In the past decade Raman spectroscopy (Raman) has moved out of the shadow of infrared spectroscopy (IR) and has become a routine analytical tool and is finding value in pharmaceutical process applications. Raman offers several advantages over IR vibrational information in identifying and quantifying chemicals, such as linear response to concentration independent of path length, ability to measure aqueous solutions without interference from water bands, and ease of sampling provided by fiber optic probes. However, process measurements, such as continuous monitoring or raw materials identification have been slow to develop due to instability of the wavenumber axis. Commercial suppliers of dispersive based Raman systems employ calibration references and software approaches to solve this difficult problem. To overcome this difficulty, just as dispersive IRs have been replaced by FT-IRs, we have developed an industrial hardened FT-Raman system. Furthermore, we have increased sensitivity by 25 times by employing an Si detector instead of an InGaAs detector. Here we present the abilities of this Raman system to address a number of pharmaceutical applications, including identifying raw materials in less than one minute using spectral library matching, process monitoring during early stage optimization, analyzing blended materials, and determining polymorphism.

OPTRA has developed a low-cost, extremely compact, rugged open-path Fourier transform infrared (OP-FTIR) spectrometer for workplace air quality monitoring. This research was funded under a United States Air Force ABIR Phase II contract. The goal of the program has been to identify and alleviate all aspects of currently available OP-FTIR systems which result in high-cost and complex user requirements. This low-resolution ssytem (Δσ = 8 cm^-1) employs an uncooled DLATGS detector and a novel encoder-based reference metrology. Other design economies include a plastic injection-molded retroreflector array to return the open-path beam. This effort has included the development of a set of algorithms based on artificial neural networks (ANNs) and partial least squares (PLS) by the University of Idaho; these algorithms are specifically tailored to low-resolution systems applied to multi-component analysis of large, organic molecules characterized by broad infrared resonance bands. The algorithms, coupled with our OP-FTIR, are designed to autonomously identify and quantify a list of 105 common industrial organic molecules in the presence of varying humidity levels. Our system includes two PCI boards which host all OP-FTIR processing and servo electronics; the boards reside in a small suit-case PC along with a user-friendly Graphical User Interface.

Fiber reinforced epoxy resins manufactured in autoclaves are expected to continue to dominate the composites market through 2010. However, the ability to obtain consistent mechanical properties from product-to-product remains difficult. This is largely due to the inability to monitor and control epoxy cure, loosely defined as the process of chain extension and cross-linking. Current autoclave process control employs a heat schedule based on a time-temperature-transformation (TTT) phase diagram that is determined by dynamic mechanical rheology. The phase diagram defines epoxy cure in terms of gelation and vitrification. We have been using an FT-Raman spectrometer to develop correlations between molecular (chain extension and cross-linking) and macroscopic (gelation and vitrification) data. The basis of a TTT phase diagram using Raman kinetic data for process control will be presented for several reactions.

Energy intensive industries such as steel, aluminum, and glass require combustion processes that are characteristically at high temperature with high levels of particulate matter. Monitoring and control of these processes for improved efficiency, pollutant reduction, and product quality requires a sensor adaptable for such harsh environments. Traditional industrial monitoring relies on extractive sampling that requires frequent maintenance due to probe plugging or corrosion and routine calibration. In addition, capturing the temporal behavior of the process can be problematic with extractive sampling systems because of the slow response time associated with the sampling line lengths and slow response analyzers. To meet the demands of these harsh combustion processes the ideal sensor would perform in-situ process monitoring, require little or no maintenance and provide real-time process information The use of tunable diode lasers based on absorption monitoring overcomes many of the problems associated with conventional extractive sampling. However, the majority of industrial combustion processes will undergo temperature variations along with changes in the atmosphere oxidation or reducing state during normal operation. Therefore, temperature monitoring along with key combustion species monitoring that describes the atmosphere e.g., O₂ and CO, is often necessary for optimal process control. The temperature is not only a useful parameter describing the state of the process, but is needed to accurately determine the species concentration since the absorption measured is dependent on temperature. To monitor both reducing and oxidizing combustion atmospheres in addition to gas temperature requires a diode laser system capable of multiple species monitoring. Here we describe an industrial prototype system operating in the near-infrared for simultaneous monitoring of O₂ (.76 μm), CO (1.5 μm), H₂O (1.5 μm) and gas temperature. The prototype system addresses the issues of added complexity with multiple species monitoring by using only two diode lasers and a beam launch and receiver optical design to discriminate the vastly different laser wavelengths while suppressing background radiation noise and beam steering from thermal gradients. Measurement results using the system for industrial process monitoring on a 100-ton/hr steel reheat furnace are presented. The measurements in this test were conducted at different zones in the furnace and at different heights relative to the processed material. The results show dynamic variations in concentration and temperature that could aid in improved atmosphere control.

