Space light-fiber coupling technology converts spatially transmitted beams into fiber-optic transmissions, facilitating free-space optical communication, and fiber laser radar systems for signal processing in optical fibers. However, it is very difficult to accomplish precise alignment between the spatial beams and the fiber with micron level. In this paper, particle swarm optimization is applied to achieve two-dimensional auto-alignment between the spatial beams and the fiber. The theory proves that when the dimension takes 2, the number of groups is 10, the inertia weight is 0.4~0.8 and the number of iteration does not exceed 100, the particle swarm optimization can converge to the maximum coupling power, and the greater the weight of the inertia, the slower the convergence speed, the larger the search area. If the inertia weight decreases linearly with the number of iterations, the spatial light-fiber coupling auto-alignment function can be quickly completed while searching the alignment space in a wide range.
A novel method is proposed to get the adaptively optimized detection threshold of strong atmospheric turbulence channel model with K distributions, by estimating high-order accumulation of the covariance of received signal. Then performance of this adaptive signal threshold estimation method is tested and verified by Monte Carlo simulation, which shows that the threshold can be adaptively changed with the atmospheric turbulence channel conditions. Finally, the effectiveness of this method is verified by the actual measurement data under light rain, moderate rain and heavy rain. It is shown that the method proposed in this paper can effectively suppress the atmospheric turbulence and improve the performance of Free Space Optical communication system.
Cassegrain antenna is commonly used in Free Space Optic communication system. The double reflection structure
determines the system has a shade problem. In this paper, the off-axis emission (semi-aperture lighting) method is
applied to solve the shade problem caused by the secondary mirror. This method is simple both in structure an implement.
ZEMAX software and Fourier optics are used to analyze the Cassegrain antenna theoretically. We can improve the
performance of Cassegrain antenna under the guidance of the analytical results. Some experiment has been carried out.
The results showed that the percentage of exit-pupil power effectively increased from 9% to 53%, the diameter of spot
was not exceeding 200mm at the distance of 600m.It is significant for engineering applications.
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