A small piece of glass-coated amorphous Fe76Si9B10P5 microwire is attached to the surface of the optical fiber at its end. At approximately 250 micrometers from the end of the optical fiber containing the microwire, a reflective surface is placed, and an optical signal from a broad-spectrum SLED source with a central wavelength of 1480 nm is introduced into the fiber. Using an optical fiber circulator and an optical spectrum analyzer, we monitor the interference in the spectral region of optical signals reflected from the end of the fiber and the reflecting surface behind the end of the fiber. By applying a transverse static magnetic field to the end of the fiber with a microwire, we change the lateral position of the optical fiber. As a result, we observe the spectral shift of the interference pattern due to the change in the optical path between the interfering optical signals. The spectral shift as a function of magnet distance d(m) from the optical fiber with the microwire is measured, which represents the potential for finding applications allowing to investigate or measure magnetic fields or gradients, or small changes in the distance between two objects in a non-contact manner.

In this article, one-dimensional photonic crystal cavities on bending waveguides (PCCoBW) used for achieving high-contrast spectra are proposed, analyzed, and experimentally verified on silicon on insulator (SOI). Both air and dielectric modes of the PCCoBW calculated by the finite-difference time-domain (FDTD) method show finger-ring-like mode profiles with the achievement of high-quality factors (Q∼106), even when the bending radius is less than 50 times the lattice constant. Straight waveguides side-coupled to the cavity are used to access and measure mode resonances. The measured spectra show a high extinction ratio over 40 dB for dielectric modes and 20 dB for air modes, respectively. Both dielectric and air resonant modes are revealed with Q-factors over 3.3 × 104 and 7.9 × 104, respectively, for the coupled PCCoBWs. The proposed PCCoBW could be implemented as high-contrast notch filtering and would benefit a broad range of applications such as optical filters, modulators, sensors, or switches.

This study proposes a Fabry–Perot interferometric system and an associated evaluation method for measuring the weight of moving trains. An optical fiber sensor, comprising a sensing fiber and a supporting structure, is securely bonded to the rail foot. As a train traverses the track, the resulting localized bending induces a change in the sensing fiber’s length, which manifests as a quantifiable phase shift in the interference signal. We developed a physical–mathematical model, based on three Gaussian functions, to describe the temporal change in sensing fiber length caused by the passage of a single bogie. This model enables the determination of a proportionality constant to accurately convert the measured phase change into train weight. Model validation was performed using a train set, including a locomotive and four variably loaded wagons, traveling at 15.47 km/h. This system offers a novel and effective approach for real-time train weight monitoring.

The measurement of the concentration of a liquid binary mixture of carvone and limonene is currently of interest in producing products in the pharmaceutical, food, and perfumery industries. A Fabry-Perot interferometer placed at the end of a conventional optical fiber is proposed for rapid and inexpensive concentration determination. The interferometer cavity consists of PDMS and two reflective Al surfaces. The time-domain interference of light for volume fractions from 0 to 100 percent carvone in the limonene mixture was measured. From the dependences, a different swelling rate and a different swelling time for the particular volume fractions are observed. We measured the time delay of selected interference extremes to determine the concentration of carvone in the binary mixture. The obtained values of the time delays range from a value for pure limonene (volume fraction 0 percent) of 0.445 s to a value for pure carvone (volume fraction 100 percent) of 11.386 s. It follows that the given methodology makes it possible to obtain a concentration result within a few tens of seconds from the start of the measurement.

In the paper, we present the results of the investigation of optical birefringence induced in spatially confined PDMS samples immersed in isopropanol and acetone. The PDMS samples are gradually deformed as they swell due to absorbing the liquid and become optically birefringent due to subsequent deformation. We investigate their birefringence in the spectral range from 400 nm to 700 nm using a plane polariscope by monitoring the change of the spectral distribution of the light passing through the PDMS samples in time. The observation time is in the order of days. The time dependences of the normalized light intensity are used to determine the time evolution of the birefringence dispersion. We propose a function Delta n(t) expressing the time dependence of PDMS birefringence induced due to its interaction with the used liquids. The function's behavior agrees very well with the time dependence of the birefringence dispersion obtained from the measured light intensity. The obtained match between calculated and measured time dependences of the normalized light intensities also manifests the appropriateness of the proposed Delta n(t) function.

The article introduces an innovative support element for an optical fiber sensor utilizing a Fabry-Pérot interferometer (FPI) designed for monitoring railway traffic. This removable support element, attached to the bottom of the railway track using permanent magnets, allows for repeated installation and relocation without compromising the sensor's functionality. The support element's metallic structure, magnetic attachment to the rail, and the bonding of the sensing optical fiber ensure adequate protection against environmental conditions. Tested on a railway track for one year, the sensor demonstrated stable positioning and consistent signal detection during the passage of train formations. This design, while tailored for FPI sensors, offers versatile application potential for other optical fiber sensors leveraging fiber Bragg gratings.

The Fabry-Perot interferometric sensing system can be used not only to determine the speed and number of axles but also, under certain conditions, to determine the technical condition of railway vehicles. The effect of a wheel defect on the track has been replaced by a body with linear momentum to limit the possibility of infrastructure damage. We investigated the influence of the magnitude of momentum and the distance of action from the location of the sensor on the response of the sensor. The findings were applied to a trainset moving at a speed of 98.5 km/h.

