We describe recent research into devices based on fibre Bragg gratings in polymer optical fibre. Firstly, we report on the inscription of gratings in a variety of microstructured polymer optical fibre: single mode, few moded and multimoded, as well as fibre doped with trans-4-stilbenmethanol. Secondly, we describe research into an electrically tuneable filter using a metallic coating on a polymer fibre Bragg grating. Finally we present initial results from attempts to produce more complex grating structures in polymer fibre: a Fabry-Perot cavity and a phase-shifted grating.

Paper described fabrication methods of high birefringence index guided holey fibers made from silica and high silica glasses. Several kinds of high birefringence holey fibers are described in the point of view their fabrication technology and basic characterization. There are: triple defect fiber with shape induced birefringence, two kinds of fibers with filling factor asymmetry induced birefringence, fibers with filling factor asymmetry induced birefringence and germanium doped core designed for Bragg gratings writing, fiber with filling factor asymmetry induced birefringence and neodymium doped core designed for fiber amplifiers and lasers, dual core fiber with circular and weakly separated cores. Methods of manufacturing we used were: MCVD method for silica and high silica glass preparation as optical fiber preform manufacturing and OVD method for porous silica glass fabrication including additional processes as hydroxylation, impregnation with suitable salts solutions, thermal decomposition, dehydroxylation and sintering lead to silica, high silica and rare earth doped glass preparation in the form of elements for microstructured fiber preforms compose.

We report below about the control of processing of composite materials in particular carbon fibre dyed into epoxy resin. In the aeronautic industry, structures made of such composite materials have a very high "mechanical property to weight" ratio and can for this reason successfully compete with metallic ones. Their utilisation is constantly increasing in this industry and this growth is leading to the development of RTM processes. In order to optimize these process nonintrusive and multi-parameter sensors are required to measure and track the internal evolution for the continuous control. We study and describe a fibre optic sensor which detects the optical refractive index variations of its environment during the fabrication of a composite part. The major innovative part of our approach is the mould which has been designed and instrumented to simultaneously provide the polymerisation degree and the refractive index analysis of the resin. From these data, we have been able to determine the thermo-optic coefficient of the resin when it is not polymerised and the evolution of the polymerisation degree versus the resin refractive index. So this result is using as calibration to determine a polymerization degree of the resin in an industrial mould.

Proposed, to the best of our knowledge, is the first extreme environment wireless all-in-one hybrid temperature plus pressure sensor using a remoted thick single crystal Silicon Carbide chip within a pressurized capsule. Analysis and experiments are reported for the pressure aspect of the sensor for pressures up to 40 atms.

The fabrication of a compact all-fibre modal interferometer that can be used to sense different parameters is reported. The device consists of a tapered large-mode-area microstructured optical fibre with collapsed air holes over a localized region. The tapering is carried out by slowly elongating the fibre while it is heated with a high-temperature oscillating flame torch. This non adiabatic method allows the collapsing of the air holes and transforms a section of the microstructured fibre into a solid one. As a consequence the fundamental HE₁₁ mode is coupled to the HE_1m cladding modes which can beat or interfere. This makes the transmission of the device versus the wavelength to exhibit an oscillatory pattern. Such a pattern shifts with strain, high temperature, or refractive index. The device is compact, can operate in a broad range of wavelengths, and can be fabricated in a few minutes which makes it attractive for optical sensing.

Optical Vortex Interferometer (OVI) is a new type of interferometer which is based on the regular net of optical vortices (OV)^1,2,3. The net is generated by the interference of three plane waves. The idea of the measurement with the OVI is as follows: if one of the interfering waves is distorted then the geometry of the vortex net is changed. In our case one of the wavefronts was tilted. We can calculate the tilt of the wave by tracking the change of vortices positions. Basically it is sufficient to determine the relative change in the positions of three optical vortices (vortex triplet). If there are 200 vortices in the measurement field then we can choose about 1 million vortex triplets. The important advantage of this measurement is that two rotation angles through two perpendicular axes can be determined into one step. Also the mechanical vibrations are automatically subtracted and the system is simple. Our first results show⁵ that using about 1000 triplets we can measure the small angle with an error of 1.2arcsec (on the base of standard deviation). Performing the analysis we observed however that the real sensitivity of the OVI is higher than resolution resulting from the basic analysis methods. We observe the change of the histogram of the calculated angle if the tilt by the angle of 0.05arcsec is introduced. In the paper we analyze this effect. If the rotation angle is small then optical vortices change their positions by the small part of the distance between the measurement points. Due to detector quantization some of vortices can be still localized as lying in the same measurement point while the others are localized as shifted. This effect causes the histogram shift. The method of recomputing such histogram shift into the value of rotation angle is presented. In result we can achieve 6-10 times better resolution of the OVI.

The fiber-optic Sagnac interferometer (FOSI) has many useful applications begin from gyro up to wide range of sensors for measurement of different physical quantities. In this paper a new its application as a sensor of the state of polarization (SOP) changes is presented. The optical part of system is based on minimum gyro configuration, however a high level polarizer is replaced by specialized polarization filter with 3dB extinction ratio. The coherence and Jones matrix formalism for the system description were applied. Utilized in the system a fiber-optic phase modulator allow measuring the SOP changes by comparison appropriate harmonic amplitudes of the output signal. Additionally, two "dead ends" of the FOSI are used for system stabilization as well as an input intensity control. This system is dedicated for easy and active stabilization of the SOP in the fiber-optic devices where the polarization fading is a main disadvantage.

In this paper, we report on a new type of CMOS electro-optical modulator (EOM), called Photonic Mixer Device (PMD), based on the Charge Pumping (CP) phenomenon, which is capable of mixing and accumulating photo-generated charge-packets synchronously with respect to a pulsed light source. The device uses two PMOS transistors with embedded photodiode to detect the intensity and phase of a modulated light signal. Using clocking between accumulation and inversion, the two transistors transfer to output charge packets which are synchronized and proportional to the light intensity. The device operates at 3.3V with no dc power consumption and is implemented in a standard 0.35μm CMOS process. Using a 1.5mW/cm² light source pulsed at 25KHz, the device estimates a phase delay with an accuracy of 0.8%.

