Abstract

Optical data links through the atmosphere suffer from turbulence-induced signal scintillation. In a coaxially-symmetric bidirectional link scenario, the variations of the axial intensities at both ends are correlated. This relation can be used as an inherent feedback mechanism, with negligible delay, to enhance the capacity of the transmission system. By experiment, we show the correlation coefficient of both received signals can reach values close to one over long atmospheric distances, provided the receiver apertures are smaller than specific intensity speckle structures, while the correlation reduces gradually with larger apertures. This allows transmission capacity to be optimized with adaptive transceiver systems that take into account the degree of correlation.

© 2012 Optical Society of America

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References

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  2. S. Bloom, E. Korevaar, J. Schuster, and H. Willebrand, “Understanding the performance of free-space optics [Invited],” J. Opt. Commun. Netw. 2, 178–200 (2003).
  3. L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media2nd ed. (SPIE Press, 2005).
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  7. M. A. Khalighi, N. Aitamer, N. Schwartz, and S. Bourennane, “Turbulence mitigation by aperture averaging in wireless optical systems,” in ConTEL 2009, 10th International Conference on Telecommunications (IEEE, 2009), pp. 59–66.
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    [CrossRef]
  10. J. H. Shapiro, “Optimal power transfer through atmospheric turbulence using state knowledge,” IEEE Trans. Commun. Technol. 19, 410–414 (1971).
    [CrossRef]
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    [CrossRef]
  12. V. A. Banakh and V. L. Mironov, Lidar in a Turbulent Atmosphere (Artech House, 1987).
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    [CrossRef]
  14. V. A. Banakh, I. N. Smalikho, and C. Werner, “Numerical simulation of the effect of refractive turbulence on coherent lidar return statistics in the atmosphere” Appl. Opt. 39, 5403–5414(2000).
    [CrossRef]
  15. R. R. Parenti, J. M. Roth, J. Shapiro, and F. G. Walther, “Observations of channel reciprocity in optical free-space communications experiments,” in Applications of Lasers for Sensing and Free Space Communications, OSA Technical Digest (CD) (Optical Society of America, 2011).
  16. F. G. Walther, S. Michael, R. R. Parenti, and J. A. Taylor, “Air-to-ground lasercom system demonstration design overview and results summary,” Proc. SPIE 7814, 78140Y (2010).
    [CrossRef]
  17. J. D. Barchers and D. L. Fried, “Optimal control of laser beams for propagation through a turbulent medium,” J. Opt. Soc. Am. A 19, 1779–1793 (2002).
    [CrossRef]
  18. N. Perlot and D. Giggenbach, “Scintillation correlation between forward and return spherical waves,” Appl. Opt. (to be published).
  19. L. C. Andrews and R. L. Phillips, Laser Beam Propagation Through Random Media (SPIE Press, 1998), p. 186.
  20. F. G. Smith, ed., The Infrared & Electro-Optical Systems Handbook, Volume 2: Atmospheric Propagation of Radiation, 2nd ed. (SPIE-Press, 1996).

2010 (2)

I. B. Djordjevic, “Adaptive modulation and coding for free-space optical channels,” J. Opt. Commun. Netw. 2, 221–229 (2010).
[CrossRef]

F. G. Walther, S. Michael, R. R. Parenti, and J. A. Taylor, “Air-to-ground lasercom system demonstration design overview and results summary,” Proc. SPIE 7814, 78140Y (2010).
[CrossRef]

2003 (1)

S. Bloom, E. Korevaar, J. Schuster, and H. Willebrand, “Understanding the performance of free-space optics [Invited],” J. Opt. Commun. Netw. 2, 178–200 (2003).

2002 (1)

2000 (1)

1992 (1)

1991 (2)

1972 (1)

1971 (3)

Aitamer, N.

M. A. Khalighi, N. Aitamer, N. Schwartz, and S. Bourennane, “Turbulence mitigation by aperture averaging in wireless optical systems,” in ConTEL 2009, 10th International Conference on Telecommunications (IEEE, 2009), pp. 59–66.

Andrews, L. C.

L. C. Andrews, “Aperture-averaging factor for optical scintillations of plane and spherical waves in the atmosphere,” J. Opt. Soc. Am. A 9, 597–600 (1992).
[CrossRef]

L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media2nd ed. (SPIE Press, 2005).

L. C. Andrews and R. L. Phillips, Laser Beam Propagation Through Random Media (SPIE Press, 1998), p. 186.

Banakh, V. A.

Barchers, J. D.

Bloom, S.

S. Bloom, E. Korevaar, J. Schuster, and H. Willebrand, “Understanding the performance of free-space optics [Invited],” J. Opt. Commun. Netw. 2, 178–200 (2003).

Bourennane, S.

M. A. Khalighi, N. Aitamer, N. Schwartz, and S. Bourennane, “Turbulence mitigation by aperture averaging in wireless optical systems,” in ConTEL 2009, 10th International Conference on Telecommunications (IEEE, 2009), pp. 59–66.

