This PDF file contains the front matter associated with SPIE Proceedings Volume 7356, including the Title Page, Copyright information, Tabe of Contents, Introduction (if any), and the Conference Committee listing.

The Computer Screen Photo-assisted Technique (CSPT) utilizes a computer screen as a light source and a web camera as a detector for optical measurements. This provides a ubiquitous instrumentation for several bioanalytical situations. In the present contribution we first describe CSPT briefly, demonstrate the possibility to make optical fingerprinting of fluorescent color indicators and give a mini-review of our recent demonstration of CSPT based surface plasmon detection. Although we have no results yet specifically aimed at real biosensing, we point out the possibilities to make affinity based biosensing with CSPT.

Micro-ring resonators have been widely employed, in recent years, as wavelength filters, switches and frequency converters in optical communication circuits, but can also be successfully used as transducing elements in optical sensing and biosensing. Their operation is based on the optical coupling between a ring-shaped waveguide and one or more linear waveguides patterned on a planar surface, typically an input and an output waveguide. When incoming light has a wavelength which satisfies the resonance conditions, it couples into the micro-ring and continuously re-circulates within it. A fraction of this resonant light escapes the micro-ring structure and couples into the output waveguide. The presence of a target analyte over the top surface of the micro-ring (i.e. within the evanescent field) changes the effective refractive index of the mode propagating into the structure, thus causing a shift in resonance wavelength which can be determined by monitoring the spectrum at the output port. Proper functionalization of the micro-ring surface allows to add selectivity to the sensing system and to detect specific interaction between a bioprobe and its proper target (e.g. protein-ligand, DNA-cDNA interactions). We present our preliminary results on the design of micro-ring resonators on silicon-on-insulator substrate, aimed at selective detection of several biomolecules. The design of the structure has been accomplished with the help of FDTD 2D numerical simulations of the distribution of the electromagnetic fields inside the waveguides, the micro-ring and near the micro-ring surface. Furthermore, all the functionalization reactions and the bio/non-bio interfaces have been studied and modelled by means of spectroscopic ellipsometry.

We report here the fabrication, charaterisation and refractive index sensing of two microchanneled chirped fiber Bragg gratings (MCFBGs) with different channel sizes (~550μm and ~1000μm). The chirped grating structures were UV-inscribed in optical fibre and the microchannels were created in the middle of the CFBGs by femtosecond (fs) laser assisted chemical etching method. The creation of microchannels in the CFBG structures gives an access to the external index liquid, thus inducing refractive index (RI) sensitivity to the structure. In comparison with previously reported FBG based RI sensors, for which the cladding layers usually were removed, the MCFBGs represent a more ideal solution for robust devices as the microchannel will not degrade the structure strength. The two MCFBGs were spectrally charaterised for their RI and temperature responses and both gratings exhibited unique thermal and RI sensitivities, which may be utilised for implementation of bio-chemical sensors with capability to eliminate temperature crosssensitivity.

The performance of a recently demonstrated silicon nitride slot-waveguide microring resonator biochemical sensor is analyzed. The slot-waveguide sensor is optically modeled by using finite element method, full-vectorial and semi-vectorial finite-difference beam propagation methods. Numerical calculations are discussed and compared to the sensor experimental performance. This study includes homogeneous sensing -by using different aqueous solutions-, surface sensing -due to both, surface etching and biomolecular layer adhesion-, and power coupling characteristics of the microring sensor. It is found that all of the aforementioned numerical methods provide good agreement with the experimental homogeneous sensitivity, surface etching sensitivity and power transmission coefficient at the resonator coupling. The analysis of the surface sensitivity due to biomolecular layer adhesion suggests biomolecule polymerization on the surface of the actual device. These results demonstrate the suitability of the proposed numerical optical models and indicate that the slot-waveguide microring device can be fully wetted with aqueous analytes, which is desirable for sensing and optofluidic applications at the nanoscale.

We have designed and realized three integrated photonic families of micro-resonators (MR) on multilayer organic materials. Such so-called 2.5D-MR and 3D-MR structures show off radius values ranging from 40 to 200μm. Both first and second families are especially designed on organic multilayer materials and shaped as ring- and disk-MR organics structures arranged upon (and coupled with) a pair of SU8-organic waveguides. The third family is related to hybrid 3D-MR structures composed of spherical glass-MR coupled to organic waveguides by a Langmuir-Blodgett lipid film about three nanometers in thickness. At first, polymer spin coating, surface plasma treatment and selective UV-lithography processes have been developed to realize 2.5D photonic micro-resonators. Secondly, we have designed and characterized photonic-quadripoles made of 3D-glass-MR arranged upon a pair of SU8 waveguides. Such structures are defined by a 4-ports or 4-waveguides coupled by the spherical glass-MR. We have achieved an evanescent photonic coupling between the 3D-MR and the 4-ports structure. Spectral resonances have been measured for 4-whispering gallery-modes (WGM) into such 3D-structures respectively characterized by a 0.97 nm free spectral range (FSR) and a high quality Q-factor up to 4.10⁴.

All-fiber coaxial Michelson interferometers are compact and very stable interferometers that can be dipped directly into water solutions for chemical and biological sensing. The sensitivity of the cladding mode to the surrounding medium can be exploited to use the interferometer as a compact fiber refractometer. Several interferometers have been fabricated and characterized as glucose sensors. A first series of devices were designed to work at 1550 nm, while a second series was prepared to work at 850 nm. Thus, the second series of interferometers enables the use of compact, robust and low cost optical spectrum analyzers. In our present experiments, the length of the fiber that forms the interferometer was within the range 1-10 cm. When the shift of the spectrum maxima were measured as a function of the glucose concentration, a slope of 350 pm/% was achieved. The use of the 850 nm sensor heads as a portable sensor system to monitor sewage treatment plants is shown.

A new fiber strain sensor based on the Laser-Self-Mixing effect in Distributed Feedback Laser diodes is presented. Compared with existing fiber strain sensors based on Fiber Bragg Gratings, that are sensitive to local strain, our device achieves comparable sensitivity (~ 1 με) distributed along the whole fiber length and requires a much simpler electronics. The sensor is based on the interferometric principle of the laser-self-mixing in the moderate feedback regime, whereby the fiber strain results in a variation of the optical path-length seen by the radiation reflected by the end facet of the fiber itself. Increasing or decreasing strain recognition is directly provided by the sign of the sawtooth-like fringes derivative.

