The combination of fiber Bragg grating arrays integrated in a soft plastic tube is promising for high resolution manometry (HRM) where pressure measurements are done with high spatial resolution. The application as a medical device and in vivo experiments have to be anticipated by characterization with a measurement setup that simulates natural conditions. Good results are achieved with a pressure chamber which applies a well-defined pressure with a soft tubular membrane. It is shown that the proposed catheter design reaches accuracies down to 1 mbar and 1 cm.

Polymerization shrinkage of dental composite materials is recognized as one of the main reasons for the development of marginal leakage between a tooth and filling material. As an alternative to conventional measurement methods, we propose optical fiber Bragg grating (FBG) based sensors to perform real-time strain and shrinkage measurements during the curing process of dental resin cements. We introduce a fully automated set-up to measure the Bragg wavelength shift of the FBG strain sensors and to accurately monitor the linear strain and shrinkage of dental resins during curing. Three different dental resin materials were studied in this work: matrix-filled BisGMA-based resins, glass ionomers and organic modified ceramics.

Surface Plasmon resonance (SPR) biosensors are optical sensors exploiting tiny surrounding refractive index changes to measure interactions between host and guest molecules. Biosensors prepared on optical fibers constitute a miniaturized counterpart to the traditional SPR prism-based sensor, so-called Kretschmann prism. They possess all the advantages inherent to the use of optical fibers and intrinsically allow in situ and real time measurements in very small volumes. The optical fiber sensors used for this study are tilted fiber Bragg gratings covered by a nano-scale-gold coating allowing the SPR generation along the outer surface of the sensors. Using orthogonally polarized lightwaves matching the TFBG eigenmodes, we are able to retrieve the surrounding refractive index with a sensitivity of 10-5 refractive index unit. This confirms that gold-coated TFBGs can be deployed for chemical species profiling in diluted solutions. In this paper, we assess the protein detection and quantification capabilities of SPR-TFBGs using a well-acknowledged label-free mechanism. A self-assembled monolayer of Biotin is formed on the gold surface of the SPR-TFBGs biosensors to quantify Streptavidin diluted in phosphate buffered saline. We demonstrate the capability of this new technology to accurately detect molecules concentrations as lows as 10-10 g/ml.

We demonstrate highly sensitive temperature and strain sensors based on an all-fiber Lyot filter structure, which is formed by concatenating two 45°-TFGs (tilted fiber gratings) with a PM fiber cavity. The experiment results show the all-fiber 45°-TFG Lyot filter has very high sensitivity to strain and temperature. The 45°-TFG Lyot filters of two different cavity lengths (18cm and 40 cm) have been evaluated for temperature sensing by heating a section of the cavity from 10°C to 50°C. The experiment results have shown remarkably high temperature sensitivities of 0.616nm/°C for 18cm and 0.31nm/°C for 40cm long cavity filter, respectively. The 18cm long cavity filter has been subjected to strain variations up to around 550με and the filter has exhibited strain sensitivities of 0.02499nm/με and 0.012nm/με for two straining situations, where its cavity middle section of 18cm and 9cm were stretched, respectively.

Optical sensing sheets, based on Fibre Bragg Grating (FBG) sensing elements embedded in exible polydimethyl- siloxane (PDMS), are produced and tested. The device shows promise in pressure mapping and tactile applications, in fields such as robotics and rehabilitation. FBGs inscribed in highly-birefringent photonic crystal fibres, reflecting two Bragg peaks, are used, and the potential to discriminate pressure and temperature is explored. The prototypes were produced by moulding technology and PDMS was cured at room temperature. One sample with FBGs embedded in the middle layer of a 2 mm thick PDMS sheet exhibited a linear pressure sensitivity of about 2:6 pm/kPa over the range of 0 - 250 kPa. Another sample was proposed and tested for temperature insensitive measurements, by realising local stress concentration at FBG sections of the embedded fibre.

In this work, we apply a recent technique for the generation of stimulated Brillouin scattering (SBS) dynamic gratings that are both localized and stationary to realize high-resolution distributed temperature sensing. The gratings generation method relies on the phase modulation of two pump waves by a common pseudo-random bit sequence (PRBS), with a symbol duration that is much shorter than the acoustic lifetime. This way the acoustic wave can efficiently build up in the medium at discrete locations only, where the phase difference between the two waves does not temporarily vary. The separation between neighboring correlation peaks can be made arbitrarily long. Using the proposed method, we experimentally demonstrate distributed temperature sensing with 5 cm resolution, based on modifications to both the local birefringence and the local Brillouin frequency shift in polarization maintaining fibers. The localization method does not require wideband detection and can generate the grating at any random position along the fiber, with complete flexibility. The phase-coding method is equally applicable to high-resolution SBS distributed sensing over standard fibers.

In this work we demonstrate two new BOTDA sensing systems based on differential (DPSK) and quadrature (QPSK) phase-shift keying modulation techniques with enhanced performances. First we demonstrate Brillouin echoes distributed sensing (BEDS) with centimeter resolution using a single intensity DPSK modulator for the pump pulse. The optical π-phase pulse is directly generated at the end of an intensity pulse using DPSK technique. This allows an easy adjustment of the delay between the intensity and phase pulse and improves the optical loss of the pump. The second technique uses an optical QPSK modulator (I & Q modulator) as a single sideband (SSB) modulator. The advantage of I & Q modulator compared to dual-drive modulator lies on the high performance of carrier suppression of 55 dB as well as side-mode suppression of 40 dB at 1535 nm. Besides the filter that chooses either the Stokes or anti-Stokes component before detecting the Brillouin response on the photodiode is no more needed. By use of the I & Q modulator the performance of BOTDA using either Stokes or anti-Stokes component is shown and discussed.

High sensing resolution in long-distance distributed fiber optic sensors, such as Brillouin Optical Time Domain Analysis (BOTDA), cannot be trivially achieved due to several issues including self-phase modulation, resolution-uncertainty trade-offs and fiber attenuation. These problems could be fixed by the use of differential pulse-pair techniques in combination with Raman amplification. In this work we present a Differential Pulse-width Pair (DPP) Raman-assisted BOTDA sensor, that can achieve 1 meter resolution in a 100 km range.

In our study, remote environmental sensing is presented using a standard optical time domain reflectometer (OTDR). The measurement of environmental parameters using optical sensors is an expanding area of research with growing importance. Fiber optic sensors are an interesting solution for that due to their high sensitivity, small size, and capability for on-site, real-time, remote, and distributed sensing capabilities. Our multiplexing sensing scheme approach uses transmissive filters (long period gratings - LPGs) interrogated by the OTDR return pulses. The loss induced at the resonance wavelengths varies with changes in the environment refractive index, temperature or other physical parameters. Experimental results show that the insertion of an erbium amplifier improves the measurement resolution in certain situations. Further analysis show that a remote multiplexed sensing scheme allows us to perform simple and low cost real time measurement of refractive index and temperature over long distances.

On-line monitoring of environmental conditions in nuclear facilities is becoming a more and more important problem. Standard electronic sensors are not the ideal solution due to radiation sensitivity and difficulties in installation of multiple sensors. In contrast, radiation-hard optical fibres can sustain very high radiation doses and also naturally offer multi-point or distributed monitoring of external perturbations. Multiple local electro-mechanical sensors can be replaced by just one measuring fibre. At present, there are over four hundred operational nuclear power plants (NPPs) in the world 1. Operating experience has shown that ineffective control of the ageing degradation of major NPP components can threaten plant safety and also plant life. Among those elements, cables are vital components of I&C systems in NPPs. To ensure their safe operation and predict remaining life, environmental monitoring is necessary. In particular, temperature and radiation dose are considered to be the two most important parameters. The aim of this paper is to assess experimentally the feasibility of optical fibre temperature measurements in a low doserate radiation environment, using a commercially available reflectometer based on Rayleigh backscattering. Four different fibres were installed in the Sub-Pile Room of the BR2 Material testing nuclear reactor in Mol, Belgium. This place is man-accessible during the reactor shut-down, allowing easy fibre installation. When the reactor operates, the dose-rates in the room are in a range 0.005-5 Gy/h with temperatures of 40-60 °C, depending on the location. Such a surrounding is not much different to some "hot" environments in NPPs, where I&C cables are located.

