Fiber optic sensors based on polymer optical fibers (POF) have the advantage of being very elastic and robust at the same time. Unlike silica fibers, standard PMMA POF fibers can be strained to more than 40% while fully maintaining their light guiding properties. We investigated POF as a distributed strain sensor by analysing the backscatter increase at the strained section using the optical time domain reflectometry (OTDR) technique. This sensing ability together with its high robustness and break-down strain makes POF well-suited for integration into technical textiles for structural health monitoring purposes. Within the European research project POLYTECT (Polyfunctional textiles against natural hazards) technical textiles with integrated POF sensors, among others sensors are being developed for online structural health monitoring of geotechnical structures. Mechanical deformation in slopes, dams, dikes, embankments and retrofitted masonry structures is to be detected before critical damage occurs. In this paper we present the POF strain sensor properties, reactions to disturbing influences as temperature and bends as well as the results of the different model tests we conducted within POLYTECT. We further show the potential of perfluorinated graded-index POF for distributed strain sensing with increased spatial resolution and measurement lengths.

We report on the development of a distributed sensor system for strain measurement using Brillouin optical frequency domain analysis (BOFDA) in single-mode silica optical fibers. Our research aims at the application of the sensor system in flood protection. The sensing fibers are embedded into the soil body of river dikes, where they perform early detection of critical soil displacement. We present a BOFDA setup that performs strain measurements with a spatial resolution better than 3 meters over a length of 2 km. Its accuracy is verified by measurements on a calibrated strain profile as well as several laboratory tests that emulate the stressing of the optical fibers by soil movement. It is shown that the BOFDA approach offers feasible solutions to known critical issues of Brillouin sensing such as spectral broadening at high spatial resolution, digital filtering for enhancement of the dynamic range, and fluctuations of the Brillouin gain due to birefringence.

Low-coherence interferometry (LCI) is an established metrological technique, that has proven its capability to measure both fast and highly accurate. To provide these advantages for the measurement inside small spaces like bore holes or micro-tubes, the design of a miniaturized probe tip is necessary. The use of fiber optics fulfills the requirements for the realization of flexible and small probes, which are at the same time suitable for lowcoherence interferometry. In this work the development of miniaturized probes in all-fiber design for the use in a LCI system is described, which consists of a modified Michelson interferometer with non-moving optical elements. Beam shaping is achieved by the use of graded-index fibers. Thus sensor tip diameters can be reduced down to 125μm for bare fiber design. Furthermore, validation measurements for the combination of probe head and LCI system are presented, that prove the potential and limitations of all-fiber probes for LCI. Conclusively an outlook for potential fields of application is given.

Optical fibre sensors are attractive devices that can bring substantial advantages over conventional sensing approaches for fission Material Testing Reactors (MTRs), such as high accuracy capabilities with limited intrusiveness and the ability to withstand high temperature. In the framework of the Joint Instrumentation laboratory (JIL), CEA and SCK CEN have joined their resources to develop, in particular, an OFS prototype with the aim to measure dimensional changes on nuclear materials irradiated in MTRs. We briefly present the objectives and the workplan of that project, in which the first phase addressed an analysis of the different measurement systems considered towards the specific environmental conditions encountered in a fission reactor. Among them, radiation is responsible for the biggest error source through the density change of silica glass due to neutron-induced compaction. The analysis has leaded us to focus mainly on an Extrinsic Fabry Perot design based on low coherence interferometry. As part of the current development, we present the results of table top experiments that allow appreciating the variation with different parameters of the response, especially the modulation of the signal returned. That permits to set partially the design and brings some tolerances data. A home made signal conditioning allows to extract the cavity length and then the change in the dimension of the sample to test.

Weakly tilted fiber Bragg gratings with gratings planes tilted at small angles with respect to the fiber axis couple light to backward going core mode and cladding modes. Their transmitted spectrum is characterized by narrow resonance dips below the Bragg wavelength corresponding to the core mode coupling. The amplitude spectral evolutions of weakly tilted fiber Bragg gratings in response to diverse physical perturbations such as temperature, mechanical strains, bending and surrounding refractive index changes are presented. Different techniques allowing to efficiently correlate the spectral evolution with the information to be measured are reported. We demonstrate that a selective monitoring of one cladding mode shift with respect to the Bragg wavelength gives temperature-insensitive strain measurements whereas a global monitoring of the cladding modes spectrum offers temperature-insensitive surrounding refractive index measurements. We also point out the possibility of using this global monitoring for bending and transverse strain sensing purposes. Finally, we present the effect of coating (the grating is covered by a polymer) on the sensitivity of weakly tilted fiber Bragg grating to surrounding refractive index changes. For every application, the performances of weakly tilted fiber Bragg gratings sensors are discussed.

Strain sensitivities of free, uncoated fiber Bragg gratings at λ_B ~1535 nm in a SMF28 standard telecommunication fiber and in a highly GeO₂ doped photosensitive fiber (F86) were determined at room temperature. Both fibers showed similar strain sensitivities of k^SMF28 = (0.7951 ± 0.0041) for the SMF28 and k^F86 = (0.7912 ± 0.0023) for the F86 fiber. The stress sensitivities of both fibers were found to be slightly different with the values of (Δλ/F)^SMF28 = (1.347 ± 0.006) nm/N for the SMF 28 fiber and (Δλ/F)^F86 = (1.309 ± 0.001) nm/N for the F86 fiber.

The ionizing radiation response of fiber Bragg gratings (FBGs) as a function of grating fabrication parameters and fiber characteristics has been investigated in a number of studies. In the present work we analyze a particular aspect of the problem, which was not considered up to now: the influence of the fiber coating on the radiation sensitivity of FBGs. The FBGs used in our study are draw tower gratings written before applying the coating in a fiber with a photosensitive 18 mol.% GeO₂-doped core. We irradiated polyimide, acrylate and ormocer coated gratings as well as mechanically stripped ormocer coated FBGs using a Co60 radiation source up to a 40 kGy dose. This total dose level corresponds to a near-Earth space radiation environment mission. We show that the coating type must be taken into account for correctly interpreting ionizing radiation effects on FBGs. Our analysis also shows that a properly designed coating can enhance or decrease the grating radiation sensitivity. Therefore, the results are of interest for both dosymetry and space communication applications of the FBGs.

Shown for the first time is the fabricated all-Single crystal Silicon Carbide (SiC) temperature probe and interface assembly designed for extreme environment temperature sensing in a gas turbine test rig. Preliminary probe test results are described regarding SiC chip temporal response, optical beam stability, and near vacuum sealing.

For a plastic optical fiber based refractometer system the influence of the directivity of the fiber coupler on the achievable resolution is analysed. It is also shown that provided the fiber length between the sensing tip and receiver is less that 2 m that interference due to Rayleigh backscatter will not comprise operation of the refractometer. A novel coupler based on a hybrid silica fiber-plastic fiber design is used experimentally to provide a comparison to the modelled results. It is shown that the high directivity (>35 dB) of this coupler can significantly enhance the resolution of the refractometer.

In this work, the feasibility of exploiting novel Cadmium Arachidate (CdA)/single-walled carbon nanotubes (SWCNTs) based composites as sensitive coatings for the development of robust and high performances optoelectronic chemosensors able to work in liquid environments has been investigated and proved. Here, nano-composite sensing layers have been transferred upon the distal end of standard optical fibers by the Langmuir-Blodgett (LB) technique. Reflectance measurements have been carried out to monitor ppm concentration of chemicals in water through the changes in the optical and geometrical features of the sensing overlay induced by the interaction with the analyte molecules. Preliminary experimental results evidence that such nanoscale coatings integrated with the optical fiber technology offers great potentialities for the room temperature detection of chemical traces in water and lead to significant improvements of the traditional fiber optic sensors based on SWCNTs layers.

HyperSpectral Imaging (HSI) is based on the utilization of an integrated hardware and software (HW&SW) platform embedding conventional imaging and spectroscopy to attain both spatial and spectral information from an object. Although HSI was originally developed for remote sensing, it has recently emerged as a powerful process analytical tool, for non-destructive analysis, in many research and industrial sectors. The possibility to apply on-line HSI based techniques in order to identify and quantify specific particulate solid systems characteristics is presented and critically evaluated. The originally developed HSI based logics can be profitably applied in order to develop fast, reliable and lowcost strategies for: i) quality control of particulate products that must comply with specific chemical, physical and biological constraints, ii) performance evaluation of manufacturing strategies related to processing chains and/or realtime tuning of operative variables and iii) classification-sorting actions addressed to recognize and separate different particulate solid products. Case studies, related to recent advances in the application of HSI to different industrial sectors, as agriculture, food, pharmaceuticals, solid waste handling and recycling, etc. and addressed to specific goals as contaminant detection, defect identification, constituent analysis and quality evaluation are described, according to authors' originally developed application.

