Details

Single-mode optical fibers can preserve the state of polarization and are widely used in fiber-optic physical sensors and optical communication. One of their most important parameters is the beat length. Among the various measurement techniques, this work focuses on the spectral method using a frequency-scanning coherent laser, whose key element is the polarization interferometer. In it, two orthogonal polarization modes propagate at different velocities; they cannot produce an interference signal without an optical polarizer, after which an output intensity signal arises and is registered by a photoreceiver. In the theoretical part, a model of the polarization interferometer is developed using the Jones matrix method, yielding expressions for the output intensity, birefringence, and beat length for different parameters and types of birefringent fibers. These expressions are used to calculate the characteristics of PANDA-type fiber, which is widely employed in laboratories. The thesis also examines the influence of polarization dispersion on birefringence and beat length, showing that dispersion can significantly degrade fiber parameters: birefringence decreases while beat length increases. The experimental part is devoted to the investigation of birefringent fibers. An optical setup based on the scanning spectral method was assembled: light passes through a polarizer, enters the fiber under test, passes through a second polarizer, and reaches the polarization detector, after which the signal is processed by a computer. The spectral transfer functions were measured, and a Fourier transform was applied to determine the beat length and birefringence. The experimental results agree well with the theoretical calculations.