Periodic arrays of nanoholes are being developed by several groups for integrated and portable real-time sensing based on surface plasmon resonance (SPR). Recent advances have allowed for nanohole sensitivity comparable to ATR SPR. Here, we will present our new advances in developing integrated and multiplexed SPR sensors using nanohole arrays. For the first time, we will present our dual-wavelength approaches that remove the need for a spectrometer, thus greatly reducing cost and size. We will also present our recent achievements in (1) in-hole sensing, demonstrating attomolar detection, and (2) flow-through sensing, where the detection time is greatly reduced due to the rapid diffusion inside the nanoholes themselves.

We report a novel high-throughput surface plasmon resonance (SPR) biosensor for rapid and parallelized detection of protein biomarkers. The biosensor is based on a high-performance SPR imaging sensor with polarization contrast and internal referencing which yields a considerably higher sensitivity and resolution than conventional SPR imaging systems (refractive index resolution 2 × 10^-7 RIU). We combined the SPR imaging biosensor with microspotting to create an array of antibodies. DNA-directed protein immobilization was utilized for the spatially resolved attachment of antibodies. Using Human Chorionic Gonadotropin (hCG) as model protein biomarker, we demonstrated the potential for simultaneous detection of proteins in up to 100 channels.

The Rhodamine 6G fluorescence enhanced by the surface electromagnetic waves coupled on surface of 1D photonic crystals is studied. The fluorescence-mediated surface electromagnetic waves (SEW) distribution is visualized by means of far-field fluorescence microscopy. The kinetics of Rhodamine 6G bleaching due to SEW is studied. The way of SEW visualization in reflectivity spectra via fluorescence process is shown. The prospective for SEW application in the optical sensors field is tested via direct spectroscopy of the photonic crystal covered by the ethanol and R6G thin film. Spectral flexibility of the SEW excitation depending on the effective photonic crystal dispersion controlled by its design rather than on material dispersion opens prospectives for the application of SEW-enhanced fluorescence microscopy in biocensing with increased spatial and concentration sensitivity and spectral selectivity.

We present the design, fabrication, and characterization of a GLAD-fabricated photonic crystal sensor with a bandgap located in the visible optical spectrum. The photonic crystal is fabricated from TiO₂ using electron-beam evaporation in a GLAD capable vacuum deposition system. Changes in humidity over a wide range (from 3% to 90% relative humidity) are detected by a colour change in the film due to movement of the photonic bandgap. The colour changes are quantified by measuring the transmittance of white light. Coupling the sensitivity of the film with a simple visual feedback system eliminates the need for complicated measurement techniques. This is desirable to minimize the cost and power consumption of the sensor device, making it amenable to large-scale production and deployment.

Two new classes of compact Laser Doppler Velocimeter (LDV) designs are presented which offer significant advantages in cost and performance over classical, fixed focus, fringe generation systems using laser beam interference. Both offer multi-axis capability and direction sensing. The first system [2] is the "Magnifier LDV". One or more laser beams are focussed at the target, and a highly magnified image of the illuminated target is projected onto optical masks which contain one (or more) groups of parallel opaque lines, each group having a different spatial frequency. Each mask is either viewed directly by a detector or indirectly via a lens-ended fiber optic link. Direction of target movement is determined by the first arrival of either a higher or lower frequency signal burst. The second system [3] is the "Projection LDV". An optical mask is placed into a diverging or converging laser beam. The optical mask contain one (or more) groups of parallel opaque lines, each group having a different spatial frequency. The normal edge diffraction is disturbed by the non-parallel beam, and a high quality image of the mask is projected as a parallel beam by transmission optics throughout the length of the laser beam. Moving the mask to and from the laser source changes the mask spacing, and hence the LDV velocity constant. The mask can be rotated into other orientations for axis matching or for multi-axis systems. Zemax optical simulations and CAD engineering designs exist for prototype systems.

A highly accurate reflective interferometric fiber-optic current sensor for alternating and direct currents up to 500 kA is investigated. The magnetic field of the current introduces a differential phase shift between right and left essentially circularly polarized light waves in a fiber coil wound around the conductor. Technology adopted from fiber gyroscopes is used to measure the current-induced phase shift. The sensor achieves accuracy to within ±0.1% over at least two orders of magnitude of current and for temperatures from -40 to 80°C with inherent temperature compensation by means of a non-90°-retarder. The paper analyzes the influence of key parameters on the sensor accuracy as well as linearity as a function of magneto-optic phase shift. Particularly, we consider residual birefringence in the sensing fiber and its effect on the high-current performance of the sensor as well as optimum parameters for the temperature compensation scheme. Applications of the sensor are in high-voltage substations and in the electrolytic production of metals such as aluminum.

We present a numerical and experimental analysis of a technical solution, capable of alleviating the problem of pump depletion in a long-range Brillouin distributed fiber sensor. This solution takes advantage of the presence of two sidebands in the probe wave to generate a dual gain-loss Brillouin interaction, giving rise to reduced pump depletion. Experimental results, carried out by using both a Brillouin optical frequency-domain analysis (BOFDA) configuration and a Brillouin optical time-domain analysis (BOTDA) configuration, permitted to evaluate the advantages and limitations of the gain-loss technique. An extensive experimental and numerical analysis has been carried out, in order to understand the differences on the effectiveness of the technique, between BOTDA and BOFDA set-ups.

Pulsed time-of-flight laser ranging is based on measuring the transit time of a short laser pulse to an optically visible target and back to the receiver. These techniques are gaining in popularity for industrial distance measurement applications. The laser pulse length typically used is in the range of 3 ns, which corresponds to about 1 m in air. This pulse length poses a challenge for detection of the echo from the target since the accuracy aimed at in a single shot is typically at the level of a few centimetres or even better with a dynamic range of more than 1:10 000. This paper studies the possibility of realizing the timing detection of the laser pulses with a straight-forward leading edge type of receiver that detects the cross-over of the received pulse with respect to a set reference level. Without any other measures the timing walk error that would be produced with this kind of receiver, would be at the level of nanoseconds. However, by measuring either the width or the slew rate of the rising edge of the received pulse, timing walk can be compensated for based on the measured dependence of the walk on the respective parameter. The advantage of these methods is that they are effective even when the optoelectronic receiver is saturated, thus enabling one to achieve wide dynamic operating range. Using these time-domain walk compensation methods we have constructed fully integrated CMOS and BiCMOS laser radar receivers that achieve timing walk error of less than +/-30ps in dynamic range of 1:10 000 -100 000.