Fibre optical current sensor (FOCS) is a promising alternative to inductive sensors for the measurement of the plasma current in future thermonuclear fusion reactors. Standard FOCS relies on the measurement of the state of polarisation (SOP) of light at the output of an optical bre surrounding a current. Because of the Faraday eect, magnetic eld induced by electrical current rotates the SOP of light travelling into the bre. According to the Ampere's theorem this rotation is proportional to the surrounded current. In future tokamaks like ITER and DEMO, the plasma current will be suciently high to generate a rotation of the SOP higher than 2 radians. These conditions may lead to uncertainties on the determination of the plasma current if no post processing is performed. In this paper we propose a solution with a Polarisation Optical Time Domain Re ectometer (POTDR) setup allowing both unambiguous plasma current measurement and also local magnetic eld measurements. This measurement is based on the assessment of the SOP rotation of the Rayleigh backscattered POTDR signal. Thanks to the presence of an input polarizer, SOP variations are converted into power uctuations that contain information about the distribution of the magnetic eld and therefore about the plasma current. Using the Jones formalism we have developed a model accounting for the modication of the SOP of light travelling into the optical bre and the evolution of the POTDR signal. In parallel experimental PODTR measurements have been performed on the Tore Supra tokamak situated at CEA Cadarache in France. A comparison between the models and the experimental results conrms the capability of the system to measure the plasma current and the local magnetic eld even if further data post processing are still required.

Ferrule-top (FT) cantilevers are a new generation of all optical micromechanical sensors obtained by carving microstructures on the top of ferrule terminated fibers. In this paper, we will demonstrate how this plug and play design can be used for the development of a new generation of sensors and actuators for harsh environments, where commercially available devices would be prone to failure. Ferrule-top sensors can work in two main modes - static and dynamic. The static mode is based on recording elastic deflection of the cantilever; the dynamic mode relies on tracking changes in its mechanical properties (resonance frequency, quality factor). Depending on the application, one can choose which mode is most suitable or combine both to achieve best performance. We will illustrate the relation between specific measured quantity (humidity, flow) and the behavior of the sensor. Further, we will show the setup in which the sensor can be actuated using light, giving the possibility to excite the cantilever without any electronics on the sensing head. This technique might by use for the development of fully optical beamsteering microdevices.

We propose a fiber optic sensor array based on bend loss assessed by optical time domain reflectometry (OTDR). The sensor mechanism is based on optical fiber bending loss compressed by external pressure. An elastomeric surface is applied to the sensor in order to communicate external pressure to the fiber coil and also, this make sensor able to deal with degradation coming from aggressive environments. The sensing system proposed is able to monitor liquid or gas pressure in different environments, such as water, oil, alcohols, some diluted acids and others, depending only of elastomeric membrane choice. In order to protect the sensor stage against environmental degradation a plastic packaging was chosen. Bend loss measurements is taken concerning the number of fiber loops involved in the sensor, pump signal wavelength and temporal width. This long for the best parameters in the sensor construction. The specific case of the sensor applied to water percolation monitoring from embankment damns is detailed in this paper; for this application the sensor array have a number of at least six stages totally independent each other, in such a way that each stage can be developed to monitor a specific environment. Sensors have shown good performance in field tests, reaching work range from 0.1 to 0.6 atm with 0.05 atm of precision.

We discuss a radioactivity sensing based on monitoring of color centers formation in Yb-doped fiber under gamma irradiation. New method exploits the dynamic effect of refractive index changes (RIC) induced by laser pumping into the fiber absorption band. In our experiment four identical samples of the single-mode aluminum silicate Yb-doped optical fiber have been γ-irradiated with different doses from a ⁶⁰Co source. All fibers passed the test in the intereferometric setup for the purpose of the pump induced RIC effect. During the test the phase shifts induced in the fiber by 1-mssquare pump pulses at 980 nm were recorded with a probe signal at eleven different wavelengths ranging from ~1.46 to ~1.61 μm. The phase traces have been normalized to their maximum values and averaged over 100 traces for each probe wavelength and also over all probe wavelengths. The averaged phase traces highlight the differences in their growing and decaying parts in respect to the case of non-irradiated fibers. These differences are found to be in correlation with the fiber irradiation dose. For non-irradiated fibers decay parts are perfectly fitted by one exponential function with the relaxation time constant equal to the Yb-ion excited state life-time ~750 μs, to be the same for all fiber samples. However, for irradiated fibers the similar fitting gives a triple exponential decay with time constants estimated as ~750, ~500 and 40μs. For higher irradiation dose the difference with one exponential fitting is more pronounced. Having in mind that the obtained difference in phase shift dynamics could be associated with excitation of some color centers induced in the fiber matrix by gamma irradiation, we represent the normalized phase shifts as a superposition of two contributions. The first contribution is due to excitation of Yb-ion, the same for all fiber samples. The second is due to excitation of color centers. The amplitude of the second part highlights a degree of fiber degradation under gamma radiation and is directly proportional to the concentration of the excited color centers that, in its turn, linearly grows with the irradiation dose. Therefore, new method is regarded as a good candidate for potential applications in fiber dosimeters.

Sensors based on the surface plasmon resonance phenomenon have particular importance in the study of bio-chemical reactions due to their high sensitivity to small refractive index changes in the surrounding medium. The combination of this effect with optical fiber configurations allows particularly miniaturized versions, especially in the form of fiber tapers. We describe a novel, fully symmetrical deposition method for deposition of a gold layer circularly around the taper waist, based on a sputtering technique and usage of a gold-ring target. With such a circular symmetric coating the plasmon resonance effect in the taper becomes completely independent of the polarization of the illumination light. Furthermore, we present numerical calculations of the effects of the taper waist diameter, gold film thickness and analyte interaction length on the plasmon resonance wavelength spectrum. Especially the sensitivity of the analyte refractive index on the plasmon resonance wavelength shift is investigated. Modeling results are compared with experimental data from gold-coated fiber-micro-tapers as sensing element.

Sharply bent optical fiber can be used as sensory systems. At first sight, application of curved optical fiber is refractometer but after immobilizing metal layer on stripped core of optical fiber its usage can be much more sophisticated. On the metal layer it is possible to excite surface plasmon polariton. In our case we use Drudes model of free electron and Monte Carlo method to calculate probability and real possibility of excitation of surface plasmon polariton on metal layer applied on the core of U-bent optical fiber. The calculated results allow for direct assessment of appropriate positions of metal layer on semi-toroid optical fiber in dependence on system parameters.

We report for the first time a multiplexed array of 12 distributed feedback fiber lasers (DFB FLs) on a single optical fiber, separated by only 100 GHz (0.8 nm) in the C-band. These lasers are pumped by a 200 mW laser diode at 1480 nm with no apparent impact on the sensor noise floor despite the fact that the residual reflections from adjacent gratings may be enhanced due to the smaller wavelength separation. Each DFB FL, especially developed for serial multiplexing, exhibits low lasing threshold typically between 1 and 2 mW, low intensity noise and very low frequency noise (less than 30 dB re 1 Hz2/Hz at 1 kHz from optical carrier). From these experimental results, extension to 32 DFB FLs array (on 100 GHz ITU grid) multiplexed on one fiber will be discussed.

An electrical dynamic interrogation technique previously reported by the authors for long-period grating sensors is now progressed by relying its operation exclusively on the modulation of a DFB Laser. The analysis of the detected first and second harmonic generated by the electrical modulation of the DFB Laser allows generating an optical signal proportional to the LPG spectral shift and resilient to optical power fluctuations along the system. This concept permits attenuating the effect of the 1/f noise of the photodetection, amplification and processing electronics on the sensing head resolution. This technique is employed in a multiplexing sensing scheme that measures refractive index variations.

In this work, a novel high birefringent (HiBi) fiber loop mirror sensor based on a "figure-of-eight" constructed with a 3×3 fiber coupler, is presented. The "figure-of-eight" is formed by two fiber loop mirrors (FLM's) made by four of the six fiber arms of the 3×3 fiber coupler. The other two remaining fiber ports of the 3×3 coupler are used as input and output fibers of the compound sensor. The sensing head is located in the one of the FLM and it is formed by a spliced section of HiBi elliptical core fiber. The spectral response of this "figure-of-eight" configuration presents two interference optical signals that can be easily tuned by a polarization controller that is located in the other FLM, and which is made only of standard singlemode fiber from two arms of the 3×3 coupler. The sensor head was optically characterized both in temperature and strain, showing wavelength dependence sensitivities of -0.23 nm/°C and - 2.6 pm/με, for temperature and strain, respectively. It is noticed that these sensitivities are practically the same for the two interference signals. Future work will explore the possibility to use the singlemode FLM to interrogate the sensor head made by HiBi fiber section, and providing elimination of phase fluctuations that can occur, increasing its potential for remote sensing applications.

This paper presents the design of a mechanical transducer for an optical-fiber accelerometer based on polarization variation. Several transducers can be imagined using either bending, twist, stretching or crushing of the fiber. The transducers are modelled analytically and are compared through the curve representing the sensitivity in function of the sensor resonant frequency. It turns out that the use of crushing shows a sensitivity several orders of magnitude higher than the other deformations. In this latter case, experimental results confirm the analytical computation of the sensitivity.

