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A NEW APPROACH IN DETERMINING THE PARAMETERS OF TRANSFER AND IMPACT IN THE OPTICAL TELECOMMUNICATIONS LINE
Portnov Eduard L.,
PHd, MTUCI, Moscow, Russia, [email protected]
Keywords: parameters of transmission and influence, fiber optics, dispersion, nonlinear effects, signal-to-noise ratio.
According to the established decisions in determining the distribution of signals over copper telecommunications lines, it is considered that two large groups of parameters affect the signal transmission: transmission parameters and parameters of influence. It is argued that comparing fiber-optic system and a wired system, you can find a lot in common: line losses - transmission settings, and settings influence a lot: dispersion, bit error ratio, the accumulated jitter, vulnerability, electromagnetic compatibility. It is noted that six of the physical phenomena can affect the signal-to-noise - dispersion - modal noise - the noise power distribution on the modes, frequency chirp,- feedback and noise from reflections, the attenuation of the signal.
The parameters of transmission in the optical transmission systems are their own losses in an optical fiber,which is caused by:-internal losses-losses caused by impurities, and losses caused by Rayleigh scattering, the losses caused by the imperfection of the optical fiber(S).
Speed in the channel S is limited by various physical factors-influence factors: dispersion (chromatic and polarization), nonlinear effects (the effects of Brillouin scattering and the Raman and Kerr effects: self-phase modulation, cross-modulation, four-wave mixing, modulation instability), power, bit rate, number of channels and the modulation format. Changing these parameters leads to increase or decrease the window performance and has a significant impact on the signal-to-noise ratio.
However, existing large differences in the transmission medium metal (copper) communication cables and optical fiber require independent solutions for each of the considered communication media.
Для цитирования:
Портнов Э.Л. Новый подход в определении параметров передачи и влияния в оптических линиях телекоммуникаций // T-Comm: Телекоммуникации и транспорт. - 2016. - Том 10. - №5. - С. 60-63.
For citation:
Portnov E.L A new approach in determining the parameters of transfer and impact in the optical telecommunications line. T-Comm. 2016. Vol. 10. No.5, pр. 60-63. (in Russian)
Fiber optics is becoming the primary means of transmission of information, actively displacing the use of copper cables in all sectors of human life. For the transmission of electric signals over fiber optical fiber use optical transport system. Its components arc electro-optics. Converter as a transmitter of light in the beginning of the line, in fact fiber-optic and electro-optic Converter as a receiver of light at the end of the line. As in the system with metal wires, have terminal devices at the beginning and at the end of the line. Optical and electrical transmission system have the same electrical interfaces. This means that when implementing fiber optic technology achieved an important goal, which primarily facilitates integration into existing networks.
As a method for the transmission of optical fibers is mainly applied in digital technology, as it provides free combination of bit transmission rates of a variety of sources (telephone network, data network, etc.). With the introduction of fiber optic technology analog technology of signal transmission continues to lose its value and is used only for special applications.
Fiber-optic cable line is not only from the signal transmitter, cable and receiver the optical signal, but also from many elements, without which the functioning of the lineage. These include both active and passive elements. The active elements include laser and led light sources are multi-purpose, modulators, photodiodes for various applications, regenerators and amplifiers of different technological solutions with a concentrated and a distributed application. Each device used in the transmission scheme of a light signal, is the source of insertion loss. For example, the optical fibers themselves contribute to the attenuation of 1.5-2.0 dB - S multimode at the wavelength of 0.85 Jim, 0,35-0,4 dB at a wavelength of 1.3 |im, 0,19-0,25 dB at a wavelength of 1.55 jxm,- singlemodc fiber, of 0.4-0.5 dB - connector, weld connection AVAILABLE - 0,05-0,2 dB splitter (2:1) --3 dB splitterf 1:2) - 3dB,a splitter (1:32)-17dB filter - 3 dB[l ]. It will also be a source of reflections, usually characterized by loss. Undoubtedly, the primary medium of transmission of signals is at present an optical fiber, placed in various cable structures.
According to the established decisions in determining the distribution of signals over copper telecommunications lines, it is considered that two large groups of parameters affect the signal transmission: transmission parameters and parameters of influence. Comparing fiber-optic system and a wired system, you can fmd a lot in common: line losses - transmission settings, and settings influence a lot: dispersion, bit error ratio, the accumulated jitter, vulnerability, electromagnetic compatibility.
