Figure 3

Dispersion curve for two criteria [criteria I \((\omega _{ce}>\omega _l>\omega _{ci})\) and criteria II (\(\omega _{ce}>\omega _{ci}>\omega _{l}\)) are shown in subplot (a) and (c) respectively]. In subplot (b) and (d), we expand the dispersion curves shown in (a) and (c) respectively. From these curves, we can observe that while criteria I has two stop bands and three pass bands, criteria II dispersion has \(\omega =ck\) all along.