  We study an ultra-compact plasmonic modulator that can be applied in photonic
integrated circuits. The modulator is a metal-insulator-metal waveguide with an
additional ultra-thin layer of indium tin oxide (ITO). Bias is applied to the
multilayer core by means of metal plates that serve as electrodes. External
field changes carrier density in the ultra-thin ITO layer, which influences the
permittivity. The metal-insulator-metal system possesses a plasmon resonance,
and it is strongly affected by changes in the permittivity of the active layer.
To improve performance of the structure we propose several optimizations. We
examine influence of the ITO permittivity on the modulator's performance and
point out appropriate values. We analyze eigenmodes of the waveguide structure
and specify the range for its efficient operation. We show that substituting
the continuous active layer by a one-dimension periodic stripes increases
transmittance through the device and keeps the modulator's performance at the
same level. The dependence on the pattern size and filling factor of the active
material is analyzed and optimum parameters are found. Patterned ITO layers
allow us to design a Bragg grating inside the waveguide. The grating can be
turned on and off, thus modulating reflection from the structure. The
considered structure with electrical control possesses a high performance and
can efficiently work as a plasmonic component in nanophotonic architectures.
