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

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

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  1. 16.711 Lecture 9 Optical Fiber Amplifier – PDL, Transient, Cross-talk Last Lecture • Amplifier Noise • OSNR and BER • System Applications

  2. 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

  3. 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

  4. 16.711 Lecture 9 Optical Fiber Amplifier – PDG, Transient, Cross-talk Polarization Dependent Gain (PDG) • PDG and input signal Power

  5. 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

  6. 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:

  7. 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

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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:

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