New face-centered photonic square lattices with flat bands

TL;DR

This paper introduces two new classes of face-centered photonic square lattices with flat bands, demonstrating their unique localization and oscillation properties, which could advance the study of flat-band modes in photonics.

Contribution

The paper presents novel Lieb-I and Lieb-II photonic lattices with specific flat-band structures and explores their localization and oscillation behaviors during light propagation.

Findings

Flat bands are related to the number of sites in the unit cell.

Light remains localized when exciting flat-band modes.

Oscillations occur in Lieb-II lattices due to flat-band mode interactions.

Abstract

We report two new classes of face-centered photonic square lattices with flat bands which we call the Lieb-I and the Lieb-II lattices. There are 5 and 7 sites in the corresponding unit cells of the simplest Lieb-I and Lieb-II lattices, respectively. The number of flat bands $m$ in the new Lieb lattices is related to the number of sites $N$ in the unit cell by $m=(N-1)/2$. Physical properties of the lattices with even and odd number of flat bands are different. We also consider localization of light in such Lieb lattices. If the input beam excites the flat-band mode, it will not diffract during propagation, owing to the strong localization in the flat-band mode. For the Lieb-II lattice, we also find that the beam will oscillate and still not diffract during propagation, because of the intrinsic oscillating properties of certain flat-band modes. The period of oscillation is determined by the energy difference between the two flat bands. This study provides a new platform for the investigation of flat-band modes.