear transfer function by a genetic algorithm
Ignacio Flores-Llamas,
Volodymyr Svyryd,
Sergei Khotiantsev
Show abstract
We describe a new method for the design of optical fibre refractometric sensors based on non-uniform Long-Period
Fibre Gratings (LPFGs). An essential part of this method is a specialized genetic algorithm with the properly designed
operators that perform the theoretical synthesis of a necessary nonuniform LPFG profile. Such a profile yields the linear
frequency response of the sensor to the refractive index of the surrounding medium. A distinctive feature of the designed
LPFG is a linear variation of the core and cladding refractive index along the LPFG length. We also present a new
mathematical model of nonuniform LPFG, which allows one to take into account the effect of LPFG sections of an
average refractive index lower and higher than that of the surrounding medium. A numerical example illustrates the
characteristics of the synthesised LPFG.
Modeling and design of a 2D photonic crystal microcavity on polymer material for sensing applications
Show abstract
In this paper report on the design of a 2D PBG filter in polymeric material. The filter is a Fabry-Perot cavity having a
self-sustained membrane configuration. A deep parametric analysis has been carried out for improving the performance,
taking also into account the fabrication tolerances Best performance in terms of lateral confinement have been obtained
in case of square lattice. As for materials, polystyrene shown best in terms of refractive index value, length of the
photonic crystal structure and attenuation value in the band gap. The filter can be used either in sensing applications or in
telecommunication field.
Hollow-core optical fiber functionalized with single walled carbon nanotubes for VOC detection
Show abstract
In this work, Hollow-core Optical Fibers (HOF) functionalized with Single Walled Carbon NanoTubes (SWCNTs) are
proposed for volatile organic compounds (VOCs) detection. The sensing probe is composed by a piece of HOF with a
termination coated and partially filled by SWCNTs. The infiltration of the SWCNTs inside the HOF holes has been
accomplished by means of the Langmuir-Blodgett technique. Reflectance and far field transmission characteristics have
been carried out within the HOF bandwidth. Finally the sensing capability of the proposed sensors has been investigated
by exposure in a proper designed test chamber to traces of toluene. The experimental results obtained demonstrate the
success of the SWCNTs partial filling within the HOF holes and the sensor capability to perform VOCs detection with a
good sensitivity and fast response times.
Optical properties of photonic crystal fibers with the strain
Show abstract
The effective index, fundamental mode width, numerical aperture are some important parameters of a fibre. The
behaviour of these parameters for a Modified Total Internal Reflection (MTIR) Photonic Crystal Fibre (PCF) is studied
when strain is applied. We chose a range of normalized frequency (&Lgr;/&lgr;) and a range of d/&Lgr; and we analyzed the
behaviour for different values of strain. The sensibilities of the studied parameter are obtained in the chosen range.
Finally, the region of maximum influence of the strain is observed.
Low-contrast photonic bandgap fibers and their potential applications in liquid-base sensors
Show abstract
A series of low-contract photonic band-gap (PBG) fibers were fabricated by filling the holes of a commercial air-silica
hollow-core PBG fiber with different refractive index liquids. The PBGs and the transmission characteristics of these
fibers were investigated theoretically and experimentally. An increase in the refractive index of liquid filling the holes
causes blue-shift of the PBG and a narrow down of the PBG width, which may be exploited for sensitive refractive index
measurement.
How to play with the spectral sensitivity of interferometers using slow light concepts and how to do it practically
Miguel Gonzalez-Herraez,
Oscar Esteban,
Fernando B. Naranjo,
et al.
Show abstract
We describe some interesting features that arise when slow and fast light structures are introduced in interferometers.
With different configurations, one can obtain a spectral sensitivity enhancement of the interferometer or an enhanced
robustness to laser frequency drifts. Furthermore, we describe simple practical ways to implement slow and fast light
media in practical interferometers. We believe that these ideas may have interesting implications in optical sensing.
