Complete photonic bandgaps in 12-fold symmetric quasicrystals

Photonic crystals are attracting current interest for a variety of reasons, such as their ability to inhibit the spontaneous emission of light(1,2). T his and related properties arise from the formation of photonic bandgaps, w hereby multiple scattering of photons by lattices of periodically varying r efractive indices acts to prevent the propagation of electromagnetic waves having certain wavelengths. One route to forming photonic crystals is to et ch two-dimensional periodic lattices of vertical air holes into dielectric slab waveguides(3-7). Such structures can show complete photonic bandgaps(8 -10), but only for large-diameter air holes in materials of high refractive index (such as gallium arsenide, n = 3.69), which unfortunately leads to s ignificantly reduced optical transmission when combined with optical fibres of low refractive index. It has been suggested that quasicrystalline (rath er than periodic) lattices can also possess photonic bandgaps(11-14). Here we demonstrate this concept experimentally and show that it enables complet e photonic bandgaps-non-directional and for any polarization-to be realized with small air holes in silicon nitride (n = 2.02), and even glass (n = 1. 45). These properties make photonic quasicrystals promising for application in a range of optical devices(14-18).