## 2 Materials and Methods
### Experimental Research Methods and Materials Used
In the experiment, an optical splitter of the PLCM-1U4U-SC (Shenzhen, China) type was used by dividing it into four channels with a ratio of 1/4, so the light wave energy was divided into each channel in the ratio of 25%. For more channels, one can use splitters with a ratio of 1/8, 1/16, or 1/32. Increasing the number of channels will require increasing the laser power, and the power of the laser used depends on the length of the fiber-optic communication line of the sensor with the data processing unit. The laser beam passing through the FOS 2 falls on the photodetector 11, which captures all the changes in intensity formed on the surface of the photo matrix. A stepped profile is formed at the exit from the OF, which the Gaussian distribution law can describe. A high-resolution photo matrix on the surface of which a light spot falls is installed at the exit from the optical fiber. The manufactured optical module (Figure 6) has a sealed housing, and its parts are glued with a sealant that does not allow penetration of external light rays, which can lead to malfunction, into the interior. At the end of the optical conductor is a fiber optic connector of SC type with a 2.5 mm diameter tip and a physical contact connector (UPC Ultra). Figure 5: Schemes for measuring the values of mechanical stresses and determining the location of the defect. 1—body of beam; 2—fiber-optic sensors; 3—rod; 4—bottom of plate; 5—top of plate; 6—load; 7—cracks; 8—connectors; 9—data processing unit; 10—module containing laser and optical splitter; 11—module of photodetector; 12—microprocessor-based data processing and matching unit; 13—direct current source; 14—power cord; 15—USB cable; 16—personal computer. For each channel, it is necessary to use a separate photo matrix, which converts the light signal into an electrical one and sends it to the microprocessor-based data processing and matching unit (12). It is connected via a USB cable (15) to the personal computer (16). To operate unit 9, a direct current source (13) with a power cord (14) is required. To operate the hardware-software complex, specially developed software is installed on the personal computer (16). The method of optical-electronic analysis of the light spot is used. The highest intensity of radiation is in zone 1. It is the brightest zone and unsuitable for study as it makes a lot of noise (Figure 7). There is a study changing the number of pixels in zone 2. Figure 8 shows a positive image of the light spot formed at the end of the optical fiber and further incident on the photo matrix under various impacts on the optical fiber. As the mechanical force on the sensor increases, the loss increases, and the emission intensity of the light spot decreases. Also, as the length of the optical fiber increases, its losses increase, and the size of the light spot decreases. It is found that this process is characteristic of the single-mode optical fiber of the G-652 standard [48] at a wavelength of 650 nm (red). Considering the degradation of the light spot, it is necessary to increase the laser power when increasing the length of the optical fiber used as a sensor. Figure 6: Optical modules. Figure 7: The light spot: 1—core; 2—transition boundary; 3—shell. Development of Theoretical Bases for Physical and Mathematical Models of Electron-Optical Phenomena in Fiber-Optic Functional Elements