“…Liu et al first provide analytical solution (AS) [115,116] of wave transport in the PCs with low refractive index material (such as photopolymers [117], liquid [118,119], or DCG [111,120,121]), and some unique properties can be seen clearly from the AS. From the detailed analysis of the AS [116], it can be seen that 2-D absolute band gaps (ABGs, band gaps for both TE and TM waves) cannot be achieved in the strict period PC structure with low refractive index materials.…”