According to (2) six notes of the physical phenomena that may affect signal/noise: variance, modal noise - the noise power distribution on the modes, frequency chirp, feedback and noise from reflections, the attenuation of the signal.
Losses in an optical fiber caused by: internal losses-losses caused by impurities, and losses caused by Rayleigh scattering, the losses caused by the imperfection of the optical fiber{S).
Losses caused by pure material (silicon) due to the electronic resonance in the UV region for wavelengths X<0.4 pin, and in the infrared region for wavelengths X>7mkm. In the second and third transparency window, this type of absorption is contributing at a level no more than 0.03 dB/km.
Loss on the presence of impurities (iron, copper, Nickel, magnesium, chromium, hydroxy!) depend on their content. The content of these impurities in today S reduced to one-billionth of
a but the effect of hydroxy! IT, which is reduced to one millionth part.
Rayleigh scattering is inversely proportional to the wavelength associated with the temperature of the glass. At wavelengths above 1 600hm dominated by infrared absorption, S imperfection leads to micro and macro bending. Parameters of influence are manifested in the form of: dispersion-polarization effects-nonlinear effects.
Dispersion is manifested in the broadening of the pulse during its propagation on EA. It is called:-modal dispersion,-chromatic dispersion determined by the dispersion material and waveguide component PMD,-polarization mode dispersion.
Modal dispersion in multimode is determined by S, in which D=2a is the core diameter of S is considerably greater than the wavelength A, and the number of modes detected at
M - V2/2 where V = (2n:a/X) V n,2. N;2 - normalized frequency.
When V < 2,405 on EA applies one fashion. In chromatic dispersion of the overwhelming importance of material dispersion. Material dispersion DM is caused when different wavelengths pass through certain materials at different speeds: N = c/v.
Material dispersion - dispersion, correlated with the dependence of the wavelength from the refractive index of the material from which it is formed S. In S in the transparency band 850nm longer waves propagate faster than short (Vl(850nm) > V2(835 hm)), and in the transparency window of 1550 nm: (Vl(1535 hm) > V2(1560hm)). In the transparency band, 1310nm at Xzd, above which DM is positive, and below Xzd - negative is defined as the wavelength Xzd zero variance. For pure Si02 Xzd = 1276 hm (it can vary 1270-1290 hm for S, the core and the cladding of which is doped to obtain the desired refractive index).
Waveguide dispersion shifts the wavelength of zero dispersion of 30-40 nm so that the total dispersion is zero near 1310 nm industrial S for. In fact, chromatic dispersion is expressed as: Dxn = DM + DB pe/nm.km
If the criteria for V.AT <1 for NRZ modulation format At < Tbit and B. L. D.AX < 1 where AT = L. D.AX.
Here AT is the time interval, and AX is the equivalent spectral width of the impulse.
Chromatic transmission line sensitive: to increase the length of the line, to increase the transfer rate.
For systems WDM for chromatic dispersion are influenced by: increasing the number of channels is the reduction of spacing between channels.
The influence of the chromatic dispersion decreases with decreasing of parameter D and for compensating chromatic dispersion.
Polarization mode dispersion is manifested in singlemodc fiber due to imperfections AVAILABLE.S operates in a singlemode fashion HE11, and taking into account the linear polarization there are two mutually orthogonal fashion.
The main problem with PMD in optical liber systems is its stochastic nature, namely, the principal slate polarization (PSP) and the DGD varies on a time scale from milliseconds (acoustic vibrations) to months (temperature changes underground fiber). Rare extremely high values of DGD prohibits designing systems based on worst case allocation of fixed OSNR reserves to provide for all possible PMD caused signal distortion. Instead, in the system are assigned some reasonable reserves (for example,
1 dB), and rare when DGD exceeds supply, leading to system failure. The proper definition of the probability of failure is an important link between fiber manufacturers, system integrators and serv ice providers. If the lack of failures cannot be answered, we need to compensate for the PMD in each channel in the receiver or increase the tolerance to PMD of the corresponding modulation formal using optical or electronic methods to compensate or mitigate.
The impact of PMD increases:-with increasing transmission speed in the channel, with increasing numbers of channels-with increasing length of span.