A grating-assisted operating-point tuning system was designed to dynamically stabilize the operating-point of a fiber Fabry-Perot interferometric sensor to compensate for manufacturing errors and environment perturbation induced drifts. The system uses a diffraction grating and a feedback control, functioning as a tunable bandpass optical filter, and can be used as an effective demodulation subsystem in sensor systems based on optical interferometers using a broadband light source. This demodulation method features unlimited signal detection bandwidth, high tuning speed, large tunable range, increased interference fringe contrast, and a potential of absolute optical path difference measurement. Sensitivity improvements were demonstrated with a fiber Fabry-Perot acoustic wave sensor system.

Bragg grating devices are widely used in the field of optical sensing and communication. Thermally tunable devices utilize the effect of temperature on the wavelength response characteristics of the fiber Bragg grating. But the low sensitivity of a Bragg grating device to temperature limits its usage to many applications. The wavelength sensitivity of a bare FBG is only 1.3 nm for a temperature change of 100°C. In order to enhance the temperature sensitivity of a fiber Bragg grating, we propose modification of the cladding of the FBG through etching and put another coating layer outside the cladding. The cladding is etched to a certain depth around the grating and the etched portion is coated with a suitable polymer. Theoretical analysis has been done to find the relationship between the wavelength shifts and the etching depths and coating thickness of the polymer. A finite element model of the cladding etched FBG coated with polymer has also been developed and the wavelength shift due to thermal expansion is analyzed under various etching depths and coating thickness. The high thermal expansion coefficient of the polymer enables to enhance the thermal sensitivity by improving the wavelength shift due to thermal expansion. Also the polymer coating on the etched fiber reduces the susceptibility of fracture and improves the reliability. It is found that that temperature sensitivity increases with increase in etching depth. But there is maximum limit to which the cladding can be etched without affecting the performance. Also it is found that increasing the coating thickness of the polymer increases the wavelength shift due to temperature change.

Fiber-optic techniques for remote sensing are now being accepted and developed for a wide range of applications. Traditional sensor technology relies on electrical components to provide the measurement of changing environmental conditions. However, when operating in remote and harsh environments, electrical sensors have a variety of limitations such as power requirements and short lifetime. In contrast, fiber-optic sensors are passive devices that are environmentally stable and have a long lifetime. The fiber Bragg grating (FBG) is a particular type of fiber-optic sensor that can be adapted to measure parameters such as temperature, pressure or strain. The measurement is encoded with the wave-length of the optical signal reflected from the FBG. Consequently, the method of measuring the absolute optical wavelength is a critical component of the fiber-optic sensing system. To reliably detect very small changes in the environment at the sensor, the interrogation system must provide accurate and repeatable wavelength measurements. The interrogator also must be robust so that it can be deployed in the field as well as in the laboratory. Performance of a fiber Bragg grating interrogator based on Michelson interferometry is discussed along with the advantages of this technique.

For intrinsic fiber optic sensors such as interferometric fiber optic gyroscopes that use polarization maintaining fibers, performance of the fibers that constitute the sensing coils is a key issue. In general, requirements include small form-factor, good bend performance, tight tolerances on fiber geometry and ability to maintain a single polarization state. Currently, bow-tie or elliptical clad type high birefringence fibers are used in such sensors. This paper deals with the development and characterization of small form-factor (80 μm) PANDA style high birefringence fibers for sensing applications at different wavelengths of interest. The rationale and advantages of the new design are discussed along with geometrical and optical characteristics of one new fiber. Performance data of the fiber in terms of cross-talk variation in the -55 to + 85°C temperature range are presented.

The blue and violet laser beams are pretty useful in the micro-lithography, massive storage device and biomedical instruments. Also it is attracting more interests in the fiber sensing application because of its wavelength. The coupling from the blue and violet laser diode to a fiber still suffers from low coupling efficiency and instability. In Blue Sky Research, we utilized patented microlens technology to facilitate the coupling for 405nm laser diode and got as high as more than 70% efficiency with superior stability. It is an ideal fiber-coupled source for various kinds of application and accommodate wavelength from 375nm to 440nm. The design and the testing are reported in this paper.

Fiber lasers have been a subject of extensive research mainly due to their natural compatibility with optical fiber communications systems and optical fiber sensors. In particular, erbium doped fiber lasers offer attractive features such as a broad emission spectrum within a range in which several fiber optic devices such as Bragg gratings are readily available. We have studied the performance of a simple computer based control system for tuning and wavelength stabilization of an erbium doped single-mode fiber laser. Tuning is achieved upon stretching a fiber grating used as one of the mirrors for the laser cavity while wavelength is monitored through an optical spectrum analyzer. The desired wavelength of emission is fed to the computer through a graphic computer interface and an actuator stretches the grating to tune the fiber laser. Once the specified wavelength is achieved the control systems stabilizes the fiber laser upon monitoring wavelength fluctuations due to parameters such as temperature variations. The response time of the system seems to be adequate for interrogation of Bragg gratings in multiplexed sensor arrangements. Accuracy for wavelength stabilization is limited only by the resolution of the optical spectrum analyzer (0.06 nm). Being a general purpose system, any other tuning methods or wavelength tracking devices such as etalons can be used. The system has therefore the potential of becoming a compact computer controlled tunable fiber laser.