Distributed, Multiplexing, System Applications, and Field Trials
High performance Brillouin distributed fibre sensor
Show abstract
We propose a novel configuration for a Brillouin distributed sensor based on Brillouin optical time domain analysis. This
new configuration eliminates many intensity noise issues found in previous schemes. Resolution of 3.5 m all over a
47 km single-mode fibre was achieved and resolution down to 30 cm in a few kilometre fibre. Noise reduction makes
possible measurements with a 16 times averaging.
Distributed fiber optic sensing for traffic monitoring purposes
M. Hlavác
Show abstract
In this paper author proposes the novel application of fully distributed intrinsic fiber optic sensors. The system is devoted
to real time long range high resolution surface road traffic monitoring. Conception of this innovative application is
described and system requirements in the view of distributed fiber optic sensors are analyzed. Two suitable sensing
principles are reviewed and their properties relative to real time recognition of traffic participants are investigated.
Pulse shapes effects on backscattering Brillouin gain for distributed fiber sensing
Show abstract
Distributed fiber sensing based on Brillouin gain scattering (BGS) principle is a useful way to develop devices capable to
measure temperature and/or strain in optical fibers. In these distributed sensors, spatial resolution is a topic of special
interest in the distributed fiber sensing field. The influence of the probe-pulse shape in the interaction between the pulsed
light and the continuous wave laser in a pump-probe system. This study has the purpose of improving the spatial
resolution of the measurement without losing stability in the BGS is presented. Also it is showed how the backscattering
Brillouin gain is affected by inducing variations on the final value of the BGS intensity. Theoretical analysis of the probe
pulse in the Brillouin shift and intensity values using triangular, sinusoidal and saw tooth shapes around the phonon
lifetime (~10ns) are presented; and also considerations and conclusions are explained.
High performance and highly reliable Raman-based distributed temperature sensors based on correlation-coded OTDR and multimode graded-index fibers
Show abstract
The performance of distributed temperature sensor systems based on spontaneous Raman scattering and coded OTDR
are investigated. The evaluated DTS system, which is based on correlation coding, uses graded-index multimode fibers,
operates over short-to-medium distances (up to 8 km) with high spatial and temperature resolutions (better than 1 m and
0.3 K at 4 km distance with 10 min measuring time) and high repeatability even throughout a wide temperature range.
Raman-based distributed temperature sensing supported by integrated-optics technology
Show abstract
Exploitation of integrated-optic capabilities in terms of compactness and low-cost are demonstrated in distributed
temperature sensing experimentation. Design and characterization of an integrated-optic circuit in SiON technology with
high index contrast suitable for Raman-based fiber sensor are presented.
One centimeter spatial resolution temperature measurements in a nuclear reactor using Rayleigh scatter in optical fiber
Show abstract
We present the use of swept wavelength interferometry for distributed fiber-optic temperature measurements in a
Nuclear Reactor. The sensors consisted of 2 m segments of commercially available, single mode optical fibers. The
interrogation technique is based on measuring the spectral shift of the intrinsic Rayleigh backscatter signal along the
optical fiber and converting the spectral shift to temperature.
A resilient Raman amplified double ring network for multiplexing fiber Bragg grating sensors
Show abstract
An amplified optical fiber double ring network for the wavelength division multiplexing (WDM) of fiber Bragg grating
(FBG) sensors is demonstrated experimentally. The network is inherently resilient to fiber failures due to the
simultaneous interrogation of all the sensors using both rings. Furthermore, power transparency at the rings is obtained
by means of Raman amplification. We optimize the performance of the network with the launched pump power that
shows low levels of amplifiers' noise. We also demonstrate how the topology allows the received powers from the
sensors to be equalized.
Hybrid wavelength-time domain interrogation system for multiplexed fiber Bragg sensors using a strain-tuned erbium-doped fiber laser
Nilton Haramoni,
Aleksander S. Paterno,
Guilherme Soares,
et al.