Highlighted are results from a commercial Siemens rig test of the fabricated all-Single crystal Silicon Carbide (SiC) temperature probe. Robust probe design options are introduced. Introduced is a fiber network-based spatially distributed sensor design suitable for turbines.

Due to their advanced weight-specific mechanical properties, the application of fibre-reinforced plastics (FRP) has been established as a key technology in several engineering areas. Textile-based reinforcement structures (Preform) in particular achieve a high structural integrity due to the multi-dimensional build-up of dry-fibre layers combined with 3D-sewing and further textile processes. The final composite parts provide enhanced damage tolerances through excellent crash-energy absorbing characteristics. For these reasons, structural parts (e.g. frame) will be integrated in next generation airplanes. However, many manufacturing processes for FRP are still involving manual production steps without integrated quality control. The non-automated production implies considerable process dispersion and a high rework rate. Before the final inspection there is no reliable information about the production status. This work sets metrology as the key to automation and thus an economically feasible production, applying a laser light-section sensor system (LLSS) to measure process quality and feed back the results to close control loops of the production system. The developed method derives 3D-measurements from height profiles acquired by the LLSS. To assure the textile's quality a full surface scan is conducted, detecting defects or misalignment by comparing the measurement results with a CAD model of the lay-up. The method focuses on signal processing of the height profiles to ensure a sub-pixel accuracy using a novel algorithm based on a non-linear least-square fitting to a set of sigmoid functions. To compare the measured surface points to the CAD model, material characteristics are incorporated into the method. This ensures that only the fibre layer of the textile's surface is included and gaps between the fibres or overlaying seams are neglected. Finally, determining the uncertainty in measurement according to the GUM-standard proofed the sensor system's accuracy. First tests under industrial conditions showed that applying this sensor after the drapery of each textile layer reduces the scrap quota by approximately 30%.

The development of a contactless sensor based on the Laser-Self-Mixing effect for the simultaneous measurement of linear and transverse degrees-of-freedom (DOFs) of a moving target is described in this paper. The sensor is made of three laser diodes with integrated monitor photodiodes, and a properly designed reflective target attached to the moving object. The proposed technique exploits the differential measurement of linear displacements by two identical self-mixing interferometers (SMIs) and makes the system more compact and easier to align with respect to traditional interferometric systems, thus providing an effective low-cost motion control system. The feasibility of the proposed sensor is experimentally demonstrated over a range of 1 m for linear motion and ± 6 mm for transverse displacements, with resolutions of 0.7 μm and 20 μm, respectively.

We have investigated the transverse magneto-optical Kerr effect (TMOKE) in thin films of ferromagnetic manganites (La_2/3Sr_1/3MnO₃, La_2/3Ca_1/3MnO₃) with visible light. In addition to the standard transverse MO Kerr effect - which is proportional to the magnetization component perpendicular to the plane of light incidence - we have observed a strong even contribution roughly proportional to the absolute value of applied magnetic field. It is well observed near the Curie temperature. This contribution is not the ordinary quadratic magneto-optical effect it but is related to the magnetorefractive effect (MRE) - the optical equivalent of magnetoresistance - which give rise a significant change of reflectivity with the applied magnetic field. This magnetorefractive effect can exceed more than ten times the linear magneto-optical effect (MOE). This finding is against common assumption that MRE is negligible in the visible spectral range and therefore both MRE and MOE should be considered. Detailed analysis of measurements in various magneto-optical configurations is provided and the method of separation of both contributions is shown. Finally we envisage the possibility to exploit this effect in remote optical magnetic field sensor, which can be useful for nondestructive, noninvasive, and local magnetic field sensing.

A three-degree-of-freedom measurement system for the acquisition of the straightness and roll errors of a moving linear stage is described. The horizontal (Δx) and vertical (Δy) straightness errors are obtained by measuring the lateral displacement of a triple prism with a laser beam and position sensitive detectors. From two simultaneously performed vertical straightness measurements the roll angle (Θz) can be calculated. The system consists of a cable-free reflector head and a detector head. The position sensitive detectors have been calibrated using a precision x,y-stage equipped with two plane mirror interferometers. Different position sensitive detectors are compared with regard to position sensitivity, linearity, null-shift stability and sensitivity to the intensity profile of the detected laser beam. In combination with an already known triple-beam plane mirror interferometer, additional information about the linear position (Δz) and the pitch (Θx) and yaw (Θy) angle can be obtained from three parallel linear measurements. Thus all six-degree-of-freedom geometric errors can be measured simultaneously. Systematic errors of the three-degree-of-freedom measurement due to misalignment of the laser beams and geometric errors of the triple reflectors are discussed. An approach for correction of those errors caused by the triple reflectors is shown. The method is based on determination of the reflector geometry and calculation using the additional information (Δz) acquired by the interferometer. Furthermore the metrological properties of the proposed system for the measurement of straightness and roll are compared to other measurement principles. Experimental results demonstrate the measurement capabilities of the system.

Optical monitoring of temperature evolution and temperature distribution in laser machining provides important information to optimise and to control technological process under study. The multi-wavelength pyrometer is used to measure brightness temperature under the pulsed action of Nd:YAG laser on stainless steel substrates. Specially developed "notch" filters (10^-6 transparency at 1.06 μm wavelength) are applied to avoid the influence of laser radiation on temperature measurements. The true temperature is restored based on the method of multi-colour pyrometry. Temperature monitoring of the thin-walled gilded kovar boxes is applied to detect deviation of the welding seam from its optimum position. The pyrometers are used to control CO₂-laser welding of steel and Ti plates: misalignment of the welded plates, variation of the welding geometry, internal defects, deviation of the laser beam trajectory from the junction, etc. The temperature profiles along and across the welding axis are measured by the 2D pyrometer. When using multi-component powder blends in laser cladding, for example metal matrix composite with ceramic reinforcement, one needs to control temperature of the melt to avoid thermal decomposition of certain compounds (as WC) and to assure melting of the base metal (as Co). Infra-red camera FLIR Phoenix RDAS provides detailed information on distribution of brightness temperature in laser cladding zone. CCD-camera based diagnostic system is used to measure particles-in-flight velocity and size distribution.

