Approaching four decades have elapsed since the first patents were filed on fibre optic sensor technology. During that time basic principles have become well characterised and established and technological approaches and sensor realisation have become commercially and practically viable. This paper reviews just some of the progress in fibre sensors highlighting in particular the mechanisms involved in turning the bench demonstrator into competitive and effective product.

The side-emitting optical fibers are specially designed to stimulate leakage of the core-transmitted radiation via their side surfaces, so creating the effect of glowing tiny wires. The basic design concepts for this kind of optical fibers are discussed, as well as some of the present and potential future applications.

A unique approach to gas detection using optical correlation spectroscopy (OCS) has been investigated. By employing a semiconductor optical amplifier (SOA) with an optical fibre delay line to generate the anti-phase signal, zero point drift errors are minimised and compatibility with single mode optical fibre systems has been achieved. Experimental results, obtained for varying concentrations of acetylene (C₂H₂) gas at different pressures, agree well with the theoretical analysis. Signal-to-noise ratio (SNR) analysis was also performed to predict the theoretical minimum detectable concentration for C₂H₂.

The operation of optical fiber sensors using optical time-domain reflectometers (OTDRs) is outlined. Limitations introduced by telecommunication OTDRs used in these sensors are discussed. Other approaches based on specialized short-range OTDRs are presented. Finally, OTDRs based on sub-picosecond fiber laser sources and fast detection and acquisition systems.

Near infra-red tuneable diode laser spectroscopy (TDLS) with wavelength modulation spectroscopy (WMS) is a powerful technique for the measurements of gas compositions, and its ability to address multiple sensing points over optical fibre networks is proving to be particularly useful. However, the complexity involved in compensating for errors arising from pressure fluctuations is a weakness. Indeed, it is desirable to develop the technique to be capable of measuring pressure. This requires the extraction of accurate linewidth information from the recovered signals, so far made difficult by the presence of a systematic distortion arising from the laser amplitude modulation. Here we report a simple detection technique to null the effects of laser amplitude modulation and recover undistorted signals from which the gas linewidth can be accurately measured. Firstly we demonstrate that the measurements of accurate gas linewidths and pressure can be made from direct detection TDLS, addressing an atmospheric water absorption line. Finally, we report the accurate and simple measurement of acetylene pressure from TDLS / WMS measurements.

This paper will present recent developments in optical fibre sensors and optical fibre based instrumentation research undertaken at Cranfield University. New sensor techniques based on nanoscale molecular coatings deposited on singlemode fibres containing long period gratings and the use of singlemode fibres and coherent imaging fibre bundles in full-field speckle interferometry and planar Doppler velocimetry will be presented.

Optical fiber technology is able to answer the demanded development of EMI immune and harsh withstanding sensors for the Electric Power Industry, particularly applied to Power Transformers, and specifically for measurements within them. Apart from temperature, the other main magnitudes of interest are vibrations and partial discharges, which are studied here on the base of the interferometric sensors that we are developing for these purposes. This work is centered on the new concept of interferometric sensing by detecting multi-fringe outputs, which is applied for the measurement of each magnitude independently or both at the same time from only one probe. A high resolution read-out of the optical phase without ambiguity is demonstrated with this approach of demodulation and with the probes designed for monitoring inside power transformers. Results of in-field trials are presented for synchronous vibrations (100 Hz - 2 kHz) of two power transformers. First results of calibration of acoustic sensing with these probes on the base of the same interferometric concept are also presented in order to apply them for the measurement of partial discharges by detecting ultrasounds (20 kHz - 200 kHz). A multi-purpose exploitation of the sensor heads installed at the core and the windings of a power transformer is explored for detecting at the same time both, vibrations and partial discharge induced ultrasonic pulses. The multi-fringe interferometric output due to vibrations is proposed as a repetitive reference for the demodulation of the higher frequency asynchronous signals.

In this paper we have described new results obtained during investigation of seismic rotational waves simultaneously by TAPS - two antiparallel pendulum seismometers system as well as by FORS-II - fiber-optic rotational seismometer. The main advantage of such approach is a possibility to recognize the velocity of seismic rotational waves which seems to be different from velocities of other seismic waves. The experimental data presented in the paper are confirmed by theoretical description of seismic rotational waves' nature.

Experimental results on the polarization fluctuations of the optical signal in a erbium doped fiber amplifier (EDFA) are reported in this paper. Its influence on the visibility of interferometric optical fiber sensors is also analyzed.

Digital holographic interferometry (DHI) is a modern technique, which allows direct access to the interference phase in holographic interferometry. In order to implement DHI in commercial application the system has to fulfill several requirements including: automatic data capture, compactness and easiness of usage (often remote), high quality of output data. In order to perform those conditions we propose the fiber optics based DHI system with enhanced quality of holograms and decreased sensitivity to vibrations and environmental changes. These special features are achieved by: fiber optics based light delivery endoscope and possibility to introduce all-fibre phase in one of the E-M beams manipulation, monolithic design of sensor head, which decrease sensitivity of the system to mechanical vibrations, combined passive and active noise suppression and DH quality enhancement. The design considerations and the results of initial experiments performed at the model of the fibre optics based DHI system are presented and discussed.

