Improved optical communications performance combining adaptive optics and pulse position modulation

A free-space optical communication channel suffers degraded performance due to blurring and scintillation of the received signal caused by atmospheric turbulence. Adaptive optics (AO) improves the communication performance of such a channel by concentrating the received power on the detector. The degree of improvement with AO correction depends on the modulation format, and on the modulation order when pulse position modulation is utilized. Gains of up to 6 dB with AO have been experimentally validated in a laboratory test bed under simulated atmospheric conditions involving turbulence and background light. The fade statistics of the turbulent atmospheric channel have also been analyzed with and without AO correction. (C) 2008 Society of Photo-Optical Instrumentation Engineers.