The development of integrated fiber optic sensors for smart propulsion systems demands that the sensors be able to perform in extreme environments. In order to use fiber optic sensors effectively in an extreme environment one must have a thorough understanding of the sensor’s limits and how it responds under various environmental conditions. The sensor evaluation currently involves examining the performance of fiber Bragg gratings at elevated temperatures. Fiber Bragg gratings (FBG) are periodic variations of the refractive index of an optical fiber. These periodic variations allow the FBG to act as an embedded optical filter passing the majority of light propagating through a fiber while reflecting back a narrow band of the incident light. The peak reflected wavelength of the FBG is known as the Bragg wavelength. Since the period and width of the refractive index variation in the fiber determines the wavelengths that are transmitted and reflected by the grating, any force acting on the fiber that alters the physical structure of the grating will change what wavelengths are transmitted and what wavelengths are reflected by the grating. Both thermal and mechanical forces acting on the grating will alter its physical characteristics allowing the FBG sensor to detect both temperature variations and physical stresses, strain, placed upon it. This ability to sense multiple physical forces makes the FBG a versatile sensor. This paper reports on test results of the performance of FBGs at elevated temperatures. The gratings looked at thus far have been either embedded in polymer matrix materials or freestanding with the primary focus of this paper being on the freestanding FBGs. Throughout the evaluation process, various parameters of the FBGs performance were monitored and recorded. These parameters include the peak Bragg wavelength, the power of the Bragg wavelength, and total power returned by the FBG. Several test samples were subjected to identical test conditions to allow for statistical analysis of the data. Test procedures, calibrations, and referencing techniques are presented in the paper along with directions for future research.

An all-fiber pressure sensor based on a fiber Bragg grating with the pressure sensitivity of 2.2x10^-2 MPa^-1 has been demonstrated. The physical configuration includes a FBG encapsulated in a polymer-half-filled metal cylinder with its end bonded to the central of a round plate attached to the surface of polymer, and the Young’s modulus of the polymer is four orders lower than FBG. This cylinder has two opening on opposite side of the wall at the polymer part. Under the pressure environment, the polymer can be pressurized along one radial direction only, and responds an axial force acting on the round plate, producing an axial strain on FBG. With a nice linearity, this sensor should be applied potentially for the measurement of mediums pressure, liquid level and depth underwater.

As the mapping of the human genome has been completed, increasing emphasis is being placed on large-scale protein separation and identification methods to define the function of proteins and their associated genes. Within the last decade the sensing technique using the surface plasmon resonance(SPR) has received a great deal of attention and has become a leading technology for affinity-based biosensing. In this paper I report a novel design of SPR fiber optic sensing elements which allows developing highly miniaturized SPR probes. A fiber-optic chemical sensor is presented which utilizes surface plasmon resonance excitation. The sensing element of the fiber has been made by removing a section of the fiber cladding and symmetrically depositing a thin layer of highly reflecting metal onto the fiber core. A white light source is used to introduce a range of wavelengths into the fiber optic. Changes in the sensed parameters are determined by measuring the transmitted spectral intensity distribution. Therefore, when a protein layer is adsorbed on the metal surface, an increase in the refractive index occurs and can be detected. Based on theoretical analysis, the sensor structure is optimized to achieve the maximum sensitivity.

The paper describes an optical fiber based sensor (FOS) for the detection of the pollutant gas, NO₂, in a mixture of gases. The design comprises of a fiber optic transflection probe with a sensor element placed at one end. In the present FOS, the transducing component is prepared by sol-gel process. An equal quantity of a diazotizing reagent together with a coupling reagent is immobilized in the sol-gel matrix, which forms an azo dye in the presence of NO2. The sensor relies on the coloration reaction occurring at the micropores of this sol-gel film in the NO₂ environment and offers a consequent variation in the optical absorption at a specific wavelength. The current sensor design gives more than 85% of variation in the output intensity at a NO₂ concentration of few parts per million in air sample.

We report a novel fiber optic relative humidity sensor based on the evanescent wave absorption spectroscopy. A comprehensive study of the sensor was made in terms of performance optimization against various parameters, which affects the sensor response and sensitivity e.g. film composition, film thickness, fiber core diameter and the sensor geometry. The sensor was compared against a commercially available relative humidity sensor and was found to be sensitive to relative humidity ranging from ~1.6 % to ~92%. We found that the sensor was having a very fast response to the relative humidity, and was fully reversible, repeatable with an extremely large dynamical range.

