ANALYSIS OF MODELS AND PARAMETERS OF SENSORS BASED ON BREGG GRIDS AND THE INFLUENCE OF PHYSICAL PARAMETERS ON THE SPECTRAL CHARACTERISTICS OF GRIDS

Abstract

The results of the project have a wide practical application in various industries, such as medical institutions and healthcare facilities, large industrial enterprises, in the automotive industry, food, agricultural and livestock industries, as well as in industrial technology, the metallurgical industry; oil and gas industry. In phase interferometric sensors (PID) based on arrays, the optical element itself acts as a sensitive element, which leads to a significant reduction in cost. The OB segment between two gratings is a Fabry-Perot interferometer. Under the influence of deformation and acoustic vibrations, the phase difference of signals from two adjacent Bragg gratings changes. Interferometric sensors are most sensitive to changes in the length of a fiber segment under the influence of external factors. The principle of operation of distributed fiber-optic measuring complexes based on PID in the simplest case (in the case of one PID) is shown in Figure 3.6 and is as follows [4]. Each of the Bragg gratings RB1 and RB2 of the sensor reflects the pulse coming to it from the pulsed laser at the same Bragg wavelength.  In this case, the time delay between the reflected pulses is equal to twice the propagation time of light in the sensitive element of the sensor – a fiber enclosed between the gratings. The reflected pulses enter the compensating interferometer (CI), which, in turn, also bifurcates each of them. The delay introduced into the propagation of pulses by the arm 2 of the CI with respect to arm 1 ensures the overlap in time of the pulse reflected from the grating RB1 at the output of arm 2 and the pulse reflected from the grating RB2 at the output of arm 1 and their phase shift by ϕ 0 =π/2.