Dense tree optical switch network

Abstract

An optical switch network, for connecting P switch input waveguides to Q switch output waveguides. The switch input waveguides enter a branching subnetwork consisting of a plurality of branching cascades. In each branching cascade, an array of 1×2 splitters connects the input waveguides of the cascade to the output waveguides of the cascade, and the output waveguides of the cascade cross within the cascade so that output waveguides that connect to the same switch input waveguide emerge from the cascade P output waveguides apart. The output waveguides of the branching subnetwork connect directly to 2×1 combiners of a combining subnetwork that connects the output waveguides of the branching subnetwork to the Q switch output waveguides. The network architecture is reversible, by exchanging the roles of the input and output waveguides and the roles of the splitters and the combiners. Each splitter has a passive state, in which the input optical signals are directed to both outputs, and two active states, in which the input optical signals are directed to only one or the other of the two outputs. Similarly, each combiner has a passive state, in which the input optical signals are superposed in output, and two active states, in which only optical signals from one or another of the inputs is directed to output. Preferably, the splitters and combiners are optical switches having normalized coupling lengths equal to odd multiples of ½.