The paper presents a modification of capillary optical fibers fabrication method from an assembled glass preform. A change of dimensional proportions in the capillary optical fiber drawn from a single preform is allowed on-line via the control of overpressure and thermal conditions in the outflow meniscus which essentially lowers the manufacturing costs. These conditions are among the solutions (velocity fields) of the Navier-Stokes equations adapted to the capillary optical fiber pulling geometry and temperature distribution in the oven. The velocity fields give solutions to other quantities of interest such as flow rate, pulling force and fiber geometry. The calculation and experimental results for capillary optical fibers were shown in the following dimensional range: internal diameters 2-200 µm, external diameters 30-350 µm, within the assumed dimensional stability (including ellipticity) better than 1%. The parameters of fabricated capillary optical fibers of high-quality low-loss optical multicomponent glasses were: losses 100 dB/km, mechanical strength above 1GPa with Weibull coeffcient in the range 3-7, internal numerical aperture 0.1-0.3, external numerical aperture 0.1-0.3, core index 1.5-1.8, transparency 0.4-2 µm, thermally and/or chemically conditioned internal surface, double polyimide protection layer, soft or hard jacketed, connectorized. The capillary optical fibers were applied in our own and several external laboratories in spectroscopy, refractometry, micro-fluidics and functional microoptic components. The paper summarizes a design, technological and application work on capillary optical fibers performed during a recent national research program devoted to optoelectronic components and modules.

Rotational seismology is one of the fastest developing fields of science nowadays with strongly recognized significance. Capability of monitoring rotational ground motions represents a crucial aspect of improving civil safety and efficiency of seismological data gathering. The correct sensing network selection is very important for reliable data acquisition. This paper presents initial data obtained during the international research study which has involved more than 40 various rotational sensors collected in one place. The key novelty of this experiment was the possibility to compare data gathered by completely different rotational sensors during artificially generated ground vibrations. Authors collected data by four interferometric optical fiber sensors, Fiber-Optic System for Rotational Events & Phenomena Monitoring (FOSREM), which are mobile rotational seismographs with a wide measuring range from 10-7 rad/s up to even few rad/s, sensitive only to the rotational component of the ground movement. Presented experimental results show that FOSREMs are competitive in rotational events recording compared with the state-of-the-art rotational sensors but their operation still should be improved.

In this paper, based on the feasible method and sensors for the full-scale prestressed monitor, the novel optical fiber sensors and the traditional monitoring sensors will be set up into two prestressed concrete beams with the same geometrical dimensions, material properties, and construction conditions, etc. to investigate the working state of the novel sensors and obtain the evolution law of prestress loss of the prestressed feature component under the static load. The results show that the evolution law of prestress loss of the loaded beam under the condition of no damage state and initial crack is the same as the non-loaded one; however, the prestress loss increases with the increase of time under the situation with the limit crack. The total loss of the prestressed beam with the limit crack is 36.4% without damage. The prestress loss of the prestressed beam under the static load increase with the development of the crack (injury).

This article proposes an unequivocal method of labeling and numbering the cladding modes propagating in single-mode opticalwaveguides with tilted periodic structures. The unambiguous determination of individual propagating modes in this type of optical fiber is crucial for their use in sensory systems. The selection of the appropriate spectral range and mode determines the sensitivity and measuring range of tilted fiber Bragg grating (TFBG) sensors. The measurement methods proposed by individual research teams using TFBGs as transducers are usually based on the selection of specific modes. Unification of the labeling of modes and their numbering enables comparison of the basic metrological parameters of individual measurement methods and reproduction and verification of the proposed sensors and methods in the laboratories of other scientific and research centers.

In this article, we study tilted fiber Bragg gratings (TFBGs) with tilt angles of 6◦ and 8◦, their transmission spectra, and spectral parameters that have a linear dependence on the refractive index of the environment. It is shown that there can be several such characteristics, such as the minimum, width and energy of the spectrum. The linear dependence of the spectrum width on the refractive index does not depend on the tilt angle. The linear dependence of the spectrum minimum is only observed for a tilt angle of 8◦. The results of this work can be used to create a sensor system based on an optical fiber.

