Tetrastack: Colloidal diamond-inspired structure with omnidirectional photonic band gap for low refractive index contrast

Omnidirectional photonic band gaps opening at low values of refractive index contrast have been found for a nonspherical colloid-based photonic crystal structure. A mechanically stable design is described for the diamondlike photonic crystal composed of colloidal tetrahedra. The proposed tetrastack structure displays omnidirectional 2–3 band gap over a large range of filling fractions, refractive index contrasts, and building block orientations. The threshold refractive index for the inverted tetrastack structure was 1.94. A gap width of 25.3% relative to the center frequency was obtained for an inverted tetrastack with a 0.21 filling fraction of silicon.