We present miniature spectrometers that offer high resolution, increased optical throughput (étendue), and are compatible with a microsatellite platform. The spectrometers are implemented using arrays of singlemode planar optical waveguides and use a Fourier technique for spectra retrieval. We discuss design, fabrication, and first experimental results for these multiaperture spectrometers implemented in silicon-on-insulator (SOI) waveguides.

Organic photodiodes have been discussed as high-speed photo sensors fabricated by solution process. Poly(9,9- dioctylfluorene) (PFO) or poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) mixed with [6-6]phenyl-C61-butyric acid methylester (PCBM) were used as photo sensitive materials. The device shows high photosensitive characteristics in the visible region. The photocurrent and photo response speed increases as increasing the reverse bias voltage. Both the devices have a cut-off frequency of approximately 60 MHz under reverse bias of 10 V. Clear response pulse signals at 80 MHz were received using a sinusoidally modulated laser light illumination. The printable organic photo sensors have a huge potential in a field of arrayed photo sensors in a large area, scanners and so on.

We studied performance of a fast-response nanographite film photodetector (PD) in the temperature range of 300- 1000 K. In experiment, we measured the magnitude of the electric signal generated in nanographite film (NGF) under irradiation of intense nanosecond laser pulses at λ=1.064 μm. In vacuum, the measurements of the PD sensitivity were performed in the temperature range of 300-800 K. We showed experimentally that the PD sensitivity at 300 K was about 30% higher than that at 625 K and 50% higher than that at 740 K. At T>625 K, the magnitude of the light-induced signal decreases as a linear function of temperature and vanish at T ≈ 1000 K. In atmospheric conditions, we observed a stable operation of the NGF-based PD during several tens of hours in the temperature range from 300 to 580 K. However, at higher temperature, degradation of the NG film resulted in a drop in the PD sensitivity.

We report a long-range near-IR methane sensor for inspection of natural gas collection, storage sites and pipeline networks. The principle is that a laser carrier beam is directed at the target surface across a test path and the backscatter from the surface is detected in a large Fresnel lens on the sensor. A Raman amplifier has been designed to amplify the TDLS optical signal generated by a 1650.95nm DFB laser diode to over 1W CW. Combining the high power output of the Raman amplifier and the highly sensitive TDLS technique, we may report 100ppm.m sensitivity at more than 100m.

Microcapillary resonators have great potential in sensors applications due to their high sensitivity and compatibility with micro-fluidic systems. Capillaries show the unique property of being capable to sense liquids with refractive index higher than the refractive index of the capillary. Whispering-gallery modes resonances excited in the capillary shift as a function of the refractive index of the medium that fills the capillary. The sensitivity, as well as the Q factor of the resonances, depends strongly on the structural parameters of the capillary, i.e. radius and wall thickness. A detailed theoretical analysis is presented. As a practical application, capillaries were used for the measurement of glucose concentration in water solution. A collection of capillaries with different wall thickness and radius were tested. The sensitivity of higher radial-order modes in large radius capillaries is also investigated. A best sensitivity of 1.24 nm / % of glucose concentration in water is reported.

Among the measures to reduce CO₂ emissions, capture and geological storage holds out promise for the future in the fight against climate change. The aim of this project is to develop a remote optical sensor working in the mid-infrared range which will be able to detect and monitor carbon dioxide gas. Thus, chalcogenide glasses, transmitting light in the 1-6 μm range, are matchless materials. The first of our optical device is based on the use of two GeSe₄ chalcogenide optical fibers, connected to an FTIR spectrometer and where CO₂ gas can flow freely through a 4 mm-spacing between fibers. Such sensor system is fully reversible and the sensitivity threshold is about 0.5 vol.%. Fiber Evanescent Wave Spectroscopy technology was also studied using a microstructured chalcogenide fiber and first tests led at 4.2 μm have provided very promising results. Finally, in order to explore the potentiality of integrated optical structures for microsensor, sulphide or selenide Ge25Sb10S(Se)65 rib waveguide were deposited on Si/SiO₂ wafer substrates, using pulsed laser deposition and RF magnetron sputtering deposition methods. The final aim of this study is to develop a rib waveguide adapted for middle-IR including an Y-splitter with a reference beam and sensor beam targeting an accurate CO₂ detection.

We show that the optical texture of a layer of liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) supported on a thiol-sensitive layer can be applied to detect 1-octanethiol and other vaporous thiols with high specificity. As demonstrated in our ellipsometry and XPS results, a thiol-sensitive layer comprising a layer of (PEI) and copper ions is capable of oxidizing thiols to disulfides and immobilizing them on the surface. Because of the hydrophobic hydrocarbon chain of 1- octanethiol, the immobilization of 1-octanethiol lowers the surface energy. Thus, after a thin layer of 5CB is supported on the surface, the lower surface energy causes 5CB to adopt different orientations in regions where copper ions were deposited. Because 5CB is a birefrigent material, different orientations of 5CB also result in distinct optical textures, which are visible to the naked eye under a pair of polarizers.

Two fluorescence spectroscopy concepts, fluorescence correlation spectroscopy and time correlated single photon counting (TCSPC) are employed in fluorescence lifetime correlation spectroscopy (FLCS) - a relatively new technique with several experimental benefits. In FLCS experiments, pulsed excitation is used and data are stored in a special time-tagged time-resolved mode. Mathematical treatment of TCSPC decay patterns of distinct fluorophores and their mixture enables to calculate autocorrelation functions of each of the fluorophores and thus their diffusion properties and concentrations can be determined separately. Moreover, crosscorrelation of the two signals can be performed and information on interaction of the species can be obtained. This technique is particularly helpful for distinguishing different states of the same fluorophore in different microenvironments. The first application of that concept represents the simultaneous determination of two-dimensional diffusion in planar lipid layers and three-dimensional vesicle diffusion in bulk above the lipid layers. The lifetime in both investigated systems differed because the lifetime of the dye is considerably quenched in the layer near the light-absorbing surface. This concept was also used in other applications: a) investigation of a conformational change of a labeled protein, b) detection of small amounts of labeled oligonucleotides bound to metal particles or c) elucidation of the compaction mechanism of different sized labeled DNA molecules. Moreover, it was demonstrated that FLCS can help to overcome some FCS experimental drawbacks.

