In this work, an In-fiber Mach-Zehnder Interferometer has been manufactured within a standard optical fiber using direct inscription with a femtosecond laser. Different geometries have been tested in order to enhance the sensitivity of manufactured devices to high temperature sensing, reducing the total device up to 300μm. The achieved results exhibit a remarkably good response for temperature sensing up to 650°C.
In this work, the regeneration process of FBGs written into both standard and bend-insensitive fiber has been studied. Several dopants present in these fibers lead to different regeneration properties which, based on previous experiments, have been tested, paying special attention to the regeneration temperature. The achieved results suggest a reduction on the regeneration temperature for FBGs written into bend-insensitive fiber that favors mechanical properties of silica.
A specific temperature and pressure optical fiber transducer is presented in this paper. By using a customized fiber reinforced plastic membrane with embedded Fiber Bragg Gratings, the fluid pressure and temperatures changes are converted in optical wavelength displacements. The membrane and the transducer custom design allows a suitable measurand discrimination. The transducer is implemented, characterized and calibrated. Its feasibility to be used on large diameter water pipes has been successfully validated by means of field trials. Many of these transducers will be optically multiplexed to monitoring these infrastructures.
A structure based on a smart material and a PID control loop is presented in this paper. A glass fiber
reinforced plastic material is instrumented with Fiber Bragg Gratings (FBG) and Shape Memory Alloy
(SMA) actuators. The smart material and the smart structure are both successfully checked by being
subjected to different operational conditions at the laboratory. Very good responses are obtained under
both slow and quicker varying conditions.
The prestressing force is transferred to the concrete during the slack period of precast concrete structures fabrication. To
contribute to a better understanding of the armor compliant behaviors during the mentioned process, a custom quasidistributed
Bragg Grating optical fiber sensor system is designed, fabricated and embedded into a prestressed concrete
prismatic beam. The experimental works, the results, their discussion and finally the obtained conclusions are presented
in this paper.
A temperature Level fiber Optic transducer based on a fiber grating-shape Memory Alloy wire structure (LOMA) is
presented in this paper. The basic sensors system works as an on/off optical device: only output light is offered by the
device when the structure temperature (T) is over a given temperature level (T>TL). The proposed fiber structure can be
used as point or as quasi-distributed sensors systems exploiting its optical multiplexing capacities. The simple and cost
effective device is successfully demonstrated in the laboratory.
A temperature and strain optical fiber transducer and its optimal design are presented. The hybrid structure is composed
of two Fiber Bragg Gratings (FBG) in a fused taper. Using the same phase mask one of the FBG is written outside of the
taper, and the other one in the middle of the taper, in the area with constant diameter. The taper diameter and the
structure length play a key role on the transducer behaviour. Useful results to optimize the transducer structure design,
from a theoretical and experimental investigation, are reported in this paper.
A hybrid Erbium-Brillouin fiber laser sensor to measure the temperature along 22 km fiber is proposed and
experimentally demonstrated. A multi-line laser oscillation is induced by the Brillouin gain of different concatenated
transducer fiber sections placed in the ring cavity. Integral temperature measurements of each fiber section are obtained
through each laser line. This sensor can be used to monitor the temperature of off-shore wind energy power cables.
A pre-excitation pulse technique in Brillouin optical time domain analysis (PP-BOTDA) for enhancement of the spatial
resolution is shown. The technique here exposed is based on the pre-excitation of the stimulated Brillouin scattering and
the subtraction of the Brillouin scattering due to the intensity dc level present in the optical pulse. A main optical pulse
with 3ns of duration followed by a pulse of 40ns and half the intensity of the main one are used for obtaining 30cm of
spatial resolution. The spatial range is 3600m on a standard single mode optical fiber.
Structural Health Monitoring (SHM) has assumed a significant role in assessing the structures safety and integrity. SHM
can be understood as the integration of sensing intelligence and possibly also actuation devices to allow the structure
loading and damaging conditions to be recorded, analyzed, localized and predicted in such a way that non-destructive
testing becomes an integral part of the structure. SHM sensing requirements are very well suited for fiber optic sensing
technology. So in this paper, after a very brief introduction of the basic SHM concepts, the main fiber optic technologies
for this application will be reviewed, several examples and the main current technical challenges will be addressed and,
finally, the conclusions summarized.
In this paper an angle transducer based on Fiber Bragg Grating (FBG) is presented. Two gratings are glued to a metallic
platen, one in each side. It is insensitive to temperature changes, given that the temperature shifts affect equally to both
FBG. When the platen is uniformly bent an uniform strain appears in both sides of the platen. It depends on the bend
angle and the platen length and thickness. The transducer has been designed to be used in the auscultation of tunnels
during their construction process and during their live time. The transducer design and its characterization are presented.
A method for the unsupervised clustering of optically thick textile dyes based on their spectral properties is demonstrated
in this paper. The system utilizes optical fibre sensor techniques in the Ultraviolet-Visible-Near Infrared (UV-Vis-NIR)
to evaluate the absorption spectrum and thus the colour of textile dyes. A multivariate method is first applied to calculate
the optimum dilution factor needed to reduce the high absorbance of the dye samples. Then, the grouping algorithm used
combines Principal Component Analysis (PCA), for data compression, and K-means for unsupervised clustering of the
different dyes. The feasibility of the proposed method for textile applications is also discussed in the paper.
