Tunable CdS/TiO₂ all-optical switches with defect layers

The switching characteristics of one-dimensional photonic crystal (PC) all-optical switches of cadmium sulfide (CdS)/titanium dioxide (TiO₂) with defect layers are investigated. The excited defect modes with high intensity, perfect symmetric and a very narrow band were found in the photonic bandgap range of the PC transmission spectrum when inserted cadmium sulfide defect layers in the PC structure. It results from the high optical non-linearity of the cadmium sulfide defect layer and the strong localized effects of the incident light. These effects are attributed to the light localization in the defect layers of the multilayer structures. Additionally, the number and position of the defect modes are tuned according to the number and separation of the defect layers. The steep response of on and off and the tuning properties of the perfect defect modes can be exploited for ultrafast all-optical switches in all-optical circuits. The results demonstrate that cadmium sulfide defective PCs are good candidates for the fabrication of ultrafast all-optical switching devices.