Damian Harasim

Temperature-insensitive simultaneous rotation and displacement (bending) sensor based on tilted fiber Bragg grating

In this paper, we present a method for the simultaneous measurement of rotation and displacement or rotation and bending using single tilted fiber Bragg grating (TFBG). The insensitivity of the proposed system to temperature changes and the stretching direction of the fiber section in the sensing structure have been demonstrated. The experimentally determined sensitivities for rotation, displacement and bending are as follows: -0.0018 1/deg., 0.0054 nm/mm, and -0.055 1/mm over the measurement ranges of approximately 25-80 degrees, 34-74 mm, and 26.4-20 mm, respectively. The presented measurement system is versatile due to the ability to tune the measurement range by changing the fiber-loop radius.

Overhead Transmission Line Sag Estimation Using a Simple Optomechanical System with Chirped Fiber Bragg Gratings. Part 1: Preliminary Measurements

A method of measuring the power line wire sag using optical sensors that are insensitive to high electromagnetic fields was proposed. The advantage of this technique is that it is a non-invasive measurement of power line wire elongation using a unique optomechanical system. The proposed method replaces the sag of the power line wire with an extension of the control sample and then an expansion of the attached chirped fiber Bragg grating. This paper presents the results of the first measurements made on real aluminum-conducting steel-reinforced wire, frequently used for power line construction. It has been shown that the proper selection of the CFBG (chirped fiber Bragg grating) transducer and the appropriate choice of optical parameters of such a sensor will allow for high sensitivity of the line wire elongation and sag while reducing the sensitivity to the temperature. It has been shown that with a simple optomechanical system, a non-invasive measurement of the power line wire sag that is insensitive to temperature changes and the influence of high electromagnetic fields can be achieved.

Improvement of FBG peak wavelength demodulation using digital signal processing algorithms

Spectrum reflected or transmitted by fiber Bragg grating (FBG) in laboratory environment usually has smooth shape with high signal to noise ratio, similar to Gaussian curve. However, in some applications reflected spectrum could included some strong noise, especially where sensing array contains large number of FBGs or while is used broadband, low power source. This paper presents a possibility for extraction fiber Bragg grating peak wavelength from spectra with weak signal to noise radio with most frequently using digital signal processing algorithms. The accuracy of function minimum, centroid and Gaussian fitting methods for peak wavelength detection is compared. The linearity of processing characteristics of extended FBG measured for reference high power and second, low power source is shown and compared.

The influence of CTFBG gratings physical parameters on their spectral properties

This paper presents the spectral properties of chirped tilted Bragg gratings (CTFBG) written on photosensitive optical fiber by using phase mask technique and excimer laser. The dependencies of manufactured structures spectra on three various values of chirp: 0,1 nm/cm, 1 nm/cm, 10nm/cm and gratings tilt angle in 0° to 2,5° range with 0,5° change have been shown in all combinations. Influence of temperature changes in -40°C to 180°C range on measured spectra have been investigated. We showed the dependencies of CTFBG spectral parameters in various cases of periodic refractive index variations angle and different chirp values given in manufacturing process.

Methods and fiber optics spectrometry system for control of photosensitizer in tissue during photodynamic therapy

Photodynamic cancer therapy is used as an alternative or in combination with conventional treatments. PDT involves three key components: a photosensitizer, a light source and tissue oxygen. The combination of these three components leads to the chemical destruction of any tissues which have either selectively taken up the photosensitizer or have been locally exposed to light. In our research we used Charge-coupled device (CCD) spectrometers to measure intensity of the fluorescence signal. Devices allow receiving and processing signal in a CCD structure at a wide range of wavelengths. We have established a system for measuring the fluorescence of tumor tissue. These results are important for determining the dose of laser radiation and optimal time for laser action without damaging healthy tumor.

Precision measurement of coordinates of power center of extended laser path images

Authors have worked out a nonstationary signal analysis method on an example of research of laser lines. This method disclosed relationship between signal approximation coefficients and geometry signal characterizations (for instance, energy center, moment of inertia). Examples, which is demonstrating an application of this method for exact coordinate determination problem in laser line at displacement compensation in laser imaging are present.

