Search

Fiber-optic sensors find numerous applications in science and industry, but their full potential is limited because of the risk of damaging the measurement head, in particular, due to the vulnerability of unprotected tips of the fiber to mechanical damage and aggressive chemical agents. In this paper, we report the first use of a new nanocrystalline diamond structure in a fiber-optic measurement head as a protective coating of the fiber tip. The nanocrystalline sheet structures, produced with the use of Microwave Plasma Assisted Chemical Vapor Deposition System (MW PA CVD), were characterized by Scanning Electron Microscopy (SEM) and successfully transferred from the deposition substrate onto the surface of the tip of a single-mode fiber sensor head. A Fabry-Perot sensing interferometer for distance measurement comprising that fiber was built. The measurement results were compared with numerical modeling. High values of achieved correlation coefficients (R2 > 0.99) between a linear model and distance measurements data indicate that the diamond sheet does not affect the correct operation of the sensor while extending its potential scope of applications.

This study presents the microsphere-based fiber-optic sensor with the ZnO Atomic Layer Deposition coating thickness of 100 nm and 200 nm for temperature measurements. Metrological properties of the sensor were investigated over the temperature range from 100 °C to 300 °C, with a 10 °C step. The interferometric signal was used to monitor the integrity of the microsphere and its attachment to the connecting fiber. For the sensor with a 100 nm coating, a spectrum shift of the reflected signal and the optical power of the reflected signal were used to measure temperature, while only the optical power of the reflected signal was used in the sensor with a 200 nm coating. The R2 coefficient of the discussed sensors indicates a linear fit of over 0.99 to the obtained data. The sensitivity of the sensors, investigated in this study, equals 103.5 nW/°C and 19 pm/°C or 11.4 nW/°C for ZnO thickness of 200 nm and 100 nm, respectively.

The objective of this study is the application of optical methods for detection of immunological agent concentration. As the agent we used the Cyclaid, produced by Apotex Inc. In this article we investigated different Cyclaid concentrations in water. We used a Fabry-Perot interferometer working in a reflective mode, the measurements were performed with source with central wavelength λ = 1550 nm. The preliminary investigation have shown that the Fabry-Perot interferometer can be used to study the Cyclaid concentration.

This study reports the interactions of modified nanodiamond particles in vitro with human blood. Modifications performed on the nanodiamond particles include oxygenation with a chemical method and hydrogenation upon chemical vapor deposition (CVD) plasma treatment. Such nanodiamonds were later incubated in whole human blood for different time intervals, ranging from 5 min to 5 h. The morphology of red blood cells was assessed along with spectral measurements and determination of haemolysis. The results showed that no more than 3% of cells were affected by the nanodiamonds. Specific modifications of the nanodiamonds give us the possibility to obtain nanoparticles which are biocompatible with human blood. They can form a basis for the development of nanoscale biomarkers and parts of sensing systems and devices useful in biomedical environments.

In this paper, we describe the fiber optic low-coherence sensors using thin film. We investigated their metrological parameters. Presented sensors were made with the use of standard telecommunication single mode optical fiber (SMF- 28). Different materials were applied to obtain thick layers, such as boron doped diamond, silver and gold. The thickness of layers used in the experiments ranged from 100 nm to 300 nm. Measurements were performed with broadband source operating at central wavelength 1300 nm. The measurement signal was acquired by an optical spectrum analyzer. Measured signal was analyzed in the spectrum domain. Any change of the phase difference between interfering beams reflected from the sensor head depends on measurand occurred in the spectrum of the measurement signal. We obtain the visibility value of the measured signal equal to 0.97.

We examine the application of selected thin dielectric films, deposited by atomic layer deposition (ALD), in a low coherence fiber-optic Fabry-Perot interferometer designed for sensing applications. Such films can be deposited on the end-face of a single mode optical fiber (SMF-28) in order to modify the reflectivity of the Fabry-Perot cavity, to provide protection of the fibers from aggressive environments or to create a multi-cavity interferometric sensor. Spectral reflectance of films made from zinc oxide (ZnO), titanium dioxide (TiO2), aluminum oxide (Al2O3) and boron nitride (BN) was calculated for various thickness of the films and compared. The results show that the most promising materials for use in fiber-optic Fabry-Perot interferometer are TiO2 and ZnO, although Al2O3 is also suitable for this application.