The discrimination of viral and bacterial sepsis is an important issue in intensive care patients. For this purpose, the simultaneous measurements of different analytes such as C-reactive protein (CRP), procalcitonin (PCT), myeloperoxidase, interleukines and neopterin, are necessary. A novel optical platform was designed and realised for the implementation of fluorescence-based immunoassays. The core of the optical platform is a plastic biochip, formed by a series of microchannels each of them devoted to the determination of a single analyte. Sandwich assays for CRP and PCT spiked in serum were performed in order to demonstrate the reliability of a multi-array device.

Diatoms are monocellular micro-algae provided with external valves, the frustules, made of amorphous hydrated silica. Frustules present patterns of regular arrays of holes, the areolae, characterized by sub-micrometric dimensions. Frustules from centric diatoms are characterized by a radial disposition of areolae and exhibit several optical properties, such as photoluminescence, lens-like behavior and, in general, photonic-crystal-like behavior as long as confinement of electromagnetic field is concerned. In particular, intrinsic photoluminescence from frustules is strongly influenced by the surrounding atmosphere: on exposure to gases, the induced luminescence changes both in the optical intensity and peaks positions. To give specificity against a target analyte, a key feature for an optical sensor, a biomolecular probe, which naturally recognizes its ligand, can be covalently linked to the diatom surface. We explored the photoluminescence emission properties of frustules of Coscinodiscus wailesii centric species, characterized by a diameter of about 100-200 μm, on exposure to different vapours and in presence of specific bioprobes interacting with target analytes. Very high sensitivities have been observed due to the characteristic morphology of diatoms shells. Particular attention has been devoted to the emission properties of single frustules.

We propose the use of perfluorinated cladded multimode polymer optical fibers tapers for fluorescent detection in aqueous environment. A graded-index polymer optical fiber with core and cladding diameters of 62.5/90 and very low refractive index (nCore = 1.356, nCladding = 1.342) has been used. The taper has been fabricated using the heat-and- pull technique. Despite to the fact that taper core is not in direct contact with the external medium, this fiber taper can be used for sensing applications. In fact, some of the guided modes are no more confined in the core region but can still be guided by the fiber in the cladding region. Therefore, in the taper region, there is an evanescent wave in the external medium, related to the cladding modes. The taper geometry and the very low refractive index of the material corecladding (1,35-1,34) permits a strong enhancement of the penetration depth increasing the fluorescence collection efficiency in aqueous environments (1.33). Fluorescence measurements in an aqueous solution containing Cy5 dye in a concentration range 3.14×10^-7M to 6.76×10^-6M have been performed.

Conoscopic Holography proved to be a very adequate solution for in-situ optical measurement in industrial inspection and quality control systems, offering high-precision with a wide range of standoff distances, while being quite insensitive to the harsh environmental conditions often encountered in industry, as it is a common-path technique. With the aim of extending their applicability, we have already addressed, with good results, several issues that improve sensors based on this technology which include: the use of phase information to obtain one-shot profile measurements at frame rate with higher precision; new signal processing techniques; and speckle reduction to diminish measurement errors. However, the undesirable effect of using the phase information is that it reduces the maximum steep that can be measured without ambiguity, which becomes an issue when working with high precisions. In this article we present our ongoing work towards using the concepts of multiple-wavelength interferometry to extend the measurement range, something that, to our knowledge, has not been done for this technology before.

A white-light spectral interferometric technique is used for measuring small thickness changes of a SiO₂ thin film grown by thermal oxidation on a Si substrate. The technique is based on recording of the spectral interferograms in a Michelson interferometer with one of its mirrors replaced by a thin-film structure. From the spectral interferograms, the nonlinear-like phase function related to the phase change on reflection from the thin-film structure is retrieved. The phase function is fitted to the theoretical one to obtain the thin-film thickness precisely provided that the optical constants of the thin-film structure are known. This procedure is used for measuring small thickness changes of a SiO₂ thin film attributed to different dopant concentrations of a Si substrate. The results of the technique are compared with those obtained by spectral reflectometry and very good agreement is confirmed.

There have been many reports of application-specific or custom designed high dynamic range (HDR) CMOS image sensors. To achieve their extended dynamic range, these sensors utilize techniques that can significantly degrade their signal-to-noise ratios (SNR). We utilize a simplified sensor model to compare two HDR techniques with a conventional APS sensor regarding their SNR and dynamic range (DR). We perform a new analysis of a mixed APS and time-to-saturation sensor that shows that it can detect similar high illuminations levels that the multiple capture sensor without degrading the SNR at lower levels. Furthermore, the time-to-saturation sensor can be adjusted on-the-fly to detect specific illumination levels with optimized image quality.

An evanescent field refractive index sensor consisting of a Bragg grating that is written into a silica-on-silicon planar optical waveguide structure by UV laser radiation is utilized to monitor the composition of liquid binary chemical systems. We have investigated various selected liquid compounds that are commonly used in the pharmaceutical and chemical industry, finding sensitivities on the order of 100nm/RIU and minimum detectable index resolution on the order of 5•10^-6 fulfilling industrial demands on detection limits and partly being superior to other electrical transducer systems. The planar structure of the sensor chip allows on chip integration of fluidic structures that we have generated by laser ablation using a pulsed fiber laser, enabling connection to the adjacencies.

In this study, well-ordered and vertically-aligned metal (nickel (Ni)/zinc (Zn)) and metal oxides (NiO/ZnO) nano heterojunctions (NHJs) were grown inside the nanopores of anodic aluminum oxide template (AAOT) using electrochemical deposition (ECD) and thermal oxidization. The prepared NHJs are with a controllable length and diameter. The electrical properties of NiO/ZnO NHJs show a rectifying behavior of a p-n junction, while the Ni/Zn NHJs show an ohmic behavior. The optoelectronic characteristics demonstrate that the NiO/ZnO NHJs have fairly good sensitivity and response to the ultraviolet (UV) light (366 nm) with decrease in Vth by about 75% and an increase in J_r by about 80% @ 6 mW/cm². The low dimension of NHJs shows profound quantum confinement effect, which would be potential applications on nano integrated photonics, such as photodetectors, optical sensors and biosensors.

