An experimental photonic time-slot interchanger using optical fibers as re-entrant delay-line memories

The system interchanges data from time-slots in its input to time-slots in its output. Carried by optical fibers and switched by photonic 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 and N time-slots with 8 bits each. An electronic controller reads the arbitrary one-to- one assignment of N input time-slots to N output time-slots (time-slot permutation) and orchestrates photonic Directional Couplers to steer the data among input, output, and N recirculating fiber-optic Delay Lines. 

While a prototype with N=3, B=8, and a pedestrian 90 MHz bit-rate is a 3-by-3 switch, where each channel carries 28.8 M-bits/second, the basic design is not limited to these numbers.