The classical streak cameras use a vacuum tube making thus fragile, cumbersome and expensive. The FAst MOS Imager (FAMOSI) project consists in reproducing completely this streak camera functionality with a single CMOS chip. The advantages of on-chip functionalities lead to a power reduction, a lower cost and miniaturization. In this paper, we show the capabilities of a prototype fabricated in the AMS 0.35 μm CMOS process. The chip is composed of 64 columns per 64 rows of pixels. The pixels have a size of 20 μm per 20 μm and a fill factor of 47 %. The Chip FAMOSI implements an electronic shutter and an analog accumulation capability inside the pixel. With this pixel architecture, the sensor can work in single shot mode when the light pulse power is sufficient and in repetitive mode, i.e. it can measure a recurrent light pulse and accumulates the successive photo charges into an internal node, for low light pulse detection. This repetitive mode utilizes an analog accumulation in order to improve the sensitivity and the signal to noise ratio of the system. Characterizations under static and uniform illumination in single shot mode have been done in order to evaluate the performances of the detector. The main noises levels have been evaluated and the experiments show that a conversion gain of 4.8 μV/e^- is obtained with a dynamic range of 1.2V. Moreover, the charge transfer characterization in single shot mode has been realized. It permits to know which potential must be apply to the charge spill transistor to obtain the whole dynamic of the output with a maximal transfer gain, what is primordial to optimize the analog accumulation. Finally, the dynamic operation of the sensors is exposed. Measurements show a sample time of 715 ps and a time resolution better than 2 ns. A 6 ns light pulse has been measured in single shot and in accumulation mode.

HDRC (high dynamic range CMOS) allows for more than 120 dB signal range in image processing. Scene details with both very high and extremely low radiant flux may thus appear within the same image. Color constancy over the entire signal range and good high speed performance are further aspects of this logarithmic imager technology. These features qualify HDRC cameras for thermography, since the signal range of Planck's temperature radiation in a two dimensional array is comparable to HDRC's intensity range. Especially in material welding and laser cutting processes, in high power light sources and in high temperature material processing, fast monitoring of the spacial and dynamic temperature distributions present a challenge to conventional thermal imaging and thus call for innovative concepts. A particular challenge is in the compensation of the emissivity of the radiating surface. Here, we present a new concept based on a modified HDRC VGA color camera, allowing for visualization and measurement of temperatures from about 800 °C up to 2300 °C. The modifications include an optical filter for minimizing UV and IR straylight and a notch filter for clipping off the green optical range in order to separate the blue and red RGB regions. An enhanced and adapted software provides a division of the neighboured red and blue pixel signals by means of simply subtracting the HDRC signals. As a result the local temperature information of the visualized scene spot is independent of emissivity. This is, to our knowledge, the first demonstration of a high speed thermal imager to date.

In this contribution we present the results of the first morphological and electro-optical characterization of Silicon Photomultipliers (SiPM) for nuclear medical imaging applications fabricated in standard silicon planar technology at the STMicroelectronics Catania R&D clean room facility. We have improved our previous Geiger Mode Avalanche Photodiodes (GMAP) technology in order to realize a photodetector with relevant features in terms of single-photoelectron resolution, timing and photon detection efficiency. The performances of our devices, investigated in several experimental conditions and here reported make ST-SiPM suitable in many applications like for example PET (Positron Emission Tomography).

In this work we present experimental results of silicon-only bipolar phototransistors fabricated in a 0.35μm commercial BiCMOS technology without process modifications. The transistors are characterized over a wide optical spectral range at 410nm, 675nm, 785nm, and 850nm, providing significantly improved -3dB bandwidths up to 390MHz @ 410nm light and responsivities of 1.76A/W @ 675nm corresponding to quantum efficiencies of 359% normalized in terms of the quantum efficiency of a silicon photodiode.

Position sensitive detectors (PSDs) comprise optical sensors used in applications such as robotic vision, machine tool alignment and other precision measurements. This paper will report on a series of Schottky Barrier crystalline silicon devices which display marked advantages including rapid response times, easier fabrication techniques and high sensitivities compared with most other research work now being concentrated on PECVD amorphous silicon structures. In this work, results from devices fabricated from substrates with a range of resistivities and various Schottky metals are presented. Some of the sensitivity measurements obtained are better than 25 mV/mm which are some of the best sensitivities reported for Schottky barrier crystalline PSDs. These results were obtained coincidentally with excellent linearities. Devices were also tested under a range of light beams including very low broadband white light levels of 0.1mW up to 10mW. The highest and most linear outputs occurred under different conditions for each substrate resistivity and Schottky metal. Also observed were the different effects that background illumination had on each set of devices, the biggest effect being on the highest resistivity devices.

Within this work a new correlating photodetector concept using current carrying photogates for Time-Of-Flight (TOF) based optical distance measurements is presented. The integrated photodetector consists of a PIN setup with a P+ doped anode, two N+ doped cathode fingers and a wide low doped intrinsic region in between. Furthermore a resistive polysilicon photogate is located in between of the readout cathode fingers on top of field oxide. Applying an electrical modulation signal to this photogate causes a linear potential drop along the resistor as a result of the control current. Therefore constant electric field is achieved in the photodetector regions below thus effecting photogenerated electrons to be directed to one or the other cathode, depending on the sign of the field. While positive charges are collected by the anode below, the modulation signal controls whether photocurrent of incident light is led to readout cathode 1 or 2. Due to this setup, applied modulation signals cause an optimal potential distribution for efficient correlation of η_sep=80% with incident optical signals. A responsivity of 0.23A/W {0.21A/W}, a rise time of 19.3ns {18.3ns} and a bandwidth of f_-3dB=22.7MHz {29.6MHz} is measured at 660nm {850nm} together with low dark current of I_dark<0.5pA. The capability of this photodetector is demonstrated at an integrated rangefinder chip in a range of 1.5m-3.5m achieving a standard deviation of σ<5cm at a white paper target and an optical power of P_opt=1.5mW. A comparison of three realized photodetectors with different shapes of the photogate is done, each with an active area of 100μm×100μm and processed in 0.6μm BiCMOS.

We present a compact and cheap sensor device based on the combination of a standard RGB-LED with a luminescence material. The multicolor LED acts as the exciting light source, the luminescence light detector and simultaneously as an optical filter. As luminescence material various phosphor materials or crystals can be used, depending on the physical property to be sensed. Possible applications will be discussed.

We report on the fabrication of Schottky-diode-based Extreme UltraViolet (EUV) photodetectors. The devices were processed on Gallium Nitride (GaN) layers epitaxially grown on 4 inch Silicon (111) substrates by Metal-Organic Chemical Vapor Deposition (MOCVD). Cutoff wavelength was determined together with the spectral responsivity measurements in the Near UltraViolet (NUV) range (200nm to 400nm). Absolute spectral responsivity measurements were performed in the EUV range (5nm to 20nm) with the synchrotron radiation using the facilities of Physikalisch- Technische Bundesanstalt (PTB), located at Berliner Elektronenspeicherring-Gesellschaft fuer Synchrotronstrahlung (BESSY). The described work is done in the framework of the Blind to Optical Light Detectors (BOLD) project supported by the European Space Agency (ESA).

The reliability of bipolar silicon-based phototransistors was investigated through evaluation tests for space applications. First of all a preliminary evaluation program including thermal cycling, vibrations and shocks test, radiation test and high-temperature operating life test was carried out to assess the overall quality of these phototransistors. During life test abnormal fluctuations of phototransistors collector current measured under constant illumination have been observed. In order to solve this problem, a failure analysis was conducted. Mobile charges located in the photobase passivation layer were found to be at the origin of these fluctuations. Based on these results a new methodology for device selection was proposed to achieve, despite to that issue, high reliability in operating conditions.

