Abstract

We report experiments comparing different focal plane array (FPA) tracking algorithms for emulated laser communication links between an aircraft and spacecraft. The links include look-angle-dependent phase disturbances caused by boundary-layer turbulence replicated by using a deformable mirror. Impairments from platform jitter, atmospheric scintillation, and propagation delay are also included. We study a hyperhemispherical dome geometry that provides a large field of regard but generates boundary-layer turbulence. Results from experiments comparing peak and centroid FPA tracking algorithms in various environments show that power delivered to the optical fiber varies with algorithm and look angle. An improvement in steady-state fiber-coupled power of up to 1.0dB can be achieved through appropriate choice of algorithm. In a real system, this advantage could be realized by implementing a tracking processor that dynamically changes its tracking algorithm depending on look angle and other parameters correlated to boundary-layer turbulence.

© 2009 Optical Society of America

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References

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  1. R. Parenti, R. J. Sasiela, L. C. Andrews, and R. L. Phillips, “Modeling the PDF for the irradiance of an uplink beam in the presence of beam wander,” Proc. SPIE 6215, 621508(2006).
    [CrossRef]
  2. “ThermaCAM” (FLIR Systems, 2004) (product brochure).
  3. S. G. Lambert and W. L. Casey, Laser Communications in Space (Artech House, 1995), Chap. 3.
  4. M. Belen'kii, K. Hughes, T. Brinkley, and J. Oldenettel, “Residual turbulent scintillation effect and impact of turbulence on Fourier telescopy system,” Proc. SPIE 5160, 56-67(2004).
    [CrossRef]
  5. R. A. Conrad, W. E. Wilcox, T. H. Williams, S. Michael, and J. M. Roth (MIT Lincoln Laboratory, 244 Wood Street, Lexington, Mass. 02420, USA) are preparing a manuscript to be called “Emulation of boundary-layer turbulence on aircraft laser communication terminals using a deformable mirror” (jroth@ll.mit.edu).
  6. J. L. Devore, “Tests and confidence intervals for a difference between two population means,” in Probability and Statistics for Engineering and the Sciences (Brooks/Cole, 2004), Sec. 9.1z, pp. 361-71.
  7. R. A. Conrad, “Impact of the boundary layer on pointing and tracking in airborne free-space laser communication links,” Master's dissertation (MIT, Aeronautics and Astronautics Department, 2008).

2006

R. Parenti, R. J. Sasiela, L. C. Andrews, and R. L. Phillips, “Modeling the PDF for the irradiance of an uplink beam in the presence of beam wander,” Proc. SPIE 6215, 621508(2006).
[CrossRef]

2004

M. Belen'kii, K. Hughes, T. Brinkley, and J. Oldenettel, “Residual turbulent scintillation effect and impact of turbulence on Fourier telescopy system,” Proc. SPIE 5160, 56-67(2004).
[CrossRef]

Andrews, L. C.

R. Parenti, R. J. Sasiela, L. C. Andrews, and R. L. Phillips, “Modeling the PDF for the irradiance of an uplink beam in the presence of beam wander,” Proc. SPIE 6215, 621508(2006).
[CrossRef]

Belen'kii, M.

M. Belen'kii, K. Hughes, T. Brinkley, and J. Oldenettel, “Residual turbulent scintillation effect and impact of turbulence on Fourier telescopy system,” Proc. SPIE 5160, 56-67(2004).
[CrossRef]

Brinkley, T.

M. Belen'kii, K. Hughes, T. Brinkley, and J. Oldenettel, “Residual turbulent scintillation effect and impact of turbulence on Fourier telescopy system,” Proc. SPIE 5160, 56-67(2004).
[CrossRef]

Casey, W. L.

S. G. Lambert and W. L. Casey, Laser Communications in Space (Artech House, 1995), Chap. 3.

Conrad, R. A.

R. A. Conrad, “Impact of the boundary layer on pointing and tracking in airborne free-space laser communication links,” Master's dissertation (MIT, Aeronautics and Astronautics Department, 2008).

