We are pursuing novel functionalities arising from unique capabilities of integrated nanophotonics. In this invited talk, we will introduce our recent two results. First one is a combination of graphene with ultra-narrow plasmonic waveguides efficiently coupled to Si waveguides. This device enables ultrafast all-optical switching with substantially small energy consumption, thanks to unique optical nonlinearity of graphene and ultrastrong light confinement in plasmonic waveguides integrated with efficient mode converters. Second one is based on a periodic modulation of non-Hermitian optical property, namely, a periodic array of gain and loss nanocavities. We will show that such non-Hermitian array leads to strange optical dispersion and nontrivial topological insulating phase, which are fully reconfigurable by controlling the injection current.
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