Abstract. In this paper, a new method of polarization mode dispersion (PMD), which can significantly limit the speed and range of transmission of fiber optic transmission systems (FOTS), compensation was developed and analyzed. In contrast to the existing types of PMD compensators, in which the optical fiber is subjected to mechanical stresses to create a photoelastic anisotropy, in this work the use of alternative method of creating photoelasticity in optical fiber (OF) by creating a helical ordered rotation of the glass microstructure (ORMG) is proposed. The helical orientation of the microstructure of the OF glass is achieved by acting on the fiber in the process of manufacture (drawing), when it is in a hot state, electromagnetic field, the power lines of which are directed in a circle. I am not sure what this sentence is trying to say. The result is an asymmetry of the dielectric constant of the fiber glass material and therefore the anisotropy of the optical properties. When the optical signal propagates in such OF, there is a double refraction, which is the cause of artificial PMD in the compensator fiber. Compensation is achieved by performing the equality of the modulus and the sign-opposite between the linear path PMD and the PMD of the anisotropic OF with the ORMG. The expression of the calculation of the PMD of the compensator, which depends on the rotation step of the microstructure of the glass, the chemical composition of the OF, the length of the line, the width of the radiation spectrum and the wavelength of the optical signal, and the optical characteristics of the OF, is analyzed, as well as the spectral dependence of polarization mode dispersion for different chemical compositions of the OF. The expression of determining the length of the OF with the ORMG is presented to compensate for the set value of the PMD in the line. The results of the studies made it possible to determine the lengths of the segments of OF with ORMG, which will provide partial or complete compensation of PMD over a wide range of wavelengths and create passive compensators for dispersion.
Дослiджуються процеси перерозподiлу енергiї оптичного сигналу мiж серцевиною i оболонкою оптичного волокна в мiсцях їх з'єднання. В аналiтичнiй операторнiй моделi отриманi замкнутi формули залежностi тривалостi сигналу на сторонi приймача вiд кiлькостi з'єднань i вiрогiдностi переходу енергiї iз серцевини в оболонку оптичного волокна. Виконано аналiз перерозподiлу енергiї за рахунок геометричної нестиковки волокон в точках їх з'єднання. Для синтезу аналiтичних моделей використано апарат теорiї вiрогiдностi i теорiї перетворення Фур'є. В якостi мiри тривалостi сигналу на сторонi приймача використовується ефективна тривалiсть iмпульсу. Чисельний аналiз дозволив зробити висновки, що дослiджуванi ефекти практично не залежать вiд початкової форми оптичного сигналу i вiд варiанту розподiлу будiвельних довжин вздовж лiнiї регенерацiйної дiлянки. Отриманi оцiнки дозволяють стверджувати, що можливi дисперсiйнi ефекти, якi викликанi перерозподiлом енергiї в точках з'єднання оптичних волокон. Данi ефекти обумовленi рiзницею групових швидкостей в рiзних середовищах оптичного волокна (в серцевинi i в оболонцi). По своєму впливу на форму сигналу вони можуть бути порiвнянi з добре вивченими ефектами за рахунок матерiальної, хвилевiдної та iнших видiв дисперсiї. На основi виконаних дослiджень висунута наукова гiпотеза про iснування ефекту дисперсiї, що викликана рознiмними i нерознiмними з'єднаннями оптичних волокон. Обґрунтовано схему лабораторної установки для виконання натурних дослiджень передбачуваних ефектiв. Особливiсть даної установки в тому, що точки з'єднання оптичних волокон можуть розташовуватись з практично довiльним кроком. Це дозволяє виконати перевiрку висунутих гiпотез в лабораторних умовахКлючовi слова: загасання в мiсцi з'єднання, оптичний сигнал, групова швидкiсть, ефективна тривалiсть iмпульса UDC 621.391.6
The article is devoted to the development of methods for improving the spectral efficiency of fiber-optic transmission systems in terms of optimizing signals in a narrowband channel. The channel width is conventionally taken in the range of 50-100 GHz. The following conditions are also considered to be fulfilled: the signal at the input has approximately circular polarization; the instantaneous power of the signal is relatively small, which makes it possible to neglect nonlinear effects such as four-wave mixing or phase self-modulation; the fiber profile in the refractive index is strictly stepped; fiber operates in single mode; the core material is an isotropic medium; the dependence of the attenuation coefficient in the frequency in the considered range can be considered a constant function. Thus, the considered model of signal transformations in a fiber is reduced to its deformation due to material dispersion. The leading optimization criterion is the minimum of the reduced base. This concept was introduced earlier in the works of the authors. This criterion requires minimizing the product of the effective spectral width on the transmission side by the effective signal duration on the receiving side. The solution of the problem in general form is given-in the formulation of the isoperimetric problem of the calculus of variations. It is shown that the solution of the optimization problem by the minimum criterion of the reduced base can be reduced to the problem of optimizing the signal base in the classical sense. A general solution of the isoperimetric problem is given as functions of a parabolic cylinder. Also presented are particular solutions of the optimization problem on parametric families from the Nyquist pulse class. The obtained solutions show that the optimal values of the variable parameters practically do not depend on the carrier frequency and on the length of the regeneration section. This allows the extension of the optimal solutions obtained for a single narrowband channel to the case of multichannel fiber-optic transmission systems using frequency (spectral) multiplexing.
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