A beam folder increases optical length with polarizing beam splitters and reflectors
that repolarize a beam by retarding it. An incident beam encounters the beam splitters
multiple times, and are both passed and rejected by the same splitters. The splitters
and repolarizing reflectors can be shaped to perform optical functions in a smaller
volume. Valves and controls can varyl the beam intensity and combine multiple beams.
Applications include projection, imaging, collimating, mixing, and balancing.
