  Zero-index materials (ZIMs) have become popular because of their unique
optical behaviors, such as infinite effective wavelengths and spatially uniform
electromagnetic distributions. The all-dielectric ZIMs, Dirac-like cone-based
zero-index materials (DCZIMs) are used in various photonic applications owing
to their superior optical properties, such as finite impedances, zero Ohmic
losses, and high compatibility with photonic circuits. We propose a more
general and simple approach that is independent of the Dirac-like cone mode for
realizing near-zero index (NZI) behavior in all-dielectric waveguides. This
approach can be applied to various dielectric materials up to the necessary NZI
bandwidth. Si3N4 and Ge NZI waveguides are demonstrated for achieving broadband
and narrowband NZI, respectively. The proposed broadband NZI waveguide achieves
a bandwidth of 140 nm for neff < 0.1 (neff = effective refractive index) at
telecommunication wavelengths, which is 2 times larger than that of the
reported NZI waveguides. Further, NZI waveguide-based beam steering was
demonstrated with a wide steering range delta theta 105 degrees across the
radiation angle of theta 0 degree. The proposed NZI-waveguide design principle
and beam steering present a feasible approach for the development of photonic
circuits and zero-index-based photonic applications.