Optical fiber strain or bend sensors have been demonstrated for complex monitoring various structures especially in aerospace, marine civil engineering and especially in optical security systems. Optical fiber sensors based on Fabry-Perot interferometers and fiber Bragg gratings are useful for point or slow-multiplied sensor systems. Distributed optical fiber system based on Sagnac interferometers used of low or high-birefringence optical fibers as strain/bend sensing elements. Special optical fibers as four core single mode fibers in Mach-Zehnder interferometer system have been used. In all described cases the high influence of temperature on sensor characteristics is very important disadvantage at measurement systems. In this paper we describe fabrication and characterization of the new four core PCF index guided fiber designed for interferometric bend measurements.

In this paper we demonstrated a fiber sensing system using the method of wavelength locking of two nearly identical fiber Bragg gratings (FBG) to interrogate the wavelength shift by directly measuring the intensity of the reflection from the sampling FBG. The light source of the sensing system is based on a fiber ring laser structure in which a reference FBG is used for locking the wavelength of the fiber ring laser pumped by a 980 nm laser diode to achieve lasing at 1555.85 nm. The wavelength locking method is able to an effective way of interrogating the wavelength shifting of a FBG by the intensity of the reflection from the sampling FBG, and is able to achieve real time sensing of the physical perturbations. In addition, the characteristics of the fiber sensing system for dynamic vibration and the key factors to acquire stable sensing are discussed.

The photo-response of AlGaN based UV detectors to a 193 nm excimer laser radiation is presented. Two devices have been tested and compared, a metal-semiconductor-metal (MSM) planar structure and a Schottky diode. These sensors have already shown good performances in the 240-280 nm region under CW illumination and have been used for the realization of 2D and linear arrays. Here the capability of these devices to detect the emission of a nanosecond pulsed excimer laser is proven and the decay time and dependency on the beam's density of energy evaluated. The measured transient response of the MSM device closely follows the nanosecond laser pulses, with a decay time shorter than 3 ns. Conversely, the Schottky diodes showed a slower rise and decay kinetics principally limited by the coupling with the junction capacitance. The decay curve of such a device has been analyzed on the basis of two decay mechanisms: the second exponential decay has been found to be in the order of 40 ns. This slow kinetic has been attributed to the presence of trap states localized at a distance from the conduction or valence band larger then the thermal energy of the carriers. Both the realized devices do follow the Rose's law with a linear response at the lower beam fluxes (density of energy 4×10^-5 - 0.2 mJ/mm²) and a transition to a sub-linear regime for higher fluxes.

In this work we aim to realize a step-by-step electro-optical probe which exploits the linear (Pockels) electro-optic effect to survey the electromagnetic field on the surface of RF integrated circuits. This probe measures the variation of light polarization induced by a lithium niobate crystal immersed in the electric field provided by the DUT. The measurements will demonstrate the main features of this system which can be summarized in non-invasiveness, wide bandwidth, linearity and small spatial resolution. The LiNbO₃ crystals have been developed by SELEX Sistemi Integrati S.p.A. Roma, and the whole research activity has been carried out under the sponsorship of the CRdC Nuove Tecnologie per le Attivita Produttive, the Campania Region Centre of Competence on New Technologies.

One of the more challenging applications of optical metrology is real-time dimensional control and surface inspection in industrial applications, where strong requirements of cost, speed of operation, ease of setup and applicability in adverse environments, greatly limit the number of applicable technologies. An optic profilometer, based on Conoscopic holography, has been designed specifically for this purpose and used in several on-line inspection systems. This device is able to obtain a distance profile of a target in a single shot; works at long distance standoff (700-1200mm) and still keeps good resolution (under 0.2mm) with a very easy and reliable setup. However, there are still some drawbacks that should be addressed. The first one is the signal processing, which is a relatively expensive process and limits the acquisition rate at no more than 70 profiles per second. The second one is speckle noise, which is an inherent problem in systems that use coherent-light illumination and triangulation, and therefor could be extrapolated to many other optical inspection systems. This paper shows the current lines of research to solve both problems and presents some initial, yet very interesting, results. These improvements can be applicable to other ranges of devices using this technology in adverse environments, for roughness and vibration measurement or surface defects detection.

This paper presents new results on a scanning wavelength interferometer for absolute distances measurements. We report its performances on one and two simultaneous targets with a Fourier Transform Technique (FTT) and a regular sampling. Then the limitations of the FTT are discussed, especially with regard to the tunable laser source performances. Finally it concludes on the new results acquired by the use of a non-uniform sampling technique which reduces the non-linearities of the sweeping speed and demonstrates a relative uncertainty of some 10^-6 for distances of 0.25 to 1 m.

In this paper a distance measurement sensor is introduced, equipped with two integrated optical systems, the first one for rotationally symmetric triangulation and the second one for imaging the object while using only one 2D detector for both purposes. Rotationally symmetric triangulation, introduced in [1], eliminates some disadvantages of classical triangulation sensors, especially at steps or strong curvatures of the object, wherefore the measurement result depends not any longer on the angular orientation of the sensor. This is achieved by imaging the scattered light from an illuminated object point to a centered and sharp ring on a low cost area detector. The diameter of the ring is proportional to the distance of the object. The optical system consists of two off axis aspheric reflecting surfaces. This system allows for integrating a second optical system in order to capture images of the object at the same 2D detector. A mock-up was realized for the first time which consists of the reflecting optics for triangulation manufactured by diamond turning. A commercially available appropriate small lens system for imaging was mechanically integrated in the reflecting optics. Alternatively, some designs of retrofocus lens system for larger field of views were investigated. The optical designs allow overlying the image of the object and the ring for distance measurement in the same plane. In this plane a CCD detector is mounted, centered to the optical axis for both channels. A fast algorithm for the evaluation of the ring is implemented. The characteristics, i.e. the ring diameter versus object distance shows very linear behavior. For illumination of the object point for distance measurement, the beam of a red laser diode system is reflected by a wavelength bandpath filter on the axis of the optical system in. Additionally, the surface of the object is illuminated by LED's in the green spectrum. The LED's are located on the outside rim of the reflecting optics. The scattered LED light is transmitted by the before mentioned bandpath filter and is captured by the imaging lens. A simultaneous mode, in which the ring for distance measurement is superimposed to the image of the object, and a time multiplexing mode were implemented thus demonstrating the flexibility and performance options of this approach.

