Formation the piеcosecond optical pulses of the assigned structure using precision lines of delay

Abstract

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.

Theoretical study of the dispersion effects occurring at optical fiber connections

“…Calculation of values of the group refractive index and the group velocity depending on material and angular frequency by means of the method given in [20,21] are shown in Fig. 1.…”

“…When calculating value of the arctan(φ) function for the upper limit in formula (21), uncertainty of division-by-zero type is obtained. Perform limit transition for the first quadrant to obtain arctan(φ→∞)→π/2.…”

The approximation of optical signals by short laser pulses in the form of a hyperbolic secant

“…На всех этих графиках слева дана аппроксимация во временной обла- Определенную сложность реализации полученных решений представляет необходимость производства системы линий задержки с малым относительным шагом (порядка 100 фс). Возможный метод решения данной задачи дан в статье [7]. Суть метода заключается в том, что линии задержки по рис.…”

“…Определенным ограничением предлагаемых в работах [2][3][4][5] методов является их ограниченная универсальность: они дают хорошие результаты для определенных форм НЧС. Принципиальная возможность аппроксимации произвольной НЧС короткими импульсами лазера гауссовой формы дана в работах [6,7], а в статье [8] дана более общая теория.…”

Phenomenological models of the main characteristics of a step optical fiber

“…Для визначення режиму роботи ОВ важливими є пов'язані з КЗ характеристики [1,2,7,8] характеристики (2) використовуються також для визначення потенціально досяжної швидкості передачі у ВОСП [7]. У роботах [9,10] пропоновані моделі частини характеристик (1) у вигляді ступеневих поліномів залежно від частоти та хімічного складу, а також методики їх структурної та параметричної ідентифікації. В даній роботі пропоновані моделі поширюються також на всю сукупність характеристик (1) та (2) з урахуванням залежності від довжини хвилі.…”