An optical fibre transducer able to work in high temperatures environments is experimentally demonstrated in the
laboratory. It is based on a permanent Long period gratings (PLPG) written using a thermo-mechanical technique. The
fabrication technique, the experimental works, their results and the conclusions are presented and discussed in this paper.
An erbium doped fiber ring laser (EDFRL) that incorporates four non-adiabatic concatenated single-mode fiber tapers
(acting as tunable filter in the laser cavity) is presented. These concatenated fiber tapers integrates a filter with a
narrower band-pass and a higher modulation depth than a single taper. The tuning of this filter was implemented
applying a controlled perturbation in the fiber taper. The proposed laser architecture was successfully demonstrated in
the laboratory in which a tuning range of 20.8nm (1544.5nm-1565.3nm) were measured.
A refractometric sensor that uses the transition region of a U-bent Plastic Optical Fiber (POF) when it is polished
laterally is presented. By polishing a lateral segment of the fiber, a part of the plastic optical fiber core is removed and an
elliptical surface is formed on the bend. It is found that that the polishing with an angle equals to the critical angle of a
straight optical fiber the sensitivity of this transducer structure is enhanced. Then, the incident light is totally reflected
and the transition losses decrease locally. In addition, the sensitivity increases compared to the polishing in the region of
bending losses. The proposed transducer is successfully checked with experimental measurements and different kinds of
liquids. Potential applications are suggested.
A processing algorithm to classify hyperspectral images from an imaging spectroscopic sensor is investigated in this
paper. In this research two approaches are followed. First, the feasibility of an analysis scheme consisting of spectral
feature extraction and classification is demonstrated. Principal component analysis (PCA) is used to perform data
dimensionality reduction while the spectral interpretation algorithm for classification is the K nearest neighbour (KNN).
The performance of the KNN method, in terms of accuracy and classification time, is determined as a function of the
compression rate achieved in the PCA pre-processing stage. Potential applications of these hyperspectral sensors for
foreign object detection in industrial scenarios are enormous, for example in raw material quality control. KNN classifier
provides an enormous improvement in this particular case, since as no training is required, new products can be added in
any time. To reduce the high computational load of the KNN classifier, a generalization of the binary tree employed in
sorting and searching, kd-tree, has been implemented in a second approach. Finally, the performance of both strategies,
with or without the inclusion of the kd-tree, has been successfully tested and their properties compared in the raw
material quality control of the tobacco industry.
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.
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.
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.
The theoretical design and experimental characterization of 1480 nm superfluorescent erbium-doped fibre sources are reported in this paper. Different configurations and three erbium doped fibres with different concentrations are used. In double pass configurations a Faraday rotator mirror is used. The comparison of the characteristics of these SFSs in terms of the output power, mean wavelength, spectral width and stability is carried out.
Using polymer optical fibre and Moire patterns an angular and displacement sensor is demonstrated. Using two transparent superimposed planar gratings on an optical mirror, Moire fringes are generated. Measuring the period and the number of periods, the relative angle and the displacement are both obtained. With this technique very low angles with very high resolution can be measure. The sensor principle are successfully checked in the laboratory.
A civil structure monitoring system based on fiber Bragg grating technology is presented. A complete set of new transducers, both for concrete and steel monitoring, is designed, fabricated, and successfully checked both in laboratory and in-field conditions.
A novel method for interrogating interferometric sensors, based on analyzing the characteristics of the light expelled from a tilted fiber Bragg grating and captured by a photodetector linear array, is presented in the paper. Also a novel algorithm for the recovery of the measured information is proposed and its performance explored. It belongs to the parametric frequency estimation methods and is an adaptation of the MUltiple SIgnal Classification (MUSIC) algorithm. Finally an insight to the possibility of interrogating multiplexed interferometric sensors is given.
The spectral properties of long period fiber gratings (LPFG) are modified when twisting is applied. Herein, results of applying torsion to UV-induced LPFGs are presented for comparing with others which have already been presented in literature and where the LPFGs are fabricated using different techniques. Both, the resonant wavelength and the peak attenuation of the resonance, have similar behaviors to those obtained by other authors. However, in spite of the fact that the values of sensitivity to twist rate are sensibly lower in the case of UV-LPFGs, its bigger mechanical strength lets them be subjected to higher twist rates, which could be useful in determinate applications.
A remote sensing system for concrete civil structures is presented. The transducers used are based on Fiber Bragg Gratings and exhibit the capability of simultaneously measure both temperature and strain. The sensing system can be controlled remotely form any place in the world via Internet and/or mobile telephony. The system will allow the long term monitorization of the structure.