Position detectors are useful for alignment and orientation sensing. Charge-coupled devices (CCDs) are used in small-area systems. Four-quadrant diodes are a low-cost, limited-accuracy alternative. In cases where either large area or reliability under harsh conditions are required, thin-film-silicon sensors may become the only reasonable choice. The paper proposes a simple structure for making such devices, describes the first experiments and discusses the key issues faced, with emphasis on laser scribing.

We present a novel concept of quasi-distributed optical fibre extensometers for embedment into concrete, with optimized, continuous transfer of the strain field to the fibre, and fully corrected from thermal variations. These sensors have been developed for structural health monitoring applications. They are composed of a combination of optical cavities and Bragg gratings cascaded along a single fibre. The cavities, which are the parts sensitive to the concrete strain, are formed by partially reflecting elements inserted into the fibre. Their length, which is also the measurement basis, can range from 10 cm to several metres. Several cavities can be cascaded along a single fibre, allowing quasi-distributed strains measurements. Bragg Gratings are inserted along the same fibre, close to the cavities, and are used to measure the temperature locally. Both types of sensors are read by a fibre optic low coherence interferometer featuring a temporal delay line. The interferometer is used in an original way to measure simultaneously the length variations of the cavities and the wavelength shifts of the Bragg gratings. In this paper we present the design of the sensor, and in particular the study of the composite packaging whose shape and mechanical properties have been optimized by finite elements modelling to minimize the intrusion effect and ensure a continuous transfer of the strain field when embedded into concrete. We develop the optical reading method, presenting the theory of the sensor interrogation, or how to get the strain and temperature information. We describe also the instrumentation. Finally we present some laboratory experiments that show very good agreement between standard sensors and OFS, and an example of implementation into a bridge near Angouleme, France.

This paper describes an optoelectronic setup which has been designed in order to evaluate some finishing process parameters of textile fabrics such as emerizing or raising. This evaluation is usually performed by trained people and our goal is to perform it in an automatic and objective way without any human operation. Our setup evaluates the periodical structure of fabrics through a temporal Fourier analysis of the degree of polarization of the light reflected by a fabric surface. The measurement sensitivity to surface hairiness is shown to be greatly improved when polarization is taken into account.

Cryogenic temperature sensing was studied using a pressurized fiber Bragg grating (PFBG). The PFBG was obtained by simply applying a small diametric load to a regular fiber Bragg grating (FBG), which was coated with polyimide of a thickness of 11 micrometers. The Bragg wavelength of the PFBG was measured at temperatures from 295 K to 4.2 K. A pressure-induced transition occurred at 200 K during the cooling cycle. As a result, the temperature sensitivity of the PFBG was found to be nonlinear and reach 24 pm/K below 200 K, more than three times the regular FBG. For the temperature change from 80 K to 10 K, the PFBG has a total Bragg wavelength shift of about 470 pm, 10 times more than the regular FBG. From room temperature to liquid helium temperature the PFBG gives a total wavelength shift of 3.78 nm, compared to the FBG of 1.51 nm. The effect of the coating thickness on the temperature sensitivity of the gratings is also discussed.

Two instruments have been designed for airborne remote sensing of landfill methane emissions using the infrared absorption of reflected sunlight. A gas correlation filter wheel and a length modulated cell have been produced to discriminate between methane and other interfering species and the performance of the two systems discussed. The two systems have been interfaced with an Indium Gallium Arsenide (InGaAs) 2D detector array and an Indium Antimonide (InSb) point detector. The InGaAs array detector response rate was found to be too slow so experiments were done using the InSb detector. The gas correlation filter wheel has been shown to detect levels of methane equivalent to 200ppmv with a 30m pathlength at the 3.3μm methane band with the InSb point detector. It has been predicted that it should be possible to detect levels equivalent to 20ppmv over a 30m pathlength at the 1.65μm band with the gas correlation filter wheel and a fast response InGaAs detector. The length modulated device was found to have far less sensitivity in comparison to the filter wheel system, but could have enhanced performance with improved design.

The paper presents the diamond-like carbon (DLC) film as a coating for multimode optical fibre, single-mode optical fibre with long-period grating (LPG) and planar optical waveguides. Thin DLC coatings significantly change sensing elements' properties. Constructed systems can be very sensitive to concentration changes of several chemical solutions (e.g. sodium chloride, calcium chloride and ethylene glycol) due to changes of refractive index of the solutions. The influence of Radio Frequency Plasma Chemical Vapour Deposition (RF PCVD) process parameters on sensitivity is discussed. A novel integrated planar waveguide sensing system with DLC film is presented. The films were analysed morphologically and optically.

A planar optical waveguide is manufactured by the functionnalisation of oxidised mesoporous silicon with Bromothymol Blue to achieve a sensitive ammonia sensor suitable for low gas concentrations. The propagated light intensity is measured at the output of the waveguide. The sensitivity at low concentrations and the short time of reaction of the sensor are enhanced by a confinement effect of the gas molecules inside the pores. The dependence of the output signal with gas concentration is demonstrated. When the ammonia flow is stopped, the reversibility of the initial characteristics of the propagated light is naturally obtained with the disappearance of the gas molecules.

In the first part of this paper, we use a specially developed sensitive polymer (PLG) which belongs to the polysiloxane family. Thin layers of this polymer are deposited onto the surface of the optical transducers. Results will be presented on the response of diffraction-based optical transducers such as gratings and also on interferometric transducers and especially integrated Mach-Zehnder (MZ) interferometers. In the first case, a relief grating is coated with the sensitive polymer. A small variation of the refractive index of this layer, due to the presence of pollutant, induces a variation of the intensity of the diffracted orders which can be measured. In the second case, one arm of the integrated MZ interferometers is coated with the polymer. The variation of the refractive index of the polymer causes a phase shift in the measuring arm which can be measured by the modification of the output intensity. Assessment of sensitivity for the detection of nitro-aromatic compounds using a PLG sensitive layer on both sensors are presented and are also compared to the response of a SAW-based sensor coated with the same polymer. In the second part of this paper, synthesis, spectroscopy and fluorescence quenching behaviour of a N-(2,5-ditertio-butylphenyl)-1,8-naphthalimide functionalised polystyrene (PST-NI) are reported. PST-NI was synthesized by free radical polymerisation of the corresponding monomer. The molecular weight (Mn) is 43 000 g.mol-1. Introduction of a bulky moiety on the naphthalimide chromophores avoids P-stacking of the polymer side chains as well as excimer formation and hence leads to very high fluorescence quantum yields in thin solid films (up to 60%). Upon 1 minute exposure to DNT vapour, it was shown that a 5.5 nm thick film of PST-NI exhibits a 45% drop in its fluorescence intensity, which makes this polymer very attractive for sensing applications.

