Satellite platform vibration causes the misalignment between incident direction of the beacon and optical axis of the satellite optical communication system, which also leads to the instability of the laser link and reduces the precision of the system. So how to simulate the satellite platform vibration is a very important work in the ground test of satellite optical communication systems. In general, a vibration device is used for simulating the satellite platform vibration, but the simulation effect is not ideal because of the limited randomness. An approach is reasonable, which uses a natural random process for simulating the satellite platform vibration. In this paper, we discuss feasibility of the concept that the effect of angle of arrival fluctuation is taken as an effective simulation of satellite platform vibration in the ground test of the satellite optical communication system. Spectrum characteristic of satellite platform vibration is introduced, referring to the model used by the European Space Agency (ESA) in the SILEX program and that given by National Aeronautics and Space Development Agency (NASDA) of Japan. Spectrum characteristic of angle of arrival fluctuation is analyzed based on the measured data from an 11.16km bi-directional free space laser transmission experiment. Spectrum characteristic of these two effects is compared. The results show that spectra of these two effects have similar variation trend with the variation of frequency and feasibility of the concept is proved by the comparison results. At last the procedure of this method is proposed, which uses the power spectra of angle of arrival fluctuation to simulate that of the satellite platform vibration. The new approach is good for the ground test of satellite optical communication systems.

In satellite laser communication systems, accurate positioning of the beacon is essential for establishing a steady laser communication link. For satellite-to-ground optical communication, the main influencing factors on the acquisition of the beacon are background noise and atmospheric turbulence. In this paper, we consider the influence of background noise and atmospheric turbulence on the beacon in satellite-to-ground optical communication, and propose a new locating algorithm for the beacon, which takes the correlation coefficient obtained by curve fitting for image data as weights. By performing a long distance laser communication experiment (11.16 km), we verified the feasibility of this method. Both simulation and experiment showed that the new algorithm can accurately obtain the position of the centroid of beacon. Furthermore, for the distortion of the light spot through atmospheric turbulence, the locating accuracy of the new algorithm was 50% higher than that of the conventional gray centroid algorithm. This new approach will be beneficial for the design of satellite-to ground optical communication systems.

The centroid estimation of the beacon spot is crucial to the pointing, acquisition, and tracking subsystem in inter-satellite optical wireless communication (IsOWC), especially for the received very weak beacon caused by a long link distance. In this work, we propose an accurate centroid positioning method to calculate the centroid of such a weak beacon with a low peak signal-to-noise ratio. The proposed method is based on the idea that uses the normalized amplitude of the gray gradient to enhance the weights near the center of the beacon spot. Both comparative numerical simulation and experimental verification are implemented, which demonstrate the effectiveness and feasibility of the proposed method. Compared to the gray centroid method, interpolation-based method, Hough transform method, and Gaussian fitting method, the proposed method has stronger robustness and higher accuracy, which could be helpful to applications in IsOWC as well as beacon-based pointing and tracking systems.

In inter-satellite laser communication systems, accurate positioning of the beacon is essential for establishing a steady laser communication link. For inter-satellite optical communication, the main factor affecting the acquisition and tracking of the beacon is the background noise, such as stellar background light. In this study, we considered the effect of the background noise on a beacon in inter-satellite optical communication and proposed a new recognition algorithm for the beacon, which uses the optical flow vector obtained from the image data. We verified the feasibility of this method by performing simulation analysis and experiments. Both simulation and experiments showed that the new algorithm could accurately obtain the position of the centroid of the beacon under the effect of the background light. Furthermore, considering the identification probability of a light spot through the background light, the locating accuracy of the new algorithm was higher than that of the conventional gray centroid algorithm. Therefore, this new approach would be beneficial for the design of satellite-to-ground optical communication systems.

Metasurfaces have attracted extensive attention due to their excellent capabilities in wavefront manipulation. However, chromatic aberration,whichis widely present in phase-modulatedtuning meta-devices, limits their applications in modern communication systems.Far-field achromatismhas been explored but only consideredfor single order diffraction. With increasing demands and studies on multi-beam diffraction, including but not limited to, phase-modulated metasurfaces and metagratings, most of them are not suitable for dispersion manipulation. In this paper, we analyze the achromaticmechanism of diffraction field and propose a feasible solution to coherently control the dispersion on multi-order diffractions simultaneously. Chiral phase is introduced in the meta-atom to engineer the dispersion characteristics. In addition, an achromatic dispersion metasurface is designed for dual-beam generation as proof of concept. The two beams with propagationdirection -35° and +35° show good angle stability at the targeted frequencies of 7 GHz, 10 GHz and 13 GHz. Moreover, the limitations on beamdirection accuracy and metasurface aperture are also discussed. An improvement method that can greatly enhance the accuracy of diffraction angle is further proposed, where the deviation between actual beam angles and expected ones is reduced to below 0.8°,with a 73% enhancement.The proposed work builds up a major advance for diffraction management and shows great potential in wireless communications and radar detection.