In this paper we present a novel Navigation and Guidance System (NGS) for Unmanned Aerial Vehicles (UAVs) based on Vision Based Navigation (VBN) and other avionics sensors. The main objective of our research is to design a lowcost and low-weight/volume NGS capable of providing the required level of performance in all flight phases of modern small- to medium-size UAVs, with a special focus on automated precision approach and landing, where VBN techniques can be fully exploited in a multisensory integrated architecture. Various existing techniques for VBN are compared and the Appearance-based Navigation (ABN) approach is selected for implementation. Feature extraction and optical flow techniques are employed to estimate flight parameters such as roll angle, pitch angle, deviation from the runway and body rates. Additionally, we address the possible synergies between VBN, Global Navigation Satellite System (GNSS) and MEMS-IMU (Micro-Electromechanical System Inertial Measurement Unit) sensors and also the use of Aircraft Dynamics Models (ADMs) to provide additional information suitable to compensate for the shortcomings of VBN sensors in high-dynamics attitude determination tasks. An Extended Kalman Filter (EKF) is developed to fuse the information provided by the different sensors and to provide estimates of position, velocity and attitude of the platform in real-time. Two different integrated navigation system architectures are implemented. The first uses VBN at 20 Hz and GPS at 1 Hz to augment the MEMS-IMU running at 100 Hz. The second mode also includes the ADM (computations performed at 100 Hz) to provide augmentation of the attitude channel. Simulation of these two modes is performed in a significant portion of the Aerosonde UAV operational flight envelope and performing a variety of representative manoeuvres (i.e., straight climb, level turning, turning descent and climb, straight descent, etc.). Simulation of the first integrated navigation system architecture (VBN/GPS/IMU) shows that the integrated system can reach position, velocity and attitude accuracies compatible with CAT-II precision approach requirements. Simulation of the second system architecture (VBN/GPS/IMU/ADM) shows promising results since the achieved attitude accuracy is higher using the ADM/VBS/IMU than using VBS/IMU only. However, due to rapid divergence of the ADM virtual sensor, there is a need for a frequent re-initialisation of the ADM data module, which is strongly dependent on the UAV flight dynamics and the specific manoeuvring transitions performed. Finally, the output provided by the VBN and integrated navigation sensor systems is used to design a flight control system using a hybrid Fuzzy Logic and Proportional-Integral-Derivative (PID) controller for the Aerosonde UAV.

High spectral resolution lidars (HSRLs) designed for aerosol and cloud remote sensing are increasingly being deployed on aircraft and called for on future space-based missions. The HSRL technique relies on spectral discrimination of the atmospheric backscatter signals to enable independent, unambiguous retrieval of aerosol extinction and backscatter. NASA Langley Research Center is developing a tilted pressure-tuned field-widened Michelson interferometer (FWMI) to achieve the spectral discrimination for an HSRL system. The FWMI consists of a cubic beam splitter, a solid glass arm, and a sealed air arm. The spacer that connects the air arm mirror to the main part of the interferometer is designed to minimize thermal sensitivity. The pressure of the sealed air-arm air can be accurately controlled such that the frequency of maximum interference can be tuned with great precision to the transmitted laser wavelength. In this paper, the principle of the tilted pressure-tuned FWMI for HSRL is presented. The pressure tuning rate, the tilted angle requirement and challenges in building the real instrument are discussed.

This paper describes the developmental and testing activities conducted by the Italian Air Force Official Test Centre (RSV) in collaboration with Alenia Aerospace, Litton Precision Products and Cranfiled University, in order to confer the Night Vision Imaging Systems (NVIS) capability to the Italian TORNADO IDS (Interdiction and Strike) and ECR (Electronic Combat and Reconnaissance) aircraft. The activities consisted of various Design, Development, Test and Evaluation (DDT&E) activities, including Night Vision Goggles (NVG) integration, cockpit instruments and external lighting modifications, as well as various ground test sessions and a total of eighteen flight test sorties. RSV and Litton Precision Products were responsible of coordinating and conducting the installation activities of the internal and external lights. Particularly, an iterative process was established, allowing an in-site rapid correction of the major deficiencies encountered during the ground and flight test sessions. Both single-ship (day/night) and formation (night) flights were performed, shared between the Test Crews involved in the activities, allowing for a redundant examination of the various test items by all participants. An innovative test matrix was developed and implemented by RSV for assessing the operational suitability and effectiveness of the various modifications implemented. Also important was definition of test criteria for Pilot and Weapon Systems Officer (WSO) workload assessment during the accomplishment of various operational tasks during NVG missions. Furthermore, the specific technical and operational elements required for evaluating the modified helmets were identified, allowing an exhaustive comparative evaluation of the two proposed solutions (i.e., HGU-55P and HGU-55G modified helmets). The results of the activities were very satisfactory. The initial compatibility problems encountered were progressively mitigated by incorporating modifications both in the front and rear cockpits at the various stages of the test campaign. This process allowed a considerable enhancement of the TORNADO NVIS configuration, giving a good medium-high level NVG operational capability to the aircraft. Further developments also include the design, integration and test of internal/external lighting for the Italian TORNADO "Mid Life Update" (MLU) and other programs, such as the AM-X aircraft internal/external lights modification/testing and the activities addressing low-altitude NVG operations with fast jets (e.g., TORNADO, AM-X, MB-339CD), a major issue being the safe ejection of aircrew with NVG and NVG modified helmets. Two options have been identified for solving this problem: namely the modification of the current Gentex HGU-55 helmets and the design of a new helmet incorporating a reliable NVG connection/disconnection device (i.e., a mechanical system fully integrated in the helmet frame), with embedded automatic disconnection capability in case of ejection.

Optical resonances of microresonators, also known as whispering gallery modes, are attracting considerable interest as highly sensitive measuring devices with a variety of applications. Such resonators can be used for pressure, force or strain measurement. Droplets, embedded in an appropriate substrate, form perfect spheres due to their surface tension and can be used as optical resonators with high quality factors. The resonance frequencies of these droplets depend sensitively on their size and shape. Pressure changes affect the droplet shape. Therefore, pressure change can be measured with high sensitivity. In the work presented here, ethanol droplets embedded in a silicone matrix are considered. The shift of the resonance frequencies of microdroplets embedded in silicone as function of the applied pressure is investigated.

We present a model of a cavity optomechanical magnetic field sensor based on a microtoroidal resonator. The magnetic field induced expansion of a magnetostrictive material is transduced onto the physical structure of a highly compliant optical microresonator. The resulting motion is read out optically with ultra-high sensitivity. According to our theoretical model sensitivities of up to 750 fT/√ Hz may be possible. The simultaneous presence of high-quality mechanical and optical resonances in microtoroids greatly enhances both the response to the magnetic field and the measurement sensitivity.

An IC-Compatible Linear-Variable Optical Filter (LVOF) for application in the UV spectral range between 310 nm and 400 nm has been fabricated using resist reflow and an optimized dry-etching. The LVOF is mounted on the top of a commercially available CMOS camera to result in a UV microspectrometer. A special calibration technique has been employed that is based on an initial spectral measurement on a Xenon lamp. The image recorded on the camera during calibration is used in a signal processing algorithm to reconstruct the spectrum of the Mercury lamp and the calibration data is subsequently used in UV spectral measurements. Experiments on fabricated LVOF-based microspectrometer with this calibration approach implemented reveal a spectral resolution of 0.5 nm.

In construction and manufacturing the surface roughness and their control plays a major role. The mechanical test probes are used in many applications, because the advantage of the higher resolution of optical systems often plays no role. But in all cases the measurement systems were uses outside of fabrication processes due to the complex and expensive equipment. To overcome these we developed a roughness sensor suitable for an automated control of machined surfaces. The sensor is able to handle high throughput and parallel systems is due to the low cost available. Our solution is compact stand-alone sensors that can be simple integrated in existing systems like machine tools or transport systems. The sensor is based on a diode laser, focusing optics and a special silicon photo diode array in a stable housing. The single-mode VCSEL at 670 nm emission wavelength is focused on the surface of the sample at distance of 5mm. The light was reflected from the test surface and detected with an 8-channel photodiode array. The position of the main reflex allows an optimization of the sensor distance to the surface. During the movement of the sample with a known velocity roughness depended signals over time were recorded at 8 cannels. This allows a detection of the angular distribution of the scattered light in combination of position dependent refection. It was shown here that we be able to achieve resolution below the spot diameter (30μm FWHM). We verify the sensor capabilities for real world applications on drilled samples with typical roughness variations in micro meter range.

This paper describes the implementation of a low-cost technology platform for fluorescence-based optochemical sensors made up of arrays of multimode waveguides and coupling structures integrated onto a flexible substrate. Such a configuration is ideal for multi-analyte detection owing to a possibility of future integration of different dyes in each waveguides. The presence of light sources, fluorescent sensing elements and photodetectors in a foil platform makes it a compact optochemical sensor, which has wide-range of applications in medical, biochemical, and environmental diagnostics. Flexible lightguides fabricated using soft-lithography based replication techniques, are used in combination with 45° micromirror coupling structures, having a loss of 0.5dB. Fluorescent dyes are incorporated with the lightguides enabling a detection of shift in fluorescence-peaks in contact with gases, which are read-out at the detection. Initial measurements yielded promising results of the waveguides mixed with fluorescent dyes showing response to toluene.

