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In-line higher order mode filters based on long highly uniform fiber tapers
Denis Đonlagić, 2006, original scientific article

Abstract: This paper presents a simple and effective design of taper-based higher order mode (HOM) filters that can effectively remove HOMs from the few-mode fibers. For this purpose, a taper manufacturing technique that allows the production of long and highly uniform tapers was developed. A filter performance was demonstrated on a standard single-mode telecommunication fiber operating at 850 nm. The HOM suppression was better than$-$39 dB, and the insertion loss ofthe fundamental mode was less than 0.15 dB.
Keywords: optical fibres, few moded fiber, fiber design, mode conversion, mode filter, noise figure, optical fiber dispersion, optical signal to noise, optical transmission systems, taper
Published: 31.05.2012; Views: 1406; Downloads: 76
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All-fiber quasi-distributed polarimetric temperature sensor
Denis Đonlagić, Miran Lešič, 2006, original scientific article

Abstract: This paper presents an all-fiber design of a quasi-distributed polarimetric temperature sensor array that utilizes commercially available single polarization and high birefringence fibers. The modulation depth of temperature induced loss and the operational temperature range of individual sensors in the network are set by the rotational alignment of fibers before fusion splicing and through fine adjustment of the sensing fiber lengths. A practical sensor network was built with sensors that operated in the temperature range from 0 to 100 C. Individual sensors in the network generatedtemperature dependent loss that changed proportionally from 0.9 to 1.8 dB. With current standard telecommunication OTDRs, more than 20 prototype sensors could be interrogated.
Keywords: fiber optics, sensors, temperature measurements, polarization, alignement, birefringence, polarization maintaining
Published: 31.05.2012; Views: 1389; Downloads: 74
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Quasi-distributed long-gauge fiber optic sensor system
Matjaž Linec, Denis Đonlagić, 2009, original scientific article

Abstract: This paper presents a quasi-distributed, long-gauge, sensor system for measurement optical path length variation. This system can be directly applied to long gauge strain and/or temperature sensing. The proposed sensor system is comprised of sensing fiber, which is divided into the sensorćs segments separated by semi reflective mirrors made out of standard optical connectors. Short duration radio-frequency modulated optical bursts are launched into the sensing fiber and phase differences among individual reflected bursts are measured to determine the optical path-length variations among neighboring mirrors. Twenty sensing fiber segments were successfully addressed by a single-signal processor, while relying on standard telecommunication PIN diode, and a Fabry Perot laser diode. The resolution of a fiber-length variation better than 5 ìm was demonstrated in practice. Since the long sections of fiber can be employed for constructing individual sensors within the sensor's array, a microstrain resolution can be achieved in practice. The drift of the sensorćs system can be predominantly attributed to the temperature sensitivity of the electronic components, which proved to be below 20 um/°C. The entire system relies on simple and widely-used components that are low-cost.
Keywords: fiber optic systems, fiber optics sensors, sensing fiber, long-gauge, strain sensing, temperature sensing, optoelectronics
Published: 31.05.2012; Views: 1413; Downloads: 79
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A low bending loss multimode fiber transmission system
Denis Đonlagić, 2009, original scientific article

Abstract: This paper presents a high bend tolerant multimode optical fiber transmission system that is compatible with standard 50 ìm graded index multimode fiber, interms of achievable bandwidth and interconnectivity losses. When the 10 loops of the proposed bend resistive multimode fiber were wrapped around a cylinder of 1.5 mm radius, bend losses below -0.2 dB were achieved in case of experimentally produced fiber. Furthermore, when the section of the proposed bend resistive fiber was inserted between two sections of a standard 50 ìm graded index multimode fiber, the total experimental measured loss proved to be below -0.15 dB.
Keywords: optical fiber transmission systems, bending loss, bend resistive multimode fiber, optical communications, fiber optics
Published: 31.05.2012; Views: 1376; Downloads: 70
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The interaction ability of cellulosic materials as a function of fine structure and Helmholtz surface energy
Tatjana Kreže, Karin Stana-Kleinschek, Volker Ribitsch, Zdenka Peršin, Majda Sfiligoj-Smole, 2005, original scientific article

