A description is given of the design, operation, and test over a 2-km path (roundtrip) of a
continuous wave, coherent laser array receiver that uses two independent aperture–receivers
whose intermediate frequencies are electro-optically co-phased in real time and then added as a
proposed way to overcome effective aperture limitations imposed by atmospheric turbulence and to
mitigate signal fading associated with atmospheric turbulence and speckle effects. The experiment
resulted in a mean carrier-to-noise ratio increase of 1.8, which is within 1% of the
theoretical predictions, when the two signals were phase locked, versus no increase without phase
locking. Further, the carrier fading strength, or normalized carrier-to-noise ratio variance, was
reduced by a factor of 0.53, which is within 2% of the theoretical prediction. The bandwidth
of the electro-optic phase-locked loop was measured to be of the order of 600 Hz, which is adequate
to compensate for atmospheric refractive turbulence fluctuations.
© 1996 Optical Society of America
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