BC (Black Carbon), which can be found in the atmosphere, is characterized by a large value of the imaginary part of the complex refractive index and, therefore, might have an impact on the global warming effect. To study the interaction of BC with light often computer simulations are used. One of the methods, which are capable of performing light scattering simulations by any shape, is DDA (Discrete Dipole Approximation). In this work its accuracy was estimated in respect to BC structures using the latest stable version of the ADDA (vr. 1.2) algorithm. As the reference algorithm the GMM (Generalized Multiparticle Mie-Solution) code was used. The study shows that the number of volume elements (dipoles) is the main parameter that defines the quality of results. However, they can be improved by a proper polarizability expression. The most accurate, and least time consuming, simulations were observed for IGT_SO. When an aggregate consists of particles composed of ca. 750 volume elements (dipoles), the averaged relative extinction error should not exceed ca. 4.5%.

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.

The paper presents a method of measuring the angle of rotation and twist using a tilted fibre Bragg grating

(TFBG) periodic structure with a tilt angle of 6◦, written into a single-mode optical fibre. It has been shown

that the rotation of the sensor by 180◦ causes a change in the transmission coefficient from 0.5 to 0.84 at

a wavelength of 1541.2 nm. As a result of measurements it was determined that the highest sensitivity can

be obtained for angles from 30◦ to 70◦ in relation to the basic orientation. The change in the transmission

spectrum occurs for cladding modes that change their intensity with the change in the polarization of light

propagating through the grating. The same structure can also be used to measure the twist angle. The

possibility of obtaining a TFBG twist by 200◦ over a length of 10 mm has been proved. This makes it

possible to monitor both the angle of rotation and the twist of an optical fibre with the fabricated TFBG.