It is established that in systems with amplifiers and long spans using polarization scrambler (the device for forcibly modulating the polarization state of the laser signal so that it seemed to be unpolarized) PMD causes an increase in the degree of polarization of such signal. It degrades the system performance due to the interaction of the losses due to polarization and the polarization failure of the amplification. In analog systems, the interaction of the losses and modal dispersion with a laser chirp leads to a distortion of the second order, proportional to the frequency modulating Further deterioration from the effects of the second order, independent of the modulation frequency occurs in the presence of additional losses due to polarization. The effect of the second order combines chromatic and polarization mode dispersion,, as the differential group delay depends on wavelength and the statistical contribution to chromatic dispersion.
Nonlinear effects manifest themselves in the form of:-nonlinear effects associated with effects of scattering (Brillouin and Raman), the Kerr Effects: phase self-modulation, Cross-phase modulation, four-wave mixing, modulation instability and soliton formation.
These effects are determined by the following parameters S and signai: dispersion characteristics of S, an Effective area of the core S, the number of channels and spacing between them, full span length, the signal intensity and width of the emitted spectral line
Of all nonlinear effects stimulated Brillouin scattering has the lowest threshold power and therefore limits the transmitted optical power in the fiber.
Stimulated Raman scattering has a higher threshold power than the Brillouin scattering and the emission of light is shifted into the region of lower frequencies with a wider band. Thus there is a redistribution of power from high in long waves channels. This effect is used as the amplification systems WDM.
The Kerr effect is manifested in the change of refractive index under the action of the square of the electric field.
When the output level of the source becomes large, the signal modulates its own phase. This leads to a broadening of the transmitted pulse and the temporary expansion or contraction of the signai, depending on the sign of chromatic dispersion. This leads to the shift of the pulse from in the direction of long waves and the cutoff of the pulse at shorter wavelengths. In systems WDM with small channel spacing, the spectral broadening under the action of modulation may cause interference between the channels (cross-modulation). This effect can be managed by compensation of dispersion, f or long lines are a limitation self-phase modulation, cross-modulation and four-wave mixing generating a signal distortion and a transient conversation that can't be removed on the receiver. Chromatic dispersion and PMD generate inter-symbol distortion. The parameters D (PS/nm.km),
S (PS/nm2.km), Aeff (pm2) and the spectral transmission loss (dB/km) can be optimized for specific system architectures. Nonlinear distortion reduces the signal-to-noise ratio at the receiver. Nonlinear transient conversation can increase Renal and get the desired value of the ratio signal/noise. n2, D, Aeff determine the nonlinear transient conversation is created for the required distances between the channels DWDM system, y - 27C.n2AA3$4> (1/W.km)
Using transmission speeds from 10 Gb/s transfer rate 40 Gb/s requirements OSNR is increased by 6 dB, PMD increases 4 times, the impact of chromatic dispersion increases 16 times, increasing the impact of nonlinear effects. Nonlinear effects limit the transmission and depend on several factors: transmission speed, optical power, optical fiber, modulation format.
To reduce or limit this effect by choosing S, the choice of modulation format, optical phase configuration, dispersion, solution, electronic equipment. It should be noted that the BER increases with the increase type in AVAILABLE capacity due to the nonlinearity of the OSNR.
The level of FWM depends from the increase in optical power in the channel, to increase the number of channels, to reduction of the spacing between channels, to reduce the absolute value of the chromatic dispersion.
Modulation instability (Ml) leads to the transformation of a continuous signal in the modulated structure in the regime of anomalous dispersion. The frequency shift and amplification of the sidebands determine the intensity of the original wave, as well as the dispersion and nonlinear coefficientsOSNR, MI can be considered as a particular case of FWM where 2 of the input photon signal converted into 2 photons with different frequencies. Ml can reduce the signal-to-noise ratio. Application filters or self-filtration in systems of large extent solves the problem. Management of dispersion and reduction of the power level, the use of lasers with external modulation also result in a reduction of MI.
Presented on the bases of known solutions for copper cables definitions for transfer parameters and the influence of the optical fibers enables to assess the contribution of each component in the signal-to-noise ratio in transmission systems and use new solutions.
References
1. G.Agr&wal. Nonlinear fiber optics. M. MIR, 1996. 323 p.
2. P.Freeman. Fibcr-optic communication systems. M, Tec lino-sphere, 2003. 440 p.
3. I.P. Kaminow, T.L. Koch. Optical fiber Telecommunication 111A. Academic Press 1997. San Diego. 595 p.
4. G.P. Agrawal. Fibcr-optic communication systems. Sccond edition. John wiley and sons. No. 4. 1997. 555 p.
5. Ivanov A.B. Fiber optics. Components, transmission systems, measurement Systems. M, Syrus, 1999. 627 p.
6. Fibcr-optic technology: current status and prospects. 2nd edition revised and expanded, edited by S.A. Dmitriev, N.N. Slepov. Moscow. LLC "Fiber optic technology", 2005. 575 p.
