Optical Amplifiers and Line Spans

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Optical Amplifiers and Line Spans
Josef Vojtech CESNET Czech Republic www.ces.net
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Overview

• Optical Amplifiers
• Optical Amplifiers in General
• Optical Fibre Amplifiers, EDFAs
• Ramans
• SOAs
• Amplifiers for (D)WDM
• Line Spans
• Single Span
• Multi Span

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Optical Amplifiers in General

• Ideal Optical Amplifier (OA)
• Large bandwidth
• High gain, polarization independent
• High output power
• Adds no noise
• Basic types of OA (according principle)
• Optical fibre amplifiers
• Raman OA
• Semiconductor OA (SOA)

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Optical Fibre Amplifiers

• Active environment special fibre doped with one
  or more rare earth element (Er, Nd, Pr, Tm,
  Te,or combination Er/Yb, Tm/Yb,..)
• PDFA
• Pr doped, suitable for (1280-1340nm)
• Ggt30dB, Pout gt16 dBm, NF lt7dB
• TDFA
• Tm doped, suitable for (1440-1520nm)
• Ggt30dB, Pout gt20 dBm, NF lt7dB

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Erbium-Doped Fiber Amplifiers

• Most widespread in telecommunications
• Suitable for C band (lowest fiber attenuation)
• common silica glass
• Advantages
• Operating range in 1520-1610nm
• Ggt45dB, Pout gt37 dBm, NF in lt3.5,7gtdB
• Multi-channel crosstalk very low
• Polarization independent
• Disadvantages
• Not small devices, cannot be integrated with
  other semiconductors
• Gain spectrum not inherently flat

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Raman Amplifiers

• Based on simulated Raman scattering, active
  environment common (non- doped) fiber
• G in lt10,15gt dB, Pout gt30 dBm, NF lt 1 dB
• Advantages
• Usable in 1250-1650 nm regions
• Bandwith can be tailored (1 pump 35nm, more pump
  up to 90nm)
• Lower NF than EDFA
• High process efficiency in DCF (loss -gt gain)
  component
• Disadvantages
• Higher interchannel crosstalk than EDFA
• High pump powers (safety issues)

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Semiconductor Optical Amplifiers

• Based on conventional laser principle, active
  environment waveguide region sandwiched between
  n and p regions
• Ggt25dB, Pout gt15 dBm, NF in lt7,10gtdB
• Advantages
• Usable in 1310 1550 nm regions
• Wide band (40-80nm)
• Small compact semiconductors, easy to integrate
• Disadvantages
• Higher NF than EDFA
• Higher interchannel crosstalk than EDFA
• Polarization sensitive

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Spectral usability of Amplifiers
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Amplifiers for (D)WDM

• EDFA needs gain flattening
• Glass composition (F, Te glass host)
• Single stage EDFA, silica host bandwidth 15nm
• Single stage EDFA, fluoride host bandwidth 25nm
• Equalizers
• Two stage, silica or fluoride host, no gain
  flattening 30nm
• Two stage, silica host, gain flattening 50nm
• Two stage, tellurite host, gain flattening 80nm
• Hybrid OA
• Multi-arm - two band operation, silica host 85nm

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Amplifiers for (D)WDM

• Hybrid EDFA/Raman
• Bandwidth can be tailored 80nm
• Lower NF than EDFA separate

Signal power in periodically amplified system.
Comparison between original (EDFA system) and
hybrid system
OSNR improvement
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Line Spans

• Main Length limitations
• Fiber attenuation
• Chromatic dispersion
• Polarization-mode dispersion
• Other penalties
• OSNR (esp. for amplifier cascades)
• Crosstalk
• Fiber nonlinearities (limitation on max transmit
  power per channel)
• Stimulated Raman and Brillouin scattering
• Four-wave mixing, Self-phase mudulation,
  cross-phase modulation

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Single span
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Multi span
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Bibliography

• Ramaswami R., Sivarijan K.N., Optical Networks,
  2nd edition, 2002.
• Agrawal G.P., Fiber-Optic Comminications
  Systems, 2002.
• Islam M.N.,Raman Amplifiers for
  Tellecomunication 1,2, 2004.
• Becker P.C., Olsson N.A., Simpson J.R.,
  Erbium-Doped Fiber Amplifiers, 1999

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Amplifier Examples
EDFA
Raman
SOA
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Thank you for your attention! Questions?