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16.711 Lecture 9 Optical Fiber Amplifier – PDL, Transient, Cross-talk. Last Lecture. Amplifier Noise OSNR and BER System Applications . 16.711 Lecture 9 Optical Fiber Amplifier – PDG, Transient, Cross-talk. Today. Polarization dependent gain (PDG) ASE induced Time Jitter

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slide1

16.711 Lecture 9 Optical Fiber Amplifier – PDL, Transient, Cross-talk

Last Lecture

  • Amplifier Noise
  • OSNR and BER
  • System Applications
slide2

16.711 Lecture 9 Optical Fiber Amplifier – PDG, Transient, Cross-talk

Today

  • Polarization dependent gain (PDG)
  • ASE induced Time Jitter
  • Cross-talk, spectral hole burning and gain clamping
  • Transient
  • Amplifier Examples
slide3

16.711 Lecture 9 Optical Fiber Amplifier – PDG, Transient, Cross-talk

Polarization Dependent Gain (PDG)

  • Why PDG is important?
  • Where the PDG originates?

(1) Polarization difference between Maximum ASE and the signal

PDG ~ 0.01dB

(2) Polarization difference between pump laser and the signal

PDG ~ 0.05dB

slide4

16.711 Lecture 9 Optical Fiber Amplifier – PDG, Transient, Cross-talk

Polarization Dependent Gain (PDG)

  • PDG and input signal Power
slide5

16.711 Lecture 9 Optical Fiber Amplifier – PDG, Transient, Cross-talk

Polarization Dependent Gain (PDG)

  • Solution to reduce PDG: Polarization scrambling
  • Improve Q factor by 2dB
slide6

16.711 Lecture 9 Optical Fiber Amplifier – PDG, Transient, Cross-talk

ASE induced time jitter

  • What is time jitter?
  • Why time jitter is important?
  • ASE induced time jitter

(1) ASE generated carrier density fluctuation

(2) Index change due to the carrier density fluctuation --- time jitter

  • Analysis is complex, approximately:
slide7

16.711 Lecture 9 Optical Fiber Amplifier – PDG, Transient, Cross-talk

Transient effect

  • Two important time scales in Optical amplifier:

(1) Stimulated emission: ~ ps

(2) Carrier life-time at energy level ~ ms

ms

ps

slide8

Population density of the upper level

  • response only to the average signal power for bit rate >10Kb/s.

16.711 Lecture 9 Optical Fiber Amplifier – PDG, Transient, Cross-talk

Transient effect

slide9

16.711 Lecture 9 Optical Fiber Amplifier – PDG, Transient, Cross-talk

Transient effect

  • Change of population density of the upper level
  • takes ~ 1ms to settle down.
slide10

16.711 Lecture 9 Optical Fiber Amplifier – PDG, Transient, Cross-talk

Transient effect

  • Ways to reduce the Transient effect.

(1) Pump feedback to keep constant population density

(2) Gain clamping, --- keep the constant input power.

slide11

16.711 Lecture 9 Optical Fiber Amplifier – PDG, Transient, Cross-talk

Cross-talk, multi-channel amplifying

  • Any multi-channel cross-talk when all channel present?
  • Why not, (valid Only for EDFA) ?
  • Cross-talk when a channel is turned on and off.
slide12

16.711 Lecture 9 Optical Fiber Amplifier – PDG, Transient, Cross-talk

Examples

  • Preamp --- receiver sensitivity improvement by EDFA:
  • Preamp --- receiver sensitivity improvement not valid for Pin arbitrary small.
slide13

16.711 Lecture 8 Optical Fiber Amplifier – noise and BER

Receiver noise

Total photo-detector current:

R is the resistance of the detector load resistor.

Total ASE power: