ИСКАЖЕНИЯ КОРОТКОГО ОПТИЧЕСКОГО ИМПУЛЬСА ПРИ ИЗМЕНЕНИИ ДЛИНЫ ОПТОВОЛОКНА В УСЛОВИЯХ НЕЛИНЕЙНОЙ МАТЕРИАЛЬНОЙ ФАЗОВОЙ ДИСПЕРСИИ
Authors: Иванов Д.В. , Иванов В.А. , Рябова Н.В. , Рябова М.И. , Овчинников В.В. 
Published: February 2025

Оптоволоконные линии связи приобретают всё большее значение в экономике. Однако повышение скорости передачи информации по ним наталкивается на необходимость преодоления эффекта зависимости фазовой скорости световых колебаний от частоты и разделения спектральных составляющих импульса по величине их группового запаздывания, называемой материальной дисперсией. В работе на основе использования принципа эквивалентности удалось свести задачу к исследованию частотной и импульсной характеристик эквивалентной оптоволокну линейной системе с дисперсией. Исследовано влияние на форму светового импульса изменения параметров дисперсии при увеличении длины пути импульса в оптоволокне с материальной дисперсией второго и третьего порядка.

Introduction. Increasing the data rate across the dispersive transmission medium is limited due to the effect of the dependence of the phase velocity of a wave on its frequency. Material dispersion in optical media (optical fiber) corresponds to the phase dispersion of an equivalent linear optical system (LOS) and manifests in a combination of the dispersion of the first, second, third, and other higher orders. It is known that the first order dispersion doesnt influence pulse shape and causes a pulse to be delayed by the time equal to the first order dispersion parameter. Hence, distortions are caused only by the nonlinear dispersion. The second order dispersion has been thoroughly studied. Less attention has been addressed to the analysis of the influence of the third order dispersion on the short pulse. Furthermore, even fewer studies have been focused on dispersion distortions of a short pulse depending on dispersion parameters. These parameters can vary with the change in the path length of a medium (for instance, due to the increase in the optical fiber length). The aim of the research was to develop the models and carry out general research into the distortions of a short optical pulse caused by the nonlinear material frequency dispersion due to the change in the fiber length. According to the equivalence principle, transmission media was modeled by an equivalent linear system with dispersion and its associated frequency and impulse responses. A numerical method was used to study the effect of varying material frequency dispersion of the third and second orders on optical pulse distortions in an optical fiber with the normal and anomalous dispersion. Results. Studies into the influence of only the second order dispersion proved the theoretical outcomes that the pulse shape doesnt depend on the type of dispersion and keeps symmetry with respect to the vertical line passing through the global maximum. With an increase in the fiber length, the pulse width increases and the pulse amplitude decreases. The analysis of the optical pulse distortions due to the influence of both the second and third orders dispersion showed that the third order dispersion causes only a break in the symmetry of pulse shape with respect to the global maximum for the values of the third order dispersion parameter lower than 0,9. In the case of the influence of only the third order dispersion, an optical pulse collapses producing a series of pulses (pulses comb) which amplitude decreases for positive dispersion parameter value and rises for negative one. The number of pulses rises with the increase in the path length. In the case of the pulse collapse, the amplitude of the main pulse does not change significantly with the change in the path length. Besides, the specific topic of the research was the soliton propagation of a Gaussian chirp pulse in an optical fiber with material dispersion. The effect is manifested in the compression of a pulse at the certain path length and occurs when the frequency sweep rate and the second order dispersion parameter are opposite in magnitude and have opposite signs. In this case, the third order dispersion deteriorates the symmetry of the process of increasing and decreasing the pulse amplitude with respect to the global maximum.