An innovative series of optical fiber sensors based on spectroscopic interrogation is presented. The sensors are custom-designed for a wide range of applications, including gasoline colorimetry, chromium monitoring of sewage, museum lighting control, for use with a platform for interrogating an array of absorption-based chemical sensors, as well as for color and turbidity measurements. Two types of custom-design instrumentation have been developed, both making use of LED light sources and a low-cost optical fiber spectrometer to perform broadband spectral measurements in the visible spectral range. The first was designed especially to address color-based sensors, while the second assessed the combined color and turbidity of edible liquids such as olive oil. Both are potentially exploitable in other industrial and environmental applications.

In this paper we present a novel concept of using photonic band gap fibers for capillary electrophoresis (CE) in a configuration where both the analyzed solution and the light are fed through the hollow core of the fiber. The tested fiber was an HC19-1550-01 with 20 μm core size, manufactured by Blaze Photonics and rated for 1550 nm wavelength. Results of initial experiments in reflectometric and electrophoretic configurations are presented, opening up the possibility of developing a fiber-optic sensor based on CE for remote detection of targeted compounds. Such a sensor can be expected to have a wide temperature range of operation to excellent thermal stability of hollow-core PBG fibers.

Experiments were performed with the objective to obtain the velocity of liquids, e.g. water and oil / water mixtures flowing through a pipe. Experimentally tested flow rates were between 0.75 and 39 m³/h, corresponding to velocities of 0.023 and 1.2 m/s. Temperature disturbances were created by injecting slugs of hot water through a side inlet. The temperature was measured at regular time intervals of 1.2 s by Fibre Bragg Gratings, which were located at 40 equidistant locations at 0.5 m spacing. Hot slug movement was clearly visible in nearly all data sets. The magnitude of the temperature rise (0.1 - 0.2 °C) at that flow rate had the same magnitude as the temperature noise. Travelling temperature waves showed a relatively strong deformation at low rates, due to relatively strong Taylor dispersion occurring at transitional flow (Reynolds number ~ 2500 at the lowest rate). Temperature disturbances travelling down the pipe were tracked by semblance processing of the temperature data taken at 34 locations after the side inlet; the data from 6 locations before the side inlet was not included. Semblance processing is a technique commonly applied in obtaining seismic wave velocities using an equidistant array of receivers, which was applied here for velocity tracking of hot liquid slugs. The best velocity estimates were obtained at flow velocities of 0.13 and 0.28 m/s, typical for a small oil well. Velocity errors were largely within a +/- 10% bandwidth.

Fibre side-polishing technology allows for refractive index measurements using optical fibre Bragg grating sensors. Evanescent field interaction between the guided fibre light mode and the analyte near to the core of the side-polished optical fibre yields a Bragg wavelength shift in dependence on the refractive index of the analyte. This refractometric sensor technique has been extended to opto-chemical measurements with specific sensitivity using transducer layers with selective absorption properties deposited on the side-polished fibre core region. Experimental results are presented for the case of a hydrogen gas sensor (palladium transducer) and a pH sensor (polyaniline transducer).

We describe a fiber optic humidity sensor comprising a moisture - sensitive overlay on a long period fiber grating (LPFG), tuned at the 1.5 microns band. The hygrosensitive material overlaid was poly(ethylene oxide)/CoCl₂ hybrid containing 10 % wt CoCl₂ in the form of micro- and nano-particles synthesized in situ in the polymer of 50000 molecular weight. A thin overlay of the material is deposited from an aqueous solution on the unclad region of the LPFG and upon exposure to different ambient humidity levels its spectral properties are modified. The experimental results obtained, show changes of the spectral resonance notch and the transmission strength of the LPFG. The material parameters associated with the sensing mechanism may include those of refractive index, absorption and morphological alterations of the overlaid material. Relative humidity (RH) variations in the range from 50% to 95% can been detected with a resolution better than 0.2% RH. The response time constant is found of the order of few hundred milliseconds.

Different types of advanced optical fibre sensor systems using similar spectral interrogation principles and potential low-cost polychromator optoelectronic signal processing instrumentation will be presented, and examples of their industrial application are demonstrated. These are such sensors as multimode fibre based humidity, temperature, and pressure sensors with extrinsic microoptical Fabry-Perot transducers for process control in gas industry, UV absorption evanescent field sensors for organic pollution monitoring in groundwater, and single mode fibre Bragg grating (FBG) multiplexed strain & vibration and temperature sensor networks for structural health monitoring applications in electric power facilities, aerospace, railways, geotechnical and civil engineering. Recent results of current investigations applying FBGs and microstructured fibres for chemical sensing will be discussed.

