An all-spheric unobstructed optical terminal for free-space quantum communication

We design and built a novel optical terminal specifically designed for free-space communication operating at light levels at the quantum limit, such as in quantum communication. Our system is particularly well suited for this task, as it is based on an all-spheric catadioptric design, which allows for large and un-obstructed apertures. This design offers an easier and cheaper approach to building high-quality optical terminals with large apertures than schemes based on offaxis parabolic mirrors. We utilized an off-axis version of the original Schwarzschild concentric design, and correct the spherical aberration by substituting the original on-axis secondary spherical mirror with an off-axis catadioptric secondary mirror. A prototype of the optical terminal was realized and tested and it meet the expected performance.