International audience; In this paper we investigated the response of a fiber-optic Fabry-Pérot sensing interferometer with thin ZnO layers deposited on the end faces of the optical fibers forming the cavity. Standard telecommunication single-mode optical fiber (SMF-28) segments were used with the thin ZnO layers deposited by Atomic Layer Deposition (ALD). Measurements were performed with the interferometer illuminated by two broadband sources operating at 1300 nm and 1550 nm. Reflected interference signal was acquired by an optical spectrum analyzer while the length of the air cavity was varied. Thickness of the ZnO layers used in the experiments was 50 nm, 100 nm, and 200 nm. Uncoated SMF-28 fiber was also used as a reference. Based on the results of measurements, the thickness of the ZnO layers and the length of the cavity were selected in order to achieve good visibility. Following, the interferometer was used to determine the refractive index of selected liquids.

Portable Raman spectrometer - design rules and applications Raman spectroscopy has become more popular due to its new prospective field applications in forensic sciences, war against terrorism, environment protection and other field chemical analysis. Raman spectrometers can be miniaturised to portable devices and their price is decreasing due to development of optoelectronics components. Unfortunately, this technology has still numerous limitations that influence their design and limit the scope of possible applications. The conception and design of the portable Raman spectrometer is described, including discussion of performance and limitations of representative components of such device available on the market. An enhanced portable Raman spectrometer using two lasers, one emitting at 355 nm and the other at 785 nm, and employing advanced signal acquisition and data processing methods is presenented. Advantages of such system are outlined and example measurement results acquired using equivalent hardware are presented. Data processing flow for identification of chemicals is also described.

Reflectance characteristics of a two-cavity extrinsic Fabry-Perot optical fiber sensor were investigated using computer modeling. Calculations were performed using a plane wave-based approach, selected for clarity of results. Based on the modeling results, it can be concluded that the two-cavity Fabry-Perot interferometer can be used to measure two different quantities, such as refractive index and temperature, independently. It is also possible to use one of its cavities as a wavelength or optical path length reference, especially when a tunable laser is used as a light source. Spectral signal processing needed in such sensor is not substantially more complicated than that used in single cavity sensors.

Suitability of zinc oxide (ZnO) layers grown using Atomic Layer Deposition for operation in optical-fiber extrinsic Fabry-Perot sensors is investigated using a numerical model. Reflectance spectra obtained using the developed model indicate that the application of these layers in optical-fiber extrinsic Fabry-Perot sensors is difficult as it may require a source whose spectrum width is about 300 nm. A series of ZnO layers grown on end faces of SMF-28 fiber were prepared and their reflectance spectra were recorded by an optical spectrum analyser in order to verify the modelling results. The spectra contain a series of peaks not predicted by the model, which is attributed to two-mode propagation in the SMF-28 fiber connecting the ZnO layer with the rest of the measurement system.

Continuous measurement of the hematocrit level in blood can potentially be performed using optical bre sensors. The Fabry Perot interferometric sensors are a promising candidate in this application. The most important step in the design of the sensor is design of the sensing interferometer. Adequate cavity length and high interference contrast are two most important requirements in this application. The design method of the sensing interferometer presented in this paper uses a Gaussian beam approximation. In order to verify the design, an optical bre Fabry Perot interferometer with adjustable cavity length was built. Its performance was tested, con rming validity of the design approach.

