Abstract
Gradient Photonic Crystals (GPCs) are attractive optical structures for manipulating and controlling the propagation of light. In long-wavelength limit (operating wavelength is much larger than the lattice period of structure), GPCs can be homogenized and served as gradient index (GRIN) effective medium. Here, a Luneburg lens is designed with ten layers of GRIN square GPCs structure in metamaterial regime based on the effective medium approximation. Inside the lens, the local effective refractive index is controlled via the filling fraction. Simulation results demonstrate excellent performance of the Luneburg lens for different incident light over a broad frequency band using the COMSOL finite-element package. When the operating wavelength is greater than the three times of the lattice spacing (it is treated as the threshold wavelength), the designed Lune-burg lens with GRIN square PCs structure is expected to lead to nearly isotropic optical properties and not affected by the complex spatial dispersion relations. The designed Luneburg lens will show the anisotropy features-fantastic anisotropy focusing direction once the operating wavelength is less than the threshold wavelength.
© 2015 Japan Society of Applied Physics, Optical Society of America
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