Laser Signal Intensity and Aperture Averaging Analysis in 16km Free-Space Optical Links

To investigate the effect of atmospheric turbulence on the long distance horizontal optical link, a 16 km horizontal link is established. The experiment lasts more than one year and data are collected in each season. We have measured scintillation index, the fluctuation of angle of arrival, probability density function (PDF), high-frequency spectrum of irradiance under aperture receiving (200mm) condition. In our experiments, the aperture averaging effect on the statistical laws of measured free-space laser signal intensity is analyzed. The aperture-averaging results show that intensity fluctuations decrease by increasing the receiver aperture diameter. Even in saturation regime, the irradiance PDF can be accepted to be lognormal when the receiving aperture is bigger than coherence radius.