We design the optical unit for an imaging time-of-flight scanner camera based on partially steerable micro mirrors. This new class of 3D cameras enables video frame rates and-in conjunction with the accompanying user software-online real-time selection of regions of interest. The challenges for the optical design comprise (i) sufficient light collection from close-up objects, (ii) maximizing optical efficiency for objects at large distances, (iii) reduction of the dynamical range of signal returns and (iv) minimization of parasitic scattering. We present a solution based on coaxial beam guidance, where the emitted beam first passes a beam splitter, is then deflected by a dedicated emission mirror in the center of a point-symmetrical, synchronized arrangement of five micro mirrors and finally passes a protective spherical glass cover. The mirror assembly is slightly displaced from the center of the dome in order to establish a secondary focus for parasitic reflections at the inside of the cover. The light scattered at the target surface which reaches the mirror array is directed towards an assembly of rhomboid prisms. These prisms reshape the distributed mirror array aperture such that a small lens with high numerical aperture suffices to focus the light onto a fast, small-area avalanche photo diode, thus maximizing the acceptance angle of the detector and permissible misalignments of the element mirrors.

We probe the dynamics of objective laser speckles as the axial distance between the object and the observation plane changes. With the purpose of measuring out-of-plane motion in real time, we apply optical spatial filtering velocimetry to the speckle dynamics. To achieve this, a rotationally symmetric spatial filter is designed. The spatial filter converts the speckle dynamics into a photocurrent with a quasi-sinusoidal response to the out-of-plane motion. Our contribution presents the technology and discusses the selectivity of the spatial filter. Specifically, we discuss how the selectivity of the spatial filter with regard to radial speckle motion is influenced by a concurrent in-plane speckle motion. The spatial filter is emulated with a CCD camera, and is tested on speckle acquisitions obtained from a controlled set-up. Experiments with the emulated filters illustrate performance and potential applications of the technology.

Optical microresonators constitute the basic building block for numerous precision measurements including single-particle detection, magnetometry, force and position sensing. The ability to resolve a signal of interest is limited however by various noise sources. In this tutorial style paper we provide a matrix formalism to analyze the effect of various modulations upon the optical cavity. The technique can in principle be used to estimate the sensitivity of microresonator based sensors and potentially to identify the optimal detection basis and cavity parameters to optimise the signal to noise ratio.

Spherical microresonators have been demonstrated to be potential label-free tools for identifying chemical species on the sub-nanoscale level. Here a novel sensor based on the high-Q spherical microresonators will be presented. Recently, it was demonstrated that WGM spherical microresonators provide surface second harmonic light generation from a low number of small molecules [1]. The sensor signal is in this case directly related to the chemical distribution found at the surface. Results will be presented for the proof of principle of a new device integrated by an inert material onto which a periodic patterning is lithographically imprinted allowing the WGM generation of the second harmonic of only those analyte molecules attached to the imprinted area. The realistic implementation of the device will be discussed, as well as its prospective capabilities for bio- and chemical-sensing for large and small molecules.

In this work, a compact low-cost system designed to detect low amounts of proteins in biological fluids is presented. The system, based on time-gated fluorescence detection principle, is composed by a Single-Photon Avalanche Diode (SPAD) pixel array, a LED excitation light source and a micro-machined reaction chamber coupled to a microfluidic network. A dual-site binding strategy based on DNA aptamers is used for target protein recognition. The microreactor, composed of an array of microwells covered with a transparent membrane, is functionalized with a primary aptamer, while a fluorescent-tagged secondary aptamer is used for the detection. Preliminary measurements demonstrate the feasibility of fluorescence lifetime detection to discriminate between different fluorophores. The detection of human thrombin protein in 300nM concentration is reported as a biological proof of principle of the biosensor.

Food quality is critically determined by its microstructure and composition. These properties could be quantified noninvasively by means of optical properties (absorption and reduced scattering coefficients) of the food samples. In this research, a spatially-resolved spectroscopy setup based on a fiber-optic probe was developed for acquiring spatiallyresolved diffuse reflectance of three sugar foams with different designed microstructures in the range 500 - 1000 nm. A model for light propagation in turbid media based on diffusion approximation for solving the radiative transport equation was employed to derive optical properties (absorption and reduced scattering coefficients) of these foams. The accuracy of this light propagation model was validated on four liquid phantoms with known optical properties. The obtained results indicated that the optical properties estimation was successfully validated on these liquid phantoms. The estimated reduced scattering coefficients μs' of the foams clearly showed the effect of foaming time on their microstructures. The acquired absorption coefficients μa were also in good agreement with the designed ingredients of these sugar foams. The research results clearly support the potential of spatially-resolved spectroscopy for nondestructive food quality inspection and process monitoring in the food industry.

We report on an optical planar Bragg grating evanescent wave refractive index sensor functionalized by a simple method against aromatic hydrocarbons such as benzene, toluene and xylene (BTX) in solvent vapor. To functionalize the sensor against BTX, substituted cyclodextrins are applied to the sensor surface using dip coating. Cyclodextrins have a hydrophobic cavity, which favors the accommodation of an organic molecule of appropriate dimensions leading to a non-covalent inclusion complex. The temporal sensor response reveals a multi-exponential rise towards an equilibrium state, whose level is found to be linearly related to the exposed analyte concentration. Taking into account the spectral resolution of the interrogation system we find a minimum concentration threshold of 200 ppm for benzene, 70 ppm for toluene and 20 ppm for m-xylene, respectively.

Non-dispersive infra-red (NDIR) gas detection has enjoyed a widespread uptake as a result of the development of sensors in the so-called pellistor format, consisting of a cylinder with external dimensions of 20 mm diameter x 16.5 mm height. We present a new design for such a sensor, making use of low-cost injection moulding technology. The new design pays particular attention to the problem of maintaining a high optical throughput while providing an acceptable optical pathlength for gas detection. A detailed analysis of the design is presented, with the results of optical raytracing, showing a raytrace estimate of 4% of the total emitted radiation reaching each of two separated detector elements and an optical pathlength of 32mm. The high throughput provides a number of advantages in helping to overcome detector noise in NDIR measurements. Finally, we show experimental results obtained with asmanufactured devices, demonstrating the superior signal to noise ratio achieved in measurement of carbon dioxide (CO₂). We believe the optical efficiency of the device, and the improved signal to noise ratio that results from this, to be a record for a device of these dimensions.

Flame spectroscopy is extensively used in the analysis of industrial combustion processes. A flame emits energy over a wide spectral region and its associated spectra contains both continuous and discontinuous components. In the literature there are models, based on either Planck's or Wien's law, for representing the flame spectral behavior under different combustion parameters; however, the non-linear nature of these models, the high dimension of the spectral data, and the superposition between the continuous and the discontinuous spectral emissions complicate the theoretical analysis of combustion processes. In this paper exploratory data analysis is used to derive data-driven models for combustion process monitoring. To do so, a database of measured spectra, collected from a real combustion process in the range of 400 to 800 [nm], is used as a priori information about the process. The database contains spectral information about continuous emissions of natural gas, oil, and bio-oil fuels at different combustion conditions. To summarize in a reduced number of terms the whole spectral information contained in the database, traditional as well as probabilistic Principal Component Analysis is conducted in order to create linear data-driven predictive models for combustion process monitoring. The predicting performance of the models is tested using the goodness-of-fit and the root-mean-squared error. The applicability of the models is finally tested by devising a simple automated solution for separating the discontinuous radiation from the continuous emission.

Wind power is one of the most promising green energy sources, especially when produced in offshore power plants. Corrective operations in wind turbines cause a considerable part of the maintenance costs of such plants. One preventive action for reducing such operations is the periodic off-line control of oil samples from the wind turbines. The time delay between sampling and availability of the results is a major disadvantage of this kind of controlling. In-situ condition monitoring is a solution to this problem. In-situ monitoring allows real time detection of random, time discrete events, thus enabling a better scheduling of preventive actions and reducing costs and downtime. Fluorescence spectroscopy is a complementary technique to absorption spectroscopy. Due to absorption of UV or visible light, the electrons of specific molecules are excited from a ground electronic state to a vibrational state of higher energy. By collision with other molecules, the excited electron looses a part of the acquired energy and relaxes to a lower vibrational state. The remaining acquired energy is emitted during the electron's transition to the ground state. The resulting frequency shift between excitation and emission energy, known as Stokes shift, is unique and characteristic for each active molecule. In this paper gear-oil condition monitoring based on fluorescence spectroscopy is proposed. Three typical commercial gear-oils for wind turbines were studied. The spectra gained by UV excitation of the samples were analyzed by means of partial least square (PLS) regression. Good prediction results were obtained for the total acid number (TAN). The latter is a measure for the oil acidity and is considered to be a proxy variable for oil age. Other parameters delivering information about gear-oil additive depletion and the related oil aging condition, like phosphor, sulfur and molybdenum concentration, were also analyzed.