Churnside, J. H.

Djordjevic, I. B.

Fried, D. L.

Giggenbach, D.

N. Perlot and D. Giggenbach, “Scintillation correlation between forward and return spherical waves,” Appl. Opt. (to be published).

Holmes, J. F.

Khalighi, M. A.

M. A. Khalighi, N. Aitamer, N. Schwartz, and S. Bourennane, “Turbulence mitigation by aperture averaging in wireless optical systems,” in ConTEL 2009, 10th International Conference on Telecommunications (IEEE, 2009), pp. 59–66.

Korevaar, E.

S. Bloom, E. Korevaar, J. Schuster, and H. Willebrand, “Understanding the performance of free-space optics [Invited],” J. Opt. Commun. Netw. 2, 178–200 (2003).

Lutomirski, R. F.

Michael, S.

F. G. Walther, S. Michael, R. R. Parenti, and J. A. Taylor, “Air-to-ground lasercom system demonstration design overview and results summary,” Proc. SPIE 7814, 78140Y (2010).
[CrossRef]

Mironov, V. L.

V. A. Banakh and V. L. Mironov, Lidar in a Turbulent Atmosphere (Artech House, 1987).

Parenti, R. R.

F. G. Walther, S. Michael, R. R. Parenti, and J. A. Taylor, “Air-to-ground lasercom system demonstration design overview and results summary,” Proc. SPIE 7814, 78140Y (2010).
[CrossRef]

R. R. Parenti, J. M. Roth, J. Shapiro, and F. G. Walther, “Observations of channel reciprocity in optical free-space communications experiments,” in Applications of Lasers for Sensing and Free Space Communications, OSA Technical Digest (CD) (Optical Society of America, 2011).

Perlot, N.

N. Perlot and D. Giggenbach, “Scintillation correlation between forward and return spherical waves,” Appl. Opt. (to be published).

Phillips, R. L.

L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media2nd ed. (SPIE Press, 2005).

L. C. Andrews and R. L. Phillips, Laser Beam Propagation Through Random Media (SPIE Press, 1998), p. 186.

Roth, J. M.

R. R. Parenti, J. M. Roth, J. Shapiro, and F. G. Walther, “Observations of channel reciprocity in optical free-space communications experiments,” in Applications of Lasers for Sensing and Free Space Communications, OSA Technical Digest (CD) (Optical Society of America, 2011).

Schuster, J.

S. Bloom, E. Korevaar, J. Schuster, and H. Willebrand, “Understanding the performance of free-space optics [Invited],” J. Opt. Commun. Netw. 2, 178–200 (2003).

Schwartz, N.

M. A. Khalighi, N. Aitamer, N. Schwartz, and S. Bourennane, “Turbulence mitigation by aperture averaging in wireless optical systems,” in ConTEL 2009, 10th International Conference on Telecommunications (IEEE, 2009), pp. 59–66.

Shapiro, J.

R. R. Parenti, J. M. Roth, J. Shapiro, and F. G. Walther, “Observations of channel reciprocity in optical free-space communications experiments,” in Applications of Lasers for Sensing and Free Space Communications, OSA Technical Digest (CD) (Optical Society of America, 2011).

Shapiro, J. H.

J. H. Shapiro, “Reciprocity of the turbulent atmosphere,” J. Opt. Soc. Am. 61, 492–495 (1971).
[CrossRef]

J. H. Shapiro, “Optimal power transfer through atmospheric turbulence using state knowledge,” IEEE Trans. Commun. Technol. 19, 410–414 (1971).
[CrossRef]

Smalikho, I. N.

Taylor, J. A.

F. G. Walther, S. Michael, R. R. Parenti, and J. A. Taylor, “Air-to-ground lasercom system demonstration design overview and results summary,” Proc. SPIE 7814, 78140Y (2010).
[CrossRef]

Walther, F. G.

F. G. Walther, S. Michael, R. R. Parenti, and J. A. Taylor, “Air-to-ground lasercom system demonstration design overview and results summary,” Proc. SPIE 7814, 78140Y (2010).
[CrossRef]

R. R. Parenti, J. M. Roth, J. Shapiro, and F. G. Walther, “Observations of channel reciprocity in optical free-space communications experiments,” in Applications of Lasers for Sensing and Free Space Communications, OSA Technical Digest (CD) (Optical Society of America, 2011).

Werner, C.

Willebrand, H.

S. Bloom, E. Korevaar, J. Schuster, and H. Willebrand, “Understanding the performance of free-space optics [Invited],” J. Opt. Commun. Netw. 2, 178–200 (2003).

Yura, H. T.