Dimension measurements in metal production are getting increasingly important to improve quality and yield. One important measurement is thickness profile, in this case of copper strip. Knowing the strip profile in entrance and exit side of milling line helps optimizing the milling depth and give information about tool wearing. In this study a comparative measurement method was traversing point measurement system. It gives profile as a series of points which take a relatively long time to measure. Now presented method is based on two-side optical triangulation formed by line illuminators and CMOS-cameras and enables instantaneous thickness profile measurement. Results from both sides are fixed together using reference plates on both ends of the measurement area. From 1.3 m stand-off distance, 1.4 m wide measurement area is achieved. This paper presents the measurement method and results of laboratory and on-line tests. Using laser line illumination the accuracy of thickness was 150 μm when measuring 9 mm thick test plate. Accuracy was limited by laser speckle during static calibration. Other illumination method based on white light was therefore tested and the accuracy was 12 μm correspondingly. Measurement time for one profile was 1 second and resolution in cross machine direction 50 mm after averaging. Now presented method enables thickness profile measurement of copper and other metal sheets. Using white light the accuracy is at same level as the present traversing point measurement. Method has also continuous reference measurement to compensate errors caused by vibration; therefore the system can be realized at reasonable cost.

In this paper a new spectroscopic analysis technique is proposed for on-line welding quality monitoring. This approach is based on the estimation of the wavelength associated with the maximum intensity of the background signal (continuum) of the welding plasma spectra. It will be demonstrated that this parameter exhibits a clear correlation with the welding quality of the seams, as it also happens with the traditional spectroscopic approach based on the determination of the plasma electronic temperature, thus allowing an identification of the appearance of weld defects. This technique offers a relevant improvement in terms of computational performance, what enables to detect smaller defects within the seam.

In this work a new method for calculating the optical properties of an absorbing film grown on substrates, including the real and imaginary part of the index of refraction is shown. In particular the thermal radiation of a growing oxide-film on a heated steel specimen is measured by a CCD camera with a near infrared (1000nm) band-pass filter. The observed radiation-signal shows significant temporal patterns due to interferences in the growing oxide film. Under the assumptions of known specimen temperature, constant optical properties (dielectric functions) of each layer and semitransparent films, it is possible to develop a model by which variations of the resulting emissivity with varying film-thickness can be explained. From this model, which is derived from the calculation of the reflectance of a thin absorbing film on an absorbing substrate, the complex index of refraction of the film can be determined without explicit knowledge of the optical constants of the respective layers. Since a matrix-camera is used to monitor the process changes of the emissivity over time, spatial information may also be derived. In this way it is possible to detect spatial inhomogeneities in the film and to determine the cause (either inhomogeneous growth rates or spatial variations of material properties). In addition, these results can be used for emissivity correction in non-contact thermal imaging. This method is not limited to oxide films and can be used for other heat treatment processes that deposit semitransparent films as well.

This paper presents a zero-crossing detection algorithm for arrays of compact low-cost optical sensors based on spatial filtering for measuring fluctuations in angular velocity of rotating solid structures. The algorithm is applicable for signals with moderate signal-to-noise ratios, and delivers a "real-time" output (0-1 kHz). The sensors use optical spatial-filtering velocimetry on the dynamical speckles arising from scattering off a rotating solid object with a non-specular surface. The technology measures the instantaneous angular velocity of a target, without being biased by any linear translation of the object. The calibration of the sensors is independent of the radius of the target, the wavelength of the light, and the distance to the object. No preparation of the surface, as is needed in the case of an indexer, is necessary here. Furthermore, any thermal dependency of the calibration factor is directly related to the thermal expansion and refractive-index coefficients of the optics (>10^-5 K^-1 for glass). By cascade-coupling an array of sensors, the ensembleaveraged angular velocity is measured in "real-time". This will reduce the influence of pseudo-vibrations arising from repeating the same measurement error for each revolution of the target, and to gain high performance measurement of angular velocity. The traditional zero-crossing detection is extended by 1) inserting an appropriate band-pass filter before the zero-crossing detection, 2) measuring time periods between zero-crossings and 3) doing peak searches in the histograms of time-periods facilitating measurement at low signal-to-noise levels. This algorithm will be compared with time-resolved Fourier analysis.

A digital seismic measuring chain is an electromechanical system able to record the lowest natural ground motions observable on Earth but also to measure signals from largest earthquakes. Its cornerstones are an inertial seismometer and a digitizer. As equipments available on the market don't answer to all seismological applications CEA/DASE (Commissariat a l'Energie Atomique/Departement analyse, surveillance, environnement) is interested in, it has developed the adequate digital seismic measuring chains. Today, the technologies used have reached their maturity. New sensing techniques need to be developed. Optical sensors are now widely used in vibrometry and displacement measurements. Such devices generally use interferometry to achieve subnanometric resolution with a large dynamic range. We have developed a prototype digital motion transducer from a Michelson interferometer in order to evaluate the potential of this technology for seismological applications. Tests were carried out to validate the operation of this transducer and to estimate its main characteristics for seismological applications. We focused on transducer motion range and intrinsic noise. Results are promising. Prototype intrinsic noise reaches levels as small as 100 fm/√Hz around 8 Hz and is better than that of present transducers all over the bandwidth of interest, motion range also. Interesting seismological applications can be considered leading to more accurate seismic measuring chains, easier to manufacture, deploy and operate.

Since many years one of the topic our research team are multi-parametric fiber optic polarization sensors. In the paper is presented a new version of the Fiber-Optic Interferometric Polarization Analyzer (FOIPA). This system is based on modified Sagnac interferometer and it was equipped with automatic current driven polarization controllers driven by special analog output card and detection system based on data acquisition card and LabVIEW software. This system was called full automatic fiber optic interferometric polarization analyzer. Used in the system automatic, temperature driven polarization controllers allow working in feedback electronic loop with data acquisition system and they function as calibration and stabilization subsystem. Specially developed detection system allow measuring amplitudes of first three tones of the AC parts of two electric signals as well as they DC voltages. That advantages have given possibility replaced an expensive lock-in amplifier and make data performance and polarization parameters calculation more faster and easier. It was necessary to implement special procedure to proper SOP identification In the paper are presented theoretical and experimental analyzes of the uncertainties, also. Finally a comparison with commercially available polarization analyzer is shown.

While building and adjusting interferometric sensors it is useful to have a clear picture of how different adjustment errors may affect optical properties of the device. While operating the interferometer it is helpful to know how different sensitivities of the instrument influence the measurement. The well-known matrix method provides a convenient means to study these effects systematically in a first order of approximation. It can be applied to calculate the influence of axial misadjustment errors, the influence of tilts as well as the effect of decentering. It will be illustrated that a relatively limited set of mathematical approaches suffices to treat these sensitivities and to study their interplay. It forms a kind of toolbox that can be used to analyze interferometer layouts in a straightforward way. The emphasis will be laid on two-beam interferometers that are described after unfolding the reference and the measurement arm, respectively. The method is advantageous to check compensation schemes and it does allow for a first-order balancing of the arms of two-beam interferometers. Extension to anamorphic optical systems, i.e. optical arrangements that feature a low symmetry, is possible and the influence of a rotation error with respect to the optical axis can be investigated as well. An advantage of the matrix approach can be seen in the fact that it also facilitates to communicate essential features of the interferometric device in a concise way. The attempt is made to present it in a way that it might be applied to a variety of interferometric sensors.

The paper deals with design and implementation of an optical extensometer based on grating (moire) interferometry, for large engineering construction monitoring. The paper presents the principles of the grating interferometry and the construction of miniaturized and portable version of grating interferometer and its implementation for out-door measurement directly at civil engineering structures. The paper presents also a concept of the low-cost full-field optical extensometer.

For translation and tilt metrology, we developed a compact fiber-coupled polarizing heterodyne interferometer which is based on a highly symmetric design where both, measurement and reference beam have similar optical pathlengths and the same frequency and polarization. The method of differential wavefront sensing is implemented for tilt measurement. With this setup we reached noise levels below 5 pm/square root of Hz; Hz in translation and below 10 nrad/square root of Hz; in tilt measurement, both for frequencies above 10^-2 Hz. While this setup is developed with respect to the requirements of the LISA (Laser Interferometer Space Antenna) space mission, we here present the current status of its adoption to industrial applications. We currently design a very compact and quasi-monolithic setup of the interferometer sensor head based on ultra-low expansion glass material. The resulting compact and robust sensor head can be used for nano-positioning control. We also plan to implement a scan of the measurement beam over the surface under investigation enabling high resolution 3D profilometry and surface property measurements (i. e. roughness, evenness and roundness). The dedicated low-noise (≤1nm/square root of Hz) piezo-electric actuator in the measurement beam of the interferometer will be realized using integrated micro-system technology and can either be implemented in one or two dimensions.

