What are A and B you drew? Do the big arcs in the front represent reflectors? What is the face shape? ?

Understood.

A concept must be corrected here. Sunlight is not parallel light, it is just close to parallel. Parallel light does not exist in nature, but the further away the light source is, the closer the light is to parallel, and the parallelism of star light is much better than that of sunlight.

As long as any optical system is in focus (the focus of the front group and the rear group coincide), it can output parallel light when it inputs parallel light. For example, telescopes, whether Kepler, Galileo, or reflective (Newton, Gregorian, Cassegrain), are all such systems. In the light path diagram you gave, the two concave mirror systems on the left are similar to the Gregorian system, and the one on the right is similar to the Cassegrain system (the two-stage Cassegrain system is meaningless) plus the folding axis system. The parameters of these two reflection systems and performance you can search online. In addition, when non-parallel light is input, any optical system will only form an image of a light source instead of outputting a beam of parallel light. If you want to use beam shrinking to increase the energy density of the beam, it is possible within a certain distance. The opposite is true for long distances. Even for lasers, when long-distance projection is required, the method to improve parallelism is exactly beam expansion.

Further discussion is welcome.