The peculiarity of the construction of an optical-electronic system for measurement of geometrical parameters of objects in the micrometer range

The optical-electronic system for measuring of geometrical parameters of micrometrical objects is a difficult process that requires the observance of certain features designing or improvement. The observance of that will provide a higher measurement accuracy compared with the accuracy metrics of measurement that were developed without compliance with these design features. Every feature of the design reduces the error of the functioning of individual nodes of the system or errors in nodes under the influence of various internal or external factors. When reducing or eliminating each factor of occurrence of the error, respectively, will increase the overall measurement accuracy. In this work, the result of introducing measurement error for each factor is determined experimentally and proved the correctness of such actions. Experimental researches of the measurement error to the stage of compliance with subtleties in the improvement of the opto-electronic system was 10 ± 1.5 μm, and after improvement with considering of the specifics of the design measurement error of geometrical parameters was 10 ± 0,33 μm.

Accuracy improvement of Fiber Bragg Grating peak wavelength demodulation using wavelet transform and various center wavelength detection algorithms

The main feature of Fiber Bragg Gratings is that they perform a direct transformation of measured parameter into a shift in the center Bragg wavelength. This paper presents a possibility for extraction FBGs peak wavelength from spectra with high influence of noise by using wavelet transform. Spectra of tested FBG were measured in 20 points with different extending force applied to tested sample. Wavelet transform and various methods of center Bragg wavelength detection are jointly applied to improve wavelength detection accuracy. Experiment results shows that application of appropriate digital signal processing algorithms for denoising FBG spectra could greatly improve accuracy and linearity of fiber sensor processing characteristics. Streszczenie. Najważniejszą właściwością światłowodowych siatek Bragga (Fiber Bragg Gratings) jest liniowe przetwarzanie zmian mierzonej temperatury bądź odkształcenia na przesunięcie centralnej fali. Artykuł ten prezentuje możliwości wyznaczenia długości fali Bragga z widm silnie zaszumionych przy zastosowaniu transformaty Falkowej .Spectra rejestrowano w 20 punktach o różnych wartościach siły rozciągającej próbkę. Transformacja Falkowa oraz różne algorytmy wyszukiwania centralnej fali Bragga zostały zastosowane jednocześnie dla uzyskania poprawy precyzji wykreślania charakterystyki przetwarzania elementu mierzącego. Wyniki eksperymentu wskazują, że zastosowanie odpowiednich algorytmów cyfrowego przetwarzania sygnałów do widm FBG może w dużym stopniu poprawić dokładność wyznaczania charakterystyki przetwarzania światłowodowego czujnika. Poprawa dokładności demodulacji światłowodowych siatek Bragga dzięki użyciu transformaty falkowej i algorytmów detekcji centralnej długości fali Słowa kluczowe: Siatka Bragga, długość fali Bragga, transformata falkowa, czujnik naprężenia.

The optical diagnostics of parameters of biological tissues of human intact skin in near-infrared range

Melanoma skin is difficult to diagnose in the early stages of development despite its location outside. Melanoma is difficult to visually differentiate from benign melanocytic nevi. In the work we investigated parameters of human intact skin in near-infrared range for different racial and gender groups. This allows to analyze statistical differences in the coefficient of diffuse reflection and use them in the differential diagnosis of cancer by optical methods subject.

Experimental study of steel welded joints localization with using fiber Bragg grating strain sensor

Optical sensing systems has a not weakening research and development in recent years. Because of its unique properties of being unsusceptible to electromagnetic interference, having wide range of operational temperature and having extreme small physical dimensions, optical fiber sensors has increasing acceptance. Fiber Bragg Gratings (FBG) is the most frequently used type of optical sensor types because of its huge multiplexing potential and potentiality of being embedded into composite material (e.g. in structural health monitoring) or attached into measured structure. Embedding or attaching FBG into an inhomogeneous environment, spectral characteristic of the sensing grating do not retain full symmetry, which is due to related differences in the distribution of the axial stress of the grating. When periodicity of the grating is constant, the peak of FBG reflection spectrum should be narrow and sharp. An inhomogeneous axial strain distribution will cause a distorsion in measured transmission or reflection spectrum. This paper shows an distorsions in FBG reflection spectrum measured from sensor attached on surface with welded joint. The sensor strain-to-wavelength shift processing characteristics obtained for homogeneous and welded steel samples were compared.