We review the basic concepts of UV detectors and discuss why astronomers and planetary geologists place requirements of the detectors to be both UV sensitive and yet visible blind. This visible-blind requirement means that although CCD (and CMOS) based cameras can be quite efficient in the UV (approximately 40%), when filters are applied to knock out the necessary visible contribution, the effective CCD sensitivity is reduced significantly. We review several detector concepts from wide band-gap semi-conductors (primarily GaN-based) to Si-based (CCD and CMOS) and low temperature detectors (e.g., transmission edge sensors [TESs], superconducting Tunnel Junctions (STJs), and metallic magnetic calorimeters (MMCs). We conclude a new mission that would use a GaN photo-cathode camera for the UV low light level applications.

We present a new detection scheme for carbon dioxide(CO₂) based on a custom-made room temperature distributed feedback (DFB) diode laser at 2.7 μm, currently representing the laser with the highest emission wavelength of its kind. The detector's especially compact and simple set-up is based on photoacoustic spectroscopy (PAS). This method makes use of the transformation of absorbed modulated radiation into a sound wave. The sensor enables a very high detection sensitivity for CO₂ in the ppb range. Furthermore, the carefully selected spectral region as well as the narrow bandwidth and wide tunability of the single-mode laser ensure an excellent selectivity. Even measurements of different CO₂ isotopes can be easily performed. This could enable future applications of this spectroscopic sensor in medical diagnostics (e.g. ¹³C-breath tests).

The theoretical background of Seebeck infrared detectors based on nonlinear free carrier absorption in doped semiconductors has been presented. The 3D-distribution of the electron and lattice temperatures created by the absorption of an optical beam with a cylindrical symmetry in layered structures was developed. Five different operation regimes of the detector are presented, showing that all beams form CW down to picoseconds can be detected. We will discuss how one can control the detectable power and intensity levels and the cross-talk in multi-pixel arrays by means of the doping concentration, geometry of the absorption region and pixellation format, the positioning of a heat sink, and micro-machining techniques. Experimental backing for the model will be given for the pulsed regime and the CW regime. We also demonstrate operation of the detector in the +1 kW power level.

This paper reports the development of a novel InSb photovoltaic infrared sensor (InSb PVS) operating at room temperature. The InSb PVS consists of an InSb p⁺/p^-/n⁺ structure grown on semi-insulating GaAs (100) substrate, with a p⁺ Al_0.17In_0.83Sb barrier layer between p⁺ and p^- layers to reduce diffusion of photo-excited electrons. Photodiodes were fabricated by wet etching process and, using a 500K blackbody, we obtained D* of 2.8x10⁸ cmHz^1/2/W and R_V of 1.9 kV/W at room temperature. S/N was improved with the serial connection of 700 photodiodes patterned on a 600x600 μm² chip. Increasing the number (N) of connected photodiodes, S/N ratio was improved by a factor of N^1/2. RV was constant for signals ranging from DC to 500Hz. From spectral response measurements a cut-off wavelength of 6.8 μm was obtained. The InSb PVS was flip-chip bonded on a pre-amplifier IC, allowing the shortest connection between the InSb PVS and the pre-amplifier, making the system immune to electromagnetic noise. The system was finally encapsulated by a Dual Flat Non-leaded (DFN) package with a window, which exposes the backside of the GaAs substrate allowing the infrared light incidence. The device external sizes are 2.2 mm x 2.7 mm x 0.7 mm and to our knowledge is the smallest uncooled sensor for the middle-infrared range reported until now.

The feasibility of diamond position sensitive detectors for deep UV light monitoring is reported. Based on voltage-division principle, a very simple one-dimensional photosensitive structures have been developed exploiting the strong variation of polycrystalline diamond conductivity under UV-light irradiation and dark conditions. Lumped and finite elements analysis have been used to compare the theoretical expectations with the experimental results obtained under excimer laser illumination. A complete characterization of such a 1D position sensitive device has been performed in terms of: the beam intensity insensitivity (over three orders of magnitude); the output signal dependence on the beam width; and the contact structure and its resistance influence on the device performances.

Until recently imaging spectroscopy was an extensive tool due to the limitations to airborne systems. Airborne imaging spectrometer systems are cost-intensive for the user and the availability for multi-temporal applications is still low. But especially for environmental analysis a high temporal resolution is required because most developments either in natural or in managed ecosystems can only be monitored through time series of remote sensing observations. In 1997 these drawbacks led to the idea of a low-cost imaging spectrometer to overcome the difficulties of the existing systems and provide data for the institute's own environmental research purposes. This was the birth of the AVIS (Airborne Visible/ Infrared imaging Spectrometer) system.

Imaging polarimetry through evaluation of the degree of polarization of light can give much information about complex scenes. A classic optical set-up usually consists in using a rotating polarizer or a tunable phase modulator as a polarization state analyzer. In this study, we implement an imaging polarimeter using a ferroelectric liquid crystal spatial light modulator as a polarization state analyzer able to run at 1000 Hz. This way, our polarimeter can overcome the classic limit of 50 Hz, provided that the camera is fast enough. Our polarimeter is compared with classical systems which use rotating polarizers.

In the present paper, we address a hybrid technique which combines the method of spectral interferometry with chromatic confocal microscopy. On the basis of some proof-of-principle experiments, it is shown that with this new concept, the axial detection range of the sensor is decoupled from the limited depth-of-focus of the employed microscope objective, and a high numerical aperture objective can be employed for detection. The attained interferometric signals consist of high-contrast wavelets, measured in the λ-domain. The position of an investigated object is measured by analyzing the spectral-phase of the attained wavelets. In particular, chirp-effects as well as the significant role of confocal filtering are discussed.

