Unrestricted superlensing in a triangular two-diemnsional photonic crystal

We demonstrate unrestricted superlensing in a triangular two-dimensional photonic crystal. We investigate simple two-point light sources imaged by a slab lenses made of this photonic crystal, and show that the refraction of light follows simple rules of geometric optics with the Snell's-law refraction at each interface, and an effective isotropic refractive index n = -1 for light propagating inside the crystal. We contrast this behavior with that of a square two-dimensional photonic crystal in the first photonic band, where the effective dielectric response is anisotropic. This leads to a restricted superlensing, which does not follow the geometric optics. (C) 2004 Optical Society of America.