Plasmonic modulator based on thin metal-semiconductor-metal waveguide with gain core

We focus on plasmonic modulators with a gain core to be implemented as active nanodevices in photonic integrated circuits. In particular, we analyze metal–semiconductor–metal (MSM) waveguides with InGaAsP-based active material layers. A MSM waveguide enables high field localization and therefore high modulation speed. The modulation is achieved by changing the gain of the core that results in different transmittance through the waveguide. Dependences on the waveguide core size and gain values of various active materials are studied. The effective propagation constants in the MSM waveguides are calculated numerically. We optimize the structure by considering thin metal layers. A thin single metal layer supports an asymmetric mode with a high propagation constant. Implementing such layers as the waveguide claddings allows to achieve several times higher effective indices than in the case of a waveguide with thick (>50 nm) metal layers. In turn, the high effective index leads to enhanced modulation speed. We show that a MSM waveguide with the electrical current control of the gain incorporates compactness and deep modulation along with a reasonable level of transmittance.