This paper proposes a method for adjusting light waves propagating in systems composed of photonic fibers, light sources and detection elements. The paper presents the properties of these connections in terms of the loss of signal transmission. Different fiber core areas were analyzed, and measurements of the mode-field diameters (MFDs) of selected fiber structures are presented. The study analyzed two types of LMA (Large Mode Area) fiber structures, and the mode-field diameters of these structures were measured on the basis of the radiation distribution obtained under near-field conditions. The results are compared to the values obtained for a SMF-28 single-mode fiber. The LMA structures analyzed in the paper are characterized by low sensitivity of the MFD parameter to the length of transmitted waves, which creates the possibility of their use as intermediate fibers when connecting optical fibers of different diameters. In the wavelength range from 800 nm to 1600 nm, a 3.5% MFD change was observed for the first investigated LMA structure, and a 1% change was observed for the second. In addition, measurements of the mode-field diameters were also made using the transverse offset method for comparison of the results.