Free Space Optical MIMO System Using PPM Modulation and a Single Optical Amplifier

The use of an optical pre-amplifler in a multiple laser multiple receive aperture system for atmospheric line-of- sight optical communications is investigated. Multiple transmit- receive paths serve to fight channel fading due to clear air scintillation. Using orthogonal polarization and repetition coding cross two lasers is shown to provide transmitter diversity. Receiver diversity can be obtained by using optical phase shifters to counter channel phase offsets. Binary pulse position modulation (PPM) is proposed and analyzed in the presence of background radiation and amplified spontaneous emission noise. Using an optical pre-amplifler in a multiple-input/multiple-output channel results in significantly better performance than using an electrical amplifier.