A Review of Rotational Seismology Area of Interest from a Recording and Rotational Sensors Point of View.

This article reviews rotational seismology, considering different areas of interest, as well as measuring devices used for rotational events investigations. After a short theoretical description defining the fundamental parameters, the authors summarized data published in the literature in areas such as the indirect numerical investigation of rotational effects, rotation measured during earthquakes, teleseismic wave investigation, rotation induced by artificial explosions, and mining activity. The fundamental data on the measured rotation parameters and devices used for the recording are summarized and compared for the above areas.

Development of Three-Axis Fibre-Optic Seismograph for Direct and Autonomous Monitoring of Rotational Events with Perspective of Historical Review.

The paper presents historical perspective of fibre-optic seismographs designed and constructed at the Institute of Applied Physics at Military University of Technology, Poland based on the so-called minimum configuration of fibre-optic gyroscope. The briefly presented history, which originated in the 1998 by the system named GS-13P, laid solid foundations for the construction of a three-axis fibre-optic seismograph. The presented system meets all technical requirements of rotational seismology in terms of measurement parameters (measuring range from 10 rad/s to several rad/s and frequency from 0.

Multispectral Portable Fibre-Optic Reflectometer for the Classification of the Origin of Chicken Eggshells in the Case of Infections.

The proper classification of the origins of food products is a crucial issue all over the world nowadays. In this paper, the authors present a device-a multispectral portable fibre-optic reflectometer and signal processing patch-together with a machine-learning algorithm for the classification of the origins of chicken eggshells in the case of infection. The sensor device was developed based on previous studies with a continuous spectrum in transmittance and selected spectral lines in reflectance.

Post-Processing of Raw Data Recorded Continuously Using a FORS-Fibre-Optic Rotational Seismograph.

Modern optoelectronic devices use the advantage of digital systems for data processing aimed at delivering reliable information. However, since commonly used DACs have limited accuracy, some artefacts can be observed in data streams, especially in systems designed for continuous, long-term process monitoring. In this paper, the authors' experience with data enhancement using a fibre-optic rotational seismograph (FORS) operating in a closed-loop mode is presented and discussed.

Optical Properties of a Tapered Optical Fiber Coated with Alkanes Doped with FeO Nanoparticles.

The presented research shows the possibilities of creating in-line magnetic sensors based on the detection of changes of light propagation parameters, especially polarization, obtained by mixing FeO nanoparticles with hexadecane (higher alkane) surrounding a biconical optical fiber taper. The fiber optic taper allows to directly influence light parameters inside the taper without the necessity to lead the beam out of the structure. The mixture of hexadecane and FeO nanoparticles forms a special cladding surrounding a fiber taper which can be controlled by external factors such as the magnetic field.

SPR Sensor Based on a Tapered Optical Fiber with a Low Refractive Index Liquid Crystal Cladding and Bimetallic Ag-Au Layers.

This paper presents a study of the influence of bimetallic layer covers of a tapered optical fiber surrounded by a low refractive index liquid crystal on the properties of light propagation in the taper structure. This research follows previous works on the effect of monometallic thin films (Au and Ag). In this case, the total thicknesses of the bimetallic layers were = 10 nm, and the participation of gold and silver was equal.

Polymer Microtip on a Multimode Optical Fiber as a Threshold Volatile Organic Compounds Sensor.

Polymer microtips are 3D microstructures manufactured on the end face of an optical fiber by using the photopolymerization process. Such micro-optic elements made on a multi-mode optical fiber were previously tested as a transducer of refractive index sensor. These studies were an inspiration to investigate the possibility of using this type of transducer to measure the presence of volatile organic compounds in the air.

Enhancement of the SPR Effect in an Optical Fiber Device Utilizing a Thin Ag Layer and a 3092A Liquid Crystal Mixture.

This paper is a continuation of previous work and shows the enhancement of the surface plasmon resonance effect in a tapered optical fiber device. The study investigated liquid crystal cells containing a tapered optical fiber covered with a silver nanolayer, surrounded by a low refractive index liquid crystal in terms of the properties of light propagation in the taper structure. Silver films with a thickness of = 10 nm were deposited on the tapered waist area.

