In free space optical data transmission systems illumination of the receiver antenna by background radiation will decrease the signal to noise ratio. We derive expressions for that degradation both for direct and for heterodyne/homodyne receivers. Examples are given for cases where the sun, the moon, the earth, and Venus illuminate earth orbiting receivers operating at wavelengths of 0.85 µm, 1.3 µm, and 10.6 µm. Direct detection receivers will typically suffer a degradation of between 5 and 15 dB at λ = 0.85 µm and λ = 1.3 µm when illuminated by the sun. Heterodyne/homodyne receivers at 10.6 µm degrade more with sun radiation (typically 4 dB) than at the smaller wavelengths (≈0.3 dB). The moon, earth, and Venus cause negligible reduction of signal to noise ratio.
© 1989 Optical Society of America
Walter R. Leeb, "Degradation of signal to noise ratio in optical free space data links due to background illumination," Appl. Opt. 28, 3443-3449 (1989)