Abstract: Many chemical or physical modification processes significantly influence the accessibility of fiber forming polymers by causing structural changes. The wettability and sorption ability improvements of polymeric materials are major tasks during finishing processes. Different pre-treatment processes are used in order to improve the accessibility of dissociable groups, hydrophilicity, dyeability, and whiteness. These are usually alkaline purification, chemical bleaching and mercerization. In a previous paper we presented the data for structural characteristics (density, crystallinity index, molecular orientation, void volume, diameter and the specific inner surface of void, etc.) of untreated regenerated cellulose fibers (viscose, modal and lyocell) [41]. We now compare the influence of different pre-treatment processes on fiber structure and the accessibility of the chemical groups of these fibers. In order to improve the accessibility, two pre-treatment processes were used: chemical bleaching of fibers and tensionless alkali treatment. The influence of these pre-treatment processes on the structure parameters was evaluated using viscosity measurements (determination of polymerization degree (DIN 54 270)) and iodine sorption ability measurements according to the Schwertassek method (determination of crystallinity index) [13, 16]. The reactivity and accessibility in a polar environment was determined using tensiometry. Contact angles between the fibers and liquids of different polarities were determined using the powder contact angle method and calculated from a modified Washburn equation [26, 28]. The surface free (Helmholtz) energy of differently treated fibers was determined from the contact angle data using the Owens-Wendt-Raeble-Kaelble approximation [30, 33, 35]. The differences in the accessibility of raw and pre-treated regenerated cellulose fibers obtained using tensiometry are compared with the results of the conventional method used to determine moisture adsorption (DIN 54 351, DIN 53 802). In regard to raw fibers, viscose shows the most hydrophilic characteristic: adsorbs the highest amount of moisture, has the fastest penetration velocities (Fig. 6), the smallest contact angle, and the highest SFE (Fig. 8). Modal fibers have the largest contact angle, the lowest SFE, and they adsorb the smallest amount of water vapor. Pre-treatments increase the sorption ability and the surface free (Helmholtz) energy while they decrease the contact angle. This makes the material more accessible to water and chemicals used in the finishing processes although the crystallinity index increases. The main modification in polymer properties caused by the treatments is an increase in the fiber SFE caused by an increase of the fiber surfaces because of swelling in the alkaline medium (washing, slack-mercerization), and due to an increase of accessible OH- and COOH-groups (bleaching). This enables the formation of an increased number of hydrogen bridges between the water molecules and the OH- and COOH-groups. Our investigations confirm the results published earlier thatthe main property necessary for the proper sorption behavior of cellulose materials are the accessible, less ordered regions and not the degree of crystallinity.
Keywords: regenerated cellulose fibers, fiber pre-treatment, iodine sorption, cristallinity, tensiometry, contact angle, Helmholtz surface energy, water adsorption
Published: 01.06.2012; Views: 1830; Downloads: 46
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Reinforcing methods for composite timber frame-fiberboard wall panels
Peter Dobrila, Miroslav Premrov, 2003, original scientific article

Abstract: This paper presents different possibilities on how to reinforce timber frame wall panels, which are mainly used as load-carrying capacity elements in the construction of prefabricated timber structures. These walls can be treated as composite elements composed of a timber frame and fiber-plaster boards. As the boards are the weaker part of the system they need to be somehow reinforced in order to assure the resistance and ductility of the elements especially in multi-level buildings located in seismic or windy areas. The aim of this research is to determine the differences in resistance and ductility between elements, reinforced using two different methods. Whilst the first, using additional fiberboards, does not improve the resistance and especially the ductility in the contended sense, it is more convenient for finding a solution when inserting diagonal steel strips, which are fixed to the timber frame.
Keywords: timber structures, stene, fiber-plaster boards, steel diagonals, mathematical models
Published: 01.06.2012; Views: 1425; Downloads: 77
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System for precise balancing and controlled unbalancing of fiber-optic interferometers
Irvin Sirotić, Denis Đonlagić, 2002, original scientific article