We have proposed and demonstrated that the optical coherence function can be synthesized into desired shapes by manipulating the optical frequency and the phase of the lightwave. Based upon this unique technique, the synthesis of optical coherence function, various distributed photonic sensing and optical information processing applications have been developed. In this paper, the principle of the synthesis of optical coherence function is summarized. A series of functional optical sensing systems, including fiber-optic reflectometries, distributed stress location sensors, multiplexed FBG sensors, are introduced. Fully distributed fiber optic strain sensing systems per Brillouin frequency shift are highlighted, and synthesized dynamic grating based sensor is also presented. Applications in two- or three-dimensional distributed measurements, such as optical tomography of scattering medium, are also reviewed.

The paper reports on thermal and spectral effects in polarimetric fiber optic strain sensors based on new types of highly birefringent (HB) fibers operating at infrared wavelengths. Spectral and temperature characteristics of the HB fibers have been optimized in view of enhancing their sensing capabilities and in order to minimize disturbing environmental effects. Longitudinal strain sensitivity was found to be independent on both the source bandwidth and temperature.

A Hetero-Core Splice Fiber Optic Sensor has a very simple structure in which a short-length, different core-size fiber is inserted in a single-mode-fiber network line with a low transmission loss for the wavelength of 1.31μm. In this study, a displacement sensor has been newly developed using a hetero-core spliced fiber optic element in a form of simple module structure and has been evaluated in terms of the accuracy as an OTDR(Optical Time Domain Reflectometer)-based measurement, for the purpose of the full-scale environmental monitoring. The developed sensor module is designed to have a coverage sensitive to a relatively large displacement in the range 0-5mm, for which a simple displacement-macrobending conversion mechanism has been adopted. A nickel alloy Invar with an extremely low linear expansion coefficient is used for the main parts of the module. Displacement is given to the module with a highly accurate micrometer of a minimum resolution of 0.5μm. The sensitivity showed a tendency proportional to the insertion length of hetero-core portion in the range from 1 to 2mm. The experiment promisingly showed sufficient reproducibility in the sensing operation with the accuracy less than 0.1% to the full span displacement of 5mm. Additionally, a pressure gauge using a hetero-core spliced fiber optic element has been newly developed in a form of module structure by applying the developed displacement sensor. The pressure gauge is designed to measure the change in length of a bellows due to pressurized air. The experiment achieved the measurement accuracy 0.3%[%FS] with highly showing the capability of all-light wave-based liquid level monitoring as a first demonstration based on a single mode fiber transmission concept, which could be very useful for environmental preservation.

Fiber Bragg gratings constitute excellent sensor elements, able to measure static and dynamic fields, such as temperature and pressure. We demonstrate that superimposed Bragg gratings written into hydrogen-loaded polarization maintaining fiber can be used to quantitatively monitor micro-strains or characterize the shrinkage of different cements. In fact, since the fiber Bragg gratings are written with a sufficient wavelength spacing between their Bragg wavelength, they exhibit different sensitivities and consequently, they allow the simultaneous measurement of temperature, strain, pressure and transversal force, which is sufficient to completely characterize shrinkage. We discuss the calibration of these superimposed gratings making use of a completely automated system allowing to load the fiber both in the axial and transversal direction and to apply controlled temperature changes.

Semiconductor microspheres coupled to optical fibers are used for optical channel dropping in the IR communication wavelenghts of 800 to 1500 nm. The observed morphology dependent resonances have quality factors of 100000. The measured quality factors are limited by the sensitivity of the experimental setup. These optical resonances provide the necessary narrow linewidths, that are needed for high resolution optical communication applications. In addition to optical communication, detection, and switching applications of this optoelectronic system is studied experimentally and theoretically. The microsphere, optical fiber system shows promise as a building block for optoelectronic integration.

An overview of some important results is presented in measurement of optical fibers by interferometric methods in two domains. Both time-domain and spectral-domain measurements are analyzed theoretically including the effect of the first-order and second-order intermodal dispersion. In the time-domain measurements, a tandem configuration of a Michelson interferometer and a few-mode optical fiber is used and the spatial interference fringes are resolved to measure the intermodal group optical path difference. In the spectral-domain measurements, the intermodal interference at the output of an optical fiber alone shows up as a periodic modulation of the source spectrum when a high-resolution spectrometer is used. Utilizing a white-light spectral interferometric method employing a low-resolution spectrometer and a tandem configuration of a Michelson interferometer and an optical fiber under test, the equalization wavelengths are resolved and the intermodal dispersion in the optical fiber can be measured over a wide spectral range. We have used the method for measuring either intermodal dispersion in circular-core, elliptical-core and bow-tie fibers or dispersion of birefringence in elliptical-core fibers.

