The system interchanges data from time slots in its input to time slots in its output. Carried by single-mode optical fibers and switched by lithium-niobate directional couplers, the data remains in photonic form from input to output. The data format is a series of frames, each with a start-bit andNtime slots withBbits each. An electronic controller reads the arbitrary one-to-one assignment ofNinput time slots toNoutput time slots (time-slot permutation) and orchestrates photonic directional couplers to steer the data among input, output, andNrecirculating fiber-optic delay lines. While a prototype withN = 3 , B = 8, and a pedestrian 90-MHz bit rate is a 3 × 3 switch, where each channel carries 28.8 Mbit/s, the basic design is not limited to these numbers.