R. A. Conrad, W. E. Wilcox, T. H. Williams, S. Michael, and J. M. Roth (MIT Lincoln Laboratory, 244 Wood Street, Lexington, Mass. 02420, USA) are preparing a manuscript to be called “Emulation of boundary-layer turbulence on aircraft laser communication terminals using a deformable mirror” (jroth@ll.mit.edu).

Devore, J. L.

J. L. Devore, “Tests and confidence intervals for a difference between two population means,” in Probability and Statistics for Engineering and the Sciences (Brooks/Cole, 2004), Sec. 9.1z, pp. 361-71.

Hughes, K.

M. Belen'kii, K. Hughes, T. Brinkley, and J. Oldenettel, “Residual turbulent scintillation effect and impact of turbulence on Fourier telescopy system,” Proc. SPIE 5160, 56-67(2004).
[CrossRef]

Lambert, S. G.

S. G. Lambert and W. L. Casey, Laser Communications in Space (Artech House, 1995), Chap. 3.

Michael, S.

R. A. Conrad, W. E. Wilcox, T. H. Williams, S. Michael, and J. M. Roth (MIT Lincoln Laboratory, 244 Wood Street, Lexington, Mass. 02420, USA) are preparing a manuscript to be called “Emulation of boundary-layer turbulence on aircraft laser communication terminals using a deformable mirror” (jroth@ll.mit.edu).

Oldenettel, J.

M. Belen'kii, K. Hughes, T. Brinkley, and J. Oldenettel, “Residual turbulent scintillation effect and impact of turbulence on Fourier telescopy system,” Proc. SPIE 5160, 56-67(2004).
[CrossRef]

Parenti, R.

R. Parenti, R. J. Sasiela, L. C. Andrews, and R. L. Phillips, “Modeling the PDF for the irradiance of an uplink beam in the presence of beam wander,” Proc. SPIE 6215, 621508(2006).
[CrossRef]

Phillips, R. L.

R. Parenti, R. J. Sasiela, L. C. Andrews, and R. L. Phillips, “Modeling the PDF for the irradiance of an uplink beam in the presence of beam wander,” Proc. SPIE 6215, 621508(2006).
[CrossRef]

Roth, J. M.

R. A. Conrad, W. E. Wilcox, T. H. Williams, S. Michael, and J. M. Roth (MIT Lincoln Laboratory, 244 Wood Street, Lexington, Mass. 02420, USA) are preparing a manuscript to be called “Emulation of boundary-layer turbulence on aircraft laser communication terminals using a deformable mirror” (jroth@ll.mit.edu).

Sasiela, R. J.

R. Parenti, R. J. Sasiela, L. C. Andrews, and R. L. Phillips, “Modeling the PDF for the irradiance of an uplink beam in the presence of beam wander,” Proc. SPIE 6215, 621508(2006).
[CrossRef]

Wilcox, W. E.

R. A. Conrad, W. E. Wilcox, T. H. Williams, S. Michael, and J. M. Roth (MIT Lincoln Laboratory, 244 Wood Street, Lexington, Mass. 02420, USA) are preparing a manuscript to be called “Emulation of boundary-layer turbulence on aircraft laser communication terminals using a deformable mirror” (jroth@ll.mit.edu).

Williams, T. H.

R. A. Conrad, W. E. Wilcox, T. H. Williams, S. Michael, and J. M. Roth (MIT Lincoln Laboratory, 244 Wood Street, Lexington, Mass. 02420, USA) are preparing a manuscript to be called “Emulation of boundary-layer turbulence on aircraft laser communication terminals using a deformable mirror” (jroth@ll.mit.edu).

Proc. SPIE

M. Belen'kii, K. Hughes, T. Brinkley, and J. Oldenettel, “Residual turbulent scintillation effect and impact of turbulence on Fourier telescopy system,” Proc. SPIE 5160, 56-67(2004).
[CrossRef]

R. Parenti, R. J. Sasiela, L. C. Andrews, and R. L. Phillips, “Modeling the PDF for the irradiance of an uplink beam in the presence of beam wander,” Proc. SPIE 6215, 621508(2006).
[CrossRef]

Other

“ThermaCAM” (FLIR Systems, 2004) (product brochure).