Study of Rotational Motions Caused by Multiple Mining Blasts Recorded by Different Types of Rotational Seismometers.

Digging two vertical shafts with the multiple blasts technique gave the opportunity to measure the induced angular motions in a horizontal plane with well-defined positions of sources. Three kinds of rotation rate sensors, sharing an underground location, were used. Two of them-a Fiber-Optic System for Rotational Events & phenomena Monitoring (FOSREM) and a prototypical seismometer housing the liquid-filled torus-sensed the rotation, while a microarray of two double-pendulum seismometers sensed both the rotation and symmetric strain.

Electro-Optical and Photo Stabilization Study of Nematic Ternary Mixture.

Liquid crystal materials composed of mixed nematic compounds find broad use in liquid crystal displays and photonic applications. A ternary mixture formed from three different nematic compounds shows peculiar behavior such as tunable electro-optical properties dependent on the frequency of the driving voltage. The paper presents an analysis of the response time and phase retardation of a frequency tunable nematic liquid crystal mixture (under code name 5005).

Rotation, Strain, and Translation Sensors Performance Tests with Active Seismic Sources.

Interest in measuring displacement gradients, such as rotation and strain, is growing in many areas of geophysical research. This results in an urgent demand for reliable and field-deployable instruments measuring these quantities. In order to further establish a high-quality standard for rotation and strain measurements in seismology, we organized a comparative sensor test experiment that took place in November 2019 at the Geophysical Observatory of the Ludwig-Maximilians University Munich in Fürstenfeldbruck, Germany.

Reflective Properties of a Polymer Micro-Transducer for an Optical Fiber Refractive Index Sensor.

A polymer microtip manufactured at the end of a multi-mode optical fiber by using the photopolymerization process offers good reflective properties, therefore, it is applicable as an optical fiber sensor micro-transducer. The reflective properties of this microelement depend on the monomer mixture used, optical fiber type, and light source initiating polymerization. Experimental results have shown that a proper selection of these parameters has allowed the design of a new class of sensing structure which is sensitive to the refractive index (RI) changes of a liquid medium surrounding the microtip.

Thermo-Optical Switching Effect Based on a Tapered Optical Fiber and Higher Alkanes Doped with ZnS:Mn.

The paper investigates the effect of thermo-optic switching resulting from the hybrid combination of a tapered optical fiber (TOF) with alkanes doped with nanoparticles of zinc sulfide doped with manganese (ZnS:Mn NP). Presented measurements focused on controlling losses in an optical fiber by modification of a TOF cladding by the alkanes used, characterized by phase change. Temperature changes cause power transmission changes creating a switcher or a sensor working in an ON-OFF mode.

SPR Effect Controlled by an Electric Field in a Tapered Optical Fiber Surrounded by a Low Refractive Index Nematic Liquid Crystal.

This paper presents the influence of a thin metal layer deposition on the surface of a tapered optical fiber surrounded by a low liquid crystal, on light propagation inside the taper structure. In this research, three types of liquid crystal cells were under investigation: orthogonal, parallel, and twist. They differed by the rubbing direction of the electrodes in relation to the fiber axis determining the initial molecule arrangement inside the cell.

Measurements of Rotational Events Generated by Artificial Explosions and External Excitations Using the Optical Fiber Sensors Network.

Measurements of artificial events can substantially confirm the data validity of constructed rotational sensors, as well as provide methods for simplifying the measurement process. The above task, especially with international cooperation, can provide full-field measurement results of the target object, which can deliver more significant data and sensor properties. The paper presents vertical rotational velocity recordings gathered during an international experiment that took place at the Geophysical Observatory of the Ludwig Maximilian University of Munich in Fürstenfeldbruck, Germany.

Technology of Polymer Microtips' Manufacturing on the Ends of Multi-Mode Optical Fibers.

The technology of polymer microtips' manufacturing on the ends of selected multi-mode fibers has been reported. The study's key element was an extended description of technology parameters' influence on the shape of these 3D microstructures. Basic technology parameters such as spectral characteristics of the light source, monomer mixture type, optical power, and exposure time were taken under consideration.

The Young Interferometer as an Optical System for a Variable Depolarizer Characterization.