Enhancement of the dynamic range of photodetectors used in advanced image sensors such as time-of-flight sensors or image sensors for automotive applications is a major research topic. In this paper an improved unipolar readout structure is presented, that is superior to the widely employed source follower readout implemented by enhancement MOSFETs. It yields a high output voltage swing and low noise, while requiring no additional processing steps. The readout structure is consisting of a low-noise JFET whose gates are formed by a floating diffusion, thus preserving in-pixel accumulation capability - which additionally improves noise performance. This structure outperforms a simple in-pixel implementation of a JFET and a photodetector in terms of the necessary area consumption, thus improving fill factor. For pixels with a pitch of several microns this readout structure is a good trade-off between area, output voltage swing and, most important, noise performance. Furthermore, since only a ground connection is needed for application, fill-factor and power-grid disturbances like DC-voltage drop can be additionally improved.

Several works have demonstrated the successfully integration of Single-photon avalanche photodiodes (SPADs) operating in Geiger mode in a standard CMOS circuit for the last 10 years. These devices offer an exceptional temporal resolution as well as a very good optical sensitivity. Nevertheless, it is difficult to predict the expected performances of such a device. Indeed, for a similar structure of SPAD, some parameter values can differ by two orders of magnitude from a technology to another. We proposed here a procedure to identify in just one or two runs the optimal structure of SPAD available for a given technology. A circuit with an array of 64 SPAD has been realized in the Tower-Jazz 0.18 μm CMOS image sensor process. It encompasses an array of 8 different structures of SPAD reproduced in 8 diameters in the range from 5 μm up to 40 μm. According to the SPAD structures, efficient shallow trench insulator and/or P-Well guard ring are used for preventing edge breakdown. Low dark count rate of about 100 Hz are expected thanks to the use of buried n-well layer and a high resistivity substrate. Each photodiode is embedded in a pixel which includes a versatile quenching circuitry and an analog output of its cathode voltage. The quenching system is configurable in four operation modes; the SPAD is disabled, the quenching is completely passive, the reset of the photodiode is active and the quenching is fully active. The architecture of the array makes possible the characterization of every single photodiode individually. The parameters to be measured for a SPAD are the breakdown avalanche voltage, the dark count rate, the dead time, the timing jitter, the photon detection probability and the after-pulsing rate.

The Laser MegaJoule (LMJ) facility will host inertial confinement fusion experiments in order to achieve ignition by imploding a Deuterium-Tritium filled microballoon [1]. In this context an X-ray imaging system is necessary to diagnose the core size and the shape of the target in the 10-100 keV band. Such a diagnostic will be composed of two parts: an X-ray optical system and a detection assembly. The survivability of each element of this diagnostic has to be ensured within the mixed pulse consisting of X-rays, gamma rays and 14 MeV neutrons created by fusion reactions. The design of this diagnostic will take into account optics and detectors vulnerability to neutron yield of at least 1016. In this work, we will present the main results of our vulnerability studies and of our hardening-by-system and hardening-by- design studies.

The work deals with studies of the grain size and surface state effect on photoelectric and transport properties of PbTe(In) films in the temperature range from 4.2 K up to 200 K under irradiation of a blackbody source and terahertz laser pulses. The PbTe(In) films were deposited on insulating substrates kept at the temperatures T_S equal to -120 (see manuscript) 250C. AFM, SEM, Auger spectroscopy and X-ray diffraction were used to study the film microstructure. Increase of the TS value led to mean grain size growth from 60 up to 300 nm. All films had a column-like structure with the columns nearly perpendicular to the substrate plane. It is shown that microstructure of the films strongly affects the photoconductivity character in the terahertz region of the spectrum. Positive persistent photoresponse is observed at low temperatures in the polycrystalline films. For these films transport and photoelectric properties are determined by the grain volume and impurity state specifics. Nanocrystalline films have all features of non-homogeneous systems with band modulation. For these films only negative photoconductivity is observed in the whole temperature range. Possible mechanisms of the photoresponse formation are discussed.

We report on the optical and structural characterization of InSb QDs in InAs matrix, grown on InAs (100) substrates, for infrared photodetection. InSb has 7% lattice mismatch with InAs forming strained QDs, which are promising for longwave IR applications, due to their type-II band alignment. This report contains material development results of InSb QDs for increasing their emission wavelength towards long-wave IR region. Samples were grown by two techniques of MBE and MOVPE, with different InSb coverage on InAs (100) substrates. Structures grown by MBE reveal QD related photoluminescence at 4 μm. AFM investigations of the MBE grown structures showed uncapped dots of ~ 35 nm in size and ~ 3 nm in height, with a density of about 2 x 10¹⁰ cm^-2. Cross-section TEM investigations of buried InSb layers grown by MBE showed coherently strained QDs for nominal InSb coverage in the range of 1.6 - 2 monolayers (MLs). Layers with InSb coverage more than 2MLs contain relaxed QDs with structural defects due to large amount of strain between InSb and InAs. Samples with such large dots did not show any InSb related luminescence. The MOVPE grown InSb samples exhibit a strong QD related emission between 3.8 to 7.5 μm, depending on the amount of InSb coverage and other growth parameters. We report the longest wavelength observed so far in this material system.

The use of a shorter delay line in a optoelectronic phase noise measurement system working in X-band, allow a characterization of the phase noise far from the carrier. Fourier frequency analysis can be extended from 10⁵ to 2.10⁶ Hz by introducing a 100 m delay line in addition of a 2 km optical fiber.

Ways of improving autocollimation sensors for monitoring angular displacements are analyzed. The results of an analysis of control elements based on tetrahedral reflectors with flat and cone reflecting sides are presented. The technical characteristics of experimental models of control elements are presented. The features of tetrahedral reflector as the control elements for three-axis angular sensors are discussed.

This paper presents the design, fabrication and characterization of Infra-Red (IR) Linear Variable Optical Filter (LVOF)- based micro-spectrometers. Two LVOF microspectrometer designs have been realized: one for operating in the 1400 nm to 2500 nm wavelength range and another between 3000 nm and 5000 nm. The IR LVOFs have been fabricated in an ICCompatible process using resist reflow. The LVOF provides the possibility to have a small size, robust and highresolution micro-spectrometer in the IR on a detector chip. Such IR microspectrometers can be fabricated at low-cost in high volume production and have huge potential in applications such as liquid identification (e.g. water in alcohol, water in oil) and gas sensing.

We present the results of a study into the noise behaviour of an Avaspec-3648 CCD UV spectrometer for use in a spectroscopic gas detection system. A comparison was made between a deuterium UV lamp and a range of newly developed UV LEDs. A number of noise phenomena were identified and quantified including source fluctuation noise, photo-response non-uniformity (PRNU), dark current noise, fixed pattern noise (FPN) and read noise. For spectral measurements the dominant noise phenomenon was PRNU, giving a noise equivalent absorption (NEA) of 8 x 10^-3 AU. A set of noise limitation techniques is presented, which decreases the NEA to 2 x 10^-3 AU.

We present the design modelling and fabrication of Silicon-On-Insulator (SOI) nanobeam cavities that are immersed in a microfluidic system for refractive index sensing. The device has sensitivity value of greater than 200 nm/RIU with a Q-factor more than 20 000 in water. It was fabricated on a SOI platform and working at telecom wavelengths. The use of the SOI platform also offers further possibilities of integration with CMOS technologies.

In the field of biomedical imaging there is a strong interest in combining modalities of positron emission tomography (PET) and magnetic resonance imaging (MRI). An MRI-compatible PET detector module has to be insensitive to the magnetic field that is why it needs to incorporate avalanche photodiodes (APD) or silicon photomultipliers (SiPM). We propose a new purely optical characterization method for these devices where no nuclear source is needed. In our method we use LED sources for both the direct illumination of silicon sensors and fluorescent excitation of the scintillator material. With this method we can measure the response characteristic and uniformity of pixels in sensor arrays as well as the optical cross-talk between neighboring pixels. In the same experimental setup we can also emulate the pulse response of the detector module (i.e. light-spread over the sensor array from a point source in the scintillator material). We present the detailed construction of the experimental setup and analyze the benefits and drawbacks of this method compared to the nuclear measurements. The viability of the idea is proven through the characterization of a SiPM array and a block detector module based on it.

It can be expected that the range of applications for FBG-based strain and temperature sensors would expand if the accuracy of this sensor technique was improved. In this study, polarization effects of FBG sensors, which contribute significantly to the measurement uncertainty of this technique, were investigated. Therefore, FBGs were inscribed into highly birefringent optical fibers. These sensor elements were attached to a specimen with defined orientations of the fiber's slow and fast axes with regard the specimen's surface. We observed a change of the fiber's birefringence in the order of 5 10^-5 as a consequence of the gluing process, that was employed to attach the fiber onto the specimen. The strain sensitivities were determined for each polarization mode and for different fiber orientations using a highly accurate strain calibration facility. It was found that in all experiments the strain sensitivity for the slow axis was significantly higher (about 0.8%) than for the fast axis. The strain sensitivity also depends on the orientation of the fiber's birefringent axes with regard to the surface of the specimen. Although the investigations were performed with FBGs inscribed into birefringent fibers, the findings are still of importance for understanding the polarization-dependant accuracy limits of FBGs in standard single-mode fibers.