The field of optical fiber sensing is highly diverse and this diversity is perceived as a great advantage over more conventional sensors in that an optical sensor can be tailored to measure any of a myriad of physical parameters. In this paper we present a niche application for optical fiber sensors in the domain of biophotonics, namely the monitoring of stress build-up during the curing process of dental resin cements. We discuss the origin of this stress build-up and the problems it can cause when treating patients. Optical fiber sensors aim at excelling in two kind of applications: firstly to perform quality control on batch produced dental cements and measure their total material shrinkage, secondly to monitor the hardening of the cement during in-vivo measurements resulting in the dynamic measurement of the shrinkage and to control the stress in a facing based restoration. We therefore investigated two types of optical fiber sensors as alternatives to conventional measurement techniques; namely polarimetric optical fiber sensors and fiber Bragg gratings written in polarization maintaining fibers. After discussing the results obtained with both optical fiber sensors, we will conclude with a critical assessment of the suitability of the two proposed sensing configurations for multi-parameter stress monitoring.

We present an optical fiber receiver which includes a monolithically integrated PIN photodiode, a transimpedance amplifier, a decision circuit and a PECL compatible output driver. This low-cost and low-power receiver was fabricated in 0.6μm BiCMOS technology. Only one minor process modification was necessary to implement the PIN photodiodewith a diameter of 150μm. A minimum number of external components is needed for interfacing with standard PECL gates. At a maximum possible data rate of 625Mbit/s, a sensitivity of -22.7dBm was measured at an optical wavelength of 660nm. At a single-supply voltage of 5V, the power consumption of the complete receiver is less than 74mW. The overall chip size is 1763μm times 648μm.

In order to make optical monitoring systems of civil engineering structures more general and organic systems, it would be effective to combine them with such comprehensive systems. This paper introduces examples of application about the surveillance system for the lifeline facilities in urban area which used the optical fiber sensor and state of the comprehensive management network system for Infrastructure facilities is proposed.

In this paper, we have presented a reliable simulation of algorithm for the recovery of the fiber Bragg grating (FBG) parameters from their reflection spectrum. An accurate method for synthesizing the physical parameters of the fiber Bragg grating has been proposed and demonstrated on the bans of its reflectivity. The method is based on gradient optimization algorithms and can be applied over each type of gratings (uniform, apodized, chirped, phase shifted). We have proposed a new technique, which has overcome some of existing disadvantages and restrictions by using information about the reflection characteristics from grating, which we have examined, and also using the transmission characteristics. As an example, the proposed technique may be successfully applied to synthesize and characterize our experimental grating which is uniformed, apodized and linearly chirped, from FBG measured reflectivity. This method could be applied for distribution strain and temperature sensing applications if only we have some previous information about the unstrained FBG and also if the possible strain profiles are known. Our algorithm for the synthesis of FBGs from reflectivity has no limitations in parameter space. We don't have to reduce the problem to small number of parameters. In most of practical cases, our technique would fast lead to accurate synthesis results. The proposed method can efficiently lead to optimal solutions and at the same time it takes into account various requirements of the examined grating. This study and simulations are supported by initial laboratory experiments, and this allow us to suppose, that there is a real possibility of complete, fast, and accurate characterization (including phase characterization) of FBG structures from reflectivity measurements.

This paper describes a special set-up which principle of operation bases on elongation procedure of fiber-optics in a low-pressure gas burner. The universal construction of set-up makes it possible to prepare different elements from any kind of optical fibers, including single-mode, multi-mode and polarization maintaining as well as optical fiber with different indices distribution and operation wavelengths. The basic element is fiber-optic biconical taper (diameter about several um on length up to 10 -15 mm), which due to a small cross-section enables achievement of optical beam propagation outside the fiber in direct way. The paper presents the overview of different elements, which structure is based on above taper, such as: X-type in-line fiber-optic couplers operating in a wide range of wavelengths, in-line optical polarizers as well as polarization switchers. An important thing about these elements is a possibility to operate in the wavelength different from the classical telecommunication range.

The optimization of fiber-optic Sagnac interferometer as a sensor for the investigation of seismic rotational waves is presented in this paper. The main parameter of this optimization is maximum system sensitivity for absolute rotation in the limited range of expected velocities. The main system construction bases on the FOG minimum configuration, however the detection by system only rotational velocity without covering it on angle changes needs other approach to this system. The presented in paper theoretical and experimental investigation shows that such system can be made on base of a standard single-mode optical fiber, however needs operation on depolarized light.

Imaging a single optical fiber onto a remote, reflective target using several wavelengths - while exploiting the chromatic dispersion of the imaging optics - can be used to sense displacements of the target. Light of each wavelength is back-reflected into the fiber at a unique target position. The basic principles of the method and the optical considerations to optimize its accuracy are described. Experimental demonstrations are presented, showing precisions of around 10-20 micrometers.

