A discrete optical switch has two, three, or four ports that allow switching operations such as ON/OFF or exchange/bypass to be carried out. If it is electrically controlled, we recognize in this category devices such as microoptic modules, reed-relaylike fibers, and lithium niobate guided-wave directional couplers. All provide transparent bidirectional optical paths of huge bandwidth and low insertion loss. Switching times can vary from milliseconds to picoseconds. Matrices formed from such elements have been demonstrated up to ~16×16 in size, by which time fabrication, optical insertion loss, and optical and crosstalk problems become very severe. Wiring large arrays of fiber-based devices rapidly generates difficult fiber handling problems just as in large integrated optic chips. The problems of lithography escalate, and the constraints Imposed by a single wiring plane restrict design freedom. Moreover, in the case of lithium niobate, with three electrodes per cross-point, a 16×16 matrix implies over 500 pin-outs even allowing for a common ground plane. Electrical connection and drive problems can thus be expected to set a limit to the speed and complexity achievable also.
© 1988 Optical Society of AmericaPDF Article