We will describe optical and electrical effects in photorefractive materials- in semiconductors and semiconductor-ferroelectric crystals. Double-functional (optical and electrical) interferometer was realized using holographic recording of dynamic gratings in the semiconductor crystal of CdTe: V. Two mechanisms of holographic phase grating recording is considered: electro-optic effect (relatively slow, in microsecond) and free-carrier gratings {Drude-Lorentz nonlinearity, fast response in nanoseconds). Fast optical response, based on Drude-Lorentz nonlinearity (also called plasma nonlinearity) play essential role in the surface- plasmon resonance phenomena.

In this paper, we proposes a general model for describing and analysing the operation of the multimode fiber optic gyroscope (MFOG). In this model, each fiber gyroscope components is modeled by an electrical field transfer matrix. The output intensity is expressed in terms of the rotation rate and of the components parameters. The simulation results show that performances enhancement can be obtained by employing a symmetrical multimode coupler and low coherent light source.

We report on the design and test of the optical subsystem of the T2L2 (Time Transfer by Laser Link) space instrument. The T2L2 experiment, developed by OCA and CNES is a next generation optical time transfer system that will allow an improvement^1,2 by one to two orders of magnitude as compared to the performances of existing microwave time transfer systems like GPS or Two-Way. The principle is derived from satellite laser ranging (SLR) technology with dedicated space equipment embarked on the satellite Jason 2, scheduled for launch in mid-2008. Satellite Laser Ranging stations (connected to the clocks to be synchronized) emit short laser pulses towards the satellite where they are equally reflected and dated by an onboard event timer. The departure and return of the laser pulses are also timed in the laser stations. The time transfer is derived aposteriori from the data triplets (departure, satellite, return) acquired on the satellite and the respective laser stations. The T2L2 instrument consists of an optical and an electronic subsystem. The optical subsystem is designed such that its field of view (FOV) covers the whole earth for the Jason 2 orbit. It features a linear and a non-linear channel consisting of optical elements and avalanche photodiodes; the linear channel's purpose is threefold: it triggers the whole timing system and measures both the background light and the laser pulse energy. The non-linear channel is for precise timing. We report on the detailed construction of the optical assembly and an exhaustive calibration and performance test campaign in terms of metrology. This test campaign was performed in the clean-room facilities at CNES, Toulouse in March/April 2007 with a dedicated test bed featuring a mode locked laser, variable geometry for different incidence angles and a reference timing system.

In time-of-flight laser distance measurement a nanosecond-class laser pulse is reflected off a target, and the distance to the target is calculated from the flight time of the pulse. The distance measurement precision is directly proportional to the jitter of the pulse (i.e. the uncertainty of the arrival time of the pulse due to noise). In this work, the effect of signal quantum shot noise on the jitter of detected laser pulses was researched. It was discovered that signal quantum shot noise drives the optimal detection level of the pulse lower because shot noise increases along with received pulse power. The effect is more significant with an AP-diode receiver than with a PIN diode receiver due to the avalanche multiplication of shot noise in an AP-diode. This jitter phenomenon was modeled in Matlab, and the result was verified by measurements.

Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV) are commonly used in the analysis of particulates in fluid flows. Despite the successes of these techniques, current instrumentation has placed limitations on the size and shape of the particles undergoing measurement, thus restricting the available data for the many industrial processes now utilising nano/micro particles. Data for spherical and irregularly shaped particles down to the order of 0.1 µm is now urgently required. Therefore, an ultra-fast LDA-PIV system is being constructed for the acquisition of this data. A key component of this instrument is the PIV optical detection system. Both the size and speed of the particles under investigation place challenging constraints on the system specifications: magnification is required within the system in order to visualise particles of the size of interest, but this restricts the corresponding field of view in a linearly inverse manner. Thus, for several images of a single particle in a fast fluid flow to be obtained, the image capture rate and sensitivity of the system must be sufficiently high. In order to fulfil the instrumentation criteria, the optical detection system chosen is a high-speed, lensed, digital imaging system based on state-of-the-art CMOS technology - the 'Vanilla' sensor developed by the UK based MI3 consortium. This novel Active Pixel Sensor is capable of high frame rates and sparse readout. When coupled with an image intensifier, it will have single photon detection capabilities. An FPGA based DAQ will allow real-time operation with minimal data transfer.

The photon correlation Laser Doppler Anemometers were developed to measure the flow velocity also in the nanometer particle range. An LDA signal processing method has been developed for dividing the raw data line of photon correlation LDA into shorter parts corresponding to single particle transit (burst). The commonly used Lee filter was applied with some modification and an intelligent burst finding algorithm was developed. By this way the LDA system was adapted for single particle counting. The complete simulation algorithm gives an opportunity for discussing the burst selecting and so the particle counting efficiency as a function of the SNR. Size estimation from the burst size was discussed and compared to the model-based signal processing technique. The minimum detectable particle size was estimated.

Organic light-emitting diodes (OLEDs) permit the monolithic integration of microelectronic circuits and light-emitting devices on the same silicon chip. By the use of integrated photodetectors, low-cost CMOS processes and simple packaging; economically produced optoelectronic integrated circuits (OEICs) with combined sensors and actuating elements can be realized. The OLEDs are deposited directly on the top metal layer. The metal layer serves as electrode and defines the bright area. Furthermore, the area below the electrodes can be used for integrated circuits. Due to efficient emitter with low operating voltage it is possible to renounce high-voltage devices depending on selected CMOS process. Thus manufacturing cost can be further reduced. Different CMOS metallizations were examined and their effects on organic light-emitting diodes were analyzed. Red (628nm) and orange (597nm) emitting p-i-n OLEDs with a radiance of 5W/m²sr at 2.8V and 3.0V and a half angle of ±45° were realized on metal layer with low roughness. Near infra-red emitters are in development. We will present an optical microsystem. The functionality of combined sensors and actuating elements as well as advantages and difficulties of the monolithic integration of OLEDs and CMOS will be discussed. The chip was manufactured in a commercial 1μm CMOS technology. The fabricated microsystem combines three different types of sensors: a reflective sensor, a colour sensor and a particle flow sensor.

We propose and experimentally demonstrate an angle-multiplexing based optical structure for verifying a credit card. Our key idea comes from the fact that the fine detail of the embossed hologram stamped on the credit card is hard to duplicate and therefore its key color features can be used for distinguishing between the real and counterfeit ones. As the embossed hologram is a diffractive optical element, we choose to shine one at a time a number of broadband lightsources, each at different incident angle, on the embossed hologram of the credit card in such a way that different color spectra per incident angle beam is diffracted and separated in space. In this way, the number of pixels of each color plane is investigated. Then we apply a feed forward back propagation neural network configuration to separate the counterfeit credit card from the real one. Our experimental demonstration using two off-the-shelf broadband white light emitting diodes, one digital camera, a 3-layer neural network, and a notebook computer can identify all 69 counterfeit credit cards from eight real credit cards.

There has been much research performed in recent years on tunable diode laser spectroscopy for detection of gases such as methane, carbon dioxide, acetylene, etc., which possess near-IR absorption lines. To attain adequate sensitivity with weak near-IR lines, wavelength modulation spectroscopy with phase-sensitive detection is normally employed. However injection current modulation of diode lasers produces both wavelength and amplitude modulation, with a phase shift dependent on the modulation frequency. This results in residual amplitude modulation on the output and in distortion of the harmonic signals derived from the absorption line. These are important issues for calibration and where it is desired to accurately recover the line-shape function in order to make simultaneous measurements of gas concentration, pressure or temperature in industrial applications. Here we discuss how calibration-free measurements may be obtained with diode lasers and explore the implications for fibre laser based systems for spectroscopy which conventionally employ thermal or piezoelectric tuning of the wavelength. In particular, we consider modulation techniques which may be applied to ring fibre lasers which use un-pumped erbium fibre as a saturable absorber to prevent mode-hopping or to DFB fibre lasers which use a short cavity with a Bragg grating to ensure single mode operation.

