В работе методом численного моделирования исследуется устойчивость работы алгоритмов цифровой обработки сигналов (ЦОС) когерентного приемника к быстрому вращению поляризации, вызванному ударом молнии в оптический кабель в грозотросе (ОКГТ). Установлено, что скорость изменения состояния поляризации (СП) является наиболее важным параметром, определяющим рост коэффициента ошибок (BER) в приемнике. Детальный анализ работы алгоритмов ЦОС в условиях быстрого вращения СП показал, что причиной роста коэффициента ошибок является ограниченное быстродействие блоков пересинхронизации и адаптивной фильтрации.

A numerical experiment for light passing through the section of the optical ground wire during a lightning strike events was carried out. The “isotropy effect” for areas in state of polarization rotation speed time profiles was discovered and explained. This effect consists in the fact that time profiles shapes of anisotropic and isotropic fibers practically coincide in short zones at the beginning and the end of lightning current rapid increase interval (lightning front), but it differ significantly in the middle part. It is shown that such a behavior of time profile is determined by the smallness of the length of interaction of light with the region of rapid change of the magnetic field at the beginning and the end of the lightning front, while the effect of the magnetic field on short sections of the anisotropic fiber practically coincides with the effect on sections of isotropic fiber of the same length. Using the model of light propagation in a fiber with a random distribution of linear birefringence, located in the magnetic field of lightning, a formula for calculating the matrix rotation speed of the polarization state for an extended fiber is obtained.

Explicit expressions for the dependence of signal-to-noise ratio on the optical filter bandwidth and its slope have been obtained. The resulting expressions were confirmed experimentally. The dependencies of critical symbol rate on two parameters, namely the bandwidth and roll-off factor, were studied both for the case of one and several filters.

we report an enhanced method to measure chirp of periodic optical signal. We use optical filters, fast photodetector and sampling oscilloscope for this purpose. A comparison with other commonly used techniques of chirp characterization showed a good agreement.

This paper describes techniques for measuring the SRS coefficient in a wide spectral range, including the region of small Stokes shifts. A simple, approximate method is proposed for evaluating the SRS coefficient near a gain peak. Spectral dependences of the SRS coefficient are presented for various telecom fibres.

Описаны методики измерения коэффициента ВКР в широком спектральном диапазоне, включая область малых стоксовых сдвигов. Предложен простой приближенный метод оценки коэффициента ВКР вблизи пика усиления. Приведены спектральные зависимости коэффициента ВКР для различных телекоммуникационных волокон.