  We investigate an optical switching mechanism for applications in active
integrated photonic circuits. The mechanism utilizes a large nonlinearity of
indium-tin-oxide (ITO) in epsilon-near-zero (ENZ) regime. The effect of
optically induced switching is investigated in hybrid plasmonic waveguides
(HPWG) with ITO layer that are often used as a platform for various active
photonic components, including optical modulators. To study the effect,
nonlinear Maxwell equations are solved numerically in time and frequency
domains. The all-optical mechanism of switching in HPWG is quantitatively
compared with an electrical gating that is often used to manipulate hybrid
modes. It is shown that the optical pumping could potentially cause more
efficient switching. The influence of light intensity on HPWG properties and
interplay between hybrid modes are investigated numerically in different
regimes. Transmittance and phase variation are calculated as a function of
light intensity for Si and Si3N4 waveguides. It is shown that the transmittance
and its intensity dependence are strongly affected by the ITO thickness. A
significant for applications step-like variation of phase and transmittance
with intensity is detected. The possibility to control the excitation
conditions for surface plasmon polaritons (SPP) in HPWG using active layer of
ITO in nonlinear regime is demonstrated and discussed.
