Regional Optical Networking Workshop

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Regional Optical Networking Workshop

• Technical Design Elements
• And Test Equipment

Steve Cotter Internet2 / National
LambdaRail scotter_at_internet2.edu
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Technical Design Elements Terminology

• Decibels (dB) used for power gain or loss
• Decibels-milliwatt (dBm) used for output power
  and receive sensitivity
• Attenuation loss of power in dB/km
• Chromatic dispersion spreading of the light
  pulse in ps/nmkm
• Bit Error Rate (BER) typical acceptable rate is
  10-12
• Optical Signal to Noise Ratio (OSNR) ratio of
  optical signal power to noise power for the
  receiver
• ITU Grid Wavelength standard for the lasers in
  DWDM systems

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Technical Design Elements Optical Budget

• Optical budget Output power Input sensitivity
• Optical budget is affected by
• Fiber attenuation
• Splices
• Patch panels / connectors
• Optical components (filters, amplifiers, etc.)
• Bends in the fiber
• Contamination (dirt, oil, etc.)

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Technical Design Elements Power Penalties

• Penalty Ranking
• Fiber loss (attenuation)
• Splices
• Connectors
• Dispersion Penalties
• Fiber Nonlinearities Penalties
• Component / Fiber Aging Penalties
• Transforms the signal
• from this
  to this

High to Low
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Technical Design ElementsPenalties

• Attenuation pulse amplitude reduction limits
  how far
• Chromatic Dispersion spreading of the pulse from
  different colored light traveling at different
  speeds within the fiber
• Polarization Mode Dispersion spreading of the
  light pulse from fast and slow axes having
  different group velocities

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Technical Design ElementsChromatic Dispersion

• Higher bit-rates and shorter pulses are affected
  by chromatic dispersion more
• Limits how fast and how far
• Combat CD by using DSF and NZDSF or dispersion
  compensators

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Technical Design ElementsDispersion Compensation

• How far can I go without dispersion compensation?
• Distance (Km) Specification of Transponder
  (ps/nm)
• Coef.of Dispersion of
  Fiber (ps/nmkm)
• A receiver with dispersion tolerance of 3400
  ps/nm is sent across a standard SMF-28 fiber
  which has a Coefficient of Dispersion of 17
  ps/nmkm.
• It will reach 200 Km at maximum bandwidth.
• (Note that lower speeds will travel farther.)

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Technical Design ElementsPolarization Mode
Dispersion

• Caused by ovality of the core due to
• Manufacturing process
• Internal stress (cabling)
• External stress
• Only discovered in the 90s
• Most older fiber not
• characterized for PMD
• Weaker phenomenon than CD but of relevance at bit
  rates of 10 Gb/s and greater

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Technical Design ElementsNonlinear Effects

• Not a problem with lower power settings
• Nonlinear
• Four-wave mixing
• Self-phase modulation
• Cross-phase modulation
• Stimulated scattering
• Raman
• Brillouin

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Technical Design ElementsFiber Types

• SMF (standard, 1310 nm optimized, G.652)
• Most widely deployed so far, introduced in 1986,
  cheapest
• Corning SMF-28
• Corning SMF-28e is considered extended band
  fiber optimized for CWDM
• DSF (Dispersion Shifted, G.653)
• Intended for single channel operation at 1550 nm
• Corning DSF
• NZDSF (Non-Zero Dispersion Shifted, G.655)
• SMF/LS (limited slope) fiber from Corning
• Later fiber types are engineered for WDM
  operation in the 1550 nm region only
• TrueWave, FreeLight, LEAF, E-LEAF, TeraLight
• These are the latest generation fibers developed
  in mid 90s
• For better performance with high capacity DWDM
  systems
• Optimized for DWDM in the C-band L-band
• MetroCor, WideLight are other types
• Low PMD ULH fibers are also out there

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Technical Design ElementsFiber Table

• The primary difference in these fiber types is
  their chromatic dispersion characteristics

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Test EquipmentBuy or Rent

• Optical Time Domain Reflectometer
• Measure attenuation along span
• Can be used to troubleshoot fiber cuts
• Optical Spectrum Analyzer
• Display and measure the power levels of all the
  lambdas on the fiber
• Helps ensure waves are balanced
• Consider purchasing two
• Want one with at least 2 nm sensitivity
• Bit Test Set
• Perform packet loss test to determine your BER
• We require a 24 hour test before accepting
  circuits
• 1310nm / 1550nm Light Source
• Optical Power Meter
• Chromatic Dispersion test set
• SONET / GE / 10GE test sets

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