International audience; Fiber-optic Fabry-Pérot interferometers (FPI) can be applied as optical sensors, and excellent measurement sensitivity can be obtained by fine-tuning the interferometer design. In this work, we evaluate the ability of selected dielectric thin films to optimize the reflectivity of the Fabry-Pérot cavity. The spectral reflectance and transmittance of dielectric films made of titanium dioxide (TiO2) and aluminum oxide (Al2O3) with thicknesses from 30 to 220 nm have been evaluated numerically and compared. TiO2 films were found to be the most promising candidates for the tuning of FPI reflectivity. In order to verify and illustrate the results of modelling, TiO2 films with the thickness of 80 nm have been deposited on the tip of a single-mode optical fiber by atomic layer deposition (ALD). The thickness, the structure, and the chemical properties of the films have been determined. The ability of the selected TiO2 films to modify the reflectivity of the Fabry-Pérot cavity, to provide protection of the fibers from aggressive environments, and to create multi-cavity interferometric sensors in FPI has then been studied. The presented sensor exhibits an ability to measure refractive index in the range close to that of silica glass fiber, where sensors without reflective films do not work, as was demonstrated by the measurement of the refractive index of benzene. This opens up the prospects of applying the investigated sensor in biosensing, which we confirmed by measuring the refractive index of hemoglobin and glucose.

It is very common for noise to have an influence on analog circuits. In order to preserve the quality of measurements taken by specific sensors and any noise dependent amplifiers which are correlated to them, all of these devices must be powered by low-noise power supplies. Therefore a necessity exists to develop new ultra-low noise power supplies which can cooperate with specified amplifiers and preamplifiers. Many well-known power supplies are particularly expensive and yet still have their disadvantages. This paper proposes a simple and inexpensive solution, which fulfills a specific criteria and can be treated as a base for improvement.

The LTCC (low temperature co-fired ceramics) method for the production of bolometers, utilising conducting films from non-stoichiometric, perovskite type lanthanum-strontium iron (LSFO) oxides is described with the measurement of parameters allowing for the choice of optimal operating conditions.

An application for modeling of polarimetric sensors is presented. Written using industry-standard LabVIEW platform, this application calculates response of a non-ideal sensor using a monochromatic source to force acting on the modulator. Problems existing when creating a modeling application in a graphic programming environment are discussed. Selected results of optical fiber sensors modeling are presented.

Results of Finite Element modeling of selected designs of membranes for interferometric pressure sensors are presented in the paper. Dependence of characteristics on the choice of materials, dimensions and shape of the membrane is discussed. Analysed membranes have somewhat limited displacement range, which may affect the accuracy of pressure sensors in which they are employed. Directions of further research on interferometric pressure sensors are also outlined.

Thermal time constant is an important parameter describing temporal behavior of bolometers as well as resistive layers used in these detectors. Measurement of the thermal time constant can yield valuable data for research and quality control. However, due to the influence of 1/f noise, this measurement is difficult to conduct, especially when the thermal time constant is longer than a second. Two setups, capable of performing such measurement in the range from milliseconds to a few seconds, were developed and are presented in the paper. Using these setups, thermal time constant of bolometers and resistive layers made from non-stoichiometric lanthanum-strontium-iron oxides (LSFO) in LTCC technology was measured. Results presented in the paper show that the setups can measure thermal time constant up to several seconds. Directions of further research are discussed.

Noise measurement is an important step in characterization of bolometers. Since this measurement is conducted with the bias applied to the bolometer and in most cases the measured noise level is well below the noise floor of FFT spectrum analyzers or other equipment used in this measurement, special pre-amplifiers and biasing circuits are needed. The requirements for these circuits are discussed in the paper along with limitations introduced by their components and the resistance of bolometers under test. Two preamplifiers, capable of measurements of bolometers whose resistance spans over five decades, are presented. Possible improvements to the existing pre-amplifiers are discussed and directions of further work are outlined.

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.

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.

A polarization ray tracing algorithm which calculates intensities of rays propagating in uniaxial birefringent media is presented. Calculations in this algorithm are performed on vectors in the global coordinate system, obviating the need for frequent conversions between global and local coordinate systems. For the first time, to the best of author's knowledge, a full ray tracing analysis of a Wollaston prism is presented as a calculation example.

