Reduced-power semiconductor all-optical switch design

Nonlinear directional couplers (NLDCs) have great potential as the basis for all-optical switching devices. However, previous studies of semiconductor-NLDCs based on two-rib horizontal geometries have indicated that large switching powers are required. The authors describe ways to help reduce the switching power by the use of vertical coupler design configurations. To achieve this, extensive modelling and design optimisation techniques have been employed using two computational methods: the spectral index (SI) method and coupled mode theory (CMT). Additional detrimental effects associated with loss are counteracted by the design of vertical NLDCs with short coupling lengths, and by operating the device at transparency. Significant reductions in switching power are predicted, when gain in the input waveguide is matched to loss in the second waveguide. Furthermore, preliminary studies of structures with matched gain to loss and nonlinearity mismatch have indicated a reduction in switching power of as much as 85%, when compared with an attenuation-free design with matched nonlinearities