All-metallic three-dimensional photonic crystals with a large infrared bandgap

Three-dimensional (3D) metallic crystals are promising photonic bandgap1,2,3 structures: they can possess a large bandgap4,5,6, new electromagnetic phenomena can be explored7,8,9, and high-temperature (above 1,000 °C) applications may be possible. However, investigation of their photonic bandgap properties is challenging, especially in the infrared and visible spectrum, as metals are dispersive and absorbing in these regions10. Studies of metallic photonic crystals have therefore mainly concentrated on microwave and millimetre wavelengths8,11,12. Difficulties in fabricating 3D metallic crystals present another challenge, although emerging techniques such as self-assembly13,14 may help to resolve these problems. Here we report measurements and simulations of a 3D tungsten crystal that has a large photonic bandgap at infrared wavelengths (from about 8 to 20 µm). A very strong attenuation exists in the bandgap, ∼30 dB per unit cell at 12 µm. These structures also possess other interesting optical properties; a sharp absorption peak is present at the photonic band edge, and a surprisingly large transmission is observed in the allowed band, below 6 µm. We propose that these 3D metallic photonic crystals can be used to integrate various photonic transport phenomena, allowing applications in thermophotovoltaics and blackbody emission.