РАСЧЕТ ДИСПЕРСИИ СИГНАЛА В ОПТИЧЕСКОМ ВОЛОКНЕ.

Аннотация

This article provides information on the calculation of signal dispersion in optical fiber. Key words: Fiber optic cables, channels, communication lines, signal, transmitted signal. РАСЧЕТ ДИСПЕРСИИ СИГНАЛА В ОПТИЧЕСКОМ ВОЛОКНЕ. Аннотация. В этой статье представлена информация о расчете дисперсии сигнала в оптическом волокне. Ключевые слова: Волоконно-оптические кабели, каналы, линии связи, сигнал, передаваемый сигнал. Dispersion process. Fiber optic cables can transmit a large number of channels over long distances, but such transmissions are not without some limitations. From the point of view of using optical fibers in communication lines, one of the limitations in signal transmission is dispersion. Dispersion is the spreading of the time or mode components of the optical pulse at the receiver side of the transmitted pulse in the spectral medium, which leads to an increase in the width of its duration moving along the entire length of the optical fiber. If the signal sent to the line reaches the receiving side in a modified and expanded state, the transmitted signal reaches the receiving side in the same expanded state (Fig. 1). Such a situation is called dispersion, and it is created due to the different speeds of the frequency components of the pulses moving along the optical fiber and the width of the spectrum of the light radiation source. Fig. 1. Expansion of pulses due to dispersion. Dispersion - t means the expansion of the pulse moving along the optical cable. The dispersion value is determined by the difference of the square of the duration of the pulses coming out of the optical fibers in the optical cable and arriving at the receiver:  t2 t2 chiq kir sharp and sharp in this formula are the time or pulse width of the pulses coming out of the optical cable and entering the optical cable at the half-amplitude level. 1 27 International scientific journal ISSN: 2181-3906 «MODERN SCIENCE АND RESEARCH» 2023 VOLUME 2 / ISSUE 11 / UIF:8.2 / MODERNSCIENCE.UZ Dispersion is when a sequence of right-angle pulses in a digital signal travels along a certain length of optical fiber, the pulses are spread, as a result, two adjacent pulses cannot be distinguished from each other, and eventually errors occur in the transmission of signals. y gives Thus, dispersion is one of the main factors limiting the bandwidth or bandwidth of a fiber optic transmission system and the communication distance. Types of dispersion. Optical fiber has three dispersion mechanisms: - intermodal dispersion; - chromatic dispersion; - polarized – mode dispersion. Chromatic dispersion consists of material dispersion, dispersion related to wave transmission and profile dispersion. Dispersion compensation methods. According to statistics, the most laid cables consist of single-mode standard SF (Standard Fiber) fibers. Currently, the attenuation values of SF fibers have been reduced to 0.16-0.22 dB/km. However, the dispersion value of these fibers at a wavelength of 1550 nm is 17-20 ns/nm·km. Such a large value of dispersion limits the transmission of information at high speeds (above 10 Gbit/s) over long distances. When single-mode standard SF fibers are used, the dispersion value should be reduced. In order to reduce the dispersion when using standard single-mode optical fibers in the fiber optic line tract, increase the length of the regeneration section, move from 2.5 Gbit/s speed to 10 Gbit/s speed, as well as apply the technology of wavelength densification. DCF (Dispersion Compensating Fiber) fibers or DCM (Dispersion Compensating Module) dispersion compensating modules are required. DCF is a dispersion compensating fiber used mainly to reduce chromatic dispersion. In DCF fibers, the dispersion value is negative and has large values. As a result of connecting DCF fibers with a negative dispersion to a working fiber with a positive dispersion, the dispersion approaches zero, that is, it is compensated. Dispersion compensation unit (DCU - dispersion compensation unit) DCU compensates for the dispersion of the transmission fiber We use a negative dispersion DCU to compensate for pulses that are "spread" (broadened) by the movement of the dispersion state in the transmission fiber (Fig. 2). Figure 2. Dispersion Compensation Unit (DCU) In the transmission fiber, the negative moving dispersion ("blue" light with a shorter wavelength propagates more slowly than the "red") is neutralized by the positive moving dispersion, that is, the lower and higher components of the frequency spectrum are transmitted at the same speed provides. We use DCU on a length of fiber where chromatic dispersion is of great importance, because DCU allows to significantly reduce the dispersion compared to the transmission fiber. 1 28 International scientific journal ISSN: 2181-3906 «MODERN SCIENCE АND RESEARCH» 2023 VOLUME 2 / ISSUE 11 / UIF:8.2 / MODERNSCIENCE.UZ