COHERENT OPTICAL ARRAY RECEIVERS FOR THE MITIGATION OF ATMOSPHERIC-TURBULENCE AND SPECKLE EFFECTS

A description is given of the design, operation, and test over a 2-km path (roundtrip) of a continuous wave, coherent laser array receiver t hat uses two independent aperture-receivers whose intermediate frequen cies are electro-optically co-phased in real time and then added as a proposed way to overcome effective aperture limitations imposed by atm ospheric turbulence and to mitigate signal fading associated with atmo spheric turbulence and speckle effects. The experiment resulted in a m ean carrier-to-noise ratio increase of 1.8, which is within 1% of the theoretical predictions, when the two signals were phase locked, versu s no increase without phase locking. Further, the carrier fading stren gth, or normalized carrier-to-noise ratio variance, was reduced by a f actor of 0.53, which is within 2% of the theoretical prediction. The b andwidth of the electro-optic phase-locked loop was measured to be of the order of 600 Hz, which is adequate to compensate for atmospheric r efractive turbulence fluctuations. (C) 1996 Optical Society of America