We present a novel surface plasmon resonance (SPR) sensor based on an integrated planar and polychromatic light source. The sensor comprises an organic light emitting diode (OLED) and a metallic sensing layer located on opposite sides of a glass prism. We successfully fabricated and tested prototype sensors based on this approach by the use of different prism geometries and OLEDs with blue, green and red emission color. We investigated the angular and wavelength dependent SPR dispersion relation for sensing layers consisting of silver and gold of different thicknesses in contact with air. Further on we demonstrated the sensor function by real time monitoring of temperature changes inside an adjacent water reservoir as well as by recording the dissolving process of sodium chloride in water. This shows that the configuration can in principle be used for bio-sensing applications. The presented technique offers the advantage that there is no necessity to couple light from external bulky sources such as lasers or halogen lamps into the sensing device which makes it particularly interesting for miniaturization. The presented SPR configuration can be monolithically integrated on one common substrate. Furthermore it is compatible with the planar glass light pipe platform for SPR sensing and the two-color approach for the determination of the thickness and the dielectric constant of thin films in a single experiment.

Within the Built and Natural Environment early analysis of structural conditions, air quality monitoring, pollutant and irritant detection by optical sensor technology is advancing. Combining the two technologies, Surface Plasmon Resonance (SPR) and Surface Enhance Raman Scattering (SERS) into a single instrument is the aim of the research, with a resulting fingerprint library of measurands being produced. The combo sensor will provide unique fingerprints of the measurands, monitoring conditions, such as the carbonation of concrete, microbial and chemical loading and ageing effects of structures, along with their severity. Analysed conditions will be crossed referenced with the library allowing smart feedback for timely maintenance. SPR and SERS work on the principle that specific surfaces, when excited by a light source passing through a glass prism, will change their rate and scale of vibration when their surface holds or is contaminated by particular a component, in this case the monitoring condition analyte. A ligand, which binds specifically to the monitoring analyte, is held in specialised surface coatings which are applied to the surface of the sensor glass or prism itself. The sensing takes place through detection of differences in the original laser light source and reflections/refractions of that light source from the glass prisms. The advances and obstacles of early research are discussed along with initial results and findings being examined in the development a new optical combo sensor.

A compact, integrated photoluminescence based oxygen and pH sensor, utilizing an organic light emitting device (OLED) as the light source and an organic photodiode (OPD) as the detection unit, is described. The main challenge in such an integrated sensor is the suppression of the excitation light at the detector, which is typically by many orders of magnitude higher in intensity than the emitted fluorescence. In our approach we refrain from utilizing edge filters which require narrowband excitation sources and dyes with an adequate large stoke shift. We developed an integrated sensor concept relying on two polarizers to separate the emission and excitation light. One polarizer is located right after the OLED, while the other one, oriented at 90° to the first, is placed in front of the OPD. The main advantage of this solution is that any combination of excitation and emission light is acceptable, even if the two signals overlap spectrally. This is especially important for the use of OLEDs as the excitation sources, as these devices typically exhibit a broad spectral emission.

A direct laser writing process has been exploited to fabricate a high order Bragg grating on the surface of a porous silicon slab waveguide. The transmission spectrum of the structure, characterized by a pitch of 10 µm, has been investigated by end-fire coupling on exposure to vapor substances of environmental interest. The analyte molecules substitute the air into the silicon pores, due to the capillary condensation phenomenon, and the transmitted spectrum of the grating shifts towards higher wavelengths. The experimental results have been compared with the theoretical calculations obtained by using the transfer matrix method together with the slab waveguide modal calculation.

The development of new radiation sources has a major impact on the progress of optical trace gas detection. Particularly distributed feedback (DFB) diode lasers have proven to be very useful devices for spectroscopic sensors due to their spectral purity, direct modulation via the injection current, their small size and low acquisition cost. In this contribution we present a new sensor for hydrofluoric acid (HF), based on a room temperature DFB diode laser at 2.47 μm in combination with a photoacoustic detection scheme. The sensor enables detection of HF concentrations of less than 10 ppb with an excellent selectivity.

The ALADIN Instrument is a Doppler Wind Lidar aboard the ESA Core Explorer Aeolus Mission. The main purpose of this payload is the measurement of tropospheric wind profiles on a global scale. The concept is based on a solid-state Nd:YAG laser associated with a direct detection frequency receiver. An optical structural and thermal model (OSTM) of the instrument has been developed to validate at an early stage of the programme the stability of the instrument. In particular, the WFE and defocus stability of the 1.5 m diameter Silicon Carbide Telescope is a critical issue regarding instrument performances. In order to test the WFE and defocus stability under thermal vacuum, a dedicated sensor has been developed. This Sensor is based on the Shack Hartman principle. The aim of the sensor is to measure the telescope primary mirror deformations in a confocal configuration by adapting a set of small mirrors on the mirror surface. The challenge was to keep these mirrors stable to better than 0.1μm decenter/0.1μrd rotation to allow unbiased monitoring of the WFE and defocus under thermal vacuum. Experimental results show the high measurement sensitivity achieved by the Hartman optical sensor.

Fibre-reinforced plastics (FRP) are particularly suitable for components where light-weight structures with advanced mechanical properties are required, e.g. for aerospace parts. Nevertheless, many manufacturing processes for FRP include manual production steps without an integrated quality control. A vital step in the process chain is the lay-up of the textile preform, as it greatly affects the geometry and the mechanical performance of the final part. In order to automate the FRP production, an inline machine vision system is needed for a closed-loop control of the preform lay-up. This work describes the development of a novel laser light-section sensor for optical inspection of textile preforms and its integration and validation in a machine vision prototype. The proposed method aims at the determination of the contour position of each textile layer through edge scanning. The scanning route is automatically derived by using texture analysis algorithms in a preliminary step. As sensor output a distinct stage profile is computed from the acquired greyscale image. The contour position is determined with sub-pixel accuracy using a novel algorithm based on a non-linear least-square fitting to a sigmoid function. The whole contour position is generated through data fusion of the measured edge points. The proposed method provides robust process automation for the FRP production improving the process quality and reducing the scrap quota. Hence, the range of economically feasible FRP products can be increased and new market segments with cost sensitive products can be addressed.

In this paper, we propose and experimentally demonstrate a pressure sensor based on birefringent single mode fiber FP cavity using optical heterodyne. The proof of concept device consists of a light source, a polarizer controller, a modulator, a RF generator, a single mode fiber Fabry-Perot cavity, a strain inspector, an erbium doped fiber amplifier, a filter, a polarizer, an optical spectrum analyzer, and a digital communication analyzer. The dynamic range of the proposed sensor is explored. The results demonstrate the new concept of fiber pressure sensors and the technical feasibility for pressure measurements.

Because of the growing demand for healthy and high quality food products many efforts are made to develop new sensing systems for food analysis. In this work we demonstrate the use of a new technique for the detection of stone fragments in fruits, based on the transmission of laser light via scattering. The goal of our research was to develop a technique which could be used for the detection of stone fragments in a broad range of product types in different conditions. We paid special attention to wet products; a product class for which stone identification with the standard X-ray based detection technique is difficult. We studied products with different sizes, textures, internal structures and water contents. In a first part we defined the specifications of the sending side. To detect as much as possible scattered light, the wavelength should not coincide with any absorption line. A literature study about the composition of fruits combined with a study of measured absorption spectra of different products allowed us to select the optimum wavelength. In a next step we performed absorbance measurements and calculated the minimum power of the incident beam applying Beer's law. After the selection of the optimum wavelength and power, we built a proof-of-principle set-up and demonstrated the use of transmission via scattering for the detection of stone fragments in olives, peaches and prunes.

This paper introduces a non-invasive human temperature screening system for use in a large public area. Our key idea is to combine an image filtering process, an image morphology algorithm, and a particle analysis process in such a way that an individual's face in live thermal image can be located so that the skin temperature can be monitored and displayed. From our experiment, we find that the temperature measurement depends on each individual's response to the ambient temperature and on the contrast of the thermal image against the black body radiation source. This indicates that using the blackbody radiation source as our temperature reference does not totally compensate the fluctuation in human skin temperature. Our field test study at the triage section of Rajavithi Hospital, Thailand, shows that the maximum skin temperatures from people's faces can be simultaneously monitored and displayed in real time. In addition, the temperature value obtained from the thermal imaging camera has less fluctuation with respect to the true core body temperature once the disturbance from the surrounding environment is compensated. Hyperthermic patients can be identified with 100% sensitivity when the temperature threshold level and the offset temperature value are appropriately chosen.

This work deals with a review of the possible principles and construction of the terrestrial optical wireless links and the problematic of the proper photodiode and laser diode selection according to the wavelength dependent atmospheric transmittance and the photodiode sensitivity. For the calculations we used the power balance equations and the catalog values of the available laser diodes and detectors. For the most commonly used free space optical links, the laser diode price and the maximum power are also considered.

