Wide bandwidth directional beaming via waveguide ports in photonic crystals

We numerically and experimentally demonstrated highly directional emission from photonic crystals (PCs). Our structures comprise branched waveguide channels with a periodic doubling scheme. An incident electromagnetic wave can be first split into multiple beams using PC waveguide structures. The beams were then emitted at the output waveguide ports of the PC with the same phase, which resulted in a highly directional radiation pattern. Our results demonstrate that the full width at half maximum of the emission beam is nearly inversely proportional to the number of output waveguide ports. Typically, for a PC with sixteen output ports, the half-power beam width measured 4.8◦, which was in good agreement with the calculated value of 4.1◦. In contrast to the traditional beaming structures, our design did not involve grating-like structures, which resulted in a wider operation bandwidth. (Some figures in this article are in colour only in the electronic version) M Animation files for figure 3 are available in the online edition.