Woodpile photonic crystals composed of air columns

Silicon-based woodpile photonic crystals (PhCs) composed of air columns have a large gap/midgap ratio exceeding 20% over a wide dimensional range of the cross section of the air column when the cross section is deformed to a rectangular shape extended normal to the stacking direction. Such a PhC structure can be formed using a simple technique based on 45° dry etching. Furthermore, introducing twin air columns with small cross sections instead of corresponding mother air columns yields a defect state at the region where the columns cross. Since the fabrication process is a planar-type Si wafer process, fabricated PhCs can be easily combined with conventional electronic circuits and optical elements, such as Si waveguides and switches.