In this work we present the development and characterization of highly-sensitive fibre optic coils hydrophone for the detection of ultrasonic signals. In particular, fibre coils are a good improvement, in front of electronic sensors, for the application proposed in this work, the detection of ultrasonic signals within power transformers. Several fibre optic coils are tested in a laboratory controlled environment within a suitable ultrasonic frequency range, typically associated to ultrasonic emission in power transformers. We develop and characterize several fibre optic hydrophone coils using a Mach-Zehnder interferometer. A detailed study is carried out on the ideal shape of the hydrophone fibre probe, for parameters such as sensitivity and frequency range. Also, a comparative analysis has been carried out on the sensitivity of commercial PZT to the sensitivity of the fibre optic system under the same test conditions.

The paper presents a measuring system of extreme ultraviolet radiation pulses (13.5 nm). The system is used for monitoring a gas-puff laser-plasma source constructed at the Institute of Optoelectronics. The radiation source and the system are used in metrology of EUV optics. The system consists of a detection head and a system of optical filters, which are housing in a special construction. Additional element of the measuring system is a special processing unit. The measuring system was used during investigations of the plasma-laser optimization. The results were comparable with the ones from a spectrograph and an Emon energy meter.

We proposed a new kind of setup for the automatic control of the quality of micro lens array, which is based on semiderivative real filter. With the use of the 4f correlator setup with a semiderivative filter placed in the Fourier plane and connected with the camera, it is possible to examine phase objects. Such a setup is shift invariant, so it enables us to simultaneously examine a set of identical elements, such as a micro lens array. Additionally, the same setup allows for a simultaneous measurement of both thin and thick phase objects. It is also possible to measure a wide range of phase gradients. The article presents the results of simulations where the semiderivative filter was used to measure phase objects such as cylindrical and spherical lenses. A special emphasis was placed upon checking how the proposed setup works for a number of similar phase optical elements, such as microlens arrays. The article also presents an analysis of how various technological limitations can influence the quality and the precision of the results obtained. Further on, it shows the initial results of the use of 3D lithography to produce semiderivative filters.

This paper presents the second generation LISE-LI of the fibre-optics Low coherence Interferometric Sensor (LISE), recently developed by FOGALE nanotech. Based on the proven concept of partial coherence interferometry, the LISE system works as a comparator of optical group delays. The group delay along the optical axis in the probe interferometer arm containing the object to be measured is compared with the group delay along the optical axis of the reference interferometer arm containing a delay line. The latter consists of a mirror that can be linearly displaced on a translation stage. The light source is a super luminescent diode emitting at near infrared wavelength (typically 1.31 μm) with a spectral bandwidth of a few tens of nm. Thanks to the limited temporal coherence of the source, multiple surfaces of the object can be detected during a single scan of the delay line. Measurement ranges are between a few mm up to 600 mm (optical thickness). The measurement zone can be placed at a working distance of up to several meters away from the instrument's exit. Applications in industry and in research laboratories include thickness measurements of individual optical elements (e.g. lenses), technical multi-layer glasses, glue and varnish layers deposited on various substrates, Si or GaAs wafers, and position measurements of multiple elements of an optical system (e.g. a photographic lens). Compared to the first generation of the system, the absolute accuracy of the second generation system is about ten times better, reaching a level of ±100 nm for thickness measurements over the full measurement range. Following an introductory description of the measurement principle, the first part of the paper focuses on the key elements in the system design, both in hardware and detection algorithm, that ensure the high accuracy level. The second part of the paper presents an experimental validation of the achieved accuracy level. We present results of thickness measurements on distance pieces made of Zerodur^®. The measured results demonstrate the absolute accuracy over the measurement range as well as the excellent long-term stability of the system.

A monitoring technique for multiple power splitter-passive optical networks (PS-PON) is presented. The technique is based on the remote sensing of fiber Bragg grating (FBG) using a tunable OTDR. To monitor the multiple PS-PON, the FBG can be used for a wavelength dependent reflective reference on each branch end of the PS. The FBG helps discern an individual event of the multiple PS-PON for the monitoring in collaborate with information of Rayleigh backscattered power. The multiple PS-PON can be analyzed by the monitoring method at the central office under 10-Gbit/s in-service.

We present a compact, non-contact, low-cost optical sensor for real time vibration detection and active vibration control of mechanical devices based on laser speckle translation. The speckle translation is processed optically with a narrow spatial filter to provide electrical signals carrying in-phase and phase quadrature information about the speckle motion. The optical sensor is integrated with an ASIC. The ASIC and an external programmable logical device (PLD) calculate a real time electrical error signal, which then is fed back a piezo-electrical crystal. For testing purposes a mechanical sinusoidal vibration is applied to the target via a piezo-electrical spacer. The error signal deforms the piezo-electrical spacer in order to counteract and minimize the vibrational motion of the target. The primary purpose of this work is to demonstrate the feasibility of producing a compact, low-cost sensor that carries out single-point measurement of submicron, in-plane translational vibration of a solid structure in real time.

Model of light scattering from spheroids in three beam anemometer is presented. In the scattering model a plane wave and Gaussian beams are considered. Preliminary simulations of scattering intensities base on extended boundary condition method. An influence of rotation angles of the spheroid and differences in scattered field between two and three beam systems are shown.

Absolute distance measurement using optical feedback with heterodyne detection has been demonstrated by sweeping the optical frequency of a single longitudinal mode (SLM) Yb:Er glass laser. This technique allows enhancing the sensitivity of the laser response to self-mixing thanks to resonant excitation close to the relaxation oscillation frequency peak. The experimental results on a non-cooperative target are in good agreement with the theory. The shape of the resulting signal is analysed both in the temporal and frequency domains considering the specific dynamic of a class B solid-state laser.

