Berlinska 4

Žilina, Slovakia

Berlinska 4

Žilina, Slovakia
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Tarjanyi N.,University of Zilina | Turek I.,Berlinska 4 | Martincek I.,University of Zilina
Optical Materials | Year: 2014

In the paper we present the results of an experimental study of photoelasticity of polydimethylsiloxane (PDMS) in its deformation in compression with relative shortening in the range in which the dependence of the mechanical stress is not a linear function of strain (up to ε = -0.45). We observed nonlinearity of the dependence of the refractive index difference between beams polarized parallel and perpendicular to the direction in which the sample is compressed on the deformation which is significantly lower than the nonlinearity of the stress-strain dependence measured at the same sample. This fact can be explained by the assumption that the birefringence involves two mechanisms: (i) a change in polarizability of atoms, which is proportional to stress and, (ii) a change in structure of the environment, which we assume to be a linear function of strain. Appropriate choice of the impact ratio of these mechanisms gives a good match between experimentally observed dependence of birefringence on deformation and dependence arising from the above mentioned assumption. The contribution of the individual effects to the observed photoelasticity we investigated within the wavelength range (400-1800) nm. We have found that: (i) the effect of the polarizability of the environment is dominant for strain larger than ε = -0.3; (ii) the difference in the refractive indices of the beams with different orientation of polarization slightly decreases with increasing wavelength and, (iii) there are visible less-pronounced local extremes in the vicinity of the absorption lines of PDMS in the near-infrared. © 2014 Elsevier B.V. All rights reserved.

Turek I.,Berlinska 4 | Tarjanyi N.,University of Zilina | Martincek I.,University of Zilina | Kacik D.,University of Zilina
Optical Materials | Year: 2014

In this paper we present results of our investigation of the effect of mechanical stress on the coefficient of absorption and the refractive index of polydimethylsiloxane (PDMS) in the NIR region. We study optical transmittance and optical paths of PDMS samples compressed up to a length expressed by the value of the relative stress -0.5. The experimentally obtained results imply that the stress-induced changes of the absorption coefficient and the refractive index of PDMS are due to a change of the density of dimethyl-siloxane groups rather than a change of the PDMS's molecular structure. Since we performed measurements for high stresses, we modified the Poisson's relation to obtain its generalized form that holds for any stress and that we named generalized Poisson's relation. To obtain this relation we assumed that an elementary increase of each of the two lateral dimensions of a sample is determined by the Poisson's constant and the actual longitudinal dimension of the sample which is subject to change during the process of deformation. Then to express the change of the density of the electric dipoles in a PDMS sample we used this relation. The realized measurements indicate that the deformation dependent changes of the optical transmittances and the optical paths of the samples are in a good agreement with the values calculated using the assumption of the dominant influence of the density of the elementary dipoles and the validity of the generalized Poisson's relation. The deformation affects the optical transmittance and the refractive index so strongly that it is necessary to take it into account when the PDMS is used as a medium for optical applications. The transmittance at the wavelength of 1700 nm and for the relative stress -0.5 decreases about three times and the change of the refractive index at the wavelength of around 1500 nm reaches a value of about 0.05. These values imply that it is possible to utilize the PDMS for constructing optical sensors that could be used for measuring stress or mechanical displacement. © 2014 Elsevier B.V. All rights reserved.

Kacik D.,University of Zilina | Tatar P.,University of Zilina | Turek I.,Berlinska 4
Optik | Year: 2016

In this work, the fabrication and experimental investigation of multimode optical fiber with a cladding material replacement is presented. A short piece of fiber's cladding is etched away and substituted by a polydimethylsiloxane (PDMS) material. This elastomer is characterized by a unique feature of refractive index changes with the increasing particle density. The device principle is based on total internal reflection. If the PDMS is pressed, there is a change of elastomer refractive index and modes confined within the fiber core are partially or totally irradiated. This demonstration paves the way for further development of fiber optic sensors, particularly attractive for weight, load, extension, and pressure parameters monitoring applications. © 2016 Elsevier GmbH. All rights reserved.

Martincek I.,University of Zilina | Turek I.,Berlinska 4 | Tarjanyi N.,University of Zilina
Optical Materials Express | Year: 2014

In this contribution we present some results of a study of a refractive index inhomogeneity near the boundary of polydimethylsiloxane (PDMS) samples. We have observed inhomogeneities of the refractive index at PDMS-glass, PDMS-brass, PDMS-Teflon, PDMS-polystyrene and PDMS-PDMS boundaries. The greatest changes of the refractive index were observed at the PDMS-PDMS boundary where an increase of the refractive index in a narrow region close to the boundary was observed. It gives the possibility for guiding light. The existence of such a waveguide was proved by the fact that the boundary also guided light when samples containing PDMS-PDMS boundaries had been bent. © 2014 Optical Society of America.

Kacik D.,University of Zilina | Turek I.,Berlinska 4 | Wuilpart M.,University of Mons | Grondzak K.,University of Zilina
Optical Fiber Technology | Year: 2013

In this paper we propose an interrogating system for the quasi-distributed measurement of strain or temperature. The system basically consists of an all-fiber low coherent interferometer that includes the cascaded fiber Bragg gratings used in its test arm. The variable optical delay line with movable mirror traditionally used as the reference arm is here replaced by a set of fibers with different optical lengths all connected to an optical switch. This switch makes it possible to set the desired length for the reference arm. Second proposed solution is to replace variable delay line by fiber with multiple reflection points placed at positions close to those used at reference arm. Temperature and strain resolutions are 0.8 °C and 10 μm/m, respectively. The advantages of the system are the possibility to interrogate identical FBGs and to interrogate sensors placed far apart. The system does not use tunable laser source or movable elements. © 2013 Elsevier Inc. All rights reserved.

Tarjanyi N.,University of Zilina | Turek I.,Berlinska 4
Physica B: Condensed Matter | Year: 2012

In the paper results of the investigation of the influence of electric properties of the environment surrounding LiNbO 3 crystals on photorefractive effect induced in these crystals by Gaussian Ar laser beam with various intensities are presented. We show spatial and temporal dependences of changes of the refractive index obtained experimentally in LiNbO 3: Fe and LiNbO 3: Fe:Mn samples surrounded by media with different electric conductivities and different permittivities (water, air, water solution of CaCl 2). The space and time dependences of the refractive index changes induced by the Ar laser beam are observed by means of the Mach-Zehnder interferometer using light from HeNe laser. The experimentally obtained results are in a good agreement with those following from numerical calculations using the manifold mirroring method. The agreement between calculated and experimental results indicates that the polarization charge at the photorefractive crystal/surrounding medium boundary significantly influences the photorefractive process in the crystal. The experimentally observed slow spontaneous decrease of the refractive index change in a sample placed into a slightly conducting medium (air) after switching off the beam also indicates that the polarization charge in the sample's surroundings affects the photorefraction. © 2012 Elsevier B.V.

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