Abstract: A system for accurate balancing and controlled unbalancing of the optical path difference in all-fiber optical interferometers is described. Interferometers with various arm lengths (1-30m) and with initial optical pathdifferences of as much as 1 cm have been successfully balanced within a 5 ▫$mu$▫m range. In addition, the proposed system allows for controlled unbalancing of arbitrary all-fiber optical interferometers with a precision better than 5 ▫$mu$▫m.
Keywords: electrical measurements, optical instruments, interferometers, fiber interferometers, optical path difference, sensor systems
Published: 01.06.2012; Views: 820; Downloads: 68
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Unobtrusive monitoring of human vital functions based on speckle interferometry with plastic optical fiber
Peter Podbreznik, Denis Đonlagić, Dejan Lešnik, Boris Cigale, Damjan Zazula, 2013, original scientific article

Abstract: In this paper, a speckle interferometer with a plastic optical fiber system is reported for unobtrusive monitoring of heartbeat and respiration. The sensor consists of a laser diode butt-coupled to the plastic optical fiber, whose exit face projects speckle patterns onto a linear optical sensor array, which leads to a simple and cost-effective construction. Speckle images are acquired in a sequence and transformed into a 1D signal by using a phase-shifting method. Band-pass filtering and Morlet-wavelet-based multiresolutional approaches were used to analyze signals for the detection of cardiac and respiratory activities, respectively. Ten young, healthy persons participated in system testing, by lying supine on a mattress with embedded plastic optical fiber. Experimental results show the proposed system and detection algorithms are highly efficient. Sensitivities of 99.4 0.6% and 95.3 3%, precisions of 98.8 1.5% and 97.9 2.3%, and mean delays between interferometric detections and corresponding referential signals of 116.6 55.5ms and 1299.2 437.3 ms were computed for heartbeat and respiration, respectively.
Keywords: plastic optical fiber, speckle interferometry, unobtrusive monitoring, heartbeat detection, respiration detection, phase-shift method, wavelet transform
Published: 10.07.2015; Views: 704; Downloads: 9
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Unobtrusive heartbeat monitoring by using a bed fiber-optic sensor
Peter Podbreznik, Denis Đonlagić, Dejan Lešnik, Boris Cigale, Damjan Zazula, 2014, original scientific article

Abstract: Demographic trends suggest that by 2050 approximately 11 % of the world population will be 80 or older. If a fast increase of chronic diseases is also considered, it becomes clear the present healthcare capacities won't be enough. The elderly and people with limited abilities must be assisted in their home environment and, thus, reduce needs for hospitalization and institutionalization. Today's computer and communication technologies provide different smart devices, which is a core of emerging intensification of homecare services, in particular remote and unobtrusive monitoring of human functional- health parameters.
Keywords: plastic optical fiber, speckle interferometry, unobtrusive monitoring of human vital signs, heartbeat detection, ballistocardiography
Published: 21.12.2015; Views: 689; Downloads: 68
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Experimental and numerical evaluation of the mechanical behavior of strongly anisotropic light-weight metallic fiber structures under static and dynamic compressive loading
Olaf Andersen, Matej Vesenjak, Thomas Fiedler, Jehring, Lovre Krstulović-Opara, original scientific article

Abstract: Rigid metallic fiber structures made from a variety of different metals and alloys have been investigated mainly with regard to their functional properties such as heat transfer, pressure drop, or filtration characteristics. With the recent advent of aluminum and magnesium-based fiber structures, the application of such structures in light-weight crash absorbers has become conceivable. The present paper therefore elucidates the mechanical behavior of rigid sintered fiber structures under quasi-static and dynamic loading. Special attention is paid to the strongly anisotropic properties observed for different directions of loading in relation to the main fiber orientation. Basically, the structures show an orthotropic behavior; however, a finite thickness of the fiber slabs results in moderate deviations from a purely orthotropic behavior. The morphology of the tested specimens is examined by computed tomography, and experimental results for different directions of loading as well as different relative densities are presented. Numerical calculations were carried out using real structural data derived from the computed tomography data. Depending on the direction of loading, the fiber structures show a distinctively different deformation behavior both experimentally and numerically. Based on these results, the prevalent modes of deformation are discussed and a first comparison with an established polymer foam and an assessment of the applicability of aluminum fiber structures in crash protection devices is attempted.
Keywords: aluminum fiber, fiber structure, orthotropy, sintering, compression, static loading, dynamic loading, energy absorption, numerical simulation
Published: 21.06.2017; Views: 367; Downloads: 205
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