УПРАВЛЕНИЕ ТОНКОЙ СТРУКТУРОЙ ТРЁХКОМПОНЕНТНЫХ АДРЕСНЫХ БРЭГГОВСКИХ ИЗМЕРИТЕЛЬНЫХ ПРЕОБРАЗОВАТЕЛЕЙ, ПОСЛЕДОВАТЕЛЬНО ЗАПИСАННЫХ В ОПТИЧЕСКОЕ ВОЛОКНО КВАЗИРАСПРЕДЕЛЁННОЙ РАДИОФОТОННОЙ СЕНСОРНОЙ СИСТЕМЫ
Authors: Аглиуллин Т.А. , Губайдуллин Р.Р. , Кузнецов А.А. , Сахабутдинов А.Ж. , Нуреев И.И. , Морозов О.Г. , Шарафиев У.Ф. 
Published: February 2025

В работе представлены результаты исследования влияния параметров многоадресных волоконных брэгговских структур (МАВБС) с дискретными фазовыми сдвигами на характеристики их спектральных откликов. Исследование проводилось с использованием математической модели МАВБС, построенной методом матриц передач. Описано влияние величины наведённого показателя преломления, длин однородных участков структуры, величин дискретных фазовых сдвигов на форму спектра излучения, прошедшего через МАВБС. Выявлены закономерности, которые могут быть использованы для управления тонкой структурой трёхкомпонентных МАВБС для достижения требуемых спектральных характеристик.

Introduction. The most significant factor that constrains the widespread usage of fiber Bragg gratings-based sensor systems is the complexity of interrogation and multiplexing devices for such sensors. In order to solve this issue, the usage of multi-addressed fiber Bragg structures (MAFBS) has been proposed. MAFBS is a specially structured fiber Bragg grating, the optical spectral response of which consists of three or more ultra-narrowband components, and the difference frequencies between these components are in the radio-frequency range and are termed to as the address frequencies. Interrogation (i.e., determination of the central wavelength of the MAFBS) is carried out due to the fact that the three-frequency (or more) optical radiation propagated through the MAFBS and passed through a filter with a linear inclined amplitude-frequency response, causes a beat-note signal at the output of the photodetector with frequencies equal to the address frequencies of the MAFBS. The amplitude of the beat-note signal is used to determine the central wavelength of the MAFBS. Since each MAFBS-sensor of the system has its own unique set of address frequencies, the array of such sensors can be interrogated without complex optoelectronic circuits. The aim of the work is to study the influence of the parameters of the MAFBS with discrete phase shifts on the shape of its spectral responses. The study was carried out with the use of the mathematical model of MAFBS based on the transfer-matrix method. The MAFBS in question included four uniform sections of a fiber Bragg grating with phase shifts between them. Conclusion. On the basis of a mathematical model, the spectral characteristics of the multi-addressed structure were obtained at various values of its parameters. The results describe the influence of the magnitude of the induced refractive index, the lengths of the uniform sections of the structure, and the magnitudes of discrete phase shifts on the shape of the spectrum of radiation transmitted through the MAFBS. Thus, an increase in the induced refractive index and the length of the outermost uniform sections of the MAFBS has the greatest effect on reducing the width of the transparency windows. Asymmetric change of address frequencies is achieved only by varying the phase shifts. The amplitudes of the spectral components are preserved only if the symmetry of the multi-addressed structure with respect to its center is maintained. Practical significance. The revealed regularities can be used to control the fine structure of three-component MAFBS in order to achieve the required spectral characteristics.