An on-line operation of micro-spectrometer and liquid drop analyzer is proposed in this paper. Comparing with a full spectral range spectrometer system, a micro-spectrometer has narrow spectral range that results in its inefficiency or inability in qualitative analysis of a mixed liquid since more than one function group of the mixed liquid might cause a peak or valley in the spectrogram at almost the same wavelength. A liquid drop analyzer (LDA) is an instrument that detects the characters of a liquid by monitoring its drop forming process. The LDA gives a fingerprint that is unique for certain liquid due to its specific chemical, physical and mechanical characters. An approach of combining micro-spectrometer with a fiber drop analyzer, by which a virtual 3D liquid fingerprint is formed, is described and it functions like a full range spectrum. The signals obtained from the micro-spectrometer and liquid drop analyzer, the method of on-line operation and database setting up, the experimental device and test results are described and discussed in the paper.

Fiber optic measurement systems are on the cutting edge of instrumentation for many industries from military and government applications to commercial needs such as the automotive, aerospace, and power turbine industries. Measurement parameters including temperature, pressure, and strain can provide valuable information. Sensor mapping allows for larger scale monitoring capabilities and provide flexibility in sensing applications. A sensor and readout system is being developed to expand the capabilities of fiber optic sensing. Several iterations of multiplexed sensors have been tested using a high-resolution fiber optic coupled dual Michelson interferometer based-instrument that has the capability of reading gaps of 25μm to 6.5mm. This measurement range opened the opportunity to read several different sensors on the same fiber, i.e. the same channel. Sensor strings combining temperature and strain extrinsic Fabry-Perot interferometric sensors were tested. These sensor strings produced were either serial multiplexed, parallel multiplexed, or a combination. This paper will discuss the capabilities of the sensors and instrumentation systems developed.

Arbitrary characteristics of optical interference have been realized, in our group, by Synthesis of Optical Coherence Function(SOCF) with electrical control and without mechanical scanning. Various applications for optical sensing have been developed by SOCF. Delta function like optical coherence function with higher spatial resolution and higher dynamic range have been achieved by using a broadband tunable super-structure-grating distributed Bragg reflector laser diode (SSG-DBRLD). This time, we improve driving circuit and frequency calibration of the SSG-DBR-LD to achieve a 5THz tunable band width. We apply the characteristics to distributed fiber optic force sensing using polarization maintaining fiber (PMF) as a sensing head. Its principle is polarization mode coupling by the force applied to the fiber. In the experiment, we improve the spatial resolution more than one digit compared with the previous data, and realize 20cm. This technique can be used as a nerve system for smart materials and structures.

We report on the detection of a loss-inducing perturbation with variable localization accuracy along a test fiber based on the analysis of transmitted and reflected powers of an unmodulated continuous-wave light source. The required accuracy of localization is provided by suitable distribution of the differential reflectivity along the fiber. We demonstrate a localization accuracy equal to ±1.0 m along the 3.939-km single-mode test fiber for the strong perturbation and ±5.0 mm along a designated 10-cm fiber part for weak perturbation.

The dislocation sensor based on the contrast phenomenon in an unbalanced fiber optic Michelson interferometer with a 3 x 3 coupler and a semiconductor multimode laser used as a source is described. Periodic contrast oscillations, which depend on a laser spectrum, occur if a measuring arm of the interferometer is elongated. So direct contrast-sensitive elongation measurement is limited only to one 200-μm long slope. In this paper we present a method of measuring range expansion up to 8 mm by linearyzation of contrast slopes. Elongation modulator in a reference arm of the interferometer is used. Experimental setup and software were worked out. For 1-m long sensor the 8-mm measuring range was obtained, where the highest difference between real and measured elongation is 25 microns

Because of the ready availability of fibre optic components from the communications industry, fibre optic systems operating in the near-IR are well suited for remote, multi-point monitoring of hazardous and environmentallyimportant gases. However a number of challenges have to be met in order exploit the potential commercial opportunities and applications for such sensors. Here we review our research on gas sensors based on fibre laser systems and absorption spectroscopy. Fibre lasers are of particular interest for sensors since on-going developments have extended their wavelength range of operation over ~1480-1620nm, encompassing the near-IR absorption lines of numerous gases. We discuss several configurations for fibre laser systems which offer the prospect of either enhanced performance or the possibility of multiplexing a number of sensor cells. However, because gas absorption lines in the near-IR spectral region are relatively weak, high sensitivity techniques are required for a number of species and we discuss methods for path-length enhancement through ring-down and intra-cavity absorption spectroscopy. Effective interrogation methods are required to attain the benefits of the various forms of cavity enhanced spectroscopy in fibre optic systems and several techniques are under investigation to realise this potential.

