Transcript Effects of EDFA Gain on RF Phase Noise in a WDM Fiber

Effects of EDFA Gain on RF Phase
Noise in a WDM Fiber Optic Link
John Summerfield , Mehdi Shadaram, and Jennifer Bratton
Photonics Research Laboratory
Department of Electrical and Computer Engineering
University of Texas at San Antonio
IEEE MILCOM 2006
Washington, D.C.
Outline
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Transmission of Reference Signals via
Optical Fibers
Noise Sources
Phase Noise
Link Under Investigation
Results
RF Transmission via Optical Fibers
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Phased Array Antenna
Reference Signals for Timing and
Synchronization
Doppler Radar
CATV
Passband Signal Transmission
Noise Sources
•Optical Transmitter
•Fiber Cable
•Optical Amplifier
•Photo Receiver
Phase Noise
Power Spectral Density
PC (W)
PSSB (W/Hz)
fc fc+fm
Frequency
 PSSB 
 dBc/Hz
S ( f m )  10 log 
 PC 
What Causes Phase Noise?
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Temperature fluctuation of the link
Fluctuation of longitudinally applied stress
Relative intensity noise of the laser
Back reflections in the cable
Bias fluctuations of the photodiode
Bias fluctuations of either directly modulated
laser or the external modulator
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Amplified spontaneous emission noise
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Etc.
Analysis
(Additive phase noise by the optical amplifier)
Et (t ) 
2GPin cos( w o t ) + E ASE ( t )
E ASE ( t ) 
M

i- M
2 S ASE d f cos [(w o + 2p i d f )t +  i ]
S ASE  ( G - 1) n SP c hf
Analysis (Cont.)
(Additive phase noise by the optical amplifier)
Assume a<< 1
it  GPoa cos(wct ) + a GPo SASEdf
 (SASE )
S ( f )  10log

 GPo 
dBc / Hz
cos[(w
M
i -M
c
+ 2pidf )t + i ]
Link Under Investigation
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8.8 Km Fiber Link with an EDFA located at 4.4
Km
Single Light source operating at 1560nm
100MHz RF reference signal
Link Under Investigation (Cont.)
Link Under Investigation (Cont.)
EDFA Output Power vs. EDFA Gain
EDFA output Power dBm
16
15
14
13
12
11
27
29
31
33
35
37
EDFA Gain dB
39
41
43
Additive RF Phase noise vs. Log Offset
Frequency
-60
-65
-70
-75
dBc/Hz
-80
-85
-90
-95
-100
-105
1
10
100
Log Offset Freq
1000
Gain Effects
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Starting at 44 dB EDFA gain, for every dB
decrease in optical gain there is a 2 dB
decrease in additive phase noise.
Maximum additive phase noise occurs at
the maximum gain with a value near -65
dBc/Hz.
Decreasing EDFA gain below 33 dB will not
necessarily result in further additive phase
noise reduction, or will reduce at a
different rate.
Additive Phase Noise vs. EDFA Gain
-60
-65
-70
dBc/Hz
-75
-80
-85
-90
-95
-100
-105
27
29
31
33
35
37
EDFA Gain dB
39
41
43
45
Conclusion
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In conclusion, the additive phase noise in
a link with an EDFA is affected by the gain
of the amplifier. In order to increase the
phase stability of the link, the EDFA should
be operated at higher optical input levels.
These higher input power levels can be
achieved by placing an EDFA as close as
possible to the transmitter.
References
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M. Shadaram, C. Thomas, J. Summerfeld, P. Chennu, “RF
phase noise in WDM fiber optic links," 7th International
Conference on Transparent Optical Networks, (Barcelona,
Catalonia, Spain, 3-7 July. 2005).
M. Shadaram, V. Gonzalez, J. Ceniceros, N. Shah, J. Myres,
S. A . Pappert, D. Law, "Phase stabilization of reference
signal in analog fiberoptic links," Proceedings of
International Topical Meeting on Microwave Photonics,
(Kyoto, Japan, 1987).
M. Shadaram, J. Medrano, S. A. Pappert, M. H. Berry and D.
M. Gookin, "Technique for stabilizing the phase of the
reference signals in analog fiber-optic links," Applied Optics,
34, (1987): 8283-8288.
A. Hajimiri, T. H. Lee., “A general theory of phase noise in
electrical oscillators,” IEEE Journal of Solid-State Circuits,
33 (1998):179-194.