The photonic band structures of two-dimensional square lattice photonic crystals made of anisotropic materials with one of the principal axes oriented along the extension direction of cylinders are studied. The band structure of the photonic crystal can be substantially engineered to achieve large bandgaps by reorienting the other two principal axes of the anisotropy media in the periodic plane of the photonic crystal. In particular, it is shown that large full bandgap for H polarization can be created for a photonic crystal with circular holes in an anisotropic matrix medium. For pillar-type photonic crystals, we show that large partial bandgaps for H polarization can be created in half of the irreducible Brillouin zone. With the use of anisotropic materials and the flexibility of arranging the principal axes, the requirement on the filling ratio, refractive index and anisotropy to achieve the largest bandgap is greatly alleviated. (c) 2006 Optical Society of America.
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