Show abstract
A system for the interrogation of fiber Bragg grating sensors using a strain-tuned EDF laser with linear cavity is
described. An optical switch is spliced to one end of the laser cavity and connects one of two high-strength draw-tower
fiber Bragg gratings (DTG). The gratings are simultaneously tuned by a stretching device and act as the end reflector of
the laser cavity. By applying a ramp signal to the actuator synchronized to the optical switch, the laser signal sweeps
over two different wavelength intervals, depending on the connected DTG. This approach represents a hybrid
wavelength-time domain interrogation for multiplexed sensors and doubles the number of sensors that may be addressed
when compared with single DTG scanning. In addition, the use of the DTG allows a fivefold increase in the strain tuned
wavelength interval over standard fiber Bragg gratings. An example application is demonstrated where the temperature
in an electrical motor is measured during the machine operation.
Nested long period grating interferometers
Show abstract
The concept of nested fibre optic long period grating (LPG) based interferometers is introduced. A number of in-series,
identical LPGs may be used to form a set of nested, multiplexed Mach-Zehnder interferometers that may demodulated
and demultiplexed by virtue of a Fourier analysis of the optical spectrum. The concept is demonstrated by the use of
three LPGs to form a nested set of interferometers.
Railway monitoring and train tracking by fiber Bragg grating sensors
F. Mennella,
A. Laudati,
M. Esposito,
et al.
Show abstract
The aim of this work is to demonstrate the efficiency of fiber Bragg grating sensors to be used for in situ railway
monitoring and train tracking applications. In the specific case, FBGs (Fiber Bragg Gratings) sensors have been bonded
to rails in order to perform two different kinds of measurements: dynamic strain to analyze the characteristic frequency
response of the rail and train tracking (speed and rail deformation when loaded by running trains). The efficiency of the
sensing system has been verified in terms of significance of the information retrieved by the sensing data resolution and
the high speed response. The obtained results confirm the real possibility to adopt fiber optic sensors based on FBG
technology as excellent devices to ensure multipoint monitoring of railway structures taking advantages of the typical
peculiarities of FBG such as long distance interrogation, easy multiplexing, electromagnetic interferences immunity.
Dual-channel fiber ring down force sensor
Show abstract
Dual-channel fiber ring down force sensor based on the principle of time division multiplexing is descried. The system
has the capability to interrogate more than two micro bend sensors by using more than one fiber delay line to control the
time of flight of the pulse. The dual-channel fiber ring down force sensor with one fiber delay coil is demonstrated with
high force sensitivities of 183.4ns/N and 163.6ns/N, respectively. Our system has also good linear responses.
Validation of FBGs sensors C-PFM multiplexing and interrogation technique
Show abstract
In this paper, we propose an improvement of the Chirped-Pulsed Frequency Modulation (C-PFM) FBGs reading
technique [8] as supported by new experimental results. The C-PFM technique, which was basically translated from its
counterpart in the field of radar signal analysis, exploits the intensity modulation of the probe signal (the light traveling
along the fiber in our case) by means of a sinusoid with a linearly variable frequency and a train of pulses, to improve the
spatial resolution of the acquisition system. The response discrimination of the FBG sensors is achieved thanks to an infiber
linear filter and a novel adaptive numerical filtering as it will be better explained in the following. Using a peculiar
time window shaping (Blackman) of the light pulse we intended to improve the cross-talk features of the reading
technique.
Bragg grating dual fiber laser system for measurement of strain
Show abstract
This work presents an optical fiber laser used as a sensor; the system consists of a laser formed by two Fabry-Perot type
coupled cavities, two gratings as references and two more gratings as sensors.
A novel method for demodulation of FBG sensor
Show abstract
Because of the characteristic of wavelength encoding, fiber Bragg grating (FBG) has the advantages of immunity to light
power fluctuation, variation in polarization and connecting loss, so it has high sensing precision. However, for the
demodulation of FBG, wavelength signal is usually converted to electric amplitude signal. By measuring the amplitude
signal, the sensing result is obtained. It is well know that the amplitude signal is easy to be disturbed in sense. For this
reason, amplitude demodulation limits the effect of wavelength encoding of FBG. This paper presents a novel method of
counting wavelength demodulation for FBG sensors using a high birefringent fiber (HBF) loop mirror. This demodulator
has simple structure, high precision, low cost and convenient to use. The resolution of the loop mirror device with 30
meter long of HBF is 0.067 nm. This counting wavelength demodulating method has the significance for widespread
practical application of FBG sensors.
