Diversity methods for fading control

Mitigation of the optical communications problem of fluctuation in the received signal intensity due to atmospheric turbulence via using multiple source telescopes and/or multiple wavelengths and /or multiple receiver telescopes is considered. It is noted that space diversity can alleviate beam wander, and that if this provides sufficient immunity, wavelength diversity can be neglected. For cases where the speckle size precludes high epsilon space diversity, a large beam must be used at the receiver (with corresponding light inefficiency) in order to alleviate beam wander. (R.R.)