The article describes the theory and technique of addressed fiber Bragg structures and a new class of microwave-photonic sensory systems based thereon, the distinctive feature of which is that the fiber Bragg structure forms two ultra-narrowband frequency components separated by a unique address frequency spacing. The offset of the central frequencies of the Bragg structures is determined via processing a beat signal of the address frequencies on the photodetector, with its parameters making it possible to evaluate the physical fields applied. We formulate and solve a problem of unambiguously determining the central (Bragg) frequency shift of the addressed fiber Bragg structures with unique address frequencies and the same Bragg frequency. These are then combined into a single multi-sensor system with multiplexed response reception on a single photodetector.

The new theory and technique of Multi-Addressed Fiber Bragg Structure (MAFBS) usage in Microwave Photonics Sensor Systems (MPSS) is presented. This theory is the logical evolution of the theory of Addressed Fiber Bragg Structure (AFBS) usage as sensors in MPSS. The mathematical model of additive response from a single MAFBS is presented. The MAFBS is a special type of Fiber Bragg Gratings (FBG), the reflection spectrum of which has three (or more) narrow notches. The frequencies of narrow notches are located in the infrared range of electromagnetic spectrum, while differences between them are located in the microwave frequency range. All cross-differences between optical frequencies of single MAFBS are called the address frequencies set. When the additive optical response from a single MAFBS, passed through an optic filter with an oblique amplitude–frequency characteristic, is received on a photodetector, the complex electrical signal, which consists of all cross-frequency beatings of all optical frequencies, which are included in this optical signal, is taken at its output. This complex electrical signal at the photodetector’s output contains enough information to determine the central frequency shift of the MAFBS. The method of address frequencies analysis with the microwave-photonic measuring conversion method, which allows us to define the central frequency shift of a single MAFBS, is discussed in the work.

The article is devoted to issues related to the propagation and transformation of vortexes in the optical range of frequency. Within the framework of the traditional and modified model of slowly varying envelope approximation (SVEA), the process of converting vortex beams of the optical domain into vortex beams of the terahertz radio range based on nonlinear generation of a difference frequency in a medium with a second-order susceptibility is considered. The modified SVEA splits a slowly varying amplitude into two factors, which makes it possible to more accurately describe the three-wave mixing process. The theoretical substantiation of the rule of vortex beams topological charges conversion is given—the topological charge of the output radio-vortex beam is equal to the difference between the topological charges of the input optical vortex beams. A numerical simulation model of the processes under consideration has been implemented and analyzed.

The work presents an approach to instrument the load-sensing bearings for automotive applications for estimation of the loads acting on the wheels. The system comprises fiber-optic sensors based on addressed fiber Bragg structures (AFBS) with two symmetrical phase shifts. A mathematical model for load–deformation relation is presented, and the AFBS interrogation principle is described. The simulation includes (i) modeling of vehicle dynamics in a split-mu braking test, during which the longitudinal wheel loads are obtained, (ii) the subsequent estimation of bearing outer ring deformation using a beam model with simply supported boundary conditions, (iii) the conversion of strain into central frequency shift of AFBS, and (iv) modeling of the beating signal at the photodetector. The simulation results show that the estimation error of the longitudinal wheel force from the strain data acquired from a single measurement point was 5.44% with a root-mean-square error of 113.64 N. A prototype load-sensing bearing was instrumented with a single AFBS sensor and mounted in a front right wheel hub of an experimental vehicle. The experimental setup demonstrated comparable results with the simulation during the braking test. The proposed system with load-sensing bearings is aimed at estimation of the loads acting on the wheels, which serve as input parameters for active safety systems, such as automatic braking, adaptive cruise control, or fully automated driving, in order to enhance their effectiveness and the safety of the vehicle.

Address fiber Bragg structures (AFBS) make it possible to effectively solve the problems of interrogation and multiplexing of sensors in multi-sensor networks with microwave photonic processing of information. Based on a complex method of transmission matrices and the coupling of directional modes, a mathematical model was constructed to determine the spectral profile of a fiber Bragg grating with two discrete symmetric phase π shifts (2π-FBG). Based on the study of the mathematical model, the possibility of selecting the necessary parameters of 2π-FBG AFBS is shown, which allow forming its spectral profile in such a way that the specified structure can be used as a sensitive element of the sensor and provides the necessary linear displacement in the optical range and preserves the required frequency separation – address – between discrete symmetric phase shifts location in the radio frequency range. The analysis of the formation and recording methods for 2π-FBG AFBS was carried out. To implement given structures, the technology, using of an ultraviolet argon laser, the classic phase masks with sequential recording of several arrays with precise movement of the fiber were chosen. Further paper deals with issues of interrogation of the developed structures in few- and multi-sensor implementations.

This work presents fabricated silica microstructured optical fiber with special equiangular spiral six-ray geometry, an outer diameter of 125 µm (that corresponds to conventional commercially available telecommunication optical fibers of ratified ITU-T recommendations), and induced chirality with twisting of 200 revolutions per minute (or e.g., under a drawing speed of 3 m per minute, 66 revolutions per 1 m). We discuss the fabrication of twisted microstructured optical fibers. Some results of tests, performed with pilot samples of designed and manufactured stellar chiral silica microstructured optical fiber, including basic transmission parameters, as well as measurements of near-field laser beam profile and spectral and pulse responses, are represented.

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