  We envision the use of an indium tin oxide (ITO) thin film as part of a
bi-layered silicon-photonics subwavelength device to boost
nonlinearity-assisted all-passive nonreciprocal behavior. The asymmetric
p-polarized oblique excitation of a mode near the epsilon-near-zero (ENZ)
frequency, with highly-confined and enhanced normal electric field component
and large absorption, allows to harness ITO's strong ultrafast nonlinear
response for the generation of a notable nonreciprocal performance in the
two-port element. Though limited by loss, we find the device's optimal
operational point and the maximum nonreciprocal transmittance ratio attainable
vs. light intensity -- including an apparent upper bound slightly over 2 --,
and we perform exhaustive numerical simulations considering nonlinear processes
of both anharmonic and thermal nature that validate our predictions, including
steady-state and pulsed-laser excitations.