7. Portnov E.L. Principles of construction of primary networks and optical cable lines. M. 1 lot line Telecom, 2009, 544 p.
8. Portnov E.L. Optic cables and passive components of the communication lines, M. Hot line - Telecom, 2007, 464 p.
9. Portnov E.L Optic communication cables, installation and measurement Textbook for high schools. - M,: Hot line-Telecom, 2012.448 p.
T-Comm Том 10. #5-2016
PUBLICATIONS IN ENGLISH
НОВЫЙ ПОДХОД В ОПРЕДЕЛЕНИИ ПАРАМЕТРОВ ПЕРЕДАЧИ И ВЛИЯНИЯ В ОПТИЧЕСКИХ ЛИНИЯХ ТЕЛЕКОММУНИКАЦИЙ
Портнов Эдуард Львович,
Московский технический университет связи и информатики, зав. кафедрой НТС, д. т. н., профессор,
Москва, Россия, [email protected]
Аннотация
Согласно установившимся решениям, принятым в определении распространении сигналов по медным телекоммуникационным линиям, принято считать, что две большие группы параметров оказывают влияние на передачу сигналов: параметры передачи и параметры влияния. Утверждается ,что сравнивая волоконно-оптические системы и проводные системы, можно найти много общего: потери в линии - параметры передачи, а параметров влияния достаточно много: дисперсия, коэффициент битовой ошибки, накопленный джиттер, незащищенность, электромагнитная совместимость. Отмечается,что шесть физических явлений могут повлиять на отношение сигнал/шум: дисперсия, модовый шум, шум от распределения мощности по модам, частотный чирп, обратная связь и шум от отражений, коэффициент ослабления сигнала. К параметрам передачи в оптических системах передачи относятся собственные потери в оптическом волокне,которые вызваны: собственными внутренними потерями,-потерями, вызванными примесями, потерями, вызванными рассеянием Релея, потерями, вызванными несовершенством оптического волокна(ОВ).
Скорость в канале ОВ ограничена различными физическими факторами-факторами влияния: дисперсией (хроматической и поляризационной), нелинейными эффектами (эффекты рассеяния Бриллюэна и Рамана, эффектами Кер-ра: самофазовой модуляцией, кросс-модуляцией, четырехволновым смешиванием, модуляционной неустойчивос-тью),мощностью, битовой скоростью, числом каналов и форматом модуляции. Изменение этих параметров приводит к увеличению или уменьшению окна работоспособности и оказывает значительное влияние на отношение сигнал/шум. Вместе с тем, существующие большие отличия в среде передачи металлические (медные) кабели связи и оптические волокна требуют независимых решений для каждой из рассматриваемых сред передачи.
Ключевые слова: параметры передачи и влияния, волоконная оптика, дисперсия, нелинейные эффекты, отношение сигнал/шум.
Литература
1. Г.Агравал. Нелинейная волоконная оптикаю М.: МИР, 1996, 323 с.
2. Р.Фриман. Волоконно-оптические системы связи. М.: Техносфера, 2003, 440 с.
3. I.P. Kaminow, T.L. Koch. Optical fiber Telecommunication IIIA. Academic Press 1997. San Diego. 595 p.
4. G.P. Agrawal. Fiber-optic communication systems. Second edition john wiley and sons. №4. 1997, 555 p.
5. Иванов А.Б. Волоконная оптика. Компоненты, системы передачи, измерения. М.: Syrus Systems, 1999, 627 с.
6. Волоконно-оптическая техника: Современное состояние, перспективы. 2-ое издание переработанное и дополненное, под редакцией Дмитриева С.А. и Слепова Н.Н. М.: ООО "Волоконно-оптическая техника", 2005. 575 с.
7. Портнов ЭЛ. Принципы построения первичных сетей и оптических кабельных линий. М. Горячая линия - Телеком 2009, 544 с.
8. Портнов Э.Л. Оптические кабели и пассивные компоненты линий связи. М.: Горячая линия - Телеком, 2007. 464 с.
9. Портнов Э.Л. Оптические кабели связи, их монтаж и измерение. Учебное пособие для вузов. М.: Горячая линия-Телеком, 2012. 448 с.
T-Comm Vol.10. #5-2016
