The article presents further development of radiophotonic sensor systems based on the usage of the addressed (AFBS) and multi-addressed fiber Bragg structures (MAFBS) as sensing elements. Addressed fiber Bragg structure is an emerging type of fiber Bragg grating, which has a spectral response with two or more narrow notches. The presented system comprises two optical filters with linear inclined frequency response, which are used simultaneously to determine the central wavelengths of the AFBSs or MAFBSs. This feature enhances the operating temperature range of the system and allows to simplify its implementation, since the necessity of temperature isolation of the optical filters is eliminated. The algorithm and the mathematical model for the thermal drift compensation of the optical filters are introduced, and their realization is discussed.
The paper discusses approaches to the numerical integration of the second-kind Manakov equation system. Emphasis is placed on the transition from writing equations in dimensional quantities to equations in dimensionless units. A combined explicit-implicit finite-difference integration scheme based on the implicit Crank- Nicolson finite-difference scheme is proposed and substantiated, which allows integrating a non-linear system of equations with a choice of non-linear term at the previous integration step. An algorithm for leveling the disadvantage associated with the definition of the nonlinear term from the previous integration step is proposed. The approach of automatic selection of the integration step, which reduces the total number of integration steps while maintaining the required accuracy of the approximate solution, is substantiated. Examples of the calculation results for some values of the disturbance propagation are given. The limitations imposed by the scheme on the length of the integrable fiber section are described, and approaches are proposed that eliminate these limitations without the need to increase the dimensions of the finite-difference scheme arrays. Requirements for initial boundary conditions were discussed.
The paper discusses mathematical modeling of the optical spectrum of the addressed fiber Bragg structure. The approach uses Lorentz function to describe the spectrum of the transparency window of the addressed structure with two symmetrical π-phase shifts. The approach allowed to define the influence of the width of transparency window on the amplitude and the full width at half maximum of the address frequency spectral component. The obtained relations can be used to estimate the bandwidth of the electric bandpass filters necessary for signal detection, as well as the desired level of optical power of the light source.
The article discusses a possibility of modeling responses of addressed fiber Bragg structures (AFBS) using the normal
Gauss distribution function. The presented study is motivated by the fact that for the reliable operation of the microwave photonic measurement system based on the use of address structures with two identical narrow-band bandwidth responses (2λ-FBG), it is necessary to ensure that a bandwidth of an inclined filter covers the operating range of the AFBS. Since this filter is necessary for estimating a shift of a central wavelength of the AFBS by determining a change in amplitudes of oscillations at a photodetector, which allows measurements of various physical fields without the use of expensive interrogators.
The article discusses a possibility of using fiber-optic sensors based on addressed fiber Bragg structures (AFBS) to assess tire dynamics in real operating conditions. The presented study is motivated by the fact that vehicle dynamics control systems require reliable and cost-efficient sensors for measuring forces acting in the tire contact patch. In this regard, a description of the new technology of multi-sensor measurements for continuous monitoring of tire state is presented. The experimental sensor prototypes use AFBSs with two identical ultra-narrow-band reflection spectra (2λ-FBG). Information from the sensors is implemented as input parameters of algorithms, which allow to estimate key tire-related characteristics, such as pressure in the contact patch, instantaneous angular velocity and effective wheel radius. One of advantages of this technology as compared to analogous devices is the use of an optical photodetector as an interrogator that greatly simplifies the system.
The work presents a concept of microwave-photonic sensor system (MWPSS) for real-time measurement of vehicle tire strain. The proposed MWPSS is based on the addressed fiber Bragg structures (AFBS) with two symmetrical π-phase shifts (2π-FBG). The system utilizes two similar 2π-FBGs with equal bandwidths, the same central Bragg wavelength, and unique address frequency spacing, thus realizing the microwave-photonic measurement methods and providing their address. One of the 2π-FBGs serves for strain measurement, and the second one takes into account the effects of temperature variation. Address frequency analysis of the multiplicative optical response allows to define the central Bragg frequency shift of each sensor and to correlate it with the value of the influencing physical fields (strain and temperature). These values are the input parameters for the estimation system of tire-road contact characteristics and vehicle dynamics control.
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