S. G. Lambert and W. L. Casey, Laser Communications in Space (Artech House, 1995), Chap. 3.

R. A. Conrad, W. E. Wilcox, T. H. Williams, S. Michael, and J. M. Roth (MIT Lincoln Laboratory, 244 Wood Street, Lexington, Mass. 02420, USA) are preparing a manuscript to be called “Emulation of boundary-layer turbulence on aircraft laser communication terminals using a deformable mirror” (jroth@ll.mit.edu).

J. L. Devore, “Tests and confidence intervals for a difference between two population means,” in Probability and Statistics for Engineering and the Sciences (Brooks/Cole, 2004), Sec. 9.1z, pp. 361-71.

R. A. Conrad, “Impact of the boundary layer on pointing and tracking in airborne free-space laser communication links,” Master's dissertation (MIT, Aeronautics and Astronautics Department, 2008).

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Figures (9)

Fig. 1
Fig. 1

Notional concept of experimental laboratory testbed emulator in which lasercom tracking schemes can be tested in a realistic environment that includes relevant impairments. The testbed includes both aircraft and spacecraft lasercom pointing, acquisition, and tracking functions. The full-duplex terminals interface through an emulated environment that introduces the impairments shown.

Fig. 2
Fig. 2

(a) Side and (b) top view of the density flow field around a 400 mm ( 16 in . ) diameter hyperhemispherical dome on an aircraft fuselage. Altitude, 8.8 km ( 29,000 ft ); airspeed, Mach 0.7; density units of scale, kg / m 3 .

Fig. 3
Fig. 3

Definitions for azimuth and elevation look angles. Curved arrows indicate positive angles.

Fig. 4
Fig. 4

Plots from an experimental acquisition showing both power-level measurements for different sensors and state values for (a) the spacecraft terminal and (b) the aircraft terminal. (c) Fiber-coupled receiver power for both terminals.

Fig. 5
Fig. 5

Bullseye plot used to display results. Angles outside the perimeter of the circle indicate azimuth look angles; italicized angles inside the top octant define elevation look angles. Thus, each octant is divided into three regions that define different look angles; the central circle corresponds to the zenith look angle ( 90 ° elevation). Gray regions indicate cases where impairments prevented the system from acquiring the link. All angles are with respect to the aircraft.

Fig. 6
Fig. 6

Differences (decibels) in mean fiber-coupled power between tracking algorithms. Positive values indicate centroid tracking preferred, and negative values indicate peak tracking preferred. Regions marked with “X” represent look angles with unstable links: (a) spacecraft and (b) aircraft. Negative-valued regions are also indicated by dashes.

Fig. 7
Fig. 7

Differences (decibels) in mean FPA peak-pixel power between tracking algorithms. Positive values indicate centroid tracking preferred, and negative values indicate peak tracking preferred. Regions marked with “X” represent look angles with unstable links: (a) spacecraft and (b) aircraft. Negative-valued regions are also indicated by dashes.

Fig. 8
Fig. 8

Differences (decibels) in mean on-aperture power density between tracking algorithms. Positive values indicate centroid tracking preferred, and negative values indicate peak tracking preferred. Regions marked with “X” represent look angles with unstable links: (a) spacecraft and (b) aircraft. Negative-valued regions are also indicated by dashes.

Fig. 9
Fig. 9

Aircraft FPA azimuth and elevation error signals for peak and centroid tracking algorithms at 90 ° / 20 ° (azimuth/elevation). The raw signals for each algorithm appear different from each other as expected. However, the traces closely resemble each other after applying 100 Hz low-pass filtering representing the tracking-control-loop bandwidth.

Tables (1)

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Table 1 Z Test Scores between Centroid (Positive Values) and Peak (Negative Values) Tracking Algorithms a

Equations (1)

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Z = x ¯ y ¯ σ 1 2 m + σ 2 2 n .

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