Figure 3
Fundamental bandgaps of the hexagonal (blue), square (green) and triangular (red) structures with an \({0.15\Lambda }\) apex curvature and \({0.01\Lambda }\) strut thickness. The triangular structure has two higher order bandgaps (yellow); yet, only the first higher order bandgap has a substantial frequency bandwidth. The SH and TH could be supported at normalized frequencies of 4.2, 2.8 and 1.4 by combining the properties of the hexagonal, square and triangular structures (black vertical lines). The SH and TH could also be supported at normalized frequencies of 5.8, \(\sim 3.87\) and \(\sim 1.93\) by combining the properties of the square and triangular structures (black vertical dashed lines). For reference, the FM effective index of a capillary29 is shown for wavelength and core diameter of 1500 nm and 14.2 \(\upmu \hbox {m}\), respectively.