We analyze theoretically fiber-optic sensor configurations working in the time domain or in the spectral domain and utilizing interference between two spatial or polarization modes. We show for example that a two-mode fiber interferometer in which the phase difference between the two modes is large and the intermodal group optical path difference (OPD) is zero at a specific wavelength of a light source of a short coherence length can be used without losing both time-domain and spectral-domain interference. Similarly, we analyze theoretically a tandem configuration of two interferometers with one of the interferometers as a receiving interferometer and the other one as a sensing two-mode fiber interferometer. We show that time-domain or spectral-domain interference lost due to the OPD between the two modes exceeding the coherence length can be restored in the configuration. We analyze both theoretically and experimentally a tandem configuration of the receiving interferometer and the sensing two-mode fiber interferometer in which spectral interference between two polarization modes is detected by a low-resolution spectrometer. The configuration is characterized by suitable adjusting of the measuring sensitivity over a broad wavelength range. We present some preliminary experimental results regarding sensing of strain using an elliptical-core optical fiber.

One of the main problem of colorimetry is sensitivity of the optical fiber sensor for displacement of examined object. It means that the sensor also works as proximity or distance measurement sensor. In order to omit a problem of cross-sensitivity of the sensor we have analyzed several configurations of optical fibers inside sensor head. Results of the tests of several types of sensor head are presented. The best solution of fiber-optic head for colorimetric application is discussed as well. In conclusions some other applications of the optimized optical fiber sensor head are shown.

This paper presents the method of research and measurement of macrobending attenuation, present during alteration of geometrical system of optical fibre loop. Presentation of a measuring device, which allows to unifying measurements in (under) conditions close to those present in industrial constructions of devices. Annexed exemplary research of macrobending loss in systems deforming optical fibre loops made from various types of optical fibres.

In the paper, authors present an example of a simple and cost effective system of electric power supply by means of optical fiber. In many cases of physical measurements, it is very important to avoid excessive distortion to measured quantity. One of this is measurement of electromagnetic field of radio frequency. This is of concern in both, far- and near field examination. RF field measurement can be performed by direct measurement of the field at a point of interest or by measurement of the field scattered by a dedicated probe. One of the most important properties of this method is its low influence to the field under test. The full advantage of the system can be taken when the probe can be powered and controlled be means of optical fiber.

Selected perturbation effects on polarization mode dispersion (PMD) in highly birefringent (HB) fibers are reported. In particular, simultaneous twist and longitudinal strain effects on PMD in HB fibers have been investigated. External twist has been found to modify both modal birefringence and differential group delay (DGD) in HB fibers, and in particular to influence the range of DGD changes under longitudinal strain. These results suggest a great potential for a perspective all fiber variable-delay PMD compensator.

In this work, the possibility to detect ppm ammonia concentrations in water environment, at room temperature, by means of Standard Optical Fibers (SOFs) sensors coated by Metal Oxides (MOXs) films has been demonstrated. Electro-spray pyrolisis technique has been used to deposit SnO₂ films onto the distal end of single-mode optical fibers. This deposition technique allows the possibility to tailor the fabricated films properties by varying the deposition parameters, such as the metal chloride concentrations, the solution volume and the substrate temperature. The sensor operating principle relies on the measurement of the light intensity reflected by the fiber-sensitive layer interface: the pollutant molecules adsorption within the MOX film causes a change in its complex dielectric function and thus in the fiber-film reflectance. Spectral characterization of the obtained sensing probes has been carried out in the range 400-1750nm. Single wavelength reflectance measurements have been carried out to test the sensor performances for ppm ammonia detection. High sensitivity to the target analyte, response times of approximately 10-20 minutes and a Limit Of Detection as low as sub-ppm has been observed.

A new impulsive pressure sensor based on the elastic bar, is presented in this paper. As the elastic bar a piece of single mode optical fiber with photo-inscribed Bragg gratings is used. The grating is an optical strain gauge that converts the stress waves in the fiber into the changes of the Bragg wavelength. Experimental setup for the proposed sensor is demonstrated. The sensor was used to measure the pressure produced by an electric discharge in water.

Use of optical systems in hazardous locations can result in ignition of surrounding explosive atmosphere. The conducted research work allowed to propose three protection concepts. The primary protection concept - inherently safe optical radiation - consists in use of optical radiation with power, energy or irradiance incapable of causing ignition of surrounding explosive atmosphere. However, the arbitrary determination of values of these parameters is considered as excessively rigorous. The work presents the proposed protection concepts in relation to zone classification. The author describes his own method to determine safe values based on probability mathematics that can be used not only to derive these values, but also to compare different measurement procedures and, as well, different tests set-up.

In this work, the experimental demonstration of fiber Bragg grating based sensors as magnetic transducers is reported. Up to now, FBGs based magnetic sensors have been proposed by using Terfenol, metallic alloy with a giant magnetostriction coefficient. Here, a novel configuration is proposed employing a new class of magnetic materials, Magnetic Shape Memory alloys (MSMs), instead of Terfenol. This class of material, with a very giant magnetostriction coefficient, changes its shape when magnetic fields are applied. High strain values, up to 10 percent can be obtained with fast response times (less than 1 ms). A fiber Bragg grating has been bonded on a MSM sample and sensor characterization has been carried out. Experimental results and the comparison with Terfenol based FBGs sensors performances are reported, showing, for MSM, a sensitivity expressed as (▵λ_B/λ_B)/( ▵H/H_m) of 1.1e-4.