Stimulated Brillouin scattering(sBs) is the most dominant nonlinear process in optical fibers. It is a laser induced acousto-optic phenomenon with inherent optical feedback. As such, it is inherently quasi-periodic and chaotic in nature. The critical factors of fiber length, power, and feedback work together in producing this complex behavior. The Brillouin Fiber Ring greatly reduces the SBS linewidth as opposed to the open-ended scheme on the one hand, but enhances nonlinear dynamical instabilities such as quasi-periodicity and chaos. There is a rich variety of temporal behavior that flows through a seemingly automatic process of change above threshold. Increasing input power causes the dynamical behavior to further change while for some powers induces a change in line position or creates multiple lines in the frequency domain. The origin of these instabilities is being studied, while developing a means to suppress them.

Luna Innovations is developing a high temperature sensor suite based on novel metal oxide transducers and patented fiber optic sensor technology. This suite will include pressure, temperature, acceleration, and skin friction sensors. Luna has demonstrated prototype ceramic fiber optic pressure sensors with a range of 2000 psig and +/- 0.1 psig absolute accuracy and 0.01 psig dynamic resolution. By applying advanced materials and packaging technologies, designs that will support pressure measurements up to 1400°C have been produced. Fiber optic temperature sensors have been tested up to 1100°C. A ceramic accelerometer has also been developed that will enable high-temperature vibration measurements. A shear stress sensor is in the early stages of development that is expected to reach 850°C. The high temperature sensor suite will provide previously unobtainable measurements in advanced air-breathing propulsion systems, as well as in high-temperature industrial applications.

Smart textiles with integrated fiber optic sensors have been studied for various applications including in-situ measurement of load/deformation on the textiles. Two types of silica multimode optical fibers were successfully integrated into 4/4 Twill-woven and Plain-woven textiles along the warp direction of the textile structures for sensing of applied load conditions. The sensing mechanism is based on the MPD (Modal Power Distribution) technique, which employs the principle of intensity modulation based on modal power redistribution of the propagating light within multimode fibers caused by external perturbations. In the presence of transverse load applied to an integrated optical fiber, the redistribution of the modal power is an indication of the applied load. The spatial modal power redistribution was clearly recorded as a function of the optical intensity profile. Based on the uni-axial tensile test results, the relationship between the mechanical behavior of the textile and the output of the embedded fiber-optic sensor was established and understood. It is clearly demonstrated that the sensitivity and dynamic range of this type of intensity-based sensor is determined by the interaction between the fabric yarns and optical fibers, which are closely related with the textile structure and the type of optical fiber.

Conventional telecommunications fibers rely on a refractive index difference between the core and cladding region to confine light to the central core region. The refractive index difference is produced by different compositions of glass in the core and cladding regions. In contrast, holey optical fibers rely on an array of air holes in the cladding to confine light to the fiber core. Ordered hole fibers have been fabricated in the past by many groups by drawing an array of glass tubes stacked around a solid central core. These holes are ordered carefully into a predetermined array. In this paper, we describe a new technique to produce holes (or pores) in the cladding region, which are randomly distributed around the solid central core. These new fibers have been made by drawing a preform, consisting of a porous outer cladding region surrounding a solid central core region, into a fiber. A gas producing powder has been incorporated into the preform such that during the fiber drawing process, the pores are formed in-situ in the preform cladding region. This in-situ gas production method produces small diameter, long, thin tubular pores in the fiber. Controlling the processing parameters can control the physical dimensions and distribution of the pores in the fiber. In some of the preforms that have been prepared, the porous cladding region has been prepared by sol gel techniques. In other preforms, the pores have been introduced by a variety of different techniques. The preform fabrication process and fiber drawing process used to produce these new holey fibers as well as the results of the morphological study elucidating the size, shape and distribution of the porous phase are presented.

Pressure measurement in ultra high temperature is very important in a wide array of industries. Optical fiber-based sensing instrumentation is particularly attractive for the measurement of a wide variety of physical and chemical parameters due to their inherent characteristic. Conventional quartz glass fiber-optic sensors show excellent performance in pressure measurement, applications, but they cannot be used for contact measurement at temperatures above 800 °C. Single-crystal sapphire has been extensively used for high temperature measurement over 1000 °C, but very little data was reported for pressure measurement. In order to extend the operating temperature of fiber-optic pressure sensors, a fiber optic pressure sensor utilizing single crystal cubic zirconia as a structure material has been developed. The pressure response of the sensor has been measured from 0 to 1700Psi. Additional experimental results from 23 °C to 1026 °C show that cubic zirconia could be used for pressure sensor at temperatures over 1000°C. This study demonstrated the general functionality of the single crystal cubic zirconia sensor for pressure measurement at high temperatures.

