Nonreciprocal ENZ-Dielectric Bilayers: Enhancement of Nonreciprocity from a Nonlinear Transparent Conducting Oxide Thin Film at Epsilon-Near-Zero (ENZ) Frequency

TL;DR

This paper proposes a bilayer device using ITO at ENZ frequency to enhance nonreciprocal light transmission through nonlinear effects, validated by detailed numerical simulations.

Contribution

It introduces a novel silicon-photonics bilayer with ITO at ENZ frequency for improved nonreciprocal behavior leveraging nonlinear optical effects.

Findings

Maximum nonreciprocal transmittance ratio slightly over 2.

Optimal operational point identified balancing nonlinearity and loss.

Numerical simulations confirm steady-state and pulsed laser performance.

Abstract

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.