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We proposed an optically controlled phased array antenna using a spatial light modulator for an adaptive satellite communications system. We have developed a prototype of an Optical Beam Forming Network, which enables control of 2 beams individually, and demonstrated at Ka band. We confirmed a good agreement between theoretical antenna patterns and calculated antenna patterns, which are simulated by using measured amplitude and phase distributions of the prototype.

In this paper, a new algorithm that measures the centroid position of a spot in the image obtained from an image sensor with sub-pixel accuracy was presented. The lens forms a spot on the image sensor, which spreads over a few pixels on the image. The algorithm is used to carry out centroid calculation using the brightness values of the spread pixels, and it increases the accuracy of the center detection of the spot image. In the calculation, a weight table is used, which has a circular form with a blurred border. The weight value is multiplied by the corresponding brightness value, which further increases the accuracy. An image containing a spot and random noise is produced in the simulation. Centroid calculation is carried out using the produced image, and the accuracy of the centroid position is evaluated. It is confirmed that the presented algorithm can detect the centroid position with an accuracy of 0.02 = 1/50 pixel when the spot is defocused. It is 1.5 times more accurate comparing with one of the traditional algorithms and the presented algorithm proves to be quite effective.

One of the key technologies for optical inter-satellite communication equipment is the rapid, highly accurate acquisition and tracking of the corresponding satellite. Therefore, we are developing a prototype of an acquisition and tracking system. This paper describes the specifications and performance test results of the prototype acquisition and tracking system. I. INTRODUCTIONThe emerging development of observation and other low earth orbit (LEO) satellites capable of greatly expanded high-volume data acquisition is expected to increase the need for high-speed data transmission. This need is compounded by the limited time window available for direct communication between an LEO satellite and a ground-based antenna and the resulting requirement for high-volume data transmission. In addition, the size of the RF communication terminal enlarges as the transmission speed increases. We are therefore engaged in the investigation and development of small, lightweight optical communication components that will enable high-speed communication by laser beam between a LEO satellite and a data relay satellite in the geostationary orbit (GEO) (Fig.1) In this paper, the specifications and configuration of the acquisition and tracking system are described. Moreover, the performance results of the control system, which consists of a fine pointing mechanism (FPM) [4] and fine pointing sensor (FPS) [3], are presented. This control system is very important for tracking the laser from the target satellite during communication.