The fiber optic sensors one can subordinate to class with open optical track, closed and half-open track. The sensor of D type is interesting construction and belongs to the last group. This sensor name comes from implemented in the head fiber optic core transverse intersection shape. A sensor of this type using range is detection of liquid type. The sensor head construction elaboration is the basic question of classic optical sensor synthesis. In peculiarity this problem concerns: the optical fiber selection, length and depth of D type area so to the transmission of optical radiation prove the sensibility on for looked extent, which has the touch with the head. In presented work authors show solution of this problem with use of intensity method on the sample of the sensor that recognize the juice from black currant with specified parameters.

The fiber optic vibration sensor consists of optic source, optical fiber, head and detection unit. The basic constructions of vibration sensors head consist of broadcasting and receiving optical fiber, plus modulator of transmitted radiation. Bar type configuration is mechanical modulator most often. This bar can be broadcasting optical fiber or make up of separate component. The vibratory component behavior can be described across reduction of mechanical arrangement to following parameters: supplementary mass plus elasticity and damping constants. In the paper the coherent method of modeling of converter propriety and experimental estimate of his parameter's value was showed. The proposed method to obtainment information about attenuation constant uses propriety of mechanical oscillation as well as registration and image processing in the intensity domain. In the face of that this method characterizes low costs of experiment.

The propagation of light in optical fiber one can describe with following methods: phase, propagation of bundle and optics of rays. At present, the foundation in model of ray optic take that ray is the flat wave with small field of intersection. This is well known, according to talked over model, that in optical fibers the following rays propagate: ballistic, meridional and skew. The presented work shows from mathematical side the description of ray propagation in optical fibers and the proposal of statistical measure of skew and meridional radiance share. For the visualization of this the close field distribution is useful. Turns out, that for large shares of skew rays close field distribution is homogeneous and its shape alters in sense of normal distribution from growing shares of meridional radiance.

This work presents a functional model of an optical amplifier, which uses the active fiber doped with erbium called EDFA (eng: Erbium Doped Fiber Amplifier).The amplification obtained takes place entirely in optical domain without conversion to electric signals, how this happens in case of amplifiers SOA. However, with regard to the environment, in which works the optical amplifier (transmitters and receiver sets), it is useful to analyze suitable amplifier model in electric domain. For executing such model, it was proposed the delimitation of fiber parameters taking into account the threshold effects of amplification.

In this work, the numerical and experimental analysis of coated Long Period Gratings (LPGs) as high sensitivity optochemical sensor is presented. The proposed structure relies on LPGs coated with nanoscale high refractive index (HRI) overlays. When azimuthally symmetric nano-scale HRI coatings are deposited along LPGs devices, a significant modification of the cladding modes distribution occurs, depending on the layer features (refractive index and thickness) and on the external refractive index. If these parameters are properly chosen, a strong field enhancement within the overlay occurs, leading to an excellent sensitivity to the coating properties. Here, the effects of the overlay thickness and the cladding mode order on sensor sensitivity and response time have been numerically and experimentally investigated. In order to provide a high sensitivity and species specific opto-chemical sensor, the LPGs were coated with nanoscale overlays of Syndiotactic Polystyrene (sPS) in the nanoporous crystalline δ form. The sensitive material was chosen in light of its selectivity and high sorption properties towards chlorinated and aromatic compounds. Sensor probes were prepared by using dip coating technique and a proprietary procedure to obtain the form sPS. Experimental demonstration of the sensor capability to perform sub ppm detection of chloroform in water at room temperature is also reported.

A liquid-level optical fiber sensor based on refractive index sensitivity of surface plasmon resonance has been proposed and demonstrated. The sensor can continuously measure a wide distance range in the liquids with a single fiber element, since the sensing interface is characterized on the fiber-cladding surface. The fiber element, having the gold film thickness of 70nm on the sensing surface, shows the capability for the use of refractive index to be sensed ranged from 1.333 to 1.428 RIU. The sensitivity has been experimentally achieved to be 2.86% change of the input light intensity per millimeter for the 40mm measurement range.

Initial researches of Two-interferometers Fibre Optic Sensor for Disturbance Localization will be presented. The sensor is typically susceptible to environmentally induced mechanical perturbation at low frequencies. The presented sensor consists of two interferometers: Sagnac and Michelson. The Sagnac transfer function is proportional to the product of two factors: firstly the rate of change, dφ/dt, of the optical signal, induced at a point by external disturbance, and secondly the distance between the disturbance point and the Sagnac coil centre. The second interferometer transfer function gives an output proportional to φ. So, if we determine a pulsation ω of the mechanical disturbance from both interferometers output signals, we will be able to localize point where the mechanical disturbance takes place along the fibre by means of simple division of these transfer function. A laboratory arrangement of the sensor and the results of numerical signal processing are also shown.