This paper presents a label-free optical biosensor based on a Young's interferometer configuration that uses a vertically integrated dual-slab waveguide interferometer as sensing element. In this element, linearly polarized light is coupled into a dual-slab waveguide chip from the input end-face, and the in-coupled zeroth order mode propagates in separated upper and lower waveguides. At the output end-face, the two closely spaced coherent beams diffract out and produce an interference fringe pattern. An evanescent wave field, generated on the surface of the upper waveguide, probes changes in the refractive index of the studied sample, causing a phase shift in the fringe pattern. Compared to a conventional integrated Young's interferometer utilizing a Y-junction as the beam splitter, the dual-slab waveguide Young's interferometer has the advantage of easy fabrication and large tolerance to the input-coupling beam. This paper builds a measurement system to investigate sensor performance using glucose solutions with various concentrations. These glucose concentration measurements are performed within the physiological range of 30mg/dl ~ 500mg/dl. The results indicate that a dual-slab waveguide interferometer yields an average phase resolution of 0.002 rad, which corresponds to an effective refractive index change of 4×10^-8 with an interaction path length of 15 mm.

Excessive UV doses have adverse effects on human health, but proper amount of UV is beneficial for people and is essential in the natural production of vitamin D^# in skin. Most of broadband UV-radiometers that have an output in sunburn units are incapable to record correctly the vitamin D synthetic capacity of sunlight because of the difference between the CIE erythema and 'Vitamin D synthesis' action spectra. The liquid-crystalline UV sensor based on provitamin D photoconversions has been developed for direct observation of vitamin D synthesis under UV irradiation. UV-induced transformation of provitamin D in cholesteric liquid-crystalline matrix is accompanied by the change of cholesteric pitch value in the LC cell. The developed UV biosensor makes possible both instrumental and visual monitoring of the vitamin D synthetic capacity of sunlight and/or artificial UV source.

A Monte Carlo model is developed for understanding the multiplication process in HgCdTe infrared avalanche photodiodes (APD). A good agreement is achieved between simulations and experimental measurements of gain and excess noise factor on midwave infrared electron injected Hg_0.7 Cd_0.3Te APD manufactured at CEA/LETI. In both cases, an exponential gain and a low excess noise factor - close to unity out to gains greater than 1000 - were observed on 5.1-μm cut-off devices at 77K. These properties are indicative of a single ionizing carrier multiplication process that is to say in our case the electron. Simulations also predict that holes do not achieve enough energy to impact ionize and to contribute to the gain, which confirms the previous observation. A comparison study is presented to explain the effect of different combinations of scattering processes on the avalanche phenomenon in HgCdTe. We find that alloy scattering with random scattering angle increases multiplication gain and reduces excess noise factor compared to the case including impact ionization only. It also appears that, in the more complete scattering environment, optical phonon scattering delays significantly the onset of avalanche.

At the present time there are a lot of optical fibers used by telecommunication companies for the data transmission. For the long-distance communications the single-mode fibers are being used for their promising values of parameters like attenuation and dispersion. These types of fibers are designed for the purpose of data transmission. The transmitted signal should not be affected by the external quantities. On the other side there are many types of optical fibers used as sensors. There are used in biomedicine, aerospace etc. The sensor types of optical fibers can not be used for data transmission because of their unappropriate values of attenuation and dispersion. The key idea of our research is to integrate both types of fibers into one fiber. The principle of sensing is based on redistribution of the optical power between individual modes around the cross-section of the end fiber-face. These fiber should preserve the significant parameters of telecommunication fibers and it should be able to measure some external quantities at he same time. This article shows the fundamental steps which must be done to operate the fiber as a sensor and the communication environment at the same time.

Stroboscopic scanning white light interferometry is a method for dynamic nanometer range profilometry that is widely applied for quality control in the MEMS industry. Monochromatic and phosphor coated (PC) white LEDs produce short light pulses for stroboscopy. The time resolution of a stroboscopic setup depends on its capability to produce short light pulses with duty cycles less than 5%. The peak wavelength and the spectral shape of PC white light diodes change with duty cycle. The spectrum of a PC white light LED was measured using Czerny-Turner-type monochromator (Jobin Yvon H 25) with an optical power meter (Ando AQ-1125). A custom made pulse amplifier drove the LED with a square wave voltage at 120 Hz. The blue peak wavelength of the white diode was blue-shifted by 7 nm when the duty cycle was reduced from 10% to 0.5%. The impact of the spectral change on the vertical resolution of the stroboscopic measurement was characterized through simulating the change in measurement uncertainty. The results were applied to characterize out-of-plane vibration of thermal MEMS bridges manufactured from SOI wafers. The simulated increase in measurement uncertainty was 1 nm, when the spectrum shifted 10 nm towards blue. Noise from background vibration obscured the effect of spectral shift. Although literature says that temperature increase shifts the spectrum of LED, and although our simulations indicate the existence of such a shift, our experimental results indicate that the deletory effect is negligible (it does not introduce bias or uncertainty to profiling measurement).

In CCD-spectrometers, the relation between the CCD-pixel number and the associated wavelength is established by means of a calibration polynomial, whose coefficients are typically obtained using a calibration lamp with known emission line wavelengths and a regression procedure. A recalculation of this polynomial has to be performed periodically, as the pixel number versus wavelength relation can change with ambient temperature variations or modifications in the optics attached to the spectrometer connector. Given that this calibration procedure has to be performed off-line, it implies a disturbance for industrial scenarios, where the monitoring setup must be altered. In this paper an automatic wavelength calibration procedure for CCD-spectrometers is proposed. It is based on a processing scheme designed for the in-process estimation of the plasma electronic temperature, where several plasma emission lines are identified for each spectral capture. This identification stage involves the determination, by means of a sub-pixel algorithm, of the central wavelength of those lines, thus allowing an on-line wavelength calibration for each single acquired spectrum. The proposed technique will be demonstrated by means of several experimental arc-welding tests.

Many fiber Bragg grating interrogation systems uses ratiometric wavelength measurement based on an edge filter. In any ratiometric scheme a 3dB coupler is a vital component which splits the signal and makes the system ratiometric. All commercial 3dB couplers exhibit a wavelength dependency and polarization dependent loss. In this paper the effects of the wavelength dependency and polarization dependent loss of the 3dB coupler in a ratiometric wavelength measurement system are investigated using both simulation and experimental techniques. The ratio response of the system is simulated considering the wavelength dependency of the coupler and is compared with that of a response with a wavelength independent coupler. A comparison study of the polarization induced ratio fluctuation and corresponding errors in wavelength with a polarization insensitive 3 dB coupler (very low PDL) and an ordinary 3 dB coupler is also presented. The results show that the 3 dB coupler has a significant influence on the ratio response and accuracy of a ratiometric wavelength measurement system.

In this paper the two-wavelength procedure for determining of the birefringence medium phase retardance order using the optical vortex birefringence compensator (OVBC) is presented. The OVBC generates regular optical vortex lattice which moves if the measured birefringent medium is placed into the compensator setup. Due to the vortex lattice regularity, tracing the lattice shift after the measured medium is inserted, there is no possibility to determine the absolute phase retardance in the monochromatic light. This is an analogy to the well known problem in the classical fringe interferometry. Having recorded interferograms for two waves with slightly different wavelengths, one can identify the centers of the two pairs of interferogram images (with and without the examined medium in the setup) and hence in that way the absolute shift of the vortex lattice. In the paper the theoretical considerations, numerical simulations, as well as the analysis of the interferograms taken from the experiment are presented.

A ratiometric wavelength measurement system based on a fiber bend loss edge filter has been proposed and demonstrated previously. Such a system offers the advantage of a high resolution, simplicity and a high measurement speed. The applications of such a system for the demodulation of the outputs of multiple Fiber Bragg grating (FBG) sensors requires the use of a high speed tunable filter to separate responses from multiple sensors. Here we present the results of modelling and analysis for a discretely tunable ferroelectric liquid crystal filter, which could be used as a channel dropper in a WDM-based demodulation system containing multiple FBG sensors.

For an all-fiber edge filter used in a rapid wavelength measurement system for optical sensing, a low polarization dependent loss (PDL) is required to ensure high measurement accuracy. The calculation of the bend loss for the TE and TM modes based on scalar approximations results in a discrepancy between the calculated PDLs and measured results. Here a full vectorial finite difference beam propagation method (FV FD-BPM) is used to compute the complex propagation constant and the field distributions of the TE and TM modes in the bending fiber, allowing the accurate calculation of the PDL of bending fiber.

