Effects of edfa gain on rf phase noise in a wdm fiber optic link
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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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Effects of edfa gain on rf phase noise in a wdm fiber optic link

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
Outline Link

  • Transmission of Reference Signals via Optical Fibers

  • Noise Sources

  • Phase Noise

  • Link Under Investigation

  • Results


Rf transmission via optical fibers
RF Transmission via Optical Fibers Link

  • Phased Array Antenna

  • Reference Signals for Timing and Synchronization

  • Doppler Radar

  • CATV

  • Passband Signal Transmission


Noise sources
Noise Sources Link

  • Optical Transmitter

  • Fiber Cable

  • Optical Amplifier

  • Photo Receiver



What causes phase noise
What Causes Phase Noise? Link

  • 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

  • Amplified spontaneous emission noise

  • Etc.


Analysis additive phase noise by the optical amplifier

= Link

w

+

E

(

t

)

2

GP

cos(

t

)

E

(

t

)

t

in

o

ASE

M

[

]

(

)

å

=

d

w

+

p

d

+

f

E

(

t

)

2

S

f

cos

2

i

f

t

ASE

ASE

o

i

=

-

i

M

=

-

c

S

(

G

1

)

n

hf

ASE

SP

Analysis(Additive phase noise by the optical amplifier)


Analysis cont additive phase noise by the optical amplifier

a Link

Assume

<< 1

M

[

]

(

)

å

=

Â

a

w

+

Â

a

d

w

+

p

d

+

f

i

GP

cos(

t

)

GP

S

f

cos

2

i

f

t

t

o

c

o

ASE

c

i

=

-

i

M

(

)

é

ù

S

=

ASE

S

(

f

)

10

log

dB

/

Hz

ê

ú

f

c

GP

ë

û

o

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


Link under investigation
Link Under Investigation Link

  • 8.8 Km Fiber Link with an EDFA located at 4.4 Km

  • Single Light source operating at 1560nm

  • 100MHz RF reference signal




Edfa output power vs edfa gain

16 Link

15

14

EDFA output Power dBm

13

12

11

27

29

31

33

35

37

39

41

43

EDFA Gain dB

EDFA Output Power vs. EDFA Gain


Additive rf phase noise vs log offset frequency

-60 Link

-65

-70

-75

-80

dBc/Hz

-85

-90

-95

-100

-105

1

10

100

1000

Log Offset Freq

Additive RF Phase noise vs. Log Offset Frequency


Gain effects
Gain Effects Link

  • 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 Link

-65

-70

-75

-80

dBc/Hz

-85

-90

-95

-100

-105

27

29

31

33

35

37

39

41

43

45

EDFA Gain dB

Additive Phase Noise vs. EDFA Gain


Conclusion
Conclusion Link

  • 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
References Link

  • 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.


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