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TRANSCRIPT
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1 2006, Cisco Systems, Inc. All righ ts reserved. Fiber in DWDM Networks
2006 Cisco Systems, Inc. All rights reserved. DWDM Elements 1
Module 3: Fiber in DWDM Networks
CA E-Service Training
Instructor: Lito Pamintuan, Technical Program Manager for Cisco Systems.
This module, Fiber in DWDM Networks, is the last of the three modules on the subject ofDWDM.
Revision 1.0
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2 2006, Cisco Systems, Inc. All righ ts reserved. Fiber in DWDM Networks
2006 Cisco Systems, Inc. All rights reserved. DWDM Elements 2
Module Objectives
Identify:
Causes, effects, and characteristics of chromatic dispersion
and polarization mode dispersion Types of non-linear effects and means of resolving them
The fiber type that is suitable for DWDM applications
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Agenda
Chromatic Dispersion and Polarization Mode
Dispersion (PMD)Fiber Non-Linear Effects
Self Phase Modulation (SPM)
Cross Phase Modulation (XPM)
Four Wave Mixing (FWM)
Fiber Types and Characteristics
In this module, we will cover the key DWDM impairments for single mode fiber:
Chromatic dispersion
Polarization mode dispersion (PMD)
Fiber non-linear effects such as:
Self-phase modulation (SPM),
Cross-phase modulation (XPM)
Four wave mixing (FWM)
We will end this module by talking about fiber types and fiber characteristics thatcompensate for these impairments.
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Chromatic Dispersion
Caused by different colors of light traveling at different speeds
Results in pulse distortion due to spectral broadening anddispersion power penalty (1-2dB)
Dispersion can be managed with Dispersion Compensation Units(DCUs) to reduce distortion .
In chromatic dispersion, wavelengths travel at different speeds, and light pulses arebroadened. This results in a power penalty between 1 to 2 dB and pulse distortion due tospectral broadening, as shown in the diagram. The slide demonstrates pulses broadeningwhile traveling through fiber. Eventually they will become one pulse, which will causemisinformation at the receiving end.
Chromatic dispersion can be managed with the use of dispersion compensation units to
reduce distortion.
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Polarization Mode Dispersion (PMD)
Different polarization states of a wavelength travel at differentspeeds, causing the pulses to widen at the other end of f iber
Polarization mode dispersion compensation techniques areemerging
n1
n2
n1 > n2
In PMD, different polarization states of a wavelength travel at different speeds. This causesthe light pulses, shown at the lower diagram, to widen while traveling along the fiber.
When two pulses widen and become one pulse, it can cause the receiving end tomisinterpret the information. This problem is more prevalent at higher bit rates because thepulses are narrower. Older fiber is more prone to PMD.
PMD compensation techniques are emerging as faster data rates are being developed.
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Agenda
Chromatic Dispersion and Polarization Mode
Dispersion (PMD)Fiber Non-Linear Effects
Self Phase Modulation (SPM)
Cross Phase Modulation (XPM)
Four Wave Mixing (FWM)
Fiber Types and Characteristics
When many wavelengths are packed in a single fiber for transmission, the light powerincreases, causing non-linear effects such as:
Self-phase modulation (SPM)
Cross-phase modulation (XPM)
Four wave mixing (FWM)
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Self-Phase and Cross-Phase Modulation
Self Phase Modulation (SPM)
An in tense opt ical s ignal modulates the f ibers refract ive index , andtherefore its own phase
Can be mitigated with localized dispersion compensation
Cross Phase Modulation (XPM)
For WDM systems, the adjacent channels modu late the fibersrefractive index, and therefore each others phase
Worsens as channels get closer
Can be mitigated with localized dispersion compensation
High light intensities change the refractive index and lead to:
An induced phase-shift of the traveling wave defined as self-phase modulation, or
A co-propagating wave defined as cross-phase modulation
Both self-phase modulation and cross-phase modulation can be mitigated with localizeddispersion compensation.
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Four Wave Mixing (FWM)
Power(a.u.)
Frequencyf1 f2 f3
f f
f113
f112f123
f223
f132
f221
f332f231
f331
In four wave mixing, high light intensities at different wavelengths interact and generatesignals at other wavelengths, causing the original signals to deteriorate.
The different wavelengths generated by four wave mixing are shown in the slide as blackarrows. Four wave mixing is at its worst when signals are located at the zero-dispersionpoint.
This can be mitigated by introducing a controlled amount of dispersion into the fiber.
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Agenda
Chromatic Dispersion and Polarization Mode
Dispersion (PMD)Fiber Non-Linear Effects
Self Phase Modulation (SPM)
Cross Phase Modulation (XMP)
Four Wave Mixing (FWM)
Fiber Types and Characteristics
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Fiber Type In DWDM
Dispersion-shi fted f iber (DSF) near the 1550nm window
Corning LEAF and Truewave fibers are referred to as Non-zero dispersion shif ted fibers (NZ-DSF)
Fiber Type Loss (dB/km)
Lambda
Zero
Dispersion
(ps/nm*km)
PMD
(ps/km1/2)
SMF-28
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Chromatic Dispersion ofDifferent Fiber Types
Dispersion
nm13101520
1497 1550
SMF-28
TW RS
LEAF
DS
SMF-28 Truewave RS
Corning LEAF
DSF
This graph shows the associated dispersion of the different fiber types.
SMF-28 at 1310nm zero-dispersion point
Truewave RS at 1497nm
Corning LEAF at 1520nm
Dispersion-shifted fiber (DSF) at 1550nm region
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Choosing the Right Fiber for WDM andDWDM Applications
SMF-28
Good for TDM at 1310nm
Bad for TDM at 1550nm
OK for WDM at 1550nm
Dispersion Shifted Fiber (DSF)
Good for TDM at 1550nm
Bad for WDM at 1550nm
NZ-DSF
Good for TDM and DWDM at 1550nm
The difference is in the dispersion characteristics
If you are planning to engineer your network using WDM or DWDM applications, choosethe proper fiber types:
SMF-28 or
NZ-DSF (Corning LEAF or Lucent Truwave RS)
Dispersion shifted fiber (DSF) does not work well with WDM and DWDM applications
although it does work well with single channel wavelength applications like TDM.
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