This article proposes an interferometric method for a variable depolarizer characterization with features that distinguish it from the polarimetric system. Information about the behavior of a vertically aligned nematic cell as a variable depolarizer can be extracted from Young interferometer measurements in real time. These results could be significant for understanding the polarization phenomena in depolarizing media such as biological tissue.

The Fiber-Optic Rotational Seismograph-Laboratory Tests and Field Application.

The paper presents construction and laboratory tests, as well as the first field application of a new fiber-optic rotational seismograph. The system is based on a fiber-optic gyroscope (FOG), with determined Angle Random Walk of the order of 10 rad/Sqrt(s) and a few rad/s maximum detectable amplitude of rotation in the frequency range from direct current (DC) to 328.12 Hz.

Ambient Refractive-Index Measurement with Simultaneous Temperature Monitoring Based on a Dual-Resonance Long-Period Grating Inside a Fiber Loop Mirror Structure.

In this work, we report the experimental results on optimizing the optical structure for ambient refractive index measuring with temperature changes monitoring. The presented optical structure is based on a dual-resonance long-period grating embedded inside a fiber loop mirror, where the long-period grating acts as the head of the refractive-index sensor, whereas the section of polarization maintaining fiber in the loop mirror ensures suitable temperature sensing. The optimization process was comprised of tuning the resonance and interferometric peaks by changing the state of polarization of propagating beams.

Tunable liquid crystal multifocal microlens array.

A novel liquid crystal microlens array with tunable multifocal capability, high optical power and fill-factor is proposed and experimentally demonstrated. A specific hole pattern design produces a multifocal array with only one voltage control. Three operations modes are possible, "Off", "Tunable Multifocal" and "Unifocal".

Review of the Usefulness of Various Rotational Seismometers with Laboratory Results of Fibre-Optic Ones Tested for Engineering Applications.

Starting with descriptions of rotational seismology, areas of interest and historical field measurements, the fundamental requirements for rotational seismometers for seismological and engineering application are formulated. On the above basis, a review of all existing rotational seismometers is presented with a description of the principles of their operation as well as possibilities to fulfill formulated requirements. This review includes mechanical, acoustical, electrochemical and optical devices and shows that the last of these types are the most promising.

Fibre optic system for monitoring rotational seismic phenomena.

We outline the development and the application in a field test of the Autonomous Fibre-Optic Rotational Seismograph (AFORS), which utilizes the Sagnac effect for a direct measurement of the seismic-origin rotations of the ground. The main advantage of AFORS is its complete insensitivity to linear motions, as well as a direct measurement of rotational components emitted during seismic events. The presented system contains a special autonomous signal processing unit which optimizes its operation for the measurement of rotation motions, whereas the applied telemetric system based on the Internet allows for an AFORS remote control.

Bicell-photodetector in the Fourier plane as a fiber optic homodyne phase demodulator: theoretical model and experimental results.

A concept of the Young interference experiment has been applied in the design of a fiber optic homodyne phase demodulator. The system is based on a bicell-photodetector in the Fourier plane. The above system has been designed, described, and verified together with an estimation of the minimization of phase measurement error in connection with the distance between photodetectors, wavelength, and focal length of the Fourier lens.

Fiber Bragg grating inscription in few-mode highly birefringent microstructured fiber.

In this Letter, we present the technology of fiber Bragg grating (FBG) inscription in highly birefringent (HB) few-mode microstructured fibers (MSFs) with two different (nanosecond and femtosecond) lasers in a Talbot interferometer setup. The spectral characteristics of FBGs written in the core region of the investigated fiber, with particular modes represented by dual peaks, are presented and discussed. Furthermore, we calculate the fundamental fiber parameters (mode effective refractive index and phase modal birefringence) from the spectral characteristics and show very good agreement with the performed numerical fiber characterization.

Experimental study of dispersion characteristics for a series of microstructured fibers for customized supercontinuum generation.

We demonstrate an experimental study of the chromatic dispersion properties for a series of microstructured fibers (MSFs) dedicated for a supercontinuum generation. With white-light interferometry application we analyze experimentally how the small variations of structural parameters, i.e.