Vibration is a ubiquitous phenomenon that occurs in everyday life and people are exposed to it almost all the time. Most often, vibration is measured using electromechanical devices such as piezoelectric, piezoresistive, or capacitive accelerometers. However, attention should be paid to the limitations of such vibration sensors. They cannot operate in the presence of strong electromagnetic fields. Measurements with electromechanical devices require physical contact between the sensor and the vibrating object, which is not always possible due to the design of the sensor and device. The possibility of a non-contact vibration measurement in harsh environments is provided by the technology of interferometric fibre optic sensors. This paper reports the principle of operation, design aspects, experimentation, and performance of a Mach-Zehnder interferometric setup for the measurement of vibration frequency. There are different sensing arms implemented in the interferometer: single-mode, polarization-maintaining, and tapered optical fibre. The paper emphasises the simplicity of the set-up structure and the detection capabilities based on the interferometric sensing giving the possibility of constructing a commercial vibration sensor for all industry demands.

The article presents a study of a hybrid structure based on the combination of a tapered optical fibre and gold nanoparticles dispersed in a liquid crystal material. Sensitivity to changes of the refractive index of the environment in which the structure is located, as well as the possibility of changing the refractive index of liquid crystals by external factors, such as temperature and electric field, were investigated. Electro- and thermally-induced changes of the refractive index of a liquid crystal through the rotation of a molecule director, which cause changes in the light propagated in a tapered optical fibre, were described. The most important issue in the article is to determine the influence of doping a liquid crystal with gold nanoparticles the concentration of which varies between 0.1 and 0.3 wt.%. The paper presents transmission measurements in a wide optical range depending on voltage, temperature, and frequency changes. Additionally, time courses of the obtained signal were measured. The study shows that the appropriate selection of nanoparticle concentration has a huge impact on the optical wave propagation. The experimental results show that the optical changes obtained for the investigated hybrid structure prefer it for use as an electro-optical switcher, filter, or sensor.

Preliminary results of laboratory and field tests of fibre optic rotational seismographs designed for rotational seismology are presented. In order to meet new directions of the research in this field, there is clearly a great need for suitable and extremely sensitive wideband sensors. The presented rotational seismographs based on the fibre optic gyroscopes show significant advantages over other sensor technologies when used in the seismological applications. Although the presented results are prepared for systems designed to record strong events expected by the so-called “engineering seismology”, the described system modification shows that it is possible to construct a device suitable for weak events monitoring expected by basic seismological research. The presented sensors are characterized, first and foremost, by a wide measuring range. They detect signals with amplitudes ranging from several dozen nrad/s up to even few rad/s and frequencies from 0.01 Hz to 100 Hz. The performed Allan variance analysis indicates the sensors main parameters: angle random walk in the range of 3 ∙ 10 ⁻⁸ - 2 ∙ 10 ⁻⁷ rad/s and bias instability in the range of 2 ∙ 10 ⁻⁹ - 2 ∙ 10 ⁻⁸ rad/s depending on the device. The results concerning the registration of rotational seismic events by the systems located in Książ Castle, Poland, as well as in the coalmine “Ignacy” in Rybnik, Poland were also presented and analysed.

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.

The main goal of the article is to present the concept of using a simulation environment when designing an advanced fibre-optic seismometer (FOS) using a field-programmable gate array (FPGA) computing system. The first part of the article presents the advanced requirements regarding the FOS principle of operation, as well as the measurement method using a closed-loop operation. The closed-loop control algorithm is developed using the high-level language C++ and then it is synthesised into an FPGA. The following part of the article describes the simulation environment developed to test the operation of the control algorithm. The environment includes a model of components of the measurement system, delays, and distortions in the signal processing path, and some of the measurement system surroundings. The article ends with a comparison of simulation data with measurements. The obtained results are consistent and prove correctness of the methodology adopted by the authors.