Abstract
A low-divergence beam is an essential prerequisite for a high-efficiency long-distance optical link, particularly for satellite-based quantum communication. A point-ahead angle, caused by satellite motion, is always several times larger than the divergence angle of the signal beam. We design a novel transmitting antenna with a point-ahead function, and provide an easy-to-perform calibration method with an accuracy better than 0.2 μrad. Subsequently, our antenna establishes an uplink to the quantum satellite, Micius, with a link loss of 41-52 dB over a distance of 500-1,400 km. The results clearly confirm the validity of our model, and provide the ability to conduct quantum communications. Our approach can be adopted in various free space optical communication systems between moving platforms.
Highlights
Quantum communication enables unconditional secure communications and fundamental tests of quantum physics [1,2,3,4,5]
In 2016, a quantum science satellite called Micius was launched into a low Earth orbit (LEO)
Future global quantum communication networks based on constellation will require the establishment of various optical links with low channel losses, including satellite to ground, ground to satellite, and satellite to satellite links
Summary
Quantum communication enables unconditional secure communications and fundamental tests of quantum physics [1,2,3,4,5]. Future global quantum communication networks based on constellation will require the establishment of various optical links with low channel losses, including satellite to ground, ground to satellite, and satellite to satellite links. Many theorical and technical studies of satellite quantum communications have been performed, including link loss analysis, noise estimation and polarization basis compensation [18,19,20,21]. Optical pointing and tracking techniques are critical tools for reducing link losses. We construct a ground-to-satellite quantum communication link with two-stage bidirectional tracking with the PID algorithm. An optical uplink within 52 dB is established and well maintained with tracking techniques, including the point-ahead method. When the LEO satellite Micius passes overhead, photons with a calibrated power sent from the ground transmitter are used to measure the link loss.
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