In this paper, we present a novel design of a fiber optic flow sensor system for single-phase fluid flow detection. This new system is based on the principle of broadband interferometry and cantilever beam bending. The fiber optic sensor system utilizes two fiber ferrule sensors that are bonded on both sides of a cantilever beam. The flow rate can be determined by monitoring the air gap changes caused by bending of the cantilever beam. Cross-sensitivity of the temperature and pressure dependence of the sensor can be compensated for automatically. The prototype sensor system was fabricated and tested on the lab-scale with preliminary evaluations completed. Field-testing was performed in the indoor and outdoor flow loops of Tulsa University in Tulsa, Okalahoma. Both the lab-scale and field-testing results verified that the designed flow sensor system could measure the single-phase fluid flow rate with high resolution and repeatability by compensating the thermal and pressure effects of the environment. The outdoor field-testing demonstrated the feasibility of the designed fiber optic flow sensor for single-phase fluid flow rate measurements in the oil fields.

The Ti-doped CdTe semiinsulating crystals of high optical quality were grown by the vertical Bridgman technique. The complex optical, photoelectric and photorefractive measurements of CdTe doped with Ti atoms were carried out. It allowed to our knowledge for the first time to determine the photorefractive characteristics of these crystals. Studies of the optical absorption and photodiffusion current made it possible to determine the nature and energy structure of impurity and intrinsic defects as well as to establish their role in the photorefractive effect. It was shown that the excited ³T₁(P) state is in resonance with the conduction band. As a result of it the auto-ionization of electrons to the conduction band under the laser excitation take place. The energy-level diagram both of impurity and intrinsic defects in the CdTe:Ti crystals was constructed. It was shown that titanium dopant have advantage over other dopants and that CdTe:Ti has better characteristics for a potential applications. Obtained parameters: high optical holographic gain coefficient (up to 0.60 cm^-1), low background absorption (about 0.1 - 0.2 cm^-1), high optical quality and homogeneity, almost electronic type photoconductivity (electron-hole competition factor equals 0.94) show that this material can be effectively used as sensor components for both optical and photoelectric applications in the near infrared region.

Introduced in this paper are a technique of fiber optic dual-wavelength pyrometer and its principle, structure and characteristics. It was successfully applied under the hostile environment in hot-blast stoves to measure high-temperature. The efforts to overcome all difficulties, such as pressure, water vapor, and probe bend caused by thermal expansion, are reported in details. The resulting device is reliable, stable and accurate, and has immunity to harmful gas corrosion. The proposed pyrometer has a long lifetime. Therefore, it can replace the conventional thermo-electric-couple for temperature measurement in a blast furnace.

To develop a nondestructive sugar analyzer for intact apples, the potential of Fourier Transform Infrared (FTNIR) method with bifurcated fiber optic sensor was evaluated. Three different kinds of mathematical treatments (original, first derivative and second derivative) in range of 800-2500nm were discussed. A total of 120 Shandong Fuji apples were tested and 80 of them were used to form a calibration data set. The relationship was established between the diffuse reflectance spectra and the sugar content by means of the partial least squares analysis (PLS) technique. The influence of the data preprocessing was investigated and the optimal wavelength range was also found in the range of 967-1831nm. Depending on data preprocessing and PLS analysis, three predictive models had a correlation coefficients of 0.97, 0.95 and 0.97 with a ratio of data standard deviation to the root mean square error of prediction (SDR) of 3.18 (>3.00), 2.55(<3.00) and 3.23 (>3.00) for original, first derivative and second derivative of spectra respectively; 3.00 was considered the minimum ratio value for only sorting fruit. The results show that the second derivative spectra data gave the best prediction result. It is concluded that the FTNIR method with bifurcated fiber optic sensor yields an accurate estimate of the sugar content in intact apples.

In common with many other application areas, visual signals are becoming an increasingly important information source for many automotive applications. For several years CCD cameras have been used as research tools for a range of automotive applications. Infrared cameras, RADAR and LIDAR are other types of imaging sensors that have also been widely investigated for use in cars. This paper will describe work in this field performed in C2VIP over the last decade - starting with Night Vision Systems and looking at various other Advanced Driver Assistance Systems. Emerging from this experience, we make the following observations which are crucial for "intelligent’ imaging systems: 1. Careful arrangement of sensor array. 2. Dynamic-Self-Calibration. 3. Networking and processing. 4. Fusion with other imaging sensors, both at the image level and the feature level, provides much more flexibility and reliability in complex situations. We will discuss how these problems can be addressed and what are the outstanding issues.