A method of examination of liquids by neural network analysis of reflectometric time domain data from optical capillaries and fibers
Show abstract
This paper presents the construction and working principles of a reflectometric intelligent fiber-optic sensor used for
liquid examination. Unlike other well-known fiber optical sensors which use information from optical wavelength
variations, the proposed system uses time domain data. The sensing element consists of a length of optical fiber and a
short section of optical capillary and works on the reflection intensity basis. The reflected signal level depends on the
optical construction of the sensor element. The changes of the monitored signal are caused mainly by variation in light
propagation conditions at the interfaces of liquid and gaseous phases. The physical effects involved are Fresnel
reflection, local numerical aperture variation and liquid lenses formation. It is possible to call out across the changes of
those effects by introducing a measuring procedure which includes submerging, submersion, emerging and emergence
of the sensing head from the examined liquid or by local heating of the liquid sample.
A new generation of SPAD: single photon avalanche diodes
Show abstract
Design and characterization of a new generation of single photon avalanche diodes (SPAD) array, manufactured by STMicroelectronics
in Catania, Italy, are presented. Device performances, investigated in several experimental conditions
and here reported, demonstrate their suitability in many applications. SPADs are thin p-n junctions operating above the
breakdown condition in Geiger mode at low voltage. In this regime a single charged carrier injected into the depleted
layer can trigger a self-sustaining avalanche, originating a detectable signal. Dark counting rate at room temperature is
down to 10 s-1 for devices with an active area of 10 μm in diameter, and 103 s-1 for those of 50 &mgr;m. SPAD quantum
efficiency, measured in the range 350÷1050 nm, can be comparable to that of a typical silicon based detector and reaches
the values of about 50% at 550 nm for bigger samples. Finally, the low production costs and the possibility of integrating
are other favorable features in sight of highly dense integrated 1-D or 2-D arrays.
Temperature and strain sensor based on weak LPG and fiber ring down
Show abstract
A fiber ring down with a weak long period grating for temperature and strain sensing is proposed and demonstrated.
The sensing devices consist of two matched fiber Bragg gratings, a section of single mode fiber, a weak long period
grating, a pulsed laser source and a photodiode. The LPG incorporated in fiber ring cavity is used as sensing element,
the induced resonance wavelength shift of which will cause an additional loss in the cavity. As a result, the amplitude of
applied temperature variation or strain can be obtained by simply measuring the fiber ring down time. The proposed
sensing system has advantages of easy configuration and rapid response.
Arc-welding quality assurance by means of embedded fiber sensor and spectral processing combining feature selection and neural networks
Show abstract
A new spectral processing technique designed for its application in the on-line detection and classification of arc-welding
defects is presented in this paper. A non-invasive fiber sensor embedded within a TIG torch collects the plasma radiation
originated during the welding process. The spectral information is then processed by means of two consecutive stages. A
compression algorithm is first applied to the data allowing real-time analysis. The selected spectral bands are then used
to feed a classification algorithm, which will be demonstrated to provide an efficient weld defect detection and
classification. The results obtained with the proposed technique are compared to a similar processing scheme presented
in a previous paper, giving rise to an improvement in the performance of the monitoring system.
Data processing method applying principal component analysis and spectral angle mapper for imaging spectroscopic sensors
Show abstract
A data processing method for hyperspectral images is presented. Each image contains the whole diffuse reflectance
spectra of the analyzed material for all the spatial positions along a specific line of vision. This data processing method is
composed of two blocks: data compression and classification unit. Data compression is performed by means of Principal
Component Analysis (PCA) and the spectral interpretation algorithm for classification is the Spectral Angle Mapper
(SAM). This strategy of classification applying PCA and SAM has been successfully tested on the raw material on-line
characterization in the tobacco industry. In this application case the desired raw material (tobacco leaves) should be
discriminated from other unwanted spurious materials, such as plastic, cardboard, leather, candy paper, etc.
