© (2006) OSA

Since the first discovery of metamaterials — materials whose optical properties arise from their designed structure — researchers have been incessantly looking for ways to exploit them. It has been pointed out that metamaterials with a refractive index of –1 can give rise to a superlensing effect by using both propagating and evanescent waves to beat the diffraction limit. Photonic crystals are among the materials that receive much attention owing to their unique photonic band structure, which offers a negative refractive index, and flexibility in their structural configuration.

Now, unlike previous work that focuses on image transfer or relies on a single photonic slab, H. Zhang and colleagues have proposed a superlens composed of layered two-dimensional photonic crystals with both square and triangular lattices1. By using computer simulations, they compare the effect on light of square–triangular, triangular–square (i.e. where the incident light falls first on the square- and first on the triangular-lattice respectively) and triangular–air–triangular layered photonic crystals, from both near-field and far-field sources. They show that although each of the various layered structures show superlensing, those consisting of only triangular-lattice photonic crystals also have greater flexibility than their single-layer counterpart — as they allow the objective distance to be changed freely while keeping the image distance constant and vice versa. This control can be implemented without loss in transverse resolution. This feature is valuable for optical-imaging systems, especially subwavelength optical lithography.