Laser Beam Propagation in Random Media: New and Advanced Topics

Optical communications in turbulence: a tutorial

“…Andrews and Phillips were one of the first to summarize the research characterizing the effects of turbulence on laser radar and communications system performance, 9,10 and Andrews and Beason recently updated our understanding of system performance effects in these areas. 11 This section discusses the origin of the SNR, the validity of the Andrews and Phillips's SNR correction, and the scintillation index as the key turbulent-intensity noise variance.…”

“…In the above equations, where L atm is the atmospheric loss; γ fiber is the fiber coupling efficiency (EFC) (if applicable); ζ is the link zenith angle; r 0rx and r 0tx are the uplink spherical-wave Fried parameter for the receiver and transmitter, respectively; 27 and C 2 n is the refractive index structure parameter. [9][10][11] The above equations for the Fried parameter are valid for l 0 ≪ r 0 ≪ L 0 , with l 0 being the inner scale and L 0 being the outer scale of the turbulence. In Eq.…”

“…28 ) The parameters SR RP and SR DP represent the Strehl ratio that is measured at the pupil plane of the receiver and the Strehl ratio that is measured at the detector plane of the receiver, respectively. [9][10][11] These parameters contain the new adaptive optics (AO) performance model that depends on the on-axis scintillation index σ 2 I ð0; RÞ or if the link range is short. [9][10][11] The scintillation index is the turbulent intensity variance given as The parameter m in Eqs.…”

“…Techniques such as aperture averaging and emerging technologies such as adaptive optics were employed with some success. [9][10][11] Aperture averaging worked well for large receiver apertures and downlink/horizontal geometries. Uplinks experienced large beam wander that aperture averaging could not help reducing.…”

“…12 This is because these turbulent conditions are dominated by turbulent phase fluctuations while moderate to strong conditions or longer ranges are dominated by amplitude scintillation that needs more than just phase correction. [9][10][11][12] What was missing from these analyses was the turbulent-intensity noise variance that also affected communications performance. This omission was the reason many of the analyses did not match experimental field results.…”