In the paper, we analyze the relationship between mechanical deformation and optical birefringence to investigate the possibilities of using birefringence to study the temporal evolution of the deformation of viscous materials. Understanding the connection between the temporal evolution of birefringence and deformation can lead to the development of methods to investigate viscous processes, diffusions, and slow deformations in viscous materials. It also enables the creation of practical non-contact optical deformation, tension/pressure sensors as well as chemical sensors.

In this paper, we present an overview of the prepared polymer elements for lab-on-fiber (LOF) developed at the University of Zilina. In recent years, lab-on-fiber has become a highly popular topic. This technique integrates the well-known properties of optical fibers with innovative polymer structure fabrication methods. The structures are created using modern 3D laser printing. With our sensors, it was possible to measure quantities such as temperature, pressure, change in refractive index, or the concentration of organic compounds such as isopropanol, acetone, toluene, and chloroform.

In the contribution, we present the design of a probe responding to the presence of a magnetic field, consisting of a capillary fiber filled with magnetic fluid and connected to polarization-maintaining optical fibers on both sides. Magnetic fluid in the capillary responds to a transverse magnetic field by changing its birefringence. As a result, there is a change in the polarization state of the optical wave passing through the fluid in the capillary, and this change is registered using an optical fiber plane polarizer placed between the fiber coming out of the capillary and the optical spectrum analyzer. A relationship between the magnitude of the magnetic field flux density and the spectral change of the signal detected by the optical spectrum analyzer is observed. The result indicates a strong potential of a magnetic fluid in the field of the optical fiber sensors of magnetic fields

Various systems are used to monitor the technical conditions of railway lines and railway vehicles during operation. This contribution presents an optical fiber monitoring system based on a Fabry-Perot interferometer. The sensing optical fiber placed on the foot of the rail is elongated due to the bending of the rail during the passage of the train. The optimized signal demodulation algorithm allows determining not only the presence of a train in a particular area, the number of axles, and the speed of the train, but also some defects related to the technical conditions of railway vehicles. The detection method is shown in the passage of a passenger train consisting of a locomotive and four wagons moving at a speed of 98.08 km/h. The advantage of the system is the possibility to determine different useful parameters of train passage with the technical conditions of vehicles during normal operation.

In this paper, we present a new innovative method and device for measuring polymer swelling and deswelling using light interference in the spectral and time domains. The method of measurement is based on two-beam interference of light, and it allows the investigation of rapid changes of swelling and deswelling of the polymer layer in the Fabry-Perot cavity occurring within a few seconds, or less. We studied swelling and deswelling processes of constrained Polydimethylsiloxane (PDMS) layers in organic solvent vapors of isopropanol, acetone, and toluene. The swelling curves of PDMS in small concentrations of solvents and also the threshold values of vapor mass concentration at saturation in air were determined. The measured saturation values were 141 g/m3 for isopropanol, 745 g/m3 for acetone, and 399 g/m3 for toluene. With our method, it is possible to measure swelling of various polymers (even non-transparent), which will be equipped with a reflective surface.

In the contribution, we present the preliminary results of an investigation of the effect of a magnetic field applied on a thin magnetic fluid layer placed between two crossed plane polarizers on its transmittance in the visible spectral range. We used samples of two different thicknesses and a supercontinuum white light source for investigation. The magnetic field was generated by a solenoid with an iron core and applied parallel to the magnetic fluid surface and at the same time, perpendicular to the direction of light propagation. We changed the strength of the magnetic field, its direction with respect to the orientation of the polarization planes of the polarizers and recorded the intensity of light transmitted through the samples. A quite strong effect of the magnetic field on the transmittance of the magnetic fluid thin layer placed between two crossed plane polarizers was observed which is promising for sensor applications utilizing the presence of an external magnetic field.

The design and method of preparing the optical fiber sensor are presented. The optical fiber sensor is based on a Fabry-Pérot interferometer. An optical cavity of the interferometer is formed by single-mode optical fiber. The sensor, connected to the measuring unit, is placed on the foot of the track between sleepers. The functionality of the sensor was verified by passing a trainset consisting of a diesel locomotive and four wagons. From the received signal it is possible to determine the presence of the train at a given time, the number of axles, the speed of the train and to estimate the load of individual axles. Due to the simple installation and multifunctionality of the proposed sensor, the sensor appears to be a good candidate for monitoring railway traffic.

Various parameters are measured to increase the safety of train operation and monitor the railway infrastructure. This contribution presents a monitoring system using an optical fiber Fabry-Pérot interferometer for speed measurement. The speed of the train was determined from the known distance of two sensors placed on the foot of the rail rather than the known geometry of the train. During the measurement campaign on the railway line in Slovakia, more than 70 train passages were determined. The speeds (from 15 km/h to 67 km/h) were divided into five groups and compared with the speeds determined by a piezoelectric-based sensor. Easy installation, a simple evaluation of the measured signal, and low sensor production costs, make the proposed sensor a good candidate for railway monitoring applications.