All-optical absorption switches in subwavelength metal-dielectric- metal plasmonic waveguides

We theoretically investigate the properties of absorption switches for metal-dielectric-metal (MDM) plasmonic waveguides. We show that a MDM waveguide directly coupled to a cavity filled with an active material with tunable absorption coefficient can act as an absorption switch, in which the on/off states correspond to the absence/presence of optical pumping. We also show that a MDM plasmonic waveguide side-coupled to a cavity filled with an active material can operate as an absorption switch, in which the on/off states correspond to the presence/absence of pumping. For a specific modulation depth, the side-coupled-cavity switch results in more compact designs compared to the directcoupled-cavity switch. Variations in the imaginary part of the refractive index of the material filling the cavity of =0.01 ( =0.15) result in ~60% (~99%) modulation depth. The properties of both switches can be accurately described using transmission line theory.