In this paper we present the field testing results of a low-cost all-fibre polarimetric current sensor for the monitoring of current in the European high-speed railway network. The sensor fulfils the requirements of robustness, sensitivity, accuracy and cost required for the monitoring of catenary current in changeover sections. Changeover sections are nonfed sections of the catenary that are placed between sections fed with different phases and that introduce discontinuities in the current collection done by the train. Since the train passes at high-speed between the two sections, an electric arc can be formed that may lead to significant damage of the infrastructure. To avoid this situation, it is essential to ensure the switch-off of the current collection before arriving and switch-on again when the changeover section is passed. An adequate protection system that monitors the current in the catenary before the changeover section allows to trigger the necessary protection mechanisms in the infrastructure. Efficient, robust and lightweight electrical current sensors are therefore essential for this security system. The sensor proposed here uses the Faraday magneto-optic Effect with a well-known polarimetric interrogation method. The optical configuration is extremely simplified through the use of few cost-effective, all-fibre devices with a simplified alignment. It allows high sensitivity for low current values, demonstrating a resolution below the ampere level with a dynamic range up to 500 A. The setup is electronically self-referenced to reduce the effect of small misalignments in the polarization, power variations in the optical source, temperature changes, birefringence effect and bending-induced attenuation in the lead fibre. A set of temperature tests in a climatic chamber were also performed in a range of temperature between -20 up to 80ºC, to assess the robustness of the device to operating temperature variations. The field tests include tests during commercial operations and special tests simulating fault conditions.

Charge-coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) matrices offer excellent features in imaging systems. A suitability evaluation of either technology according to a specific application requires a complete characterization of the different detector types. A system is optically characterized by the modulation transfer function (MTF), which represents its response in spatial frequency of this system. One of the methods to measure the MTF uses a laser speckle pattern as the object. Here, we comparatively examine the results provided by the speckle method to determine the MTF for detectors of two types: CCD and CMOS. We generate the speckle pattern using a laser and an integrating sphere with an aperture at its exit port. The aperture determined the spatial-frequency content of the pattern registered in the detector. The precision in determining the MTF of the CCD was studied using two different apertures: a single-slit and a double-slit. For the single-slit, we propose a new procedure of fitting the experimental data which resolves the drawbacks of the conventional procedure. To study the CMOS detector, we used the single-slit because it offered lower uncertainty and better reproducibility. The differences between the MTF values of the CCD and the CMOS detectors proved significant for the spatial frequencies higher than 50 cycles/mm, which is half of the interval studied with both arrays. For these spatial frequencies, our results demonstrate that the CCD detector presented MTF values higher than those of the CMOS array.

Laccases are cuproproteins belonging to the group of oxidoreductases that are able to catalyze the oxidation of various aromatic compounds (particularly phenols) with the concomitant reduction of oxygen to water. They are characterized by low substrate specificity and have a catalytic competence which widely varies depending on the source. Additionally, laccases have also very peculiar optical properties due to their copper active sites which participate to the reduction processes. All these characteristics make laccases very flexible biotic element for biotechnological applications. During the years, a number of studies have been devoted at exploiting catalytic properties of laccases and very few at profiting of their optical properties. Some preliminary studies by absorption, fluorescence FT-IR and Raman spectroscopies of commercial laccases have evidenced their potential usefulness for optical biosensing of phenol compounds as cathecol. Moreover the sol-gel process offers a convenient and versatile method for preparing optically transparent matrices at room temperature that can represent a very convenient support for laccase immobilization. Also for immobilised enzymes the above-mentioned techniques have allowed a detailed characterization of their optical properties that confirmed the potentials of laccases in optical biosensors and represented a fundamental step in the designing of an optimised optical biosensing scheme.

The present paper focuses on the development of an optimized version of the Proximity Electronics (PE) for dust analysers based on static light scattering. This kind of instruments, aimed to the systematic measurement of the size of dust grains in Martian atmosphere, was developed by the Cosmic Physics and Planetology Group at the INAF Astronomical Observatory of Capodimonte (OAC) and University Parthenope (LFC group), in Naples, Italy. One of these instruments, the MEDUSA Experiment, was selected for the Humboldt Payload of the ExoMars mission, the first mission to Mars of the ESA Aurora Programme. Thereafter, this mission was revised because of increasing costs and lack of funds and the MEDUSA experiment has been completely re-engineered to meet more demanding constraints of mass and power consumption. The dust analyser under development is named MicroMED, as it is a lighter and more compact version of MEDUSA. MicroMED is provided with an Optical System (OS) based on the same concept of the one present in MEDUSA, but with a low power PE and low power laser source. This paper reports the features and the tests results of three versions of low power PE developed for MicroMED, and also compares two basic approaches, one based on a linear amplifier, derived from the solution implemented in two different MEDUSA breadboards (B/Bs), and the other one based on a logarithmic amplifier, with better performance in terms of compactness and low power consumption.

In this paper we studied the photosensitivity and scatter properties of several types of photopolymers that are used in the printing industry. We applied different measurement methodologies to experimentally characterize both the absorption and scatter properties of the photopolymers. In a first part we measured the absorption spectra of different unexposed photopolymers in the range between 350 and 1600 nm. From these spectra we calculated the absorbance coefficients. After this, we repeated this procedure for the cured material which we obtained by illuminating the photopolymers with a laser source. We investigated the absorption properties for different illumination times in the range between 0 and 2000 ms. From these measurements we could calculate for the different materials the difference in absorbance between the cured and the non-cured material. Depending on the material the absorbance of the non-cured material was a factor 20 to 60 higher compared to the absorbance of the cured material. These results were used as input for the optical model. In a next step we measured the BTDF for the different materials and calculated the scatter angle at 1/e². As a result we obtained scatter angles between 2° and 6°. In a last step we verified and confirmed these differences in scatter behavior by measuring the MTF of a real imaging system that included the photopolymer.

In this paper we studied the reflectance spectra of different green vegetables. The main objective was to identify the wavelength(s)(areas) that are the most sensitive to variations in pigment composition. With this we try to meet the ever growing demand from society to classify food products on their quality which is related to the state of ripening and degradation. The group of investigated samples consisted of a group of seven different green vegetables. Because these products have different pigment compositions they formed the ideal test samples for our research. For each product type we measured the reflectance spectra between 400 and 800 nm for 30 samples. From these spectra we investigated three different types of measurands: the measurands that are nowadays commonly used to monitor color differences, the vegetation indices that are defined to monitor plant leaves and measurands that are taking into account the entire reflectance spectrum in the visible part of the electromagnetic spectrum. The main conclusion of our research was that a combination of the first two mentioned types of indices allowed us to identify the different product groups in an optical way.

This paper presents the design and fabrication of semi-reflective in-fiber mirrors and their usage for the realization of different miniature fiber sensors. The fabrication of a semi-reflective in-fiber mirror is based on the selective chemical etching and splicing of standard single-mode fibers (SMF). The mirror's reflectance can be set precisely in between any range between 0.1% and 9.5 %. The practical usability of the produced in-fiber mirrors was evaluated by the fabrication of an in-line temperature sensor and evanescent field refractive index (RI) sensor. A temperature sensor is an intrinsic type of in-line FPI, formed between an in-fiber mirror and a flat-cleaved optical fiber tip. As an example, a temperature sensor that was optimized within a range from 0 to 100°C showed a temperature resolution better than 0.1 °C, and a repeatability better than 0.2 °C. The evanescent RI sensor was created by the splicing of a small-diameter SMF between two in-fiber mirrors and removing of the intermediate fiber-cladding by chemical etching. The effective index of the fundamental mode depended on the surrounding-medium RI, which was interrogated by a spectrally-resolved technique. A high sensitivity of 830 nm/RIU was measured at RI of 1.444.

A simple multiple-angle light scattering system was developed for the differential measurement of particle concentrations in suspension even in high concentration where multiple scattering effects are significant based on size. The system combines multiple-angle detection to collect scattered angle dependent light intensities, and Partial Least Square Regression method (PLS-R) to compose the predictive models for analyzing scattered signal obtain concentrations of samples under investigation. The system was designed to be simple, portable and inexpensive. It employs a diode lasers (red AlGaInP-based) as a light source and a silicon photodiode as a detector and optical components, all of which are readily available. The technique was validated using 1.1 μm and 3.0μm polystyrene latex beads in both mono-dispersed and poly-dispersed suspensions. The measurement results showed good agreement between the measured results and reference values. Their deviations from the reference values are 2.4% and 1.5% relating to references' concentrations of 1.3×10⁸ and 1.2times;10⁷ particles/ml for 1.1 m and 3.0 μm in mono-dispersed solutions and 2.3 % and 3.5% relating to references' concentrations of 1.1times;10⁸ and 4.4 times;10⁵ particles/ml for 1.1 μm and 3.0 μm in mixed solutions, respectively. This system is a compact but high performance system allowing multiple particle sizes in high concentration to be measured simultaneously.