This study proposes the use of a ZnO-nanowire (ZnO-NW)-based heterojunction structure for applications of nano optoelectronic sensors and photovoltaic devices. Nano heterojunctions (NHJs) were formed via e-beam deposition of ptype nickel oxide (NiO) onto the vertical-aligned ZnO-NWs grown by hydro-thermal growth method. The dark J-V curve shows that the prepared NiO/ZnO-NWs NHJ has a diode-like behavior with a forward threshold voltage (V_th) of 1.2 V and a leakage current (J_r at -1V) of 0.02 μA/cm², respectively. It also exhibits a superior response to UV (366 nm) and AM 1.5G light illuminations. The V_th and the photocurrents (i.e., J_r at -1V) under UV (366 nm @ 6 mW/cm²) and AM 1.5G light were 0.7 V/0.06 μA/cm² and 0.5 V/ 3.2 μA/cm², respectively, revealing an increase in the diode current of about 3× and 160×, respectively.

The key idea of research in hybrid optical fibers is motivated by the demand of fibers, which could be used as a medium for telecommunication transmission and as an optical sensor at the same time. Every optical fiber sensor on the market has unappropriate properties for telecommunication transmission. And, on the other hand, the convenient fibers used for transmission are designed to be insensitive to the external influences. We have designed a fiber with refractive index profile which preserves the telecommunication properties of the single-mode fibers and at the same time it enables to use this fiber as a sensor on another wavelength. Principle of this sensor is based on redistribution of the optical power between individual guided modes. This article shows some results from experiments on hybrid fibers in sensoric regime. Telecommunication properties were verified by the reflectometric method. It has shown that the fiber has attenuation camparable with commonly used single-mode fibers.

We show evidence of rapid photo-erasure of ultra stable Type-II fibre Bragg gratings written with a femtosecond laser into the active medium when employed as high reflectors in >1kW medium power Yb³⁺-doped Q-switched fibre laser cavities.

In this work we describe the development of a compact all-fiber pulsed light source composed by a fiber-Bragg-grating-based distributed-feedback fiber laser. We demonstrate that the temporal and spectral characteristics of this fiber laser are suitable as light source for Brillouin back-scattering sensors. Using a 10 km fiber spool, we have measured the Stokes and anti-Stokes processes at different pump powers and they were clearly discernible around the central (Rayleigh backscattering) peak at the appropriate wavelength shift (88 pm at room temperature). Our results indicate that this compact all-fiber source is a good alternative for Brillouin sensor applications.

The fiber optical dew point hygrometer based on change of reflection coefficient for fiber cut has been developed and examined. We proposed and verified the model of condensation detector functioning principle. Experimental frost point measurements on air with different frost points have been performed.

Microstructured optical fibers have the potential to provide improved performance relative to more traditional spectroscopic fiber sensors. In fact the manipulation of the geometry of the fiber cross section can allow to maximize the interaction of light and sample. Recently, solid air-suspended core fibers have been appointed as the most promising design for evanescent field sensing. In this kind of device, sensing is carried out through the interaction between evanescent tails of index-guided modes and sample, which fills cladding holes. Suspended core fibers are made by three silica webs joining in the fiber center and forming the core. This design can provide an evanescent field power fraction greater than any other structure previously proposed, together with a wide transmission band. In this paper, the electromagnetic field behaviour of the guided modes of a range of suspended-core fibers is investigated, using a full-vectorial finite element based modal solver. The impact of different design parameters and materials on guidance, the amount of power in the cladding and the possibility of obtaining effective single-mode guidance are also investigated.

Physical backgrounds for highly sensitive optical sensors of mechanical perturbations based on flow phenomena in liquid crystals are presented. It is shown that linear declinations of the optical axis of a nematic liquid crystal induced by a pressure gradient from the initial homeotropic orientation which are registered via polarized light can be considered as the basic mechanooptical effect for sensor applications. The ways of optimization of technical characteristics of liquid crystal sensors including usage of electric fields are discussed. The examples of sensors of acceleration, vibration and inclination based on the same principals are considered. It is shown that usage of liquid crystals provides an extremely high threshold sensitivity and electric control of the main technical parameters of optical sensors.

The performance of an all-fiber ratiometric wavelength measurement system is compared for the case of two edge filters and the case of one edge filter. The two fiber edge filters are used with overlapping and opposite slope spectral responses, a so called "X-type spectral response", each based on singlemode-multimode-singlemode (SMS) fiber structures. Noise and polarization dependent loss (PDL) are the two parameters that determine the resolution and an accuracy of the system. It is demonstrated that the use of two SMS edge filters for a ratiometric wavelength measurement system can increase the resolution and the accuracy when compared with a system using only one edge filter.

A discretely tunable Surface-Stabilized Ferroelectric Liquid Crystal based Lyot Filter, with tuning speeds in the order of microseconds, is demonstrated experimentally as a channel dropper for the demodulation of multiple Fibre Bragg Grating sensors. The 3-stage Lyot Filter designed and experimentally verified can be used together with the high-speed ratiometric wavelength measurement system employing a fibre bend loss edge filter. Such systems can be used for the demodulation of distributed Fibre Bragg Grating sensors employed in applications such as structural monitoring, industrial sensing and haptic telerobotic surgical systems.

The paper is devoted to the simulation and reflectance performance of the cascaded non-uniform fiber Bragg gratings (FBG). In a FBG, periodically spaced regions in the fiber core are varied. FBGs are key enabling technologies for fiber optical sensing for their high sensitivity and potentially low cost. Uniform, chirped, phase-shifted and sampled FBGs can be used in the sensing systems. The cascaded FBG configuration is created by several sections where each section has a specific number of segments. In our simulations the transfer matrix method has been used assuming the entire grating made up of sections. Using this method the FBG reflectance spectra have been simulated in MATLAB. The simulated reflectances of FBGs with several sections alternating along the length of the FBG have been described. The simulation results show that the FGB reflectance at the Bragg wavelength and the reflectance bandwidth depend on the Bragg grating periodicity that means on the periodicity in the sections. The bandwidth and the amplitude reflectance at the Bragg wavelength for the length grating of 10 mm with several sections have been studied. The effects of sections of different Bragg grating periods and refractive index profiles (the Gaussian profile or the sinc profile) have been numerically investigated. From the simulations one can see that the maxima of the energy of FBGs reflected by several apodized sections depend on the grating length. Moreover, it has been found out that the undesirable sidelobes between main reflectance maxima can be partly suppressed by using an appropriately designed cascaded grating.

