In the satellite-to-ground downlink lasercom systems, efficient coupling of atmospherically distorted spatial light into single-mode fibers is a key technology for fiber-coupled optical receiver. Statistical distribution of fiber-coupling efficiency is important to analyze the performance of a receiver. We use the simulation of beam propagation to examine statistical distribution of fiber-coupling efficiency for the satellite-to-ground downlink. The distributions of the fiber-coupling efficiency for different numbers of speckles are obtained, and the cumulative density functions of the fiber-coupling efficiency are also given. In order to validate the accuracy of numerical simulation method, the dependence of average fiber-coupling efficiency on the ratio of lens size to speckle size is attained, which is highly consistent with the prior theoretical works. The results will be helpful in the design of the satellite-to-ground downlink lasercom system based on fiber-coupling technology.
Two theoretical models of single-photon acquisition probability based on the fundamental-mode Gaussian beam are established for free-space quantum key distribution and are compared in theory and simulation. The parameters that influence the single-photon acquisition probability are the transmitter's tracking-pointing error, the far-field divergence angle, the link distance between the transmitter and receiver and the receiver's antenna aperture. The single-photon acquisition probability is analyzed in the numerical simulation and its orders of magnitude are given for the ground-to-ground, satellite-to-ground and satellite-to-satellite links. The results of the theoretical analysis and the numerical simulation show that it is feasible to acquire single-photon for the satellite-to-ground and satellite-to-satellite quantum key distribution.
The laser diode is widely used in optical fiber communications and intersatellite optical communication. And there are some differences between the modulator of laser diode in these two communications. This paper has mainly analyzed the modulation in these two communications. And because the high power AlGaAS semiconductor lasers operating around 800 nm have been successfully qualified for deployment in many intersatellite optical communication programs, in this paper we have given the experimental simulation results of some modulation methods by using the model of laser diodes. From the simulation results, we have compared the methods of laser diode modulation. And we can know which method is suitable for optical space communications, which demand both high power and high bandwidth.
In an intersatellite optical communication system, as the vibration of a satellite's platform it will influence bit error rate of the system. In this paper, the influence of vibration is researched in theoretical and experimental. The experimental results are given and the theoretical results are accorded with experimental results very well. This researching work will be important and useful for research of intersatellite optical communications.