Appl. Opt. (5)

IEEE Trans. Commun. Technol. (1)

J. H. Shapiro, “Optimal power transfer through atmospheric turbulence using state knowledge,” IEEE Trans. Commun. Technol. 19, 410–414 (1971).
[CrossRef]

J. Opt. Commun. Netw. (2)

I. B. Djordjevic, “Adaptive modulation and coding for free-space optical channels,” J. Opt. Commun. Netw. 2, 221–229 (2010).
[CrossRef]

S. Bloom, E. Korevaar, J. Schuster, and H. Willebrand, “Understanding the performance of free-space optics [Invited],” J. Opt. Commun. Netw. 2, 178–200 (2003).

J. Opt. Soc. Am. (2)

J. Opt. Soc. Am. A (2)

Proc. SPIE (1)

F. G. Walther, S. Michael, R. R. Parenti, and J. A. Taylor, “Air-to-ground lasercom system demonstration design overview and results summary,” Proc. SPIE 7814, 78140Y (2010).
[CrossRef]

Other (7)

L. C. Andrews and R. L. Phillips, Laser Beam Propagation Through Random Media (SPIE Press, 1998), p. 186.

F. G. Smith, ed., The Infrared & Electro-Optical Systems Handbook, Volume 2: Atmospheric Propagation of Radiation, 2nd ed. (SPIE-Press, 1996).

V. A. Banakh and V. L. Mironov, Lidar in a Turbulent Atmosphere (Artech House, 1987).

R. R. Parenti, J. M. Roth, J. Shapiro, and F. G. Walther, “Observations of channel reciprocity in optical free-space communications experiments,” in Applications of Lasers for Sensing and Free Space Communications, OSA Technical Digest (CD) (Optical Society of America, 2011).

M. A. Khalighi, N. Aitamer, N. Schwartz, and S. Bourennane, “Turbulence mitigation by aperture averaging in wireless optical systems,” in ConTEL 2009, 10th International Conference on Telecommunications (IEEE, 2009), pp. 59–66.

L. C. Andrews and R. L. Phillips, Laser Beam Propagation through Random Media2nd ed. (SPIE Press, 2005).

J. W. Strohbehn, ed., Laser Beam Propagation in the Atmosphere (Springer,1978).

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Figures (7)

Fig. 1.
Fig. 1.

Bidirectional propagation through an extended volume of atmospheric turbulence cells generally results in different intensity distributions at both receiver planes. However, equal intensities exist exactly on-axis for spherical waves [8,9].

Fig. 2.
Fig. 2.

Geometry of both transceiver terminals which were installed with tip-tilt-tables on geodetic tripods. Position of photodiode and Tx-direction could be adjusted separately to allow co-alignment of Tx-beam with Rx-field-of-view. As Tx-lasers MQW-type laser diodes were used (PL15 from PD-LD Inc.).

Fig. 3.
Fig. 3.

Map of measurement paths at Adelaide, South Australia (underlying Map data ©2011 Google, Whereis®, Sensis Pty Ltd.).

Fig. 4.
Fig. 4.

Height-above-ground profiles (solid lines), Cn2-profile (dot-dash lines), and weighted Cn2-profilew(z)*Cn2(z) (dotted lines, weighted with w(z) of a spherical wave) of propagation paths B, D, C, E (A is similar to B, only half of its path length).

Fig. 5.
Fig. 5.

Typical simultaneously measured normalized received power vectors. From top down: Path “C” with 50 mm aperture and CCF=0.91, Path “C” with 127 mm aperture and CCF=0.74, Path “D” with 50 mm aperture and CCF=0.61, and path “D” with 127 mm aperture and CCF=0.27. Rx-A solid line, Rx-B dashed line, 300 ms of Rx data samples each.

Fig. 6.
Fig. 6.

Correlation coefficients versus square root of link distance. There is an approximately linear increase in CCF with the square root of the range, up to 15km. The CCF-saturation to 1 should be expected around 15 km when the aperture becomes significantly smaller than the speckle size. It is believed that this situation could not be reached even with the long path E(20 km) because multiple scattering prevented reciprocal speckle structures to increase further with distance.

Fig. 7.
Fig. 7.

Correlation coefficient versus receiver aperture diameter normalized by the Fresnel size λ·L. The correlation values increase significantly when the ratio is below one. Measured values (asterisks) are compared with theoretical values without an inner obscuration (circles) and regarding the inner obscuration of 26 mm in our experiment (diamonds). The theoretical values are calculated according to [18]. The scenario letters (A to E) are indicated on top of each set of values, where each scenario provides two sets due to the two aperture sizes.

Tables (2)

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Table 1. Parameters of the Experimental Setup Common to All Tests

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Table 2. Summary of Measurement Results of All Five Test Scenarios Sorted by Distance

Equations (5)

Equations on this page are rendered with MathJax. Learn more.

DTxλ·Latm.
ρ=E{(h1μ1)(h2μ2)}σ1σ2,
Cn2(h)=Cn2(h0)·(hh0)k,
σR,sp2=2.25k7/6L5/60LCn2(z)w(z)dz,
w(z)=(zL)5/6(1zL)5/6.

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