Optical EngineeringCompact optical antennas using free-form surface optics for ultrahigh-speed laser communication systems
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It is envisioned that the next generation of ultrahigh-speed laser communication systems will utilize compact optical antennas equipped with advanced beam tracking and effective fiber coupling mechanisms. Such laser communication systems will be used not only for space communications but also to provide optical links for long-distance terrestrial communications. We present the design of a high-speed laser communication system developed utilizing compact optical antennas with off-axis free-form surface (FFS) mirrors. We describe FFS optical devices and their design contribution in realizing compact optical antennas. Furthermore, an innovative fiber coupling device made from a glass ferrule and fiber is introduced, and with this device it is possible to couple the laser beam seamlessly to a single-mode fiber. We also present a fine tracking mechanism that uses a miniature fine pointing mirror (FPM) incorporated in the antenna. The machanism functions by feeding back the incident angle of the signal detected by a quadrant detector (QD) to the FPM. The achievable actuator response frequency for tracking is approximately 2 kHz, and it has been demonstrated to effectively mitigate the effects of laser beam angle-of-arrival fluctuation as a result of atmospheric turbulence.