Experimental Comparison of Tracking Algorithms in the Presence of Aircraft Boundary-Layer Distortions for an Emulated Free-Space Laser Communications Link

We report on experiments comparing different focal plane array (FPA) tracking algorithms for emulated laser communications links between an aircraft and spacecraft. The links include look-angle-dependent phase distur-bances caused by boundary-layer turbulence replicated using a deformable mirror. Impairments from platform jitter, atmospheric scintillation, and propagation delay are also included. We study a hyper-hemispherical 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 1.0 dB 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. c © 2008 Optical Society of America OCIS codes: 010.1330 (Atmospheric turbulence), 060.2605 (Free-space opti-cal communication). 1