Retroreflecting elements adapted for use in two-by-two optical routing elements. Each retroreflecting element is configured to selectively retroreflect two optical rays. A first reflective surface, such as may be provided by a mirror, is inclined with respect to a reference plane. A second reflective surface, such as may also be provided by a mirror, is opposed to and inclined with respect to the first reflective surface. The two surfaces are configured for rotation about an axis to multiple positions such that in a first position, a first ray is retroreflected along a first path and second ray is reflected along a second path, and in a second position, the first ray is reflected along the second path and the second ray is reflected along the first path.