All-optical space switches with gain and principally ideal extinction ratios

Asymmetric Mach-Zehnder interferometer (MZI) configurations are proposed to build all-optical space switches with gain and principally ideal extinction ratios. Actually, three asymmetries in MZI configurations with semiconductor optical amplifiers (SOA´s) on their arms are discussed. The asymmetries in the all-optical switches are necessary to overcome the extinction ratio limitations that are due to the disturbing gain changes that arise when control signals are introduced into the SOA´s to induce the necessary refractive index change for switching. Starting from a generic MZI configuration with SOA´s on the arms, a description in terms of transmission matrices is used and applied to identify 1×2 and 2×2 all-optical switch configurations with high on-state transmissions and close to ideally large extinction ratios. The theoretical predictions are verified and found to be in excellent agreement with experiments for a switch with symmetric MZI splitters in a monolithically integrated InP waveguide version that allows operation with equally or unequally biased SOA´s