This work is devoted to present and demonstrate a novel approach for the fabrication of micro-structured fiber Bragg gratings (MSFBGs). The MSFBG consists in a localized stripping of the cladding layer in a well defined region in the middle of the grating. The introduction of a perturbation along the grating leads to the formation of a defect state in the FBG spectral response that is tunable through the surrounding medium refractive index. Here, a two steps MSFBG fabrication technique, based on arc-discharge technique as fiber pre-treatment and maskless wet chemical etching to sensitize FBG to external refractive index, is proposed. Compared to the lithographic fabrication approach, previously proposed by the same authors and based on laser micromachining tool, this new simple and lowcost technique overcomes some technological drawbacks related to the presence of a mask and consequent undercutting etching. Furthermore, we experimentally demonstrate the potentiality of the presented approach to realize reliable MSFBGs enabling the prototyping of advanced photonics devices based on this technology.

Many robotic and industrial systems require 3D range-sensing capabilities for mapping, localization, navigation, and obstacle avoidance. Laser-scanning systems that mechanically trace a range-sensing beam over a raster or similar pattern can produce highly accurate models but tend to be bulky and slow when acquiring a significant field of view at useful resolutions. Stereo cameras can provide video-rate range images over significant fields of view but tend to have difficulty with scenes containing low or confusing textures. A new generation of active light, time-of-flight range sensors use a 2D array of sensor elements to produce a 3D range image at video rates. These sensors pose unique calibration challenges, requiring both the usual calibration of lens distortion (intrinsic calibration) and calibration of the time-of-flight range measurement (3D calibration). This paper presents our application of a photogrammetric calibration approach using inexpensive printed optical targets and off-the-shelf software to solve both intrinsic and range calibrations for the MESA Imaging SwissRanger 3100 range imaging sensor. We further identify specific calibration issues stemming from this sensor's correlation of reflectivity with measured range.

Compost obtained from different organic waste sources (municipal solid waste, biomass, etc.) is more and more utilized as a relatively low-cost product suitable for agricultural purposes reducing at the same time land filling of wastes. Compost product should comply with specific characteristics in order to be competitive with other fertilizer and amendment products. Main aim of the study was to investigate the possibility offered by hyperspectral imaging to evaluate the compost quality in order to develop control strategies to be implemented at plant scale. Reflectance spectra of selected compost samples have been acquired in the visible-near infrared field (VIS-NIR): 400-1000 nm. Correlations have been established between physical-chemical characteristics of the compost products and contaminants (glass and plastic particles) and their detected reflectance spectral signature.

Silica optical fibres that were developed for telecommunication networks extend their use for sensors and smart structures. Their reliability and expected lifetime has appeared as a major concern. Series of experiments were implemented in order to assess fibre behaviour in different environmental conditions, including chemical corrosion and mechanical stress. Optical fibres were aged in water under controlled stress overlapping microwave energy for different durations. Fibre samples were wound on different diameter mandrels applying consequently a non-uniform tensile, respectively compression stress in function of the fibre's section. Different experimental combinations were implemented in order to separate aging factor effects. Then, these aged / stretched fibres were dynamic tensile tested at different strain rates and results were statistically treated using Weibull theory. In certain cases and testing conditions, comparison with as received fibres has revealed strength increase with a generally mono-modal defect distribution on the fibre surface. Base on previous and current results, the structural relaxation phenomenon at the silica cladding - polymer coating interface might be evidenced.

Aerosol particles play important role in both global climate system and earth observation application. We have developed a portable scanning Mie lidar, with the combination of spectrograph, active and passive earth observation satellite data, and the ground sensor data, severe weather research and earth observation atmospheric correction work could be conducted. To obtain more accurate aerosol information, we are developing a new multi-channel Raman lidar system. Also we have developed a simulation model for system performance simulation and data simulation. In this paper, the lidar system development, simulation modeling, and primary experimental work result will be described.

We are currently developing a magnesium diboride (MgB2) detector array for use in future space-based spectrometers. This 2-D array is intended for use in high-resolution investigations of the outer planets and their icy moons. The state of the array processing, the current pixel design as well as signal-to-noise considerations is briefly discussed. Expected pixel sensitivities and comparison to current state-of-the-art infrared (IR) detectors will be briefly discussed.

Italian extra virgin olive oils from four regions covering different latitudes of the country were considered. They were analyzed by means of absorption spectroscopy in the wide 200-2800 nm spectral range, and multivariate data processing was applied. These spectra were virtually a signature identification from which to extract information on the region of origin and on the most important quality indicators. A classification map was created which was able to group the 80 oils on the basis of their region of origin. Furthermore, a model for the prediction of quality parameters such as oleic acidity, peroxide number, K232, K270 and Delta K, was developed.

We describe novel type of the single-beam dynamic holographic interferometer, that have two optical (based on beam coupling) and one electrical channels (based on the holographic current). Two optical channels are due to the simultaneous recording of the dynamic reflection and transmission gratings. Transmission-grating channel is sensitive to the transversal phase modulation, while reflection-grating channel allow detecting longitudinal phase modulation. Simultaneous detection of three phase-modulated signals allows improving reliability and sensitivity of the dynamic holographic interferometry. We develop model that explain transient enhancement of the holographic current and beam coupling in the crystal with two mobile charge carriers of different signs with contribution from the gradient-force current. Calculations for the ramp phase modulation and step-like phase modulation predict quadrature response for the beam coupling and phase-sign sensitive response for the holographic current. Theoretical model is compared with the experiments on the ferroelectric-semiconductor SPS and semiconductor CdTe crystals.

There are some interfering elements, which are able to influence the signal functions of a car's rear light. One of these elements is the sensitivity to external light sources, which is able to affect the intensity of the rear lamps by the impact of direct sunrays in a flat angle. Recognition of the signals could be made more difficult or impossible. This effect is called phantom light effect. Today the regulations of the ECE do not contain these influences. To investigate the meaning of the effects to the traffic safety, there has been a test with a sun simulator. The task of this test is to measure the luminance of signals from different actual taillights with and without sunlight. Another part of the investigations are some psychophysical tests involving about 20 persons. The dimension of phantom light effects at taillights will be quantified by the analysis of the luminance pictures. With these cognitions some possibilities to reduce the phantom light effect with little changes in the optical design of taillights will be performed. One example will be shown.

Increasingly, cars are fitted with interior ambient lighting which is switched on while driving. This special kind of interior light emphasizes the interior design of the car, it makes a car look special and gives the buyers a new option to personalize their automobiles. But how does ambient interior light influence the driver? We conducted a series of over 50 tests to study the influence of interior ambient light on contrast perception under different illumination levels, colors and positions of the illuminated areas. Our tests show that in many cases the ambient lighting can improve the visual contrast for seeing objects in the headlamp beam. But the test persons mentioned that the tested brightness looked too bright and that they felt glared. The measured values instead proved that no disability glare exists. Therefore, provided that the drivers can adjust the intensity of the ambient light to avoid glare, the ambient light has no negative effect on the drivers' contrast perception.

Actual studies show that 40 % of all accidents occur at night, but the part of the drives during the night represent only 20 % of all drives [1]. So the risk potential to be involved in an accident at night is almost three times higher in comparison to daytime. A headlamp is primary used to illuminate the road. Secondary the signal aspect is an identifying feature for other road users. As simple as these tasks seem to be, it is not easy to perform it in every situation because of environmental factors. Especially the weather conditions, but also the type of road and the traffic density causes difficulties. The ambition of the design of a headlamp is an adaptive system which is able to adjust on various factors to perform these tasks. In many cases there are already technical possibilities to realise new adaptive concepts, but up to now only a few cars are equipped with these technology. An example is the levelling system. Every modern car has a manually static or an automatically static levelling system. But because of the vehicle dynamics and the vertical road geometry it would be advisable to integrate an automatically dynamic levelling system. This System is currently used in the cars of the upper class. It would increase the road safety if this technology would be integrated in every car. This study describes the requirements for modern headlamps, discusses already existing systems and shows the technical possibilities to realise new concepts.

