Design of low-energy on-chip electro-optical 1 x M wavelength-selective switches

A theoretical design is presented for a 1 x M wavelength-selective switch (WSS) that routes any one of N incoming wavelength signals to any one of M output ports. This planar on-chip device comprises of a 1 x N demultiplexer, a group of N switching "trees" actuated by electro-optical or thermo-optical means, and an M-fold set of N x 1 multiplexers. Trees utilize 1 x 2 switches. The WSS insertion loss is proportional to [log(2) (M+N+1)]. Along with cross talk from trees, cross talk is present at each cross-illuminated waveguide intersection within the WSS, and there are at most N - 1 such crossings per path. These loss and cross talk properties will likely place a practical limit of N = M = 16 upon the WSS size. By constraining the 1 x 2 switching energy to similar to 1 fJ/bit, we find that resonant, narrowband 1 x 2 switches are required. The 1 x 2 devices proposed here are nanobeam Mach-Zehnders and asymmetric contra-directional couplers with grating assistance. (C) 2017 Chinese Laser Press