Hyperspectral images are recorded by a spectroscopic sensor consisting of a monochromatic camera and a passive Prism-
Grating-Prism device. Performance results are compared with a spectral interpretation algorithm based on Artificial
Neural Networks (ANN).
Detection of premature browning in ground beef using an optical-fibre-based sensor
Show abstract
This paper reports on an optical fibre based sensor system to detect the occurrence of premature browning in ground
beef. Premature browning (PMB) occurs when, at a temperature below the pasteurisation temperature of 71°C, there are
no traces of pink meat left in the patty. PMB is more frequent in poorer quality beef or beef that has been stored under
imperfect conditions. The experimental work pertaining to this paper involved cooking fresh meat and meat that has been
stored in a freezer for, 1 week, 1 month and 3 months and recording the reflected spectra and temperature at the core of
the product, during the cooking process, in order to develop a classifier based on the spectral response and using a Self-Organising Map (SOM) to classify the patties into one of four categories, based on their colour. The combination of both
the classifier and temperature data can be used to determine the presence of PMB for a given patty and can thus be used
for Quality Control by food producers.
Minimum detectable signal and optimal operating point in intensity noise-limited fiber optic gyroscopes
Elnatan C. Ferreira,
Fernando F. de Melo,
J. A. Siqueira Dias
Show abstract
The relative intensity noise in sinusoidally modulated fiber optics gyroscopes is analyzed in order to determine
which is the value of the minimum detectable signal by the demodulator electronics circuits. The analysis is
conducted for both the well known lock-in amplifier demodulator and the mean value demodulator (MVD). Numerical
results show that, in intensity noise-limited fiber optics gyroscopes, the MVD allows for the demodulation
of smaller signals when compared to the lock-in amplifier.
Distributive tactile sensing using fibre Bragg grating sensors
Show abstract
We describe experiments aimed at assessing the applicability of fibre Bragg grating sensors to distributive tactile
sensing. Strain signals from flexible surfaces instrumented with Bragg grating sensors are processed using neural
networks so as to obtain the location, shape and orientation of objects placed on the surfaces.
Unambiguous signal demodulation extending the measuring range of fiber Bragg gratings sensors using artificial neural networks: a temperature case
Leonardo S. Encinas,
Antonio C. Zimmermann,
Celso L. N. Veiga,
et al.
Show abstract
This paper presents a novel approach that uses Artificial Neural Networks - ANN to extend the measurement
range of Fiber Bragg Gratings - FBG interrogators based on fixed narrow band filter demodulation. Interrogators
with fixed spectral filters use only one edge of the filter to demodulate the signal. The system proposed
uses narrow band FBG's filters, where the entire filter bandwidth is applied to demodulate the signal. Furthermore,
the approach has possibility to concatenate n filters, obtaining a measuring range n×bandwithF, where
bandwithF is the bandwidth of a demodulating FBG filter. The great advantage of this method relies on the
use of ANN to combine these signals, mitigating the ambiguities created in the both edges of each FBG filters,
and generating a continuous linear output measuring range. Despite of this proposed demodulation method can
be used for strain measurements, yet it is in the temperature sensing that the method offers better contribution.
Wide temperature measuring ranges are common in the petrochemical industry, such as distillation columns (0
to 700°C), or in power plants to measure the temperature of transformer windings (-30 to 150°C). This paper
presents theoretical results of a temperature measurement system in power transformers application.
