Inter-satellite laser communication system based on double Risley prisms beam steering

We designed an intensity modulation direct detection free-space laser communication terminal. In this system, the output power of the signal-modulated semiconductor laser amplified by two-stage fiber amplifier is 2 W, and the modulation contrast is 15 dB. Tracking of the incident beam and demodulation of the communication signal are realized by using a quadrant avalanche photodiode (APD). By means of rotating double Risley prisms, the ranges of the pitching angle and azimuth angle are ±35 and ±180  deg, respectively. The focal length of the transceiver lens is 125 mm, and the final communication field of view is 4 mrad. Without error correction coding, the sensitivity of −44.5  dBm was achieved, while the bit-error rate was below 10−3 at 70 Mbps. We also established a laser communication experiment at the laboratory; the platform jitter below 5 Hz can be effectively suppressed. The laser communication system has a compact structure, low power consumption, and effective suppression of low-frequency and high-amplitude angle jitter of the platform. The experiments demonstrate that the laser communication terminal can be used in an inter-satellite laser communication with a distance of thousands of kilometers. The theoretical analysis and experimental results are presented in the paper.