Mirror-folded free-space crossbars with holographic implementation

Free-space optical crossbars that utilize elements such as beam splitters and holograms can in principle be folded by two parallel plane mirrors and implemented in a single plane, or even in a single line, parallel to the mirrors. Such crossbars, each performing either a processing or an interconnection function, can in turn be cascaded along a common plane or line between a single set of two mirrors to perform a large class of operations. By use of all possible inputs and outputs, novel power-conserving operations can also be performed. We report on the holographic implementation of a reconfigurable 2 × 2 mirror-folded generalized crossbar with a thermoplastic holographic camera; the bypass, the exchange, and the broadcast states are demonstrated.