The article examines the development of methods of one to increase the spectral efficiency of the fiber optic systems of transmission. The essence of the method is shown with the use of alphabet as signals with peak modulation and frequency manipulation. On the receiving side, such signals are distinguished by successive application of selective operations on the frequency subcarrier and spectral analysis of the low-frequency envelope of the signal. A short optical pulse with duration of 3-10 ps with a given shape of the low-frequency envelope is formed on the transmitting side. In order to form such a pulse the method of approximation of a given function with a weighted sum of short pulses of duration about 100 fs is used. With such short functions, it is proposed to use laser pulses in the mode-locking mode. Such pulses have a sufficiently short duration and are approximately Gaussian. To form the output signal, a single laser pulse is divided into several directions (about 100). Further in each direction, the pulse is amplified (or attenuated) in accordance with the necessary amplitude of the readout. In each direction the pulse is then delayed by the necessary time in the delay line. The output signals from the delay lines are summed and transmitted to the input of the trunk optical fiber. It is shown that this method can be implemented using existing technologies. As a problematic part the creation of a system of delay lines with slightly different delay time is considered. The time difference step is approximately 100 fs. As a method of manufacturing such systems of delay lines, it is proposed to use optical fibers of the same length with a slightly different composition of alloying additives. This method allows regulating the difference in group velocities (group refractive indices) with sufficient accuracy and provides the necessary accuracy of the delay step of the initial pulse. The performed calculations show that the use of the proposed methods makes it possible to substantially increase the throughput of fiber-optic transmission systems using modern technologies for manufacturing optical components.

national academy of telecommunications, Odessa, Ukraine Background. Increasing the spectral efficiency of fiber-optic transmission systems (FOTS) is a topical problem. Currently used single-wave FOTS on the basis of equipment type STM allow the transfer of data at rates up to 40 Gbit/s. Given the available optical bandwidth of approximately from 175 THz till 375 THz, the bandwidth of the possible transmission band is about 200 THz. The value of the spectral efficiency index is about 0.005 bits/Hz. Usage of DWDM systems with widely spaced carriers allows increasing the spectral efficiency approximately an order of magnitude, which in principle does not solve the initial problem. Experimental developments are known in which the transmission rate is reached up to 160 Tbit / s. A special optical fiber with 348 transparency windows is used. The spectral efficiency of such systems reaches unity. The problem with the widespread use of such systems is the need to replace an already mounted optical cable. For comparison, in industrial mobile communication systems, the spectral efficiency is of the order of 0.5 till 5 bits / Hz. Objective. Development of theoretical ideas on the formation methods of optical signals with a given structure that allows increasing the bandwidth of FOTS taking into account the dispersion factors and the dependence of the attenuation coefficient on the frequency. These theoretical studies have the ultimate goal of increasing the spectral efficiency of the FOTS using the existing cable infrastructure. Methods. The formation of a low-frequency component of an optical signal with a given shape under conditions when the basic optical pulses are formed by a pulsed laser in the state of locking mode. In this case, the spectral composition of the optical signal can be formed in such a way as to balance the effects of dispersion and distortion of the spectrum due to the dependence of the damping coefficient on the frequency. Results. The theoretical substantiation of the principle possibility of approximating processes of a certain form by a sequence of Gaussian pulses is given. Convergence estimates of the corresponding functional series are obtained. The results are valid for narrowband transmission channels with a width of the order of 100 GHz and for the length of the regeneration sections of the order of 100-300 km. Conclusions. There is a fundamental possibility of short optical signal generation with a given shape using Gaussian impulses. Pulses of approximately Gaussian shape give the laser in the state of locking mode.

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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