Multi-point fibre optic hot-spot network integrated into a high power transformer
Show abstract
A multi-point fibre optic temperature sensor network integrated inside a power transformer for continuous monitoring of
hot-spots on windings, cellulose insulations and oil, is demonstrated and tested. The temperature sensors are based on
proprietary encapsulated fibre Bragg grating (FBG) sensors and the optical interrogation unit uses a special designed
narrowband high power broadband fibre source. The fibre optic sensing network is integrated into a 440 MVA power
transformer having 12 temperature sensing points, distributed over several physical locations inside de transformer
(windings, cellulose insulators, magnetic circuit and cooling oil entrance and exit).
Temperature influence of an air conditioner in refractive index measurements using long-period fiber gratings
Show abstract
The influence of temperature in the measurements of surrounding refractive index using long-period fiber gratings is
studied for room temperature variations. For temperature changes close to 2°C it is verified wavelength shifts lower than
0.1 nm for the grating immersed in air and as high as 1.1 nm for a hydrocarbon sample whose refractive index is 1.4530.
Sensitivity evaluations of long-period fiber gratings and evanescent fiber sensors require a temperature system control
that keeps the temperature constant. Otherwise, it should be considered compensation systems that consider not only the
temperature changes but also the refractive index and the thermal-optical coefficient of the materials under analysis.
Progress in miniaturization of a multichannel optical fiber Bragg grating sensor interrogator
Show abstract
An effort to develop a miniaturized multichannel optical fiber Bragg grating sensor interrogator was initiated in 2006 under the Small Business Innovative Research (SBIR) program. The goal was to develop an interrogator that would be sufficiently small and light to be incorporated into a health monitoring system for use on tactical missiles. Two companies, Intelligent Fiber Optic Systems Corporation (IFOS) and Redondo Optics, were funded in Phase I, and this paper describes the prototype interrogators that were developed. The two companies took very different approaches: IFOS focused on developing a unit that would have a high channel count and high resolution, using off-the-shelf components, while Redondo Optics chose to develop a unit that would be very small and lightweight, using custom designed integrated optical chips. It is believed that both approaches will result in interrogators that will be significantly small, lighter, and possibly even more precise than what is currently commercially available. This paper will also briefly describe some of the sensing concepts that may be used to interrogate the health of the solid rocket motors used in many missile systems. The sponsor of this program was NAVAIR PMA 280.
Characterization of railway traffic and its effects on a short span bridge by using a hybrid fibre optic/electrical measurement system
Show abstract
The characterization of traffic effects on a short span railway bridge in Northern Portugal with a new hybrid platform
that allows the simultaneous assessment of signals generated by a sensing network composed of both electrical and fibre
Bragg grating based sensors was demonstrated. A Bridge Weight-in-Motion algorithm was also developed, which allows
on-motion determination of train speed and weight distribution with only three fibre Bragg grating sensors.
Smart synthetic material arresting cable based on embedded distributed fiber optic sensors
Show abstract
Redondo Optics Inc. in collaboration with the Cortland Cable Company and the US. Navy under a Navy
sponsored SBIR program is in the process of developing an embedded distributed fiber optic sensor
(EDIFOSTM) system for the real-time, structural health monitoring, damage assessment, and lifetime
prediction of full scale synthetic material arresting gear cables. The EDIFOSTM system uses a distributed
array of fiber Bragg grating sensors, sensitive to stress/strain, impact damage, kinking and bending, and
temperature, embedded within the strands of a synthetic material arresting cable structure. Fiber Bragg
grating sensors are a mature technology typically used for the in-situ structural health monitoring of
advanced structures. The periodic grating produces an optical, wavelength-encoded signal whose properties
are dependent on the structural, and mechanical environment of the sensor fiber. The FBG sensor
interrogation system monitors the status of each of the individual FBG sensors distributed along the
embedded sensor fibers and transforms this information in real-time in to a graphical display of the
stress/strain and temperature state of the entire arresting gear cable. An alarm system triggers to pinpoint
those locations of potential damage.