The principle of the operation of a fiber optic chemical sensor (FOCS) is a chemically sensitive receptor part, which can be called as a chemooptical interface. This interface converts information on the analyte into changes of optical signal. In the case of the designed system, an appropriate reagent exhibiting changes in absorbance is immobilized on a polymeric support in a form of small beads. Such modified polymers are then loaded into a tube in order to construct a flow through sensor. The following reagents were used: bromothymol blue as pH-sensitive indicator, Chlorophosphonazo III as calcium-sensitive indicator, and 4-(2-pyridylazo)-resorcinol (PAR) as heavy metal indicator. The paper describes the immobilization procedures, tests of the flow through sensors with their calibration characteristics as well as system design considerations.

The base of time-of-flight fiber optic sensors using short laser pulses was presented. This kind of sensors can work in the transmission mode or in the reflection mode. Because attenuation of these sensors is small, they may be operated in sensor networks having tens or hundreds measuring points. The example of a time-of-flight fiber optic sensor is a segment of a singlemode optical fiber that is affected by temperature or longitudinal stress. The changes of temperature or strain applied to the fiber change the propagation time of light in the fiber. In the paper a time-of-flight sensor is presented. Using a picosecond semiconductor laser source and a photon avalanche photodiode detector, the system iscapable of measuring of temperature and force acting on the fiber. The performance of such sensor was tested for temperature in 20÷110 °C range or stress force in 0÷8 N range.

Operation of an underwater acoustical pressure transducer using an active Fiber Bragg Grating (FBG) attached to a profiled membrane is described. Presented results of Finite Element modeling of the transducer show strain gradients acting on the FBG. A model of passive FBG and DFB fiber laser was developed using coupled-mode method. Using a program based on that model, the effect of strain gradients on the operation of presented sensor was investigated.

Tilted fiber Bragg gratings and long period gratings enhance the coupling to the cladding modes and constitute excellent refractometers. In this paper, we study how the cladding diameter influences the coupling to the cladding modes for these two types of gratings. Our experiments are made on different tilted Bragg gratings, characterized by different tilt angles. For every grating, we study the evolution of the sensitivity to the surrounding refractive index as function of the cladding radius. We also investigate two ways to correlate the spectral evolution of a tilted fiber Bragg grating with respect to the external refractive index. The first method is based on the local monitoring of the transmitted spectrum while the second one makes use of the correlation between a reference spectrum and a perturbed spectrum. These methods offer both very good accuracy and repeatability.

Due to their variability Fiber Bragg Grating (FBG) sensors are introduced in a growing number of applications. Furthermore these sensors are predestined for serial networking, whereby the two properties spectral selectivity and reflectivity led directly to wavelength division multiplex (WDM) and time division multiplex (TDM), respectively. But, both technologies show big disadvantages with regard to the efficiency of resource utilisation. In contrast to WDMA, in our proposed system using sequence inversion keyed direct sequence code division multiplexing (SIK-DS-CDM), the FBG spectra can overlap. Also the light pulses, reflected with a unique delay by each sensor, can superimpose. Hence more information per time reaches the receiver compared to TDMA. A simulation with 20 FBGs in a spectral range of 2nm shows the abilities of this system, whereby theoretical works regarding optimal codes and network structure deal with its conditions.

Burner systems and their control are getting more and more sophisticated and there is a growing need to obtain information about the course of combustion process in individual flames. Optical sensors offer the benefit of being selective, rapid and able to gather data from extremely hostile environments (e.g. the combustion zone of pulverised coal burners or gas turbines). Passive optical sensors offer the further advantage of simplicity, which make them attractive candidates. With the rapidly growing capability of these technologies for sensor hardware, there is an increased interest and need to develop data interpretation strategies that will allow optical flame emission data to be converted into meaningful combustor state information. The article describes various approaches to apply artificial neural network approaches to estimate parameters of combustion. One is acquiring information about emission of nitrogen oxides and carbon monoxide from fiberoptic systems for flame monitoring, developed in Department of Electronics of Lublin University of Technology and another is identification of flames in gas burners.

