Scientists at Kyoto University (Kyoto, Japan) and the Ministry of International Trade and Industry (Ibaraki, Japan) have lithographically constructed a photonic crystal that has a full photonic bandgap at a 1.2-µm wavelength and is made from either gallium arsenide or indium phosphide, both semiconductors amenable to integration with light-emitting devices. The bandgap effect reaches more than 40 dB, or a reflection of 99.99%. If full bandgap is defined as more than 80% attenuation, then the bandgap covers the 1.3- to 1.55-µm telecommunications region.
The crystal is made in a "woodpile" configuration, in which layers of stripes are stacked in orthogonal directions. Every layer is shifted from its counterpart two layers below by half a period. The structure is assembled by bringing two wafers together in a wafer-fusion process, then removing one substrate; the process is repeated for up to eight layers. A stripe period of 0.7 µm necessitates a 30-nm alignment tolerance between layers to prevent a loss of the full bandgap. The researchers introduced a defect consisting of two removed orthogonal stripes, creating a waveguide with a 90° bend with a predicted transmission of greater than 95%. Contact Susumu Noda at [email protected].