A new interrogation scheme for civil engineering transducers is presented. Although it was developed in the first place for Fiber Bragg Grating based transducers, it has also demonstrated a good performance when interrogating other type of sensors such as those based on Low Finesse Fabry-Pérot Cavities. The proposed unit is able to extract the required information from the transducers by measuring the characteristics of the near field radiation created in the surroundings of a tilted fiber Bragg grating. This working principle makes it very attractive and suitable for civil engineering structural
monitoring. Among the technical characteristics of the scheme, the following should be highlighted: inherent capability for extracting information of wavelength multiplexed FBG-based transducers, very wide wavelength operation range, and good wavelength resolution.
The photonic sensing technology is an area of very rapid growth and increasing interest nowadays. This is due in part to devices such as Fiber Bragg Gratings (FBG), whose inherent characteristics make them very suitable for different sensing fields such as civil engineering, aeronautics or medicine just to mention a few. Among the characteristics that make these devices so versatile, one can find their electromagnetic immunity due to the fact that they are made of dielectric material, both their low size and weight, and their ability to be multiplexed in the same fiber. Even more important is the fact that the information is wavelength encoded and so it is not altered by the attenuations of the transmission channel. This last characteristic transforms these devices into very reliable ones. A new FBG-based transducer for monitoring civil engineering structures is presented in this paper. It is able to monitor both strain and temperature at the same time, giving them very useful information about the actual behavior of their host structure. These transducers were fully characterized and tested in laboratory in order to evaluate their performance. The paper is organized as follows: first of all a brief theoretical introduced to FBG is given, and after that the design of the trasnducer is discussed. Then the characterization process, as well as its results, are presented. At the end, the final laboratory test in a well-known structure is described.
Structural health and behavior monitoring have always been both a common concern and need in civil engineering. Several classical approaches have been given to this problem including the widley used strain gauges as well as the topographic measurements. These two techniques are almost always used to monitor the behavior of the structures whereas the health monitoring is accomplished by a simple periodic visual inspection. These approaches present serious problems that limit their practical use in real structures such as: lack of fiability, long-term drift, impossibility of full-time measurements, or lack of thoroughness. Centering the discussion in the strain gauges, for being the most representative of the classical civil engineering monitoring methods, it must be said that due to their electric nature they are exposed to both electromagnetic interference and corrosion. The latter greatly reduces their operating life time pushing it typically to less than one year after installation. That is whey new ways of monitoring civil structures were looked for, and that is how photonic fiber sensing came up. Characteristics shared by all fiber senors are their electromagnetic immunity for being manufactured using a dielectric material, low weight, small size, and compatibility with construction materials. As can be seen these inherent characteristics make them very suitable for their use in civil engineering structures. An example of a quasi-distributed transducer is presented in this communication. First the theoretical fundamentals of the transducer and its behavior is explained, and an in-field experiment consisting on monitoring a bridge is described and its results reported.
Although several Fiber Bragg Grating (FBG) based transducers have been successfully applied to the measurement of strain and temperature on civil engineering applications, important research work must be done to obtain transducers able to be used out of the laboratory. One of these research topics are the study of good interfaces between the optical fiber and the structural part to be measured. In this work a wide range of fixing techniques and interfaces have been investigated for fiber Bragg grating based transducers. Several transducers were constructed and fixed to a steel girder. Conventional strain gauges and professional displacement metering devices was added to the test specimen to make comparisons. A complete characterization setup using a laboratory test machine to test the transducers was designed. The test included several static and dynamic cycles and was applied to the steel girder while all the transducers were monitorized simultaneously. Results obtained with traditional and with the optical fiber mentioned technologies show a very good agreement.
The use of Fiber Bragg Grating (FBG) technology for the measurement of strain and temperature in civil engineering structures have been previously well demonstrated. A lot of work have to be done to achieve the new transducer technique to be able to compete with well established strain gauges. The measurement of strain and temperature within concrete beams is a niche of application where fiber optic transducers have advantages over conventional techniques. Fiber optic sensors can be inserted in a concrete beam for this purpose and debt to the known characteristics of fiber optic a higher durability can be achieved. In order to prove the ability of this type of transducers to make the measurements a set of FBG were fixed to the steel bars within the concrete beam and other set of long gauge FBG based transducers were embedded in the beam. The former were used for steel bar strain measurement and the later were employed for structural concrete beam sensing. During the concrete curing process, temperature of the beam were monitorized. After that, a complete flexural test was made while the beam was monitorized using traditional laboratory measurement techniques. Interesting conclusions have been obtained and will be presented.
Strain and temperature measurement using one Fiber Bragg Grating transducer is demonstrated. The device is constructed in a hydrogenated standard telecommunication optic fiber with one-step optimized UV writing process. A complete strain and temperature characterization is reported to assess the viability of this device.
We report on the integration of optical fiber containing Bragg gratings in the structure of both optical and power cables. It is hon that fiber Bragg gratings provide an efficient method to monitor quasi-distributed mechanical strength along optical cables. This technology is also applied to the monitoring of temperature in power cables for transmission/distribution infrastructures. We show that there are no losses introduced during the cabling process, and the temperature sensitivity of the fiber Bragg grating was found to be only slightly affected by the extrusion process. Results are presented for cable operation in real environment.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.