The article shows the possibility of using TFBG gratings to measure the radius of curvature of fiber bending in conditions of variable polarization of the introduced light. Most of the modern, stable light sources generate light with a high degree of polarization. Due to the spatial asymmetry, the direction of the light polarization plane affects the spectral parameters of individual modes. For this reason, in the measurement systems using TFBGs presented so far it becomes necessary to determine and control the state of light polarization directly in front of the periodic structure. The article presents the determined spectral parameters of the cladding modes which allow bending measurements regardless of the direction of polarization of the introduced light. Thanks to this, the measuring system can be constructed without providing control of the introduced light polarization angle, which makes its construction simpler. When using TFBGs with an angle of 2°, the accuracy of determining the bending radius in the range from 15 mm to 30 mm when changing the angle of the plane of polarization in the full range is 0.318 mm in the case of changes in the transmission coefficient. For changes in the wavelength of the selected cladding mode, the accuracy is 0.3203 mm, with the input light polarization being changed in the range from 0° (P type) to 90° (S type).

The article presents an analysis of the impact of bending optical fibers with tilted Bragg gratings on their spectral parameters. This article proves that it is possible to a choose TFBG cladding mode and the optical spectrum range related to it that allows the best metrological properties to be obtained when measuring bend. The results contained in the paper explain why the minima in the spectral characteristics, corresponding only to some cladding modes, change their shape during TFBG bending, which is important for application of Bragg gratings as bending sensors. It has been presented that in the case of TFBG we are able to aggregate the knowledge obtained during experiment to the form of a physical model of the fiber bending sensor.

In the paper, an extended analysis of the polarization properties of a liquid crystal cell with a biconically tapered single-mode telecommunication optical fiber was presented. These properties are a result of a sample geometry and used LC materials. They were analyzed by using two theoretical models based on the matrix decomposition methods, i.e., polar and singular-value one. By measuring Mueller matrices, information about losses, depolarization, dichroism and birefringence was obtained. In the experiment two types of tested samples filled with well-known 6CHBT and E7 liquid crystals were prepared and all optical parameters were shown as the voltage dependence. The tested samples have dichroic properties and for both models calculated PDL is similar and it increases from 2.6 to 6.6 dB for E7 and from 0.4 to 2.7 dB for 6CHBT with voltage changes within the range of 40 – 190 V. Optical losses simultaneously decrease from 30 dB to 27 dB and from 36 dB to 28 dB, respectively. The birefringence properties cannot be directly comparable due to differences between both applied models but voltage fluctuations of these parameters are not significant. These results confirm expected dichroic properties of designed device and complete knowledge about its working principles. Moreover, presented analysis validates usefulness of the singular-value decomposition model applied to dichroic optical fiber elements.

Thermo-optic properties enhancement of the bi-stable temperature threshold sensors based on a partially filled photonic crystal fiber was reported. Previously tested transducers filled with a selected group of pure n-alkanes had in most cases differences between switching ON and OFF states. Therefore, the modification of filling material by using additional crystallization centers in the form of gold nanoparticles was applied to minimize this undesirable effect. The evaluation of the thermodynamic properties of pentadecane and its mixtures with 14 nm spherical Au nanoparticles based on the differential scanning calorimetry measurements was presented. Optical properties analysis of sensors prepared with these mixtures has shown that they are bounded with refractive index changes of the filling material. Particular sensor switches ON before melting process begins and switches OFF before crystallization starts. Admixing next group of n-alkanes with these nanoparticles allows to design six sensors transducers which change ON and OFF states at the same temperature. Thus, the transducers with a wider temperature range for fiber-optic multi-threshold temperature sensor tests will be used.

On the basis of a unipolar corona discharge, a method of non-contact and continuous measurement of linear parameters of thin and ultra-thin dielectric fibres and optical fibres (10 to 125 microns) in the process of their manufacture was developed. The measurement method differs from the commonly known methods by high accuracy and reliability of measurement and resistance to changes in the electrical characteristics of the discharge gap and the state of ambient air.