The photodiode (PD) is a key component in optical transmission and optical measurement systems which receive optical signals and convert them into electric signals. High speed, high responsivity, high power and low dark current are desirable attributes of the PD in these applications, but also a simple fabrication process for high yield and low cost is essential for industry production. In this paper, an undercut-air-bridge high speed InGaAs/InP PIN structural photodiode is presented. By utilizing the crystal orientation dependent wet etching of InP material and designing the arms of the bridge with proper angle, the air bridge was easily obtained, which greatly eased the fabrication. The fabricated devices with 120μm×3μm ridge waveguides work robustly up to 30GHz in the measurements and potentially faster with optimized material.

This work reports the surface functionalisation of evanescent waveguide sensors to immobilise E. coli. In biosensors, the surface functionalisation is an important treatment to ensure that the sensor properly detects the cells of interest. In this paper, we study the thin film surface functionalisation of a TiO₂ evanescent waveguide sensor and their effect on light transmission for the early detection of E. coli in post colon surgery. TiO₂ deposited using atomic layer deposition (ALD) is used as waveguide material. Four layers are used in the functionalisation : the self-assembled monolayer (SAM), the protein, 1-ethyl-3-(3-dimethylaminopropyl) (EDC) and the antibodies. Aminopropyltriethoxysilane (APTES) is used as SAM and reacts with -OH group (hydroxyl). The -OH group must be provided on substrate. In order to have the proper -OH group we deposited 10 nm SiO₂ on the waveguides using PECVD and then treated the samples in oxygen plasma chamber for 2 minutes to create the groups. Afterward APTES is immediately applied on the surface after every layers of the functionalisation process. The second layer (Protein A) of the functionalisation is then put on APTES as interlayer. EDC is used as crosslink agent between APTES and antibodies. The light of Superluminescent light emitting diodes (SLEDs) (λ = 1.3 μm, 400 mA) is channelled using an optical fibre into the functionalised waveguides. The transmitted light is measured with a photodiode. The sensitivity of the sensor was evaluated using several different drain fluid concentrations in medium.

A theoretical model of surface plasmon resonance (SPR) fiber-optic sensor based on the theory of attenuated total internal reflection is presented. The analysis of the sensor response is carried out in frame of optics of multilayered media. Some of the studied SPR sensors use the oxide or semiconductor overlayer for the protection of the metallic layer generating the surface plasmon wave. In the same time, the overlayer can help to improve the sensitivity of the sensor. The semiconductor overlayer protects the metal against the oxidation, but a native oxide layer can be formed on its top surface, when exposed to the atmosphere. This effect has been scarcely addressed, even if it can have an influence on the functionality of the sensor. In our case, the structure contained a metallic layer covered by silicon with oxide layer. The influence of the oxide layer thickness on the sensor performance in wavelength domain is studied in detail. The calculation of optical power transmitted through the multimode sensing fiber is carried out in order to evaluate the response of the sensor. The effect of the dispersion of all involved media is taken into account. The thickness of the metal layer in the sensing structure has been optimized to achieve the most pronounced dip at the resonance condition. The performance of the sensor is described in terms of sensitivity and detection accuracy.

Quartz-enhanced photoacoustic spectroscopy with a near infrared distributed feedback diode laser at 1.53 μm is demonstrated for acetylene detection at atmospheric pressure and room temperature. The P(9) absorption line in the ν₁+ν₃ band of C₂H₂ is selected for light absorption and photoacoustic pressure wave excitation. A pair of resonant tubes with optimal dimensions is used in combination with a quartz tuning fork for photoacoustic signal enhancement. The wavelength of diode laser is modulated at half of the resonant frequency of tuning fork for second harmonic signal detection. The effect of residual amplitude modulation is theoretically analyzed and compared with the experimental results. A noise-limited minimum detectable concentration (1σ) of 2 part-per-million (ppm) is achieved with a 7-mW laser power and a 1-s lock-in time constant, corresponding to a normalized noise equivalent absorption coefficient of 5.4×10^-8 cm^-1 W/√Hz.

A demodulation scheme is presented for a hybrid sensing system based on a polarimetric fiber sensor and a fiber Bragg grating (FBG) for composite structural health monitoring (SHM). The demodulation module is comprised of a Thin Film Filter Wavelength Division Demultiplexer (TFF WDM- Demux) and an Electro-optic (EO) modulator. Unlike "laboratory-use" demodulation systems which typically do not need a compact form factor, the proposed miniaturized demodulation system is compact, lightweight and has low power consumption. The bandpass responses of the TFF WDM- Demux are designed to match the peak reflected wavelengths of the FBGs so that the differential wavelength information can be converted to intensity variations recorded by the array of detectors connected to the output channels of the TFF WDM- Demux. In the polarimetric sensor demodulation section of the system, an electrical control voltage is applied to the electro-optic modulator in order to shift the polarimetric sensor output to the maximum sensitive linear response region. Two types of polarimetric fiber sensors are used; a Panda fiber and a polarization maintaining photonic crystal fiber. The polarimetric strain sensors provide the average strain and temperature information, while the fiber Bragg grating sensors give localized strain information. The demodulation system uniquely allows for the multiple outputs of FBG and polarimetric sensors to be converted to a common optical intensity domain, for strain and temperature measurements.

In this work, we analyze a remote optical sensor system based on Raman amplification, composed by one Long Period Grating (LPG) as a sensor head, separated by 50 km from the optical source, and the interrogation unit composed by two Fiber Bragg Gratings (FBGs) modulated by two Piezoelectrics Transductors (PZTs). Optical fiber sensor systems are typically limited to operate at distances of only few kilometers due to the attenuation effects and noise present in the optical fiber that adversely affects the performance of the sensor interrogation process. We present experimental and simulated results obtained in the context of the analysis of remote optical fiber sensors. The simulation models compute the Raman interaction between the pumps and the sensor signals and allow speeding up the analyses regarding the setup to be experimentally implemented in order to measure/monitor environmental temperature. Experimental results obtained in the implemented setup show that under Raman amplification the power ratio between the two central wavelengths of the FBGs has a linear relation with the change of the LPG resonance induced by environmental temperature.

For condition monitoring of large scale electrical power transformers, a fiber-optic multi-stress sensor system was constructed by combining fiber-optic acoustic sensors and fiber Bragg grating temperature sensors in a fiber-optic Sagnac interferometer. To separate the grating signals from the interferometer output, an attenuator was placed at an asymmetrical position in the Sagnac loop. By balancing the counter propagating light intensities with the attenuator, the background noises could be suppressed to obtain grating signals with enough signal-to-noise ratio. With the preliminary experiments, the temperature and the vibration information at multiple locations could be measured simultaneously with single optical circuit and signal processing unit.

We used a bimetallic strip to increase the sensitivity of a fiber Bragg grating temperature sensor. The temperatureinduced deflection of the strip strained the FBG sensor, increasing the Bragg wavelength shift in addition to the temperature-induced one. The total Bragg wavelength shift is about 4 times larger than that of the intrinsic FBG temperature sensor. With experiments in various conditions, the sensitivity characteristics according to the bimetal parameters were analyzed and the feasibility of the suggested sensor has been shown

We demonstrated a tunable long wavelength photodetector by using heteroepitaxy growth of InP-based In_0.53Ga_0.47As-InP p-i-n structure on GaAs based GaAs/AlAs Fabry-Perot filter structure. High quality heterepitaxy was realized by employing a thin low-temperature buffer layer. A wavelength tuning range of 10.0 nm, a quantum efficiency of 23%, a spectral linewidth of 0.8 nm and a 3-dB bandwidth of 6.2 GHz were simultaneously obtained in the device. Moreover, a Si based long wavelength photodetector with the same device structure was also fabricated successfully by using Si/GaAs and GaAs/InP heteroepitaxy. Crack-free GaAs on Si and high-quality epilayer with area of 800μm×700μm was obtained by using mid-patterned growth and thermal-cycle annealing. The Si-based photodetector with spectral linewidth of 1.1nm (FWHM) and quantum efficiency of 9.0% was demonstrated.

A miscellaneous of 86 beers was characterized by non-destructive, fast and reagent-free optical measurements. Diffuselight absorption spectroscopy performed in the visible and near-infrared bands was used to gather a turbidity-free spectroscopic information. Also, conventional turbidity and refractive index measurements were added for completing the optical characterization. The near-infrared spectra provided a straightforward turbidity-free assessment of the alcoholic strength. Then, the entire optical data set was processed by means of multivariate analysis looking for a beer clustering according to the own character and identity. Good results were achieved, indicating that optical methods can be successfully used for beer authentication.

