Crossed chiral band approximation for wideband self-collimation of light

Abstract

We propose a perspective to the evaluation of the wide bandwidth phenomenon, by introducing the band tailoring and chiral band approximation on the self-collimation effect for low-symmetric photonic structures. In the case of the crossing of the bands, we claim the excitation of the lower mode can provide the utilization of the entire bandwidth by suppressing the intersection regions where the frequencies tend to mix. Thereby, we design broadband self-collimation capable, defect-free photonic structures and examine their performances. A fractional bandwidth of $0.35$ (${a}\backslash{\lambda}=0.429-0.607$) and $0.37$ (${a}\backslash{\lambda}=0.481-0.701$) are achieved for radii of ${r}=0.25{a}$ and ${r}=0.23{a}$, respectively. We explore the full-range collimation using transmission and E-field intensity analysis in addition to band diagrams and group velocity dispersions. Moreover, we indicate all-angle collimation validity even for highly tilted sources up to an angle of $80^\circ$.