Driving at night is dangerous. Although only 25% of all driving tasks are performed at night, nearly half of all fatal accidents happen in this time. In order to increase safety when driving under poor visibility conditions, automotive front lighting systems have undergone a strong development in the last fifteen years. One important milestone was the introduction of Xenon headlamps in 1992, which provide more and brighter light for road illumination than ever before. Since then the paradigm of simply providing more light has changed toward providing optimised light distributions, which support the driver's perception. A first step in this direction was the introduction of dynamic bend lighting and cornering light in 2003. In 2006 the first full AFS headlamp (Adaptive Front Lighting System) allowed an optimised adoption of the light distribution to the driving situation. These systems use information provided by vehicle sensors and an intelligent algorithm to guide light towards those areas where needed. Nowadays, even more information about the vehicle's environment is available. Image processing systems, for example, allow to detect other traffic participants, their speed and their driving directions. In future headlamp systems these data will be used to constantly regulate the reach of the light distribution thus allowing a maximal reach without providing glare. Moreover, technologies that allow to constantly use a high-beam light distribution are under development. These systems will illuminate the whole traffic area only excluding other traffic participants. LED light sources will play a significant role in these scenarios, since they allow to precisely illuminate certain areas of the road, while neighbouring parts will be left in dark.

The automotive lighting technology is in considerable progress due to new components, e.g., High-Power-LEDs and light guides, and new sophisticated production techniques. Furthermore, great importance is being attached to the appearance of front and tail lamps. White High-Power-LEDs have reached a development stage that affords its reasonable application to low beam headlamps. This challenging illumination function requires sophisticated design techniques in order to preserve the advantages associated with this source type. Thus, high efficiency and stylish appearance have to be reconciled, e.g., with the use of freeform surfaces. Beside the demands from manufacturers and customers, car lamps have to meet several regulations (ECE, SAE, etc.). This contribution describes the illumination design of a LED-based low beam headlamp using advanced mathematical methods, e.g., 3D-Tailoring, automatic optimization, and Virtually Reflecting/Refracting Surfaces (VRS). We propose this new surface type with non conventional reflection/refraction properties as an advantageous design tool for the first layout and for automatic optimization, as well. For efficiency reasons, special attention will be paid to the creation of the cut-off line without using additional stops.

Present car-headlamps can adapt their light distribution to the traffic situation only in a predefined way. The next generation of headlamps will offer a more flexible adaptation of their light distribution like an adaptive Cut-Off-Line in "Advanced Frontlighting Systems" (AFS). Addressable light sources in future active headlamps enable functions like glare free high beam or marking light. There are several possibilities to design such an addressable light source. In this contribution one solution using a digital micro mirror device (DMD) is presented. With this device an adaptive light distribution can be generated by modulating every pixel of the DMD individually. For the design of an optical system for a DMD headlamp a DMD-Projector was analyzed. The procedure of generating a light distribution can be divided into two processes: a.) illumination of DMD b.) projecting the image of the DMD on the street. In a DMD projector the illumination of a DMD is a very complex optical system with many optical elements. Some of these optical elements are not necessary for a car headlamp because of different requirements for car headlamps and DMD projectors. The illumination system can be simplified if these elements are eliminated. Also the aspect ratio of the imaging system for the DMD has to change 4:3 (DMD) to 7:2 (light distribution on the street).

Optical hydrogen sensors are intrinsically safe since they produce no arc or spark in an explosive environment caused by the leakage of hydrogen. Safety remains a top priority since leakage of hydrogen in air during production, storage, transfer and distribution creates an explosive atmosphere for concentrations between 4% (v/v) - the lower explosive limit (LEL) and 74.5% (v/v) - the upper explosive limit (UEL) at room temperature and pressure. Being a very small molecule, hydrogen is prone to leakage through seals and micro-cracks. Hydrogen detection in space application is very challenging; public acceptance of hydrogen fuel would require the integration of a reliable hydrogen safety sensor. For detecting leakage of cryogenic fluids in spaceport facilities, Launch vehicle industry and aerospace agencies are currently relying heavily on the bulky mass spectrometers, which fill one or more equipment racks, and weigh several hundred kilograms. This paper describes the successful development and test of a multi-point fiber optic hydrogen sensor system during the static firing of an Evolved Expandable Launch Vehicle at NASA's Stennis Space Center. The system consisted of microsensors (optrodes) using hydrogen gas sensitive indicator incorporated onto an optically transparent porous substrate. The modular optoelectronics and multiplexing network system was designed and assembled utilizing a multi-channel optoelectronic sensor readout unit that monitored the hydrogen and temperature response of the individual optrodes in real-time and communicated this information via a serial communication port to a remote laptop computer. The paper would discuss the sensor design and performance data under field deployment conditions.

In short-reach connections, large-diameter multimode fibres allow for robust and easy connections. Unfortunately, their propagation properties depend on the excitation conditions. We propose a launching technique using a fibre stub that can tolerate fabrication tolerances in terms of tilts and off-sets to a large extent. A study of the influence of displaced connectors along the transmission link shows that the power distributions approach a steady-state power distribution very similar to the initial distribution established by the proposed launching scheme.

Automotive applications are one of the largest vision-sensor market segments and one of the fastest growing ones. The trend to use increasingly more sensors in cars is driven both by legislation and consumer demands for higher safety and better driving experiences. Awareness of what directly surrounds a vehicle affects safe driving and manoeuvring of a vehicle. Consequently, panoramic 360° Field of View imaging can contributes most to the perception of the world around the driver than any other sensors. However, to obtain a complete vision around the car, several sensor systems are necessary. To solve this issue, a customized imaging system based on a panomorph lens will provide the maximum information for the drivers with a reduced number of sensors. A panomorph lens is a hemispheric wide angle anamorphic lens with enhanced resolution in predefined zone of interest. Because panomorph lenses are optimized to a custom angle-to-pixel relationship, vision systems provide ideal image coverage that reduces and optimizes the processing. We present various scenarios which may benefit from the use of a custom panoramic sensor. We also discuss the technical requirements of such vision system. Finally we demonstrate how the panomorph based visual sensor is probably one of the most promising ways to fuse many sensors in one. For example, a single panoramic sensor on the front of a vehicle could provide all necessary information for assistance in crash avoidance, lane tracking, early warning, park aids, road sign detection, and various video monitoring views.

Nowadays drivers have to get along with an increasing complex visual environment. More and more cars are on the road. There are not only distractions available within the vehicle, like radio and navigation system, the environment outside the car has also become more and more complex. Hoardings, advertising pillars, shop fronts and video screens are just a few examples. For this reason the potential risk of driver distraction is rising. But in which way do the advertisements at the roadside influence the driver's attention? The investigation which is described is devoted to this topic. Various kinds of advertisements played an important role, like illuminated and non-illuminated posters as well as illuminated animated ads. Several test runs in an urban environment were performed. The gaze direction of the driver's eye was measured with an eye tracking system. The latter consists of three cameras which logged the eye movements during the test run and a small-sized scene camera recording the traffic scene. 16 subjects (six female and ten male) between 21 and 65 years of age took part in this experiment. Thus the driver's fixation duration of the different advertisements could be determined.

The computation of the heat transfer equations solution generally implies the use of commercial codes, often expensive. An important goal of solving heat transfer problem in a given context is to obtain an accurate solution using accessible tools at a low computational time cost. Because of complexity of the problem, a variety of different approximations are used and their validity limit must be tested in each case performing comparisons with experimental results. In this paper we present a simple, rapid and accurate method to compute the temperature evolution during the heating or cooling of a metal circular cylinder. For moderate temperature values only the conductive transfer can be considered and the resulted heat transport equation is solved. The initial temperature distribution is described by Dirichlet type boundary conditions. Taking into account a sufficiently large number of terms in the analytical solution expression so that the initial boundary condition is fulfilled (in our case N = 500), we obtain a simple yet accurate approximation of the full transport solutions. The results are consistent with experimental data and in excellent agreement with simulations performed with much more complex codes for the investigated temperature domain. The method can be adapted to the temperature measurement inside the engine. Using the specific advantages of the optical fibers might be a reliable tool for improving the temperature control in the engine and consequently the performances of the automobile.

The interest of introducing diffractive optical components in industrial laser marking applications is presented. These components represent a new contribution of the optical micro-technology for the domain of the near infrared lasers having an average power of tens of watts. Optical functions ranging from gratings or dot matrices to complex modifications of the beam intensity distribution can be implemented. Automotive industry and industry in general is concerned by the identification of parts in a purpose of traceability. The applications include the marking on any kind of materials of bar codes, serial numbers, alphanumeric characters, logos, etc. This operation can be realized in one step at high cadences by direct marking thanks to the shaping of the laser beam. To optimize the quality of the shaping, fiber lasers which have a good beam quality factor are used. Laser parameters (energy density, exposure duration) required for the marking of two materials, polyamide and stainless steel, are investigated to demonstrate the feasibility of the process.