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 Where the PDG originates? Polarization Dependent Gain (PDG) (1) Polarization difference between Maximum ASE and the signal (2) Polarization difference between pump laser and the signal PDG ~ 0.01dB PDG ~ 0.05dB Why PDG is important?

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

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 ps ms

8. 16.711 Lecture 9 Optical Fiber Amplifier – PDG, Transient, Cross-talk Transient effect Population density of the upper level response only to the average signal power for bit rate >10Kb/s.

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: Total ASE power: R is the resistance of the detector load resistor.