Features of Fiber Bragg Gratings Fabrication by Non-Destructive Ultrashort Laser Pulses

Under the influence of high-energy optical radiation, periodic structures can be formed inside the fiber, called Bragg gratings. A fiber Bragg lattice is a section of fiber in which the refractive index periodically changes along the direction of its propagation. FBGs act as narrowband optical filters, reflecting the Bragg wave from the received spectrum. The FBG period determines the wavelength of the reflection, and the length and amplitude of the reflected wave depend on the wavelength of the lattice. The uniqueness of my work lies in the multi-pass dot recording of the lattice using a femtosecond laser. It is known that the spectral parameters of the FBG depend both on the geometric parameters of the structure, such as length and period, and on the magnitude of the refractive index modulation in the exposed regions. By studying the dynamics of the spectral parameters of the VBR in the process of multi-pass recording, it is possible to draw conclusions about the change in the average refractive index and, as a result, about the physics of the phenomena occurring. This project has the following objectives. First, we need to take measurements in both photosensitive and non-photosensitive fiber, and collect three types of spectral data: the amplitude of the reflected wave, its width and the length of the reflected wave. Secondly, it is necessary to study the change in the average refractive index, which is important due to the lack of information about the processes occurring during the formation of the Bragg structure in the fiber core by the multi-pass method. The main part of my project is to understand exactly how the refractive index of a substance gradually changes using available spectral methods. Such as the spectral characteristics of the transmitted signal through an optical fiber, which is a graph of the dependence of power on wavelength.