This paper outlines a measurement method of properties of microstructured optical fibers that are useful in sensing applications. Experimental studies of produced photonic-crystal fibers allow for a better understanding of the principles of energy coupling in photonic-crystal fibers. For that purpose, fibers with different filling factors and lattice constants were produced. The measurements demonstrated the influence of the fiber geometry on the coupling level of light between the cores. For a distance between the cores of 15 μm, a very low level (below 2%) of energy coupling was obtained. For a distance of 13 μm, the level of energy transfer to neighboring cores on the order of 2-4% was achieved for a filling factor of 0.29. The elimination of the energycoupling phenomenon between the cores was achieved by duplicating the filling factor of the fiber. The coupling level was as high as 22% in the case of fibers with a distance between the cores of 8.5 μm. Our results can be used for microstructured-fiber sensing applications and for transmission-channel switching in liquid-crystal multi-core photonic fibers.
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.