The power spectrum density of the intensity of jittery but coherent trains of linearly chirped Gaussian pulses after a high-dispersion line with arbitrary first (β₂) and second order(β₃) dispersion is computed in the small-signal approximation. Before the dispersive line the timing jitter of the input train causes noise sidebands around the harmonics of the train. The noise bandwidth of these jitter sidebands depends on the pulse-to-pulse correlation. The result of the propagation in a dispersive line is a multiplicative factor in the noise spectral density. This term depends on the dispersive characteristics of the line and the pulse parameters but not on the timing jitter's correlation. The structure of this new factor is peaked, resulting in narrowband noise patterns at specific locations of the spectrum. The bandwidth of the dispersion-induced noise patterns is in general broader than the timing jitter's bandwidth. When the lines are Talbot dispersive devices, i. e., are designed to multiply the repetition rate of the train), jitter noise around the harmonics of the output train is left untouched. Therefore the jitter structure of the multiplied train is inherited from the initial train. More general RF spectral patterns, depending on the pulse-to-pulse jitter correlation, are also analyzed.

The National Museum in Warsaw is in possession of a collection of 1100 miniature paintings. Miniature paintings are specific exhibits, since they are both very precious and extremely sensitive to environmental conditions present in the museum exhibition halls. One of the most important factors imposing deterioration of the museum exhibits, is the optical radiation: ultraviolet (UV), visible (VIS) and infrared (IR). Exhibit conservation requirements, concerning the illuminance levels for particularly sensitive museum objects impose strict limitations for illuminance value to 50÷150 lx. Light should be devoid of both UV and IR components. The optical fibre lighting systems are perfectly suited to meet all the above mentioned lighting requirements. Each of 5 showcase featured an illuminator with a 50 W tungsten halogen lamp, UV filter and double IR filter. Thanks to such an illuminator structure, the visual radiation was devoid of harmful radiation components thus it was possible to use plastic optical fibres with 1 mm of diameter without any cooling fans. Fanned illumination systems utilized in the museum conditions, cause significant noise levels. The value of the illumination parameter within the showcases met the targeted value of 100 lx with the average internal showcase temperature raising by less than 1 °C.

The results of numerical simulations of an original narrow band erbium doped distributed absorption filter fiber amplifier (DAF-EDFA) were demonstrated. Numerical simulations were carried out for both: a standard, single stage, forward pumped reference EDFA without gain equalization and an amplifier containing a distributed absorption filter (DAF). Results of the examination of the EDFA containing a distributed absorption filter were presented. The population inversion for different input signal powers, forward and bacward ASE evolution along the fiber, and the gain and pump efficiency characteristics were compared for the examined DAF-EDFA and reference EDFA amplifiers. The reported approach allows significant reduction of ASE propagation in both directions. As a result, the elimination of the effect of inversion depletion at input EDF section was observed. It was shown that in the proposed approach a significant improvement of gain characteristics and power conversion efficiency can be obtained.

The theoretical design and experimental characterization of 1480 nm superfluorescent erbium-doped fibre sources are reported in this paper. Different configurations and three erbium doped fibres with different concentrations are used. In double pass configurations a Faraday rotator mirror is used. The comparison of the characteristics of these SFSs in terms of the output power, mean wavelength, spectral width and stability is carried out.

In the presented work, we report the original numerical results of the properties of ring optical frequency comb generators employing the acousto optic frequency shifter (AOFS) and the single stable master laser (ML). A key element of the examined source is the AOFS controlled by the RF generator which determines frequency comb interval and stability. In each loop round-trip, AOFS splits the optical beam into two, where the deflected beam is frequency shifted. The multiple divisions, spectrum shifting and optical beam amplification in the ring configuration result in generating of an optical frequency comb. Performed numerical simulations allow spectral analysis of the generated optical frequency comb. We tested configurations with single and two cascaded AOFS operating at 1.5625 GHz. Calculations were carried out for a variety of input laser powers and different quantity of optical output frequencies whose number was controlled by an optical feedback filter bandwidth. It was shown that for different configurations and component parameters it was possible to obtain 20 - 30 uniform peaks with the amplitude difference of less than 0.5 dBm and OCNR in the range of 35-45 dB. We demonstrated that the main problem of the simultaneous multiwavelength fiber ring laser operation can be overcome by using a non resonant ring configuration with a quasi steady state operation. This method ensures generating of an optical comb with stable carrier frequency spacing. It allows diminishing the interchannel spacing and building up an ultra dense wavelength division multiplexing system.

The paper presents an optical-fiber hydrogen sensor. The sensor utilises a layered Fabry-Perot interferometer and includes gasochromic metal oxides (V₂O₅, Nb₂O₅, CeO₂). The structure contains at the end a multi-mode optical fiber as the sensing element. The sensor permits to detect and to measure the concentration of hydrogen in a gaseous medium. A comparison of the properties of selected gasochromic metal oxides in the interferometric sensor structures has been presented.

A shape measurement method combining the fibre-optic interferometric fringe projection method and effective numerical spatial phase unwrapping method is proposed in this paper. Simplicity of the system arrangement determining low set-up cost is the main advantage of the presented approach. The paper presents a detailed theoretical method description. It is based on a specially worked out procedure of an automated analysis of the fringe patterns obtained by the Fourier transform and phase unwrapping based on the Mathematica software procedures. Experimental results of the measurements made for a real object show usefulness and efficiency of the proposed method.