In this work we summarize some of the results we obtained during our research of different physical phenomena which take place when a visible or near-infrared laser beam falls in onto a biological product, more in particular on a vegetable or on a fruit. The most important phenomena are surface reflection, selective absorption, fluorescence, absorption in the near-infrared and internal reflection. While the emphasis lays on the identification of the product type we will show that some of the demonstrated sorting principles can also be used for quality sorting: for example a determination of the ripeness of green vegetables or of the water/oil content of vegetables and fruits and a detection of the presence of the very harmful aflatoxines.

Quasi single mode fiber is a fiber supporting a few modes only. If the operational wavelength of the light source will be shorter than the cut-off wavelength is, then the fiber will support except fundamental mode LP₀₁ several higher modes too. Such fiber conserve themselves the advantageous characteristics for telecommunication application (small attenuation, slight dispersion), but it is possible to use them for sensor-based applications utilizing the mode coupling among several guided modes. This paper describes design of optical fiber working as a conventional telecommunication fiber at wavelength of 1550 nm and temperature sensing fiber at the wavelength of 850 nm. In the paper the basic theory together with the simulation of the mode distribution will be shown temperature changes within the interval 20°C-100°C.

We analyze theoretically and experimentally spectral interference of a white light in a tandem configuration of a birefringent crystal and a sensing birefringent fiber. We express analytically the spectral interference law taking into account the dispersion of birefringence in the crystal and in the fiber. We reveal that the visibility of spectral interference fringes is highest for the group optical path difference (OPD) in the crystal compensating the group OPD in the fiber. We model two types of spectral interferograms knowing dispersion characteristics of the sensing fiber and using a quartz crystal of the positive or a calcite crystal of the negative birefringence. Sensing capabilities of the configuration are demonstrated by the change of the phase of spectral interference fringes due to the change of fiber length. We perform two experiments with a highly birefringent fiber of a suitable length and a birefringent quartz crystal of two suitable thicknesses. We confirm, in accordance with the theory, that the wavelength-dependent phases of spectral interference fringes vary with the fiber length.

LLL night vision system is a sort of the photoelectric imaging system. In this paper, the fundamental theory and conception about visual simulation software platform Creator-Vega is introduced, which is an applied tool and can simulate the workflow of the LLL sensor in the night vividly. Combined with using VC functional software, an application software frame is set up. The interface and functional menus of software are proposed in the paper. The software can provide the evaluation for design of LLL night vision system. The performance simulation results of photoelectric imaging device are given.

The Cenozoic Geology of Taiwan rises from the ocean, and therefore many areas in Taiwan do not have solid rocks. Suffering from the rock fall induced by earthquakes and frequent flood disasters in recent years, the geology even shows the flimsiness. Falling stones are frequently found on the highway, and sometimes disasters take place. Because the optical fiber has the features of low loss and wide bandwidth, it has replaced the coaxial cable and became the mainstream of the communication system in recent years. Owing to interferometer has high sensitivity characteristic is usually applied to long distance, weak signal detection. In general, weak signal is difficult to monitor if the vibration is located at far away place. The configuration of our sensing system is made of an interferometer and fiber Bragg Grating. A demodulation circuit is used as the signal processor to measure the phase difference caused by vibration. The fiber optic sensor is an all fiber system with good accuracy for low frequency vibration measurement. According to our test, the dynamic range detected by the optic fiber sensor is 38 dB where the frequency ranges between 50 ~ 400 Hz. The minimum detectable signal level is around 1.95 x 10^-2 rad.

An integrated algorithm for the detection of dim point/extended size, slow/fast-moving targets has been presented in this paper. In the proposed algorithm, essentially an innovation over an existing algorithm reported by Nengli Dong et al [7], morphological operations are carried out on the incoming IR data to improve signal to noise ratio (SNR). Methods of entropy thresholding and conjunction functions are integrated together. Conjunction function based algorithm has been significantly modified to take care of fast moving targets, a limitation of the method proposed by Nengli Dong et al. Our proposed algorithm is able to detect point as well extended size targets with low contrast and having frame to frame movements varying from sub-pixel to tens of pixels.

Multimode interference occurring in a singlemode-multimode-singlemode fiber structure is numerically investigated with a wide-angle beam propagation method using the cylindrical coordinate. Two application examples in optical sensing are presented. 1) The wavelength sensitivity of the singlemode-multimode-singlemode structure is utilized and with an appropriate length of the multimode fiber section, the device is developed as an edge filter for a ratiometric wavelength measurement system. 2) When the multimode fiber cladding is removed, it becomes the singlemode-multimode core-singlemode structure and can be developed as an all-fiber refractometer sensor with an optimal length of multimode core section. The designed refractometer can offer an estimated resolution of about 5.4x10^-5 for refractive index from 1.33 to 1.45, which is competitive as compared to existing waveguide based optical refractometer sensors while offering a much simpler configuration.

Results of single and multiple light scattering simulations for erythrocytes (RBC) modelled as spheroids are presented. The normal conditions as well as changes of osmotic pressure, hematocrit level and haemoglobin saturation were analysed. The computations were carried out with the use of the T-Matrix and Monte Carlo methods. The obtained results were compared with simulations based on spherical and cylindrical models. There were no significant qualitative differences between the cylindrical and spheroid models in case of multiple scattering. Somewhat larger differences between the spherical and the two other models were observed.

The light scattering maps analysis methods are presented. The maps were recorded for composite materials content glass fibres with use the measurement system based on argon laser and CCD cameras. The methods give possibility to determine the placement and concentration of fibres in material.

The paper deals with a special type of sensing optical fiber, the annular core fiber. This fiber is composed of a narrow annular low-loss glass optical core and glass optical cladding which are applied onto the inner wall of a silica capillary. In the paper transmission characteristics are determined theoretically from the solution of the Helmholtz equation as well as experimentally from measurements of the near field and angular distributions of the output power from the fiber excited by an inclined collimated beam. The sensitivity of the fiber to gaseous toluene is determined under the excitation of the fiber by an inclined beam at 670 nm, when refractive-index changes in the evanescent field are responsible for the sensitivity. These measurements are compared with those carried out with reference capillary silica fibers and PCS fibers. It is shown that the annular core fibers have the highest sensitivity in comparison with the reference fibers. A detection limit of 0.06 % can be determined from the sensitivity measurements.