Interferometric sensors exhibit very high measurement resolution. In order to attain high accuracy, these sensors are often implemented as polarization interferometers, in which stable and well-defined states of polarization are maintained. By using correction techniques originally developed for metrology and outlined in this paper, accuracy of discussed sensors can be further increased by adjusting gains and offsets in detection setup. Sensors that can use this technique are presented and problems arising in implementation of polarization interferometric sensors are discussed.

A novel design of an interferometric hydrophone transducer is presented. It consists of a coil of fiber embedded in a layer of epoxy. Finite Element modeling of such transducer is difficult due to anisotropic mechanical properties of its structure. An approach based on laminate modeling techniques was adopted. Static and modal Finite Element analysis was conducted, as was a coupled-field acousto-mechanical analysis.

A novel design of an underwater acoustical pressure transducer based on a Fiber Bragg Grating is presented. In this transducer the sensing grating is writen in a rare-earth doped fiber and operates as an optically pumped Distributed Feedback (DFB) laser. Presented sensor has higher resolution, compared to a sensor using a passive Fiber Bragg Grating. A profiled membrane is used in the transducer to achieve equalization of stress acting on the grating along its length. Results of Finite Element modeling of the transducer are presented.

The use of Single Mode Polarization-Maintaining Side-Hole (SMPM-SH) fibers for direct measurement of transverse force has been studied theoretically and experimentally. Based on results of Finite Element modeling reported elsewhere it was known that certain SMPM-SH fibers exhibit higher sensitivity to transverse force than a standard SMPM fiber. In order to verify these predictions, an experiment was performed. Measurement results agreed well with theoretical predictions. However, more systematic research is needed to determine the relationship between the sensitivity, dimensions and geometry of the holes.

Principles of integrated optical sensors based on polarimetric interferometry are presented in the paper. A wide area of their applications in biochemistry includes monitoring of protein concentration in solutions, detection of antibodies as well as indirect investigation of chemical reactions, based on precise measurement of complex refractive index. In order to address a problem of irreversibility of wide group of biological processes and chemical reactions as well as to decrease cost of the sensors, authors propose to develop disposable measurement converters and to use optical components made from sol-gel derived hybrid polymers. The technology of hybrid materials synthesis and subsequent planar waveguides manufacturing as well as their properties are shown.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical Coherent Tomography (OCT) is an imaging techniqu that enables a range of clinical applications where imaging can be carried out in situ and in real time. In OCT, cross-section images are generated by transverse scanning light beam across investigated tissue and by measuring the delay and magnitude of the back-scattered light. Among several detection techniques which can be used to implement OCT, Optical Low-Coherent Reflectometry (OLCR) or Optical Frequency Domain Reflectometry (OFDR) are the most promising. The paper presents merits of both techniques.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The influence of splicing inaccuracy of fiber segments of polarimetric sensors on visibility of polarization modes interfering at the sensor output was investigated. Two types of sensors were analyzed using Jones matrix formalism: one with single and one with double temperature compensation.

Algorithms of Chemicals Detection Using Raman SpectraRaman spectrometers are devices which enable fast and non-contact identification of examined chemicals. These devices utilize the Raman phenomenon to identify unknown and often illicit chemicals (e.g.drugs, explosives) without the necessity of their preparation. Now, Raman devices can be portable and therefore can be more widely used to improve security at public places. Unfortunately, Raman spectra measurements is a challenge due to noise and interferences present outside the laboratories. The design of a portable Raman spectrometer developed at the Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology is presented. The paper outlines sources of interferences present in Raman spectra measurements and signal processing techniques required to reduce their influence (e.g.background removal, spectra smoothing). Finally, the selected algorithms for automated chemicals classification are presented. The algorithms compare the measured Raman spectra with a reference spectra library to identify the sample. Detection efficiency of these algorithms is discussed and directions of further research are outlined.

Methods of operating point stabilization of interferometric sensors using tunable lasers are presented. These methods employ circuits which control the wavelength of an external cavity tunable semiconductor laser. Modes of operation of the control circuits and problems related to their design are discussed. The limitations restricting the use of discussed control circuit types are analyzed. An interferometric force sensor was built and tested. Results of measurements carried out using the sensor are presented.