Given the crosstalk and loss of a single optical directional coupler, we predict the Signal-to-Noise Ratios (SNRs) of switches made from interconnected couplers. Of the seven 4x4 architectures simulated, three are strictly nonblocking, two are nonblocking in the wide sense, and two are rearrangeably nonblocking. The simulation models each coupler in an architecture, traces the signal and accumulates noise throughout the architecture, and gives the SNR at any output. For typical values of crosstalk per directional coupler, all of the 4x4 architectures compared here have good enough SNRs for non-cascaded use. The active splitter/active combiner and duobanyan switches have a large enough SNR to be cascaded without regeneration.
J. R. Erickson,
"Signal-To-Noise Ratio Simulations For Small, Guided-Wave Optical Networks", Proc. SPIE 0752, Digital Optical Computing, (11 August 1987); doi: 10.1117/12.939931; https://doi.org/10.1117/12.939931