Using three fibre gratings with excessively tilted structures in the cavity, we have experimentally demonstrated a multiwavelength switchable erbium-doped fibre ring laser system. The three tilted gratings act as in-fibre polariser and polarisation dependent loss filters to induce the polarisation hole burning effect in the cavity for the operation of the laser at single, double, triple and quadruple wavelengths. The laser system has demonstrated good stability under room temperature conditions and also achieved a high degree of polarization (~30dB), high optical signal to noise ratio (up to 63dB) and high side mode suppression (~50dB). The system has also been investigated for temperature and strain sensing by subjecting the seeding fibre Bragg gratings (FBG) to temperature and strain variations. Since the loss band of the polarisation dependent loss filter is broader than the bandwidth of the seeding FBG, the laser output shifts in wavelength with the applied temperature and strain. The fibre ring laser has shown good responses to the temperature and strain, providing sensitivities of approximately 11.7 pm/°C and 0.85pm/με respectively.

Analytical description of the transfer function of an optical gas sensor takes into account a fine structure of gas absorption spectra and spectral characteristics of optopair elements and their temperature drift. Such approach permits one to estimate as early as at the designing stage the expected accuracy of measurements that can be provided by non-dispersive infrared (NDIR) gas sensors of different configuration as the environment temperature changes and/or in the presence of interference from foreign gases. Moreover, analytical description of the transfer function allows increasing the accuracy of gas concentration measurements. Calculated and experimental results of the study of laboratory models of small-size NDIR sensors based on mid-infrared (3-5 μm) immersion diode optopairs are given. The presented results confirm the validity of the proposed approach for the NDIR gas sensor description and promising prospects for using the sensors based on immersion diode optopairs in portable gas analysers.

A size of tapered silica fibre probes makes them suitable for exploration of small objects, as e.g. cells. Fibre-optic probes of enhanced mechanical durability can be advantageously used particularly for investigation of plant cells with hard walls. The paper deals with preparation of suitable optical probes based on coated fibre tapers and their using for local detection of extracellular pH in samples simulating native conditions of plant cells. Fibre tapers from single-mode and polymer-clad-silica fibres were prepared by tapering apparatus of own construction. The drawn tapers were immediately coated with a thin layer of Indium-Tin-Oxide in order to protect them from embrittlement. A CO₂ laser was used for cutting the tapered fibres in narrow taper waist. Opto-chemical transducer 2',7'- Bis(2-carbonylethyl)-5(6)-carboxyfluorescein was immobilized onto the end-face of cut fibre tapers by a thin TEOS layer. The pH was determined by fluorescence spectroscopy using excitation wavelength 473 nm. The fibre taper probes of waist diameter from 80 μm to 2 μm and of suitable optical and mechanical properties were prepared. Suitability of opto-chemical transducer 2',7'-Bis(2-carbonylethyl)-5(6)-carboxyfluorescein for detection of samples simulating native conditions of pH ranging from 5.0 to 7.0 was confirmed. This approach has allowed us to determine extra-cellular pH of in-vitro samples.

The new quasi-distributed frequency-output fiber-optic recirculating sensors for high-voltage measurements and perimeter security system have been proposed. Fiber-optic sensor was constructed as a closed optoelectronic contour formed by a source of radiation, an optical fiber delay line, spectral reflective elements, photoreceiver and regeneration block. The sensitive element of this device was the optical fiber. The change of recirculation frequency or period of the contour carried out identification of measured parameters with high accuracy. Sensitivity of these sensors was estimated. Temperature dependence of measurement accuracy was investigated.

Optical fiber sensors are suitable for measuring almost all magnitudes these days. This article describes one new possible area of optical fiber sensors. These sensors use for their function fundamentals of redistribution of power inside optical fiber. This principle should allow constructing a very sensitive optical fiber sensor. We designed novel optical fiber that affords utilizing of optical fiber for telecommunications and measurement at the same time. This fiber is designed to work on two wavelengths. This fiber works on telecommunication wavelength of 1550 nm in single mode regime and works on measurement wavelength of 850 nm in quasi-single mode regime. The refractive index profiles of real fabricated optical fiber samples and their development are shown in this article as well. All fiber samples were made thanks to grant cooperation with Academy of Science of the Czech Republic. The aim of this article is that brings new approach to utilization of optical fiber as a sensor based on redistribution of optical power among several guided modes and to show novel optical fiber structure design that agrees with conditions for such operations.

Diffractive optical elements (DOE) are used for various purposes, such as a beam shaper, beam splitter and so on. In order to design DOEs, iterative Fourier transform algorithm (IFTA) is widely used. IFTA is fast and effective optimization method and can handle large size data. In the IFTA, propagation in the far field and near field is described by Fourier transform and Fresnel transform, respectively. Iterative angular spectrum approach (IASA) is one of iterative methods based on angular spectrum technique. IASA adopt angular spectrum technique as expression of propagation in near field instead of Fresnel transform. Angular spectrum technique is based on scalar diffraction theory and satisfies Helmholtz equation; therefore angular spectrum technique is the accurate method for the calculation of diffraction. We designed a DOE by using IASA and evaluated its diffraction characteristics based on vector diffraction theory. In this paper, we report on the outcome.

Optical tweezers technique combined with local confocal luminescence spectroscopy is suggested as a tool for investigation of local optical fields. Utilizing this method plasmon-enhanced optical fields inside a pair of dielectric 2 μm spheres partially covered by 70 nm silver nanoparticles are visualized via field enhanced luminescence of rhodamine dye solution. Positions of the particles are controlled with submicrometer accuracy by two optical traps formed by strongly focused laser beams with λ=980nm. A supplementary beam from CW laser with λ=532nm provided for luminescence excitation is also focused into the sample cavity just to the trapping area. In order to obtain spatial filtering of the signal and separate luminescence signal from an area near the spheres pin-hole based confocal system is designed. The focal volume available for luminescence signal collection turns out to be approximately 3μm x 3 μm x 5 μm. Since optical field is enhanced in the region near plasmon-active 2 μm spheres the enhancement of luminescence intensity is observed. Collective plasmonic effects in two-particle measurements are also considered.

We discuss the application of stress-induced changes in the crystal of a monolithic Nd:YAG laser as a possibility for micro force measurement. In fact, the application of an unknown force on the resonator-amplifier of a laser, formed by a transparent photo elastic material, can lead to a change of the laser frequency by as much as several gigahertz depending on the force intensity. In addition, the rates of change of the two orthogonally polarizations of the same mode with applied force are different. Hence, the strength of the applied force can be deduced from frequency measurement of the beat signal between the two polarizations of the oscillating mode or between the mode polarized in the orthogonal direction of the force and a reference frequency of a stabilized laser.