Many of the components associated with the deployment of Intelligent Transportation Systems (ITS) to support a traffic management center (TMC) such as remote control cameras, traffic speed detectors, and variable message signs, have been available for many years. Their deployment, however, has been expensive and applied primarily to freeways and interstates, and have been deployed principally in the major metropolitan areas in the US; not smaller cities. The Knoxville (Tennessee) Transportation Planning Organization is sponsoring a project that will test the integration of several technologies to estimate near-real time traffic information data and information that could eventually be used by travelers to make better and more informed decisions related to their travel needs. The uniqueness of this demonstration is that it will seek to predict traffic conditions based on cellular phone signals already being collected by cellular communications companies. Information about the average speed on various portions of local arterials and incident identification (incident location) will be collected and compared to similar data generated by "probe vehicles". Successful validation of the speed information generated from cell phone data will allow traffic data to be generated much more economically and utilize technologies that are minimally infrastructure invasive. Furthermore, when validated, traffic information could be provided to the traveling public allowing then to make better decisions about trips. More efficient trip planning and execution can reduce congestion and associated vehicle emissions. This paper will discuss the technologies, the demonstration project, the project details, and future directions.

The use of automatic license plate recognition systems for vehicle traffic flow monitoring in congested areas, both metropolitan and state/interstate highway, is the most effective method of determining traffic flow patterns today. The infrared camera image capture systems are robust and the resulting data is fed to a central computer server that calculates travel time across monitored segments in real time. Results are posted within a network environment and can be made available to anyone interested via Internet access to the results. This paper reviews the infrared camera technology in use today, discusses its application to travel time monitoring and reviews a case study documenting the results of a specific travel time study.

Conventional aircraft repair techniques employ bolted or riveted metallic reinforcements, which frequently introduce additional stress concentrations leading to further cracking and creating areas difficult or impossible to inspect. Bonded composite repairs (“patches”) result in the elimination of stress concentrations caused by additional fastener holes, improved strength to weight ratio and present a sealed interface. This reduces even further the danger of corrosion and fretting under the repair, gives greater flexibility in design and lessens application time while lengthening fatigue life. Embedding optical fibres and sensors into the patch, and combining this with advanced data collection and processing systems, creating a so-called “smart patch”, will enable the real-time assessment of aircraft structural integrity resulting in reliable prediction of maintenance requirements for repaired structures. This paper describes the current state of the art in smart patch technology, and includes a detailed description of the measurement problem and of the work being undertaken to solve it, at both the component and system level. An analysis of typical crack behaviour, based on FE modelling is presented and this demonstrates the need for optical strain sensors having a very short gauge length. The paper discusses the advantages and limitations of very short Fibre Bragg Gratings (FBGs) in this context and also provides early experimental data from 1mm and 2mm gratings which have been fabricated for this purpose. The paper also describes the impact of the measurement and environmental constraints on the design of the FBG interrogation system and presents the results of initial trials. The work is being undertaken in the framework of a collaborative project (ACIDS) which is co-funded by the European Commission.

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.

Optical fibre strain sensors using Fibre Bragg Gratings (FBGs) are poised to play a major role in structural health monitoring in a variety of application from aerospace to civil engineering. At the heart of technology is the optoelectronic instrumentation required to convert optical signals into measurands. Users are demanding compact, lightweight, rugged and low cost solutions. This paper describes development of a new device based on a blazed FBG and CCD array that can potentially meet the above demands. We have shown that this very low cost technique may be used to interrogate a WDM array of sensor gratings with highly accurate and highly repeatable results unaffected by the polarisation state of the radiation. In this paper, we present results showing that sensors may be interrogated with an RMS error of 1.7pm, drift below 0.12pm and dynamic range of up to 65nm.

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.

Acoustic emission detection is a well-established method of locating and monitoring crack development in metal structures. The technique has been adapted to test facilities for non-destructive testing applications. Deployment as an operational or on-line automated damage detection technology in vehicles is posing greater challenges. A clear requirement of potential end-users of such systems is a level of automation capable of delivering low-level diagnosis information. The output from the system is in the form of "go’, "no-go’ indications of structural integrity or immediate maintenance actions. This level of automation requires significant data reduction and processing. This paper describes recent trials of acoustic emission detection technology for the diagnosis of damage in composite aerospace structures. The technology comprises low profile detection sensors using piezo electric wafers encapsulated in polymer film ad optical sensors. Sensors are bonded to the structure’s surface and enable acoustic events from the loaded structure to be located by triangulation. Instrumentation has been enveloped to capture and parameterise the sensor data in a form suitable for low-bandwidth storage and transmission.

The 1.7 mm diameter pressure sensor utilizes the principle of light intensity changes, transmitted by two optical fibers, upon reflection from a specially shaped, metal diaphragm deflecting under the effect of pressure. In an ultra low-cost and durable design suitable for automotive applications the sensor compensates for all major temperature effects encountered in combustion engines. The auto-referencing function performed by the sensor’s signal conditioner compensates for the temperature induced LED, photodiode, and fiber-to-opto-electronics coupling errors, sensor thermal drift, as well as fiber bending related light intensity changes. The direct bonding of optical fibers to the photodiode and LED chips results in minimum thermal errors and high part-to-part consistency. Sensor head materials and dimensions are optimized to compensate for the sensitivity changes associated with the diaphragm’s Young’s modulus temperature dependence. The miniature signal conditioner, based on an LED-photodiode transceiver and an ASIC, can be integrated within an automotive connector or a package small enough to fit inside the engine head. Over the signal conditioner temperature range of -40°C to 150°C and the sensor head continuous range of -40°C to 300°C a typical total accuracy of 1-2% is achieved.