A single mode fiber optic vibration senor is designed and demonstrated to monitor the vibration of a simply supported beam. A rectangular beam (length 30.8 cm, width 2.5cm and thickness 0.5mm) made of spring-steel is arranged as simply supported beam and is made to vibrate periodically. To sense the vibrations a telecommunication fiber is chemically etched such that its diameter reaches 50μm and is glued using an epoxy at the centre of the beam. A broadband light (1550nm) is launched into Fiber Bragg Grating (FBG) through a circulator. The light reflected by the FBG (1540.32nm) is coupled into the centre etched fibre through the circulator and is detected by photodiode connected to a transimpedance amplifier. The electrical signal is logged into the computer through NI-6016 DAQ. The sensor works on transmission power loss due to the mode volume mismatch and flexural strain (field strength) of the fiber due to the bending in the fiber with respect to the bending of the spring-steel beam. The beam is made to vibrate and the corresponding intensity of light is recorded. Fast Fourier transform (FFT) technique is used to measure the frequencies of vibration. The results show that this sensor can sense vibration of low frequency accurately and repeatability is high. The sensor has high linear response to axial displacement of about 0.8 mm with sensitivity of 32mV/10μm strain. This lowcost sensor may find a place in industry to monitor the vibrations of the beam structures and bridges.

This study focused on the development of high sensitivity pressure sensor based on reduced clad FBG encapsulated in a stainless steel cylinder, partially filled with silicon rubber. The sensor works by means of transferring radial or lateral pressure into an axially stretched- strain along the length of the FBG. The experiment is carried out using two different FBG's have core/clad diameters of 9/125μm (FBG1) and 4/80μm (FBG2). FBG2 is chemically etched to reduce the cladding diameter which significantly enhances the pressure sensitivity. The shift of the Bragg wavelength in response to applied pressure is monitored with an optical spectrum analyser (OSA). The measured pressure sensitivity of FBG2 and FBG1 are found to be 5.85 x 10^-2 MPa^-1 and 2.07 x 10^-2 MPa^-1, which are approximately 18870 and 6677 times respectively higher than that can be sensed with a bare FBG. A very good linearity is observed between Bragg wavelength shift and pressure. This compact, low cost and robust design of the sensor can find applications in the areas of low and medium pressure measurement.

Tilted fiber Bragg gratings (TFBGs) present a refractive index modulation blazed by a few degrees in the plane perpendicular to the optical fiber axis. This results in two kinds of couplings: self-backward coupling of the core mode and numerous backward couplings between the core mode and the cladding modes. TFBG transmitted amplitude spectra are therefore characterized by several tens of cladding mode resonances that possess their own sensitivity to the surrounding refractive index (SRI). TFBGs naturally allow the realization of refractometers accurate to 10^-4 RIU (refractive index unit) in the SRI range between 1.33 and 1.45 (refractive index of silica). In this work, we demonstrate that a dense thin film of zinc oxide, a high refractive index material (n=1.9), deposited by RF sputtering in two steps, on the TFBGs tightly modifies their transmitted amplitude spectra. While the wavelength difference between orthogonally polarized modes in nude TFBGs remains within a few picometers, the association of a nanoscale metal oxide coating increases this difference up to 500 picometers. This results in two main assets: the sensitivity is extended to SRI values above 1.45 while the strong polarization dependency makes the demodulation process easier.

This paper presents a sensor based on a Tilted Fiber Bragg Grating (TFBG) covered with a mesoporous coating consisting of ZnO nanoparticles for the detection of volatile organic compounds. TFBGs are Bragg gratings that are tilted by a small angle inducing a coupling between the forward-going fundamental core mode and the backward-going cladding modes. They present a transmission amplitude spectrum consisting of several tens of resonances, which present their own sensitivity to the surrounding refractive index. Specific sensors can be built by using TFBGs covered with a dedicated coating that changes its refractive index when in contact with target chemical species. This concept was illustrated with ethanol and a mesoporous ZnO coating whose refractive index changes due to the gas adsorption on the ZnO particles. The exposure to ethanol vapors of the covered TFBG yields important modifications of the transmission amplitude spectrum in the range 1510-1590 nm. All cladding mode resonances show a red shift while their peak-to-peak amplitude decreases with increasing ethanol concentration in air. The response, defined as the amplitude or the wavelength change of a resonance peak, is fast (1s), linear, reversible and without hysteresis (red shift of 60 pm/vol% ethanol and -3.3 dB/vol% at 1550 nm).

To achieve the quantitative optical non-invasive diagnosis of blood during extracorporeal circulation therapies, the instrumental technique to extract extracellular spectra from whole blood was developed. In the circuit, the continuous blood flow was generated by a centrifugal blood pump. The oxygen saturation was maintained 100% by an oxygenator. The developed glass optical flow cell was attached to the outlet tubing of the oxygenator. The halogen lamp including the light from 400 to 900 nm wavelength was used for the light source. The light was guided into an optical fiber. The light emitted by the fiber was collimated and emitted to the flow cell flat surface at the incident angle of 45 degrees. The light just reflected on the boundary between inner surface of the flow cell and plasma at 45 degrees was detected by the detection fiber. The detected light was analyzed by a spectral photometer. The obtained spectrum from 400 to 600nm wavelength was not changed with respect to the hematocrit. In contrast, the signal in the spectral range was changed when the plasma free hemoglobin increased. By using two spectral range, 505±5 nm and 542.5±2.5 nm, the differential spectrum was correlated with the free hemoglobin at R²=0.99. On the other hand, as for the hematocrit, the differential spectrum was not correlated at R²=0.01. Finally, the plasma free hemoglobin was quantified with the accuracy of 22±19mg/dL. The result shows that the developed plasma surface reflectance spectroscopy (PSRS) can extract the plasma spectrum from flowing whole blood.

The paper describes the realization of a complete optical imaging device to clinical applications like brain functional imaging by time-resolved, spectroscopic diffuse optical tomography. The entire instrument is assembled in a unique setup that includes a light source, an ultrafast time-gated intensified camera and all the electronic control units. The light source is composed of four near infrared laser diodes driven by a nanosecond electrical pulse generator working in a sequential mode at a repetition rate of 100 MHz. The resulting light pulses, at four wavelengths, are less than 80 ps FWHM. They are injected in a four-furcated optical fiber ended with a frontal light distributor to obtain a uniform illumination spot directed towards the head of the patient. Photons back-scattered by the subject are detected by the intensified CCD camera; there are resolved according to their time of flight inside the head. The very core of the intensified camera system is the image intensifier tube and its associated electrical pulse generator. The ultrafast generator produces 50 V pulses, at a repetition rate of 100 MHz and a width corresponding to the 200 ps requested gate. The photocathode and the Micro-Channel-Plate of the intensifier have been specially designed to enhance the electromagnetic wave propagation and reduce the power loss and heat that are prejudicial to the quality of the image. The whole instrumentation system is controlled by an FPGA based module. The timing of the light pulses and the photocathode gating is precisely adjustable with a step of 9 ps. All the acquisition parameters are configurable via software through an USB plug and the image data are transferred to a PC via an Ethernet link. The compactness of the device makes it a perfect device for bedside clinical applications.

Fluorescent chemical sensors have been widely exploited for the detection and quantification of trace explosives. Their performances are mainly dependent on the sensitive material. Fluorescent organic materials are very efficient in terms of sensitivity, selectivity and response time but their degradation is a major drawback. Sol-gel materials offer a much longer life span, especially in the case of inorganic sensitive coatings. The elaboration of sol-gel sensitive films is detailed in this paper. Two examples of sol-gel fluorescent sensitive materials are presented: a hybrid organic-inorganic film and an inorganic material.

The paper presents the exemplary application and comparison of a macrobend seismic optical fiber accelerometer and ferrule-top cantilever fiber sensor for long distance vibration monitoring with use of typical telecommunication optical transmission systems including optical fibers, transmitters and receivers. Use of telecommunication optical systems allows developing cost-effective monitoring and sensing architecture. All-optical fiber sensors do not create any fire hazard due to transmitting low power light through the optical fibers and lack of electrically driven parts in sensing part. Optical fiber macrobend seismic sensor consists of single mode optical fiber bended into a loop of radius around few millimeters with attached small seismic mass around 0.3 grams. We achieve signal that is proportional to the geometrical deformation of the loop. The ferrule-top cantilever (made by Optics11 - Amsterdam, Netherlands) optical fiber sensor is fabricated on a rectangular 3 mm x 3mm x 7 mm glass ferrule equipped with a central borehole and laser curved cantilever with dimensions of 200 microns wide, 30 microns thick and around 3 mm long. Construction allows measuring bending of the cantilever. Both optical fiber sensors in this setup measure force and acceleration similar to the piezoelectric accelerometers. The advantage of these devices is insensitivity to electromagnetic interference because of all-optical sensor head. We compared parameters and measurement capabilities of both sensor types.