Active vibration control using fiber Bragg grating sensors and piezoelectric actuators in co-located configuration
Show abstract
In this paper, the feasibility of an active vibration control scheme using Fiber Bragg Grating (FBG) sensors and
piezoelectric (PZT) actuators for vibration suppression of an aluminum plate is investigated. Four FBGs have been
bonded to the structure below the same number of PZT actuators in co-located configuration. A Proportional-Derivative
controller has been used to generate the command signals required to drive the actuators. Preliminary results from
"closed loop" configuration tests are reported showing up to 17 dB of noise reduction at 80 Hz.
Structural health monitoring of the church of Santa Casa da Misericórdia of Aveiro using FBG sensors
Show abstract
This paper presents a structural health monitoring system, based on fibre Bragg gratings, developed for the church of
Santa Casa da Misericordia of Aveiro. This system comprises 19 displacement sensors and 5 temperature sensors. All
the sensors were custom made according to the monitoring points' characteristics. The results obtained over the first
months are presented. The objective of this work is to gather data that will bring a deeper knowledge of how this
structure behaves and to help planning the recovering interventions in this historical building.
Damage detection under a composite patch using an embedded PZT-FBG ultrasonic sensor array
Show abstract
An array of piezoelectric ultrasonic exciters/sensors and fiber Bragg grating sensors is embedded between an Aluminum
plate and a composite patch. Using Lamb waves, the array is shown to be capable of detecting a developing damage in
the aluminum plate, as well as locating it.
Smart sensors and active adaptive control exploitation for vibration damping of a cantilever beam
Show abstract
In this work we present the first experimental results of a new multidisciplinary activity concerning active structural
control. Specifically, exploiting Fiber Bragg Grating (FBG) sensors and Piezoelectric actuators, an adaptive control
approach was adopted to damp the vibrations of a cantilever beam. The strain sensor used for the structural vibration
detection is a Bragg Grating written on a single-mode optical fiber for telecom applications. The reading technique used
to detect the variations in the &lgr;B of the grating due to the local strain variations, exploits a narrow band laser tuned to the
mean wavelength of the grating reflectance spectrum roll-off, as it will be better explained in the following. The results
obtained so far demonstrate how the combined application of novel strain sensors and a clever control approach can
provide a benefit in terms of bandwidth, damping speed and reduced design effort.
Residual strain measurement in bonded composite repairs for aging aircraft by embedded fiber Bragg grating sensors
U. Ben-Simon,
I. Kressel,
Y. Botsev,
et al.
Show abstract
Embedded Fiber-Bragg-Grating sensors are used for tracking the initiation of structural bonding and measuring the
residual strains, during the curing process, of bonded composite patches used for aging aircraft structural repairs. FBG
reading are shown to have direct correlation with the residual strains that are important in assessing the long-term
durability of the repaired structure under fatigue load spectrum.
Strain measurements using an interferometrically interrogated embedded fibre optic rosette
Klas Levin,
Jérôme Matrat
Show abstract
The objectives were to demonstrate the performance of an embedded optical strain rosette in carbon/epoxy composite
laminates using a time domain multiplexed system. The effective in-plane strain components can be determined with an
optical strain rosette if at least three sensors oriented in different directions are used. Experimental results were obtained
in tension, compression and shear loading. The experimental results showed that embedded optical strain rosette and the
surface-bonded resistive strain gauges gave similar in-plane strains.
Alarm system of optical fibre using the thermal-optical sensibility of the PNIPAAm polymer
Show abstract
An alarm system as extrinsic sensor on optical fibers for detecting and controlling inflammable liquids based on thermosensitive
proprieties of the PNIPAAm hydrogel is presented. The changes on the optical proprieties of the PNIPAAm
with the temperature (being its LCST 32°C), induce abrupt changes on the light intensity and they act as an alarm signal,
which is transmitted by optical fibers and after they will be processed by an optoelectronic circuit, responsible to active
an alarm. An appropriate system consists of the hydrogel connected between its ends to two segments of plastic optical
fibers (source and receiver) and they turn on the alarm when a photo detector does not receive light when the hydrogel
becomes when it reaches threshold of temperature. The characterization of the hydrogel and the experimental results are
presented for a prototype.