RF Phase Noise in WDM Fiber Optic Links

1
RF Phase Noise in WDM Fiber Optic Links

• Mehdi Shadaram, Cecil Thomas, John Summerfield,
  and Pushkar Chennu
• Department of Electrical and Computer
  Engineering, University of Texas at San Antonio,
  San Antonio, TX 78249
• Department of Electrical and Computer
  Engineering, University of Texas at El Paso, El
  Paso, TX 79968

2
Abstract

• A WDM fiber optic link is considered for
  transmitting the reference signals for distances
  of less than 10 km. The quantification and
  analysis of phase noise caused by the link is the
  main objective of this work. The RF phase noise
  is investigated under different experimental
  setups so that the additive effect of different
  components in the link can be examined. Moreover,
  the influence of wavelength selection and power
  on the noise is also studied.

3
RF Transmission via Optical Fibers

• Phased Array Antenna
• Reference Signals for Timing and Synchronization
• Doppler Radar
• CATV
• Passband Signal Transmission

4
RF Phase Noise
5
What Causes Phase Noise?

• 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.

6
Analysis(additive phase noise by the optical
amplifier)
7
Analysis (continued)
8
Analysis (continued)
9
Analysis (continued)
10
Saturated gain and corresponding noise figure
with respect to input signal power at wavelength
of 1550 nm.
11
Small signal gain (GodB)40 dB
12
Experimental Setup
13
RF phase noise for different output powers of
source
14
RF Phase noise against EDFAs input power
15
Conclusion
In conclusion, the 1550 - 1555 nm wavelength
range is the optimum range for analog signal
transmission through fiber, since it offers
lowest values for phase noise. It is a matter of
fact that the light signal also has the lowest
attenuation in this range. The RF phase noise
exhibits significant variations (gt10dB) as the
output power of the laser source is varied. The
reason for this trend is that these variations in
power increase thermal and shot noise in the
photo-receiver which in turn causes an increase
in the average RF phase noise of the system. In
addition, including the EDFA in the link
increases the average phase noise in the system
by 2 to 3 dB.
16
References

• Shah, N, Shadaram, Phase stabilization of
  reference signals in analogue fiber optic links,
  Electronics Letters, Volume 33, Issue 13, 1164
  1165, June 1997.
• Shadaram M., Mody, A.N. Usevitch, B. Lafaw, D
  Performance Evaluation Of M- QAM Fiber-Optic
  Links in the Presence of the External Modulator
  Bias Fluctuations, Microwave Photonics, 1997. MWP
  '97, International Topical Meeting, September
  3-5, 1997.
• Shadaram, M. Gonzalez, V. Ceniceros, J. Shah,
  N. Mayers, J. Pappert, S. Lafaw, D., Phase
  stabilization of reference signals in analog
  fiber-optic links, Microwave Photonics, 229
  232,1996. MWP '96. Technical Digest. 1996
  International Topical Meeting on , 3-5 Dec. 1996.
  
• R. K. Khan, H. Kabir, S. M. Shamim Hasan, T. X.
  Wu, and M. Shadaram, Performance evaluation of
  multi-wavelength M-QAM signal transmitted through
  fiber optic link with EDFA, Optical Fiber
  Technology Journal, Vol. 10, Issue 3, July 2004,
  pp. 266-274.
• L. Angrisani, A. Baccigalupi, M. DArco, A
  Digital Signal Processing Approach for Phase
  Noise measurement, IEEE Transactions on
  Instrumentation and Measurement Vol. 50, No. 4,
  930 935, August 2001.