Diagnostic optical communication experiments were performed comparing noncoherent and coherent detection techniques. Three different receiver–transmitter configurations with variable apertures were used during the experiments that were performed over a 1-km real atmospheric path. In every case, it was found that the coherent system fading, due to atmospheric turbulence, was considerably greater than the noncoherent system fading. This result shows the greater sensitivity of the coherent system to the time-varying wavefront breakup produced by atmospheric turbulence. A coherent homodyne experiment at 10.6 μ over a 2-km round-trip path was also performed. Its results indicated that a coherent system at 10.6 μ is less susceptible to atmospheric turbulence than a coherent system at 6328 Å.
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