Ice accretion on flying surfaces affects the aerodynamic performance and handling qualities of aircraft, and may require different pilot corrective action, dependent upon the surface that ice is accreting onto. The current methodology for ice detection usually relies on an indirect method, normally based on ambient air temperature, and liquid water content. When a pre-set threshold level is reached, the ice protection system is activated, whether or not ice is accreting on critical surfaces. This method is not cost effective or efficient for an ice protection system. Air Conformal Ice Detection System (ACIDS) obviates these problems by using a 'direct’ method of detection and measurement the presence and thickness of ice. This paper outlines some of the preliminary experimental work done on the optical properties of ice grown in an icing tunnel on the leading edge of an aerofoil leading to the development of a Fibre Optic Direct Ice Detector sensor (DID) with emphasis. The result of this studies have shown that with suitable processing it is possible to use fibre optic sensors to determine the thickness of ice and texture of the ice accreted in the vicinity of the sensor. In the latter part of this paper basic fibre optic architecture is discussed and together with some preliminary results for representative icing runs.

The term Intelligent Highway is usually intended to mean external systems that are added to pre-existing highways. However, the ability to construct basic passive electronic elements is demonstrated employing electrically dissimilar Portland cement pastes. These electronic elements include resistors, rectifying pn-junctions, piezoelectric and piezoresistive sensors, and thermocouple junctions. It may therefore be possible to build intelligence into the highway itself utilizing cement-based electronic devices. As compared to semiconductor-based electronic components, those derived from cement have minimal materials and processing costs, do not require clean rooms, and are mechanically more rugged. Results and characterizations are presented for resistive elements and rectifying pn-junctions derived from admixtures of stainless steel fiber (n-type) and carbon fiber (p-type) in Portland cement. These elements are then combined to produce a monolithic cement-based digital logic 2-input AND gate.

Mexico City’s Light Train, one of the electrical transportation systems belonging to the government of Mexico City, services 40,000 passengers daily in the southern sector of the city. Along its trajectory, the Train has to go through several crossings in which safety for vehicles and pedestrians is of paramount importance. We have developed a prototype security system for these crossings based on infrared (IR) detection systems and laser barriers. All the subsystems used in the prototype are controlled by a PC/104 CPU board via the serial communications port and an A/D card. An IR transmitter installed in the train constantly sends information to several receivers deployed at different locations within the crossing. Once the train is detected, the computer activates a set of alarms and barriers in a logical sequence in order to clear the crossing for the train. The laser barrier, formed by a set of eight transmitters and receivers located at different heights within the crossing, is activated as well and is used as a means to detect other emergency situations such as vehicles or pedestrians stranded in the crossing. Discrimination between real and false alarm situations is achieved by encoding both the IR transmitters and the laser beams. In this paper we will discuss experimental and field trials of the prototype system which will be installed in one crossing this year. Once in place, the Light Train of Mexico City will have its first automated crossing.

A new genetic approach to fatigue crack monitoring in aero-engine blades is presented. The approach consists of simultaneously using two diagnostic features: the real and imaginary parts of the Fourier transform of vibroacoustical signals. This approach is more fundamental than traditional approaches based on the power spectral density, phase spectrum and Hartley transform; each of these approaches is a special case of the proposed approach. Numerical examples are given based on the processing of signals generated using a nonlinear model of tested blades. The generated signals are the forced vibroacoustical oscillations of cracked and un-cracked blades. The numerical examples show that crack detection ismore effective when using the new approach than when u sing the power spectral density approach. The presented experimental results using un-cracked and cracked turbuine blades from an aero-engine are matched with numerical results. The proposed approach offers an effectiveness improvement over the traditional approach based on power spectral density.

Monitoring the concentration of gaseous O₂, CO₂ and CH₄ is needed for many environmental, medical and industrial applications. We model the COSM method of correlation spectroscopy, where two broadband light sources are intensity modulated in antiphase, the first being directed via the measurement cell after first passing through the reference sample, the second being more directly-coupled. The subsequent difference in fractional attenuation in the measurement cell indicates the concentration of target gas in this cell. Using data from the HITRAN database, comprehensive analyses are presented to predict the optical modulation index and the signal to noise ratio at the detector, as a function of optical filter properties, and for various gas temperatures and pressures (concentrations). The predicted detection sensitivities are presented for each gas.