Presented study brings some theoretical results derived for Kretschmann SPR configuration with gold patterned structure at coupling prism (SF 10 glass). As the analyzed medium, air or water with simulated contamination are considered. The thickness of Au nano-layer is fixed at 44 nm, its patterning is supposed to have planar or lamellar feature with variable governing parameters (i.e. period, shape and fill-factor). The reflectivity is calculated for wavelength of 632.8 nm in the incidence angle interrogation by rigorous coupled wave algorithm (RCWA) implemented in own Matlab code. The partially new view to sensitivity criteria is applied to optimize SPR systems of various kinds.

In this paper we present a novel method for the measurement of the thickness of the sensing layer applied on the tip of an optical fiber and fiber tapers. The method is based on analysis of distributions of the fluorescence intensity over this layer. In experiments the fluorescence of the sensing layer prepared by the sol-gel method was investigated be means of a confocal microscope Zeiss LS5 Duo. The fluorescence was excited at 477 nm by an Ar laser and detected in a spectral range from 518 to 600 nm. The fluorescence distribution was determined by scanning the layer in the direction of the taper axis (z-direction) with a step of 500 nm in an overall length of 42 μm and 26 μm. The layer thickness was estimated from the measured distribution of fluorescence intensity. Assumptions of method are that close to the layer boundary the fluorescence intensity decreases with z², the concentration of fluorescence centers in the layer is homogenous and attenuation of excitation wavelength in the sensing layer is neglected. This method has made possible to investigate sensing layers with thicknesses of about 1 μm.

We report a novel biosensor platform based on surface plasmon-enhanced fluorescence spectroscopy (SPFS) and a responsive N-isopropylacrylamide (NIPAAm) hydrogel binding matrix. This binding matrix highly swells in aqueous environment and it can be modified with receptor biomolecules by using active ester coupling chemistry. After the binding of target analyte molecules contained in a sample by receptor biomolecules immobilized in the hydrogel matrix, the captured analyte molecules can be compacted on the surface through the collapse of the gel triggered by an external stimulus. A thin hydrogel NIPAAm-based film was attached to a gold sensor surface and modified with mouse IgG receptor molecules. The affinity binding of antibodies against mouse IgG that were labeled with Alexa Fluor chromophores was observed by surface plasmon-enhanced fluorescence spectroscopy. We demonstrate that the collapse of the hydrogel matrix results in the enhancement of measured fluorescence intensity owing to the increase in the concentration of captured molecules within the evanescent field of surface plasmons.

We report the performances of LWIR (λc = 9.0 μm at 80K) HgCdTe electron injected avalanche photodiodes (e-APD). In these devices, the exponential gain curve, up to gains equal to 23 at 100K, and the low excess noise factor close to unity (F ~ 1-1.25) are indicative of a single carrier multiplication process, which is electron impact ionization. The dark current is mainly due to a diffusion current at low reverse bias and tunneling currents at high reverse bias. A Monte Carlo model has been developed for understanding the multiplication process in Hg_1-xCd_xTe e-APDs. We find a good agreement between first simulation results and experimental measurements of the gain and the excess noise factor in both MWIR (x = 0.3) and LWIR (x = 0.235) e-APDs at 80K. Furthermore, simulations do not show any heavy hole impact ionization. This model which enables to perform phenomenological studies aims at identifying the main physical and technological parameters that influence the gain and the excess noise. In the present work, it is used to study the influence of the thickness of the ndoped region on the gain and the excess noise factor. We found that F still decreases while the thickness of the n- layer decreases. However, an optimum thickness of the n- layer exists around 1μm in terms of gain-voltage characteristic.

The biological tissues consist of cells which dimensions are bigger than a wavelength of visible light. Therefore a Mie scattering of transmitted and reflected light occurs and different polarization states arise. The back-scattered polarized laser light exhibits multiple scattering from the surface and subsurface layers of the sample. Notwithstanding this phenomenon is different if the cellular tissues are live or dead. In the case of porcine meat, there are temporal and dynamic changes not only as a result of chemical process, but also geometric deformations due to the water evaporation from intracellular and extracellular sites. Although multiple scattering in tissue randomizes incident polarization states, the shift of polarization can be clearly observed in diffusive scattering pattern due to the muscle orientation and meat aging. Accordingly, these temporal changes due to the multiple scattering of backscattered light allow measure the freshness of processed meat.

The Transverse Field Detector (TFD) is a recently proposed Silicon pixel device designed to perform color imaging without the use of color filters. The color detection principle is based on the dependence of the Silicon absorption coefficient from the wavelength and relies on the generation of a suitable transverse electric field configuration, within the semiconductor active layer, to drive photocarriers generated at different depths towards different collecting electrodes. Each electrode has in this way a different spectral response with respect to the incoming wavelength. Pixels with three or four different spectral responses can be implemented within ~ 6 μm of pixel dimension. Thanks to the compatibility with standard triple well CMOS processes, the TFD can be used in an Active Pixel Sensor exploiting a dedicated readout topology, based on a single transistor charge amplifier. The overall APS electronics includes five transistors (5T) and a feedback capacitance, with a resulting overall fill factor around 50%. In this work the three colors and four colors TFD pixel simulations and implementations in a 90 nm standard CMOS triple well technology are described. Details on the design of a TFD APS mini matrix are provided and preliminary experimental results on four colors pixels are presented.

Radiofrequency tissue fusion consists in heating apposed tissue faces, which results in their sealing. Tissue transformations must be controlled to obtain reliable reproducible seal. In this paper we demonstrate how to extract information on the two main tissue transformations, thermal damage and dehydration, from continuous wave transmission spectra. A fibre based near infrared transmission spectroscopy system is presented and described theoretically. Show demonstrate that such system can be fully modeled using ray optics considerations for the coupling of the light into optical fibers, and MC simulations of light propagation in tissue. We then develop an algorithm based on the absolute measurement of attenuation and the modified Beer Lambert Law that enables the extraction of absolute tissue hydration and information on the degree of thermal damage, via scattering losses. We also discuss the basis and limit of absolute measurement during broadband submicronic tissue transmittance spectroscopy.