We report experimental findings for tailoring the temperature and strain coefficients of Type I and Type IA fibre Bragg gratings by influencing the photosensitivity presensitisation of the host optical fibre. It is shown that by controlling the level of hydrogen saturation, via hot and cold hydrogenation, it is possible to produce gratings with lower thermal coefficients. Furthermore, there is a larger difference between the Type I and Type IA thermal coefficients and a significant improvement in the matrix condition number, which impacts the ability to recover accurate temperature and strain data using the Type1-1A dual grating sensor.

New approach to high-speed detection and modulation based on application of capacitance modulation is offered. Application of capacitance modulation allows to increase sensitivity and noise immunity of high-speed photodetectors in microwave range.

We present a method for measuring weak absorption in optical materials, using a new diferential interferrometry technique. Both thermal shift phase and thermal characteristic time may be determined by fitting the observed time-resolved interferometric signal.

A phase extraction technique based on data dependent system (DDS) method in higher order modal interference (LP₀₁ and LP₀₂) within the birefringent optical fiber is presented. A frequency modulated optical signal from a laser diode was launched into the fiber and the higher modes were excited. The interference patterns recorded at the output end of the fiber was digitized and characterized by means of autoregressive model. Self coherence function of an interferogram was obtained from the autoregressive parameters and this would provide the phase change due to the measurand. The modulation of group delay was obtained from the phase curve through unwrapping. An application has been made for measurement of strain in an array of simply supported beam and cantilever beam at different locations under different loading conditions. Results have been compared with those obtained using Fourier transform method and parametric method for different applied strain (200-2000 μstrain).

The photodetector based on optical rectification effect (ORE) was created using nanostructured carbon (nanographite) films. Sensitivity of the photodetector was studied in dependence on the carbon films size. It is shown that amplitude of electrical pulses generated by the photodetector depends on the thickness, length and width of the film area. The maximal sensitivity is reached at the film thickness of about 2.5 micrometers. It is shown also that the photoelectrical pulses appearing on the nanographite film have different nature than those appearing in on the silicon substrate.

Diffraction gratings were designed and fabricated on a SiN/SiO₂ planar waveguide to couple light from a low power 488 nm laser beam into the planar waveguide. The light propagating in the waveguide was then used to detect fluoresceine from volume on the planar waveguide surface. The results demonstrate the capability for very simple and fast analytical throughput for quantification of fluorescent samples, essentially without cross-talk. The transmission measurements show about 10% diffraction efficiency with 0.06° FWHM. The diffraction efficiency and the incidence angle for the maximum diffraction efficiency were observed to be highly dependent on the process parameters used to fabricate the gratings. The fluorescence signal was observed to be linear for fluoresceine concentrations between 10^-9 and 10^-3 M.

Optical sensors have gained a wide range of applications from biological-warfare detection to improving clinical diagnosis. A waveguide-based sensor can be sensitive to a number of parameters - external and internal to the sensor. A mathematical model to investigate the effect of parameter fluctuations on sensor performance is presented. The model may also be used for the testing of sensors.

In this paper, we present a bifrequency acousto-optic polarization splitter (BAOPS) used to select independently the two polarization states of an arbitrary polarized input beam with two acoustic carriers. We make use of a dual frequency anisotropic interaction in the crystal, two acoustic waves diffract the optical beam, each frequency being tuned for interaction with only one of the beam polarizations. We explain how this double interaction is made possible by a proper cut of the paratellurite crystal and for a chosen launching angle of the input beam. In a first part we derive the theory underlying the acousto-optic interaction and the design of the paratellurite device. Then we describe our experimental setup, show some experimental results and discuss them.

Birefringence in fiber Bragg gratings can result from two distinct effects that combine with the intrinsic fiber birefringence: the birefringence induced by the UV photo-writing and the birefringence due to a transversal load. In both cases, it leads to polarization dependent loss and differential group delay inside gratings. This paper aims to provide a characterization, both theoretically and experimentally, of the polarization dependent loss and the differential group delay generated by uniform Bragg gratings written into single mode optical fibers. We demonstrate that the measured polarization properties can be accurately reconstructed by means of the coupled mode theory and the Jones formalism. We also demonstrate that the PDL and DGD evolutions contain information about birefringence and can thus be used for transverse force sensing purposes. Experimental results obtained on fiber Bragg gratings transversally loaded by an external force confirm the simulated evolutions.

We report on the development of a new type of hydrophone based on an optical fiber interferometer sensor. This interferometer based on dual Sagnac ring configuration to pick up the underwater acoustic signal. Using the unbalanced arms of the Mach-Zehnder interferometer (MZI), the underwater acoustic wave induces the phase difference on optic fiber hydrophone interrogator to demodulate the acoustic field signals by PGC modulation circuit. The configuration is easily implemented and can detect weak signal in a high noisy water environment. The underwater hydrophone systems primarily with B&K system, projector 8104 and receiver 8103, have been successfully worked. As well, B&K 8104 acoustic response increases with frequency but also causes the echo noise in the meantime. The experimental results show that over the frequency range of 7 to 11 KHz, the hydrophone has an almost flat response with an average sensitivity and dynamic range of -211.47 dB re/μPa and 33dB, respectively.

Near-infrared (NIR) absorption spectroscopy with tunable diode lasers allows the simultaneous detection of the three most important isotopologues of carbon dioxide (¹²CO₂, ¹³CO₂, ¹²C¹⁸O¹⁶O) and carbon monoxide (¹²CO,¹³CO, ¹²C¹⁸O). The flexible and compact fiber-optic tunable diode laser absorption spectrometer (TDLAS) allows selective measurements of CO₂ and CO with high isotopic resolution without sample preparation since there is no interference with water vapour. For each species, linear calibration plots with a dynamic range of four orders of magnitude and detection limits (LOD) in the range of a few ppm were obtained utilizing wavelength modulation spectroscopy (WMS) with balanced detection in a Herriott-type multipass cell. The high performance of the apparatus is illustrated by fill-evacuation- refill cycles.

In this paper the new method of parallel glass plat test is presented. In the method an Optical Vortex Interferometer (OVI) is used. The OVI generate the regular net of optical vortices by interference of three plane waves. One wave is deformed after crossing measured parallel glass plate. The deformation of the wave-front is measurable because the deformation of vortex net structure arises from the wave-front deformation. The record of the vortex points' positions before and after parallel glass plate insertion in the optical arrangement is essential. Shown in this paper the analysis vortex points positions change gives high precision information about real shape of the parallel glass plate.

