Потери в оптическом волокне
Потери в оптическом волокне
Окна прозрачности
Потери в оптическом волокне
Потери на изгиб
Глобальная волоконно-оптическая сеть
Базовые конфигурации оптических сетей
Точка – точка (Point – to – point) |
Дерево (Hub) |
Шина (Bus)
Кольцо (Ring)
Звезда(Star)
Сигналы в оптических телекоммуникациях
Сигналы в оптических телекоммуникациях
Форматы модуляции
Electric field of optical carrier: E(t) = êAexp(jwt+f)
Polarization Amplitude
Frequency |
Phase |
•One or more field properties can be modulated to carry information. Example:
–On-off keying (OOK): binary amplitude modulation
–Binary DPSK, Quadrature DPSK : phase modulation
–Quadrature Amplitude Modulation (QAM): amplitude and phase modulation
Сигналы в оптических телекоммуникациях
Амплитудная модуляция OOK System:
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E(t) |
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Es (t) n(t) |
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Laser |
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Optical |
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Mod. |
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filter |
Electrical |
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Non-return-to- zero (NRZ) OOK
Signal Return-to-zero
OOK Signal
E(t)
1 0 1 1
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t
Symbol constellation for OOK
Im{E}
Re{E}
01
Bit set {0, 1} symbol set {0, 1}.
One symbol transfers one bit information.
Easy to modulate and detect.
Detected Signal:
i Es n 2 Es 2 2 Re(Es n* ) n 2
Probability
density function of i
i
0 
1
Сигналы в оптических телекоммуникациях
Двоичная фазовая модуляция |
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2-DPSK System: |
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E(t) |
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Differential |
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Optical |
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Encoder |
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Mod. |
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Filter |
Es Interferometer |
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E(t) |
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Bit set {0, 1} symbol set {-1, 1} i.e. {ej , ej0} |
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NRZ-2-DPSK |
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One symbol transfers one bit information |
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signal |
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E(t) |
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Bit 0: leave phase alone, bit 1: introduce a |
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RZ-2-DPSK |
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phase change |
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signal |
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t |
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(t T ) 2 |
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(t T ) 2 |
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(t) E |
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(t) E |
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Im{E} |
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constellation |
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Re{E} |
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