Effects of EDFA Gain on RF Phase Effects of EDFA Gain on RF Phase Noise in a WDM Fiber Optic LinkNoise in a WDM Fiber Optic Link

John Summerfield , Mehdi Shadaram, and Jennifer BrattonJohn Summerfield , Mehdi Shadaram, and Jennifer BrattonPhotonics Research LaboratoryPhotonics Research Laboratory

Department of Electrical and Computer EngineeringDepartment of Electrical and Computer EngineeringUniversity of Texas at San Antonio University of Texas at San Antonio

IEEE MILCOM 2006IEEE MILCOM 2006Washington, D.C.Washington, D.C.

OutlineOutline

Transmission of Reference Signals via Transmission of Reference Signals via Optical FibersOptical Fibers

Noise SourcesNoise Sources Phase NoisePhase Noise Link Under InvestigationLink Under Investigation ResultsResults

RF Transmission via Optical FibersRF Transmission via Optical Fibers

Phased Array Antenna Phased Array Antenna Reference Signals for Timing and Reference Signals for Timing and

SynchronizationSynchronization Doppler RadarDoppler Radar CATVCATV Passband Signal TransmissionPassband Signal Transmission

Noise SourcesNoise Sources

•Optical Transmitter•Fiber Cable•Optical Amplifier•Photo Receiver

Phase NoisePhase Noise

Power Spectral Density

fc fc+fm

Frequency

C

SSBm P

PfS log10)(

dBc/Hz

PC (W)

PSSB (W/Hz)

What Causes Phase Noise?What Causes Phase Noise?

Temperature fluctuation of the linkTemperature fluctuation of the link Fluctuation of longitudinally applied stressFluctuation of longitudinally applied stress Relative intensity noise of the laserRelative intensity noise of the laser Back reflections in the cableBack reflections in the cable Bias fluctuations of the photodiodeBias fluctuations of the photodiode Bias fluctuations of either directly Bias fluctuations of either directly

modulated laser or the external modulatormodulated laser or the external modulator Amplified spontaneous emission Amplified spontaneous emission

noisenoise Etc.Etc.

AnalysisAnalysis(Additive phase noise by the optical amplifier)(Additive phase noise by the optical amplifier)

)()cos(2)( tEtGPtE ASEoint io

M

MiASEASE tfifStE

2cos2)(

hfnGS SPASE )1(

Analysis (Cont.)Analysis (Cont.)(Additive phase noise by the optical amplifier)(Additive phase noise by the optical amplifier)

Assume << 1

M

MiicASEocot tfifSGPtGPi 2cos)cos(

Hz

GP

SfS

o

ASE /dB log10)( c

Link Under InvestigationLink Under Investigation

8.8 Km Fiber Link with an EDFA located at 4.4 Km8.8 Km Fiber Link with an EDFA located at 4.4 Km Single Light source operating at 1560nmSingle Light source operating at 1560nm 100MHz RF reference signal100MHz RF reference signal

Link Under Investigation (Cont.)Link Under Investigation (Cont.)

Link Under Investigation (Cont.)Link Under Investigation (Cont.)

EDFA Output Power vs. EDFA GainEDFA Output Power vs. EDFA Gain

11

12

13

14

15

16

27 29 31 33 35 37 39 41 43

EDFA Gain dB

ED

FA

ou

tpu

t P

ow

er d

Bm

Additive RF Phase noise vs. Log Offset Additive RF Phase noise vs. Log Offset FrequencyFrequency

-60

-65

-70

-75

-80

-85

-90

-95

-100

-105

dB

c/H

z

1 10 100 1000Log Offset Freq

Gain EffectsGain Effects

Starting at 44 dB EDFA gain, for every dB Starting at 44 dB EDFA gain, for every dB decrease in optical gain there is a 2 dB decrease in optical gain there is a 2 dB decrease in additive phase noise. decrease in additive phase noise.

Maximum additive phase noise occurs at Maximum additive phase noise occurs at the maximum gain with a value near -65 the maximum gain with a value near -65 dBc/Hz.dBc/Hz.

Decreasing EDFA gain below 33 dB will not Decreasing EDFA gain below 33 dB will not necessarily result in further additive phase necessarily result in further additive phase noise reduction, or will reduce at a noise reduction, or will reduce at a different rate.different rate.

Additive Phase Noise vs. EDFA GainAdditive Phase Noise vs. EDFA Gain

-60

-65

-70

-75

-80

-85

-90

-95

-100

-105

dB

c/H

z

27 29 31 33 35 37 39 41 43 45EDFA Gain dB

Conclusion

In conclusion, the additive phase noise in a In conclusion, the additive phase noise in a link with an EDFA is affected by the gain of link with an EDFA is affected by the gain of the amplifier. In order to increase the the amplifier. In order to increase the phase stability of the link, the EDFA should phase stability of the link, the EDFA should be operated at higher optical input levels. be operated at higher optical input levels. These higher input power levels can be These higher input power levels can be achieved by placing an EDFA as close as achieved by placing an EDFA as close as possible to the transmitter.possible to the transmitter.

ReferencesReferences

M. Shadaram, C. Thomas, J. Summerfeld, P. Chennu, “RF M. Shadaram, C. Thomas, J. Summerfeld, P. Chennu, “RF phase noise in WDM fiber optic links," 7th International phase noise in WDM fiber optic links," 7th International Conference on Transparent Optical Networks, (Barcelona, Conference on Transparent Optical Networks, (Barcelona, Catalonia, Spain, 3-7 July. 2005).Catalonia, Spain, 3-7 July. 2005).

M. Shadaram, V. Gonzalez, J. Ceniceros, N. Shah, J. Myres, M. Shadaram, V. Gonzalez, J. Ceniceros, N. Shah, J. Myres, S. A . Pappert, D. Law, "Phase stabilization of reference S. A . Pappert, D. Law, "Phase stabilization of reference signal in analog fiberoptic links," Proceedings of signal in analog fiberoptic links," Proceedings of International Topical Meeting on Microwave Photonics, International Topical Meeting on Microwave Photonics, (Kyoto, Japan, 1987).(Kyoto, Japan, 1987).

M. Shadaram, J. Medrano, S. A. Pappert, M. H. Berry and D. M. Shadaram, J. Medrano, S. A. Pappert, M. H. Berry and D. M. Gookin, "Technique for stabilizing the phase of the M. Gookin, "Technique for stabilizing the phase of the reference signals in analog fiber-optic links," Applied Optics, reference signals in analog fiber-optic links," Applied Optics, 34, (1987): 8283-8288.34, (1987): 8283-8288.

A. Hajimiri, T. H. Lee., “A general theory of phase noise in A. Hajimiri, T. H. Lee., “A general theory of phase noise in electrical oscillators,” IEEE Journal of Solid-State Circuits, 33 electrical oscillators,” IEEE Journal of Solid-State Circuits, 33 (1998):179-194.(1998):179-194.