The optical vortices were intensively studied during last decade. In the literature there are papers presenting application of the optical vortices. The regular net of optical vortices generated by the three plane waves interference allows for the new kind of the interferometer - the Optical Vortex Interferometer (OVI). The precision of the OVI depends on the localization accuracy and the phase reconstruction. The localization methods give errors if we use beamsplitters with coatings changing the polarization state of the light. There are six beamsplitters used in this interferometer. In the setup we used non-polarizing coatings. We observed pleochroism effect, which occurs in these coatings. It is the cause of errors in the localization of optical vortices. In this paper we study the effect of pleochroism and we show the way to avoid errors in the localization of optical vortices in the OVI.

Liquid level and pressure sensors have been developed using plastic optical fibers, which offer many advantages with respect to silica ones, such as large core dimension, high numerical aperture, easy handling, low cost and high flexibility. Low cost and compact opto-electronic circuits have been designed and realized to drive the proposed sensors. Sensor characteristics and performances have been experimentally measured and discussed.

Shape sensing of reflecting free form surfaces is achieved by deflection of an array of light pencils. The pencils showing very high depth of focus are produced by means of micro-optical components. Each pencil that interacts with the surface under test is redirected by reflection. Imaging intensity measurements, e.g. by a CCD-camera, at several propagation distances allow for determination of the propagation angle of each reflected pencil. By using the vector law of reflection the local slope of the surface at the location of reflection can be determined. Height data is obtained by depth from gradient methods known, e.g., from Hartman-Shack sensors. Both simulations and experimental results show a typical resolution of a view μm or 0.1 mrad for height or angle measurements, respectively.

The measurement signal (S) to noise (N) ratio (S/N) of novel 128×128 FPA in temperature range 77 -130K was carried out. FPA for spectral range 8-12 μm was fabricated by B⁺ implantation process into graded MCT P-p heterojunction with potential barrier. MCT P-p heterojunction with specific MCT composition throughout the thickness was grown by MBE on GaAs substrate by ellipsometric control in situ. The potential barrier was determined by the difference of MCT composition at absorber and p-n junction location layers and equal to ΔX_CdTe = 0,025. It was shown that based on P-p heterojunction FPA operated temperature and wavelength increases over routine one without P-p heterojunction. Keywords: graded gap layers, heterojunction, MCT, photodiodes, FPA.

A new nanopolycrystal of vanadium dioxide has been prepared. The average grain size is 8-10nm and the phase transition temperature drops down to 35°C. The temperature coefficiency of resistance (TCR) is 6-7%/°C in semiconductor zone. A linear senor has been fabricated based on the nanostructure of vanadium dioxide thin films and the test indicates that the characteristics has been improved greatly compared with sensors based on using conventional vanadium dioxide thin films.

The paper presents construction of a simple fiber-optic color sensor designed for recognition of objects from a set comprising an a prori defined, limited number of colors. Color sensing is based on diffusive reflectivity of examined surfaces measured in several separate spectral channels. Number and positions of channels depend on predetermined set of colors. The channels are fed by selected LED's sequentially, i.e. in Time-Division Multiple Access mode. Collected serially analogue signals are converted onto digital data enabling some processing variants. In order to extend the performance capability of such a sensor and to enable measurements of others colors, a simple neural network was applied.

A compact fluorometric sensor equipped with a LED source and a high sensitivity PMT detector has been implemented for the selective detection of native fluorescence of aflatoxin AFM1 in liquid solutions. This compact and easy-to-handle device is addressed to the rapid monitoring of AFM1 in milk, enabling the detection of concentrations up to the legal limit, which is 50 ppt. The system is suitable for preliminary screening at the earlier stages of the industrial process, and makes it possible to discard contaminated milk stocks before their inclusion in the production chain.

Multi-wavelength and multi-angle absorption spectroscopy performed in the visible spectral range, that is, 'scattered colorimetry', has been used to map a library of 25 diverse and commercially-available Belgian light beers. The resulting map shows four main clusters, relative to blonde, amber, red, and weiss beers, respectively, demonstrating that scattered colorimetry is a valid method for beer authentication and fingerprinting.

An optical sensor for the detection of olive oil aroma is presented. It is capable of distinguishing different ageing levels of extra-virgin olive oils, and shows effective potential for achieving a non destructive olfactory perception of oil ageing. The sensor is an optical scanner, fitted with an array of metalloporphyrin-based sensors. The scanner provides exposure of the sensors to the flow of the oil vapor being tested, and their sequential spectral interrogation. Spectral data are then processed using chemometric methodologies.

Knowledge of the gas flow distributions, their mass velocity and turbulences, in chemical reactors, thermodynamic engines, pipes, and other industrial facilities may help to achieve a more efficient system performance. In our novel approach, optical fibre Bragg grating (FBG) sensors have been used for measuring the temperature of a heated element, adapting the principles of conventional hot-wire-anemometers. Because of the multiplexing capability of FBG sensors, the gas mass flow distribution can be measured along the sensor array. The length of the heated and sensor-equipped element can be easily adapted to the cross section of the gas flow, from <10 cm up to several metres. The number and distances of FBGs distributed over this length defines the spatial resolution and is basically limited by the sensor signal processing. According to FBG sensor lengths < 5 mm, spatial resolutions of gas flow measurements of less than 1 cm can be achieved.

Tesat-Spacecom has developed a series of fiber coupled single frequency lasers for space applications ranging from onboard metrology for space borne FTIR spectrometers to step tunable seed lasers for LIDAR applications. The cw-seed laser developed for the ESA AEOLUS Mission shows a 3* 10^-11 Allen variance from 1 sec time intervals up to 1000 sec. Q-switched lasers with stable beam pointing under space environments are another field of development. One important aspect of a space borne laser system is a reliable fiber coupled laser diode pump source around 808nm. A dedicated development concerning chip design and packaging yielded in a 5*10⁶h MTTF (mean time to